Sync agent instructions from main

.gitattributes

@@ -15,33 +15,72 @@
 
 # Exact source/recovery oracles and archived ledgers retain their measured bytes.
 # Keep ordinary text diffs; only disable checkout/check-in newline conversion.
+PROJECT_GOAL.md -text whitespace=cr-at-eol
 harness/fixtures/release1-native/** -text
 harness/fixtures/interface-operation-probe/** -text
 harness/history/2026-09-06-ledgers-before-consolidation/** -text
+harness/history/2026-09-10-ledgers-before-continuation-refresh/** -text
 harness/history/2026-09-10-ledgers-before-second-consolidation/** -text whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol
 harness/experiments/textual-authoring-20260911-local/** -text whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol
-harness/experiments/constructor-defaults-20260911/** -text whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol
-harness/experiments/constructor-defaults-20260911/results/*.arcadia whitespace=-blank-at-eol,cr-at-eol
-harness/experiments/behavior-creation-native-20260911/** -text whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol
-harness/experiments/analysis-context-20260911/** -text whitespace=cr-at-eol
-harness/experiments/textual-authoring-20260911/** -text whitespace=cr-at-eol
-harness/experiments/textual-authoring-20260911/observed/split-entry.arcadia whitespace=-blank-at-eol,cr-at-eol
-harness/fixtures/scenario-authoring/base/** -text whitespace=cr-at-eol
+harness/history/2026-09-11-ytr83r-integration/** -text whitespace=cr-at-eol
 crates/oa-desktop/src/recovery/fixtures/*.json -text
 harness/fixtures/source7-native/** -text
 harness/fixtures/basic-editing/** -text
+harness/fixtures/scenario-authoring/base/** -text whitespace=cr-at-eol
+harness/experiments/textual-authoring-20260911/** -text whitespace=cr-at-eol
+harness/experiments/textual-authoring-20260911/observed/split-entry.arcadia whitespace=-blank-at-eol,cr-at-eol
+harness/experiments/analysis-context-20260911/** -text whitespace=cr-at-eol
+harness/experiments/constructor-defaults-20260911/** -text whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol
+harness/experiments/constructor-defaults-20260911/results/*.arcadia whitespace=-blank-at-eol,cr-at-eol
+harness/experiments/behavior-creation-native-20260911/** -text whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol
 harness/behavior-creation-contract.rs -text whitespace=cr-at-eol
+harness/experiments/source-cli-independent-20260911/** -text whitespace=cr-at-eol
+harness/fixtures/scenario-lifecycle-native/**/*.arcadia -text whitespace=cr-at-eol
+harness/experiments/lifecycle-native-ytr83r-20260911/** -text whitespace=cr-at-eol
+harness/experiments/lifecycle-native-ytr83r-20260911/*.log -text -whitespace
+harness/experiments/lifecycle-native-ui-oa-20260911/** -text -whitespace
+harness/experiments/lifecycle-native-ui-sa-20260911/** -text -whitespace
+harness/experiments/wsl-postboot-ytr83r-20260911/** -text -whitespace
 
 # Preserve checksum-bound font notices verbatim through Git round trips.
 scripts/windows-notices/GNOME-Cantarell-61362600e104-COPYING -text
 scripts/windows-notices/Fira-OFL.txt -text
 scripts/windows-notices/FiraSans-Regular-NOTICE.txt -text
+scripts/windows-notices/llvm-6dfe1677ab8d-libunwind-LICENSE.TXT -text
 
-# Preserve exact inputs of the frozen D4D9 authoring milestone build.
-crates/oa-desktop/src/semantic_review/artifacts_view.rs -text
-crates/oa-desktop/src/semantic_review/attachments_view.rs -text
-crates/oa-desktop/src/semantic_review/keyed_rows.rs -text
-crates/oa-desktop/src/semantic_review/keyed_tests.rs -text
-crates/oa-desktop/src/semantic_review/keyed.rs -text
-crates/oa-desktop/src/semantic_review/ordered.rs -text
-docs/openapi.json -text
+harness/experiments/lifecycle-header-overflow-before-20260911/** -text -whitespace
+harness/history/2026-09-11-ytr83r-record-migration/STATE-before.md -text -whitespace
+
+harness/fixtures/staged-source-authoring/** -text whitespace=cr-at-eol
+harness/staged-source-authoring-contract.rs -text whitespace=cr-at-eol
+
+harness/experiments/contextual-lifecycle-integration-ytr83r-20260911/** -text -whitespace
+harness/experiments/windows-runtime-321897f-20260911/** -text -whitespace
+harness/child-work-native-contract.rs -text whitespace=cr-at-eol
+harness/fixtures/child-work-native/** -text whitespace=cr-at-eol
+harness/experiments/windows-gates-865483b-20260911/** -text -whitespace
+harness/experiments/native-child-oa-865483b-20260911/** -text -whitespace
+harness/experiments/packaged-server-865483b-20260911/** -text -whitespace
+
+harness/experiments/canvas-union-a57c334-20260911/** -text -whitespace
+harness/experiments/windows-gates-a57c334-20260911/** -text -whitespace
+harness/experiments/native-child-continuation-865483b-20260911/** -text -whitespace
+harness/experiments/lifecycle-header-correction-native-865483b-20260911/** -text -whitespace
+harness/release-native-child-continuation-review-20260911.md -text -whitespace
+
+harness/experiments/packaged-gui-close-865483b-20260911/** -text -whitespace
+harness/release-grapheme-shortening-review-20260911.md -text -whitespace
+harness/experiments/staged-source-native-a57c334-20260911/** -text -whitespace
+harness/experiments/grapheme-windows-cb91525-20260911/** -text -whitespace
+harness/experiments/canvas-native-close-a57c334-20260911/** -text -whitespace
+harness/release-staged-native-a57-independent-review-20260911.md -text -whitespace
+harness/release-saved-destination-independent-review-20260912.md -text -whitespace
+harness/experiments/repair-union-windows-33e30c1-20260912/** -text -whitespace
+harness/experiments/canvas-camera-a57c334-20260912/** -text -whitespace
+harness/release-camera-a57-independent-review-20260912.md -text -whitespace
+
+harness/experiments/canvas-repair-package-33e30c1-20260912/** -text -whitespace
+harness/experiments/canvas-repair-native-33e30c1-20260912/** -text -whitespace
+harness/experiments/canvas-repair-server-33e30c1-20260912/** -text -whitespace
+
+harness/experiments/canvas-repair-publication-20260912/** -text -whitespace

Cargo.lock

@@ -2139,6 +2139,15 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "oa-cli"
+version = "0.2.0"
+dependencies = [
+ "oa-core",
+ "serde",
+ "serde_json",
+]
+
 [[package]]
 name = "oa-core"
 version = "0.2.0"
@@ -2167,6 +2176,7 @@ dependencies = [
  "serde_json",
  "tempfile",
  "tokio",
+ "unicode-segmentation",
 ]
 
 [[package]]

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["crates/oa-core", "crates/oa-desktop", "crates/oa-server"]
+members = ["crates/oa-core", "crates/oa-desktop", "crates/oa-server", "crates/oa-cli"]
 resolver = "2"
 
 [workspace.package]

README.md

@@ -18,7 +18,7 @@ From the repository root:
 cargo run --locked -p oa-desktop --bin arcadia-studio
 ```
 
-Build both desktop and server release executables:
+Build the desktop, server and source CLI release executables:
 
 ```sh
 cargo build --release --workspace --locked
@@ -51,6 +51,21 @@ The earlier V2 package record describes `dist/ArcadiaStudio-Windows.zip` and `di
 
 The current [Windows packaging instructions](docs/windows-packaging.md) stage both executables, verify their runtime DLL dependencies, and produce an archive with checksums and provenance. Native acceptance fixtures and independent expected results are retained in [the release fixture directory](harness/fixtures/release1-native/README.md).
 
+## Work with source files from the command line
+
+The `arcadia` CLI checks an explicit `.arcadia` entry file and its includes without
+starting the desktop or server:
+
+```sh
+cargo run --locked -p oa-cli --bin arcadia -- check examples/text-first/project.arcadia
+```
+
+`stabilize ROOT` previews the identities needed for persistent editing;
+`rename-alias ROOT OLD NEW` previews an alias change and its references. Add
+`--write` to save that invocation's candidate, or `--json` for structured
+diagnostics and changed-file text/diffs. Preview leaves files untouched.
+See [source CLI commands](docs/source-cli.md) for examples and exit codes.
+
 ## Model operational needs and system responsibilities
 
 The desktop starts at **Home**, where you can create a model, open a local project, continue recent files or recover retained work. Missing recent files stay visible with **Locate**; **Remove** only forgets their history entry. Choose **Explore rescue example** for a model combining people, an organization, a System of Interest, information and physical exchange items, normal/degraded behavior and code/CAD evidence.

crates/oa-cli/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "oa-cli"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+rust-version.workspace = true
+
+[[bin]]
+name = "arcadia"
+path = "src/main.rs"
+
+[dependencies]
+oa-core = { path = "../oa-core" }
+serde.workspace = true
+serde_json.workspace = true

crates/oa-cli/src/lib.rs

@@ -0,0 +1,451 @@
+//! Source-only authoring. Preparation captures bytes; only core owns disk writes.
+use oa_core::{
+    Command, language,
+    persistence::MigrationReport,
+    prepare_command,
+    source_files::{self, DiskProject, SourceFileError},
+    source_project::{self, CompiledSourceProject, ProjectLimits, SourceDiagnostic},
+    validation::Severity,
+};
+use serde::Serialize;
+use std::path::{Path, PathBuf};
+
+pub const LIMITS: ProjectLimits = ProjectLimits {
+    max_files: 256,
+    max_include_depth: 32,
+    max_include_edges: 1024,
+    model: language::ParseLimits {
+        max_source_bytes: 64 * 1024 * 1024,
+        max_graph_objects: 100_000,
+        max_records: 250_000,
+        max_step_references: 500_000,
+    },
+};
+
+#[derive(Debug, Clone)]
+pub enum Operation {
+    Check,
+    Stabilize,
+    RenameAlias { old: String, new: String },
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct Location {
+    pub path: String,
+    /// Half-open UTF-8 byte offsets. Line/column are one-based Unicode scalars.
+    pub start: usize,
+    pub end: usize,
+    pub line: Option<usize>,
+    pub column: Option<usize>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct Diagnostic {
+    pub severity: String,
+    pub code: String,
+    pub message: String,
+    pub coordinate_space: String,
+    pub location: Option<Location>,
+    pub related: Vec<Location>,
+    pub object_id: Option<String>,
+    pub field: Option<String>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct Change {
+    pub path: String,
+    /// Exact captured and proposed UTF-8 text, including line endings.
+    pub before: String,
+    pub after: String,
+    pub diff: String,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct Report {
+    pub format_version: u32,
+    pub entry: String,
+    pub operation: String,
+    pub status: String,
+    pub exit_code: u8,
+    /// True only after a successful changed save. False on failure does not
+    /// promise rollback: consult the specific error/recovery outcome.
+    pub written: bool,
+    pub diagnostics: Vec<Diagnostic>,
+    pub changes: Vec<Change>,
+    pub identities_to_stabilize: usize,
+    pub migration: Option<MigrationReport>,
+    pub notes: Vec<String>,
+}
+
+impl Report {
+    pub fn failure(
+        entry: &Path,
+        operation: &str,
+        exit_code: u8,
+        code: &str,
+        message: String,
+    ) -> Self {
+        let mut report = Self::empty(entry, operation);
+        report.fail(exit_code, code, message);
+        report
+    }
+
+    fn empty(entry: &Path, operation: &str) -> Self {
+        Self {
+            format_version: 1,
+            entry: entry.to_string_lossy().into_owned(),
+            operation: operation.into(),
+            status: "checked".into(),
+            exit_code: 0,
+            written: false,
+            diagnostics: vec![],
+            changes: vec![],
+            identities_to_stabilize: 0,
+            migration: None,
+            notes: vec![],
+        }
+    }
+
+    fn fail(&mut self, exit_code: u8, code: &str, message: String) {
+        self.status = "rejected".into();
+        self.exit_code = exit_code;
+        self.diagnostics.push(Diagnostic {
+            severity: "error".into(),
+            code: code.into(),
+            message,
+            coordinate_space: "operation".into(),
+            location: None,
+            related: vec![],
+            object_id: None,
+            field: None,
+        });
+    }
+}
+
+fn located(issue: SourceDiagnostic, space: &str) -> Diagnostic {
+    let d = issue.diagnostic;
+    Diagnostic {
+        severity: match d.severity {
+            Severity::Error => "error",
+            Severity::Warning => "warning",
+        }
+        .into(),
+        code: d.code,
+        message: d.message,
+        coordinate_space: space.into(),
+        location: Some(Location {
+            path: issue.path,
+            start: d.span.start,
+            end: d.span.end,
+            line: Some(d.line),
+            column: Some(d.column),
+        }),
+        related: issue
+            .related
+            .into_iter()
+            .map(|at| Location {
+                path: at.path,
+                start: at.span.start,
+                end: at.span.end,
+                line: None,
+                column: None,
+            })
+            .collect(),
+        object_id: d.object_id.map(|id| id.to_string()),
+        field: d.field,
+    }
+}
+
+fn disk_error(report: &mut Report, error: SourceFileError) {
+    let code = match &error {
+        SourceFileError::Conflict(_) => "external_change",
+        SourceFileError::RecoveryRequired(_) => "recovery_required",
+        SourceFileError::RecoveryFailed { .. } => "recovery_failed",
+        SourceFileError::Path(_) => "unsafe_path",
+        SourceFileError::Limit(_) => "source_limit",
+        SourceFileError::UnknownExpectation(_) => "unknown_disk_expectation",
+        SourceFileError::Invalid(_) => "invalid_save_candidate",
+        SourceFileError::Io { .. } => "io_error",
+    };
+    report.fail(3, code, error.to_string());
+}
+
+/// A candidate owns its original expectations and is consumed by saving.
+/// Callers cannot replace its source/model/expectations after preparation.
+pub struct Prepared {
+    report: Report,
+    snapshot: DiskProject,
+    compiled: CompiledSourceProject,
+    mutable: bool,
+}
+
+impl Prepared {
+    pub fn report(&self) -> &Report {
+        &self.report
+    }
+
+    pub fn into_report(self) -> Report {
+        self.report
+    }
+
+    pub fn write(mut self) -> Report {
+        if !self.mutable {
+            self.report
+                .fail(2, "usage", "check/lint does not accept --write".into());
+            return self.report;
+        }
+        match source_files::save_project(&self.snapshot, &self.compiled, LIMITS) {
+            Ok(_) => {
+                self.report.written = !self.report.changes.is_empty();
+                self.report.status = if self.report.written {
+                    "written"
+                } else {
+                    "unchanged"
+                }
+                .into();
+            }
+            Err(error) => disk_error(&mut self.report, error),
+        }
+        self.report
+    }
+}
+
+pub fn prepare(entry: &Path, operation: Operation) -> Result<Prepared, Box<Report>> {
+    let name = match operation {
+        Operation::Check => "check",
+        Operation::Stabilize => "stabilize",
+        Operation::RenameAlias { .. } => "rename-alias",
+    };
+    let mut report = Report::empty(entry, name);
+    let snapshot = source_files::load_project(entry, LIMITS).map_err(|error| {
+        disk_error(&mut report, error);
+        Box::new(report.clone())
+    })?;
+    let raw = snapshot.reachable_bundle();
+    // The loader may include warnings from stabilized compilation. Only its
+    // discovery/IO diagnostics are authoritative on the original bytes.
+    let mut diagnostics: Vec<_> = snapshot
+        .diagnostics
+        .iter()
+        .filter(|d| {
+            matches!(
+                d.diagnostic.code.as_str(),
+                "pending_save"
+                    | "source_encoding"
+                    | "source_limit"
+                    | "invalid_path"
+                    | "missing_include"
+                    | "project_limit"
+            )
+        })
+        .cloned()
+        .collect();
+    for diagnostic in source_project::lint_bundle(&raw, LIMITS) {
+        if !diagnostics.contains(&diagnostic) {
+            diagnostics.push(diagnostic);
+        }
+    }
+    let disk_refusal = snapshot.diagnostics.iter().any(|d| {
+        matches!(
+            d.diagnostic.code.as_str(),
+            "pending_save" | "missing_include" | "invalid_path"
+        )
+    });
+    let invalid = diagnostics
+        .iter()
+        .any(|d| d.diagnostic.severity == Severity::Error);
+    report.diagnostics = diagnostics
+        .into_iter()
+        .map(|d| located(d, "input"))
+        .collect();
+    if invalid {
+        // Do not run declaration analysis or any updater on invalid raw text.
+        // Failed lint may also have allocated provisional object identities.
+        for diagnostic in &mut report.diagnostics {
+            diagnostic.object_id = None;
+        }
+        report.status = "invalid".into();
+        report.exit_code = if disk_refusal { 3 } else { 1 };
+        return Err(Box::new(report));
+    }
+    let explicit_ids: std::collections::BTreeSet<_> = raw
+        .files
+        .values()
+        .flat_map(|text| language::analyze(text).declarations)
+        .filter_map(|d| d.id.map(|id| id.to_string()))
+        .collect();
+    for diagnostic in &mut report.diagnostics {
+        if diagnostic
+            .object_id
+            .as_ref()
+            .is_some_and(|id| !explicit_ids.contains(id))
+        {
+            diagnostic.object_id = None;
+        }
+    }
+    let mut compiled = source_project::compile_bundle(&raw, LIMITS).map_err(|diagnostics| {
+        report.status = "invalid".into();
+        report.exit_code = 1;
+        report
+            .diagnostics
+            .extend(diagnostics.into_iter().map(|d| located(d, "candidate")));
+        Box::new(report.clone())
+    })?;
+    report.identities_to_stabilize = raw
+        .files
+        .values()
+        .map(|text| {
+            language::analyze(text)
+                .declarations
+                .into_iter()
+                .filter(|d| d.id.is_none())
+                .count()
+        })
+        .sum();
+    report.migration = compiled.decoded.migration.clone();
+    let mutable = !matches!(operation, Operation::Check);
+    if let Operation::RenameAlias { old, new } = operation {
+        let project = &compiled.decoded.project;
+        let Some((id, _)) = project
+            .identities()
+            .into_iter()
+            .find(|(_, alias)| *alias == old)
+        else {
+            report.fail(
+                1,
+                "unknown_alias",
+                format!("No declaration has alias '{old}'."),
+            );
+            return Err(Box::new(report));
+        };
+        let command = prepare_command(project, &Command::SetAlias(id, new)).map_err(|error| {
+            report.fail(1, "semantic_command_rejected", error.to_string());
+            Box::new(report.clone())
+        })?;
+        compiled = source_project::update_bundle_with_identity_map(
+            &compiled,
+            &command.project,
+            &command.identity_map,
+            LIMITS,
+        )
+        .map_err(|diagnostics| {
+            report.status = "invalid".into();
+            report.exit_code = 1;
+            report
+                .diagnostics
+                .extend(diagnostics.into_iter().map(|d| located(d, "candidate")));
+            Box::new(report.clone())
+        })?;
+    }
+    if mutable {
+        for (path, after) in &compiled.bundle.files {
+            let before = raw.files.get(path).cloned().unwrap_or_default();
+            if &before != after {
+                report.changes.push(Change {
+                    path: path.clone(),
+                    diff: unified_diff(path, &before, after),
+                    before,
+                    after: after.clone(),
+                });
+            }
+        }
+        report.status = "preview".into();
+        report.notes.push("This invocation's complete proposed changed-file texts and diffs are reported. Without --write nothing is saved; a later invocation may allocate different missing UUIDs. This is not a saved plan or a digest of unchanged dependencies.".into());
+    }
+    report.notes.push("Diagnostic object IDs are omitted for declarations without authored IDs; lint's temporary identities are not the candidate's identities.".into());
+    report.notes.push("Disk writes use the core journal/conflict checks. This is not cross-process atomic visibility or a power-loss durability guarantee; pending saves are never implicitly recovered. A failed write may require explicit journal recovery.".into());
+    Ok(Prepared {
+        report,
+        snapshot,
+        compiled,
+        mutable,
+    })
+}
+
+/// One bounded hunk per file: common prefix/suffix plus three context lines.
+/// Linear in input size; no quadratic LCS allocation for large modules.
+fn unified_diff(path: &str, before: &str, after: &str) -> String {
+    let a: Vec<_> = before.split_inclusive('\n').collect();
+    let b: Vec<_> = after.split_inclusive('\n').collect();
+    let prefix = a.iter().zip(&b).take_while(|(a, b)| a == b).count();
+    let suffix = a[prefix..]
+        .iter()
+        .rev()
+        .zip(b[prefix..].iter().rev())
+        .take_while(|(a, b)| a == b)
+        .count();
+    let start = prefix.saturating_sub(3);
+    let a_end = (a.len() - suffix + 3).min(a.len());
+    let b_end = (b.len() - suffix + 3).min(b.len());
+    let a_start = if a_end == start { start } else { start + 1 };
+    let b_start = if b_end == start { start } else { start + 1 };
+    let mut out = format!(
+        "--- a/{path}\n+++ b/{path}\n@@ -{a_start},{} +{b_start},{} @@\n",
+        a_end - start,
+        b_end - start
+    );
+    let mut emit = |prefix: char, line: &str| {
+        out.push(prefix);
+        out.push_str(line);
+        if !line.ends_with('\n') {
+            out.push_str("\n\\ No newline at end of file\n");
+        }
+    };
+    for line in &a[start..prefix] {
+        emit(' ', line);
+    }
+    for line in &a[prefix..a.len() - suffix] {
+        emit('-', line);
+    }
+    for line in &b[prefix..b.len() - suffix] {
+        emit('+', line);
+    }
+    for line in &a[a.len() - suffix..a_end] {
+        emit(' ', line);
+    }
+    out
+}
+
+pub struct Arguments {
+    pub entry: PathBuf,
+    pub operation: Operation,
+    pub write: bool,
+    pub json: bool,
+}
+
+pub const HELP: &str = "arcadia check ROOT [--json]\narcadia lint ROOT [--json]\narcadia stabilize ROOT [--write] [--json]\narcadia rename-alias ROOT OLD NEW [--write] [--json]\n\nROOT is an explicit .arcadia entry file; includes resolve relative to it.\nMutation commands preview by default. --write applies this invocation's candidate.\nMissing UUIDs in a preview are provisional until written. No canonical formatting.\nExit: 0 valid/success (engineering warnings allowed), 1 invalid source or semantic\ncommand rejection, 2 usage, 3 disk/path/conflict/pending-journal/output failure.\nNo implicit journal recovery. Limits: 64 MiB, 256 files, include depth32/edges1024,\n100000 graph objects, 250000 records, 500000 ordered references.\n";
+
+pub fn arguments(args: &[std::ffi::OsString]) -> Result<Arguments, String> {
+    let mut positional = Vec::new();
+    let (mut write, mut json) = (false, false);
+    for arg in args {
+        if arg == "--write" && !write {
+            write = true;
+        } else if arg == "--json" && !json {
+            json = true;
+        } else if arg.to_string_lossy().starts_with('-') {
+            return Err(format!(
+                "Unknown or repeated option: {}",
+                arg.to_string_lossy()
+            ));
+        } else {
+            positional.push(arg);
+        }
+    }
+    let command = positional.first().and_then(|s| s.to_str()).unwrap_or("");
+    let operation = match (command, positional.len()) {
+        ("check" | "lint", 2) if !write => Operation::Check,
+        ("stabilize", 2) => Operation::Stabilize,
+        ("rename-alias", 4) => Operation::RenameAlias {
+            old: positional[2].to_str().ok_or("Alias must be UTF-8")?.into(),
+            new: positional[3].to_str().ok_or("Alias must be UTF-8")?.into(),
+        },
+        _ => return Err(HELP.into()),
+    };
+    Ok(Arguments {
+        entry: PathBuf::from(positional[1]),
+        operation,
+        write,
+        json,
+    })
+}

crates/oa-cli/src/main.rs

@@ -0,0 +1,102 @@
+use oa_cli::{Report, arguments, prepare};
+use std::{
+    io::{self, Write},
+    path::Path,
+    process::ExitCode,
+};
+
+fn human_report(report: &Report, show_diff: bool) -> io::Result<()> {
+    let mut err = io::stderr().lock();
+    for d in &report.diagnostics {
+        let at = d
+            .location
+            .as_ref()
+            .map(|l| {
+                format!(
+                    "{}:{}:{}",
+                    l.path,
+                    l.line.unwrap_or(0),
+                    l.column.unwrap_or(0)
+                )
+            })
+            .unwrap_or_else(|| report.entry.clone());
+        writeln!(
+            err,
+            "{at}: {}[{}] ({}): {}",
+            d.severity, d.code, d.coordinate_space, d.message
+        )?;
+    }
+    writeln!(
+        err,
+        "{}: {} file changes; {} identities to stabilize",
+        report.status,
+        report.changes.len(),
+        report.identities_to_stabilize
+    )?;
+    if let Some(migration) = &report.migration {
+        writeln!(
+            err,
+            "Source migration: schema {} → {} (separate from identity stabilization)",
+            migration.from_schema, migration.to_schema
+        )?;
+    }
+    for note in &report.notes {
+        writeln!(err, "{note}")?;
+    }
+    if show_diff {
+        let mut out = io::stdout().lock();
+        for change in &report.changes {
+            write!(out, "{}", change.diff)?;
+        }
+        out.flush()?;
+    }
+    err.flush()
+}
+
+fn run() -> io::Result<u8> {
+    let args: Vec<_> = std::env::args_os().skip(1).collect();
+    if args.len() == 1 && (args[0] == "--help" || args[0] == "-h") {
+        io::stdout().write_all(oa_cli::HELP.as_bytes())?;
+        return Ok(0);
+    }
+    if args.len() == 1 && args[0] == "--version" {
+        writeln!(io::stdout(), "arcadia {}", env!("CARGO_PKG_VERSION"))?;
+        return Ok(0);
+    }
+    let json = args.iter().any(|a| a == "--json");
+    let mut displayed = false;
+    let report = match arguments(&args) {
+        Err(error) => Report::failure(Path::new(""), "usage", 2, "usage", error),
+        Ok(args) => match prepare(&args.entry, args.operation) {
+            Err(report) => *report,
+            Ok(prepared) => {
+                if args.write {
+                    if !args.json {
+                        human_report(prepared.report(), true)?;
+                        displayed = true;
+                    }
+                    prepared.write()
+                } else {
+                    prepared.into_report()
+                }
+            }
+        },
+    };
+    if json {
+        serde_json::to_writer_pretty(io::stdout().lock(), &report)?;
+        writeln!(io::stdout())?;
+    } else {
+        human_report(&report, !displayed)?;
+    }
+    Ok(report.exit_code)
+}
+
+fn main() -> ExitCode {
+    match run() {
+        Ok(code) => ExitCode::from(code),
+        Err(error) => {
+            let _ = writeln!(io::stderr(), "Output failed: {error}");
+            ExitCode::from(3)
+        }
+    }
+}

crates/oa-cli/tests/source_cli.rs

@@ -0,0 +1,425 @@
+use oa_cli::{LIMITS, Operation, Prepared, prepare};
+use oa_core::{Id, Project, source_files, source_project};
+use serde_json::Value;
+use std::{
+    collections::BTreeMap,
+    fs,
+    path::{Path, PathBuf},
+    process::Command,
+};
+
+struct Fixture(PathBuf);
+impl Fixture {
+    fn new() -> Self {
+        let path = std::env::temp_dir().join(format!("arcadia-cli-test-{}", Id::new_v4()));
+        fs::create_dir(&path).unwrap();
+        Self(path)
+    }
+    fn put(&self, name: &str, text: &str) {
+        let path = self.0.join(name);
+        fs::create_dir_all(path.parent().unwrap()).unwrap();
+        fs::write(path, text).unwrap();
+    }
+    fn entry(&self) -> PathBuf {
+        self.0.join("project.arcadia")
+    }
+    fn read(&self, name: &str) -> String {
+        fs::read_to_string(self.0.join(name)).unwrap()
+    }
+    fn prepare(&self, op: Operation) -> Prepared {
+        prepare(&self.entry(), op).unwrap_or_else(|report| panic!("{report:#?}"))
+    }
+    fn model(&self) -> Project {
+        let disk = source_files::load_project(&self.entry(), LIMITS).unwrap();
+        source_project::compile_bundle(&disk.reachable_bundle(), LIMITS)
+            .unwrap()
+            .decoded
+            .project
+    }
+    fn cli(&self, args: &[&str]) -> (i32, Value) {
+        let mut command = Command::new(env!("CARGO_BIN_EXE_arcadia"));
+        command
+            .arg(args[0])
+            .arg(self.entry())
+            .args(&args[1..])
+            .arg("--json");
+        let output = command.output().unwrap();
+        assert!(
+            output.stderr.is_empty(),
+            "{}",
+            String::from_utf8_lossy(&output.stderr)
+        );
+        (
+            output.status.code().unwrap(),
+            serde_json::from_slice(&output.stdout).unwrap(),
+        )
+    }
+}
+impl Drop for Fixture {
+    fn drop(&mut self) {
+        let _ = fs::remove_dir_all(&self.0);
+    }
+}
+
+const SIMPLE: &str = "// 雨: authored defaults stay omitted\r\narcadia 7;\r\nproject rescue \"Rescue\" {\r\n    oa_entity team \"Team\" {}\r\n}\r\n";
+
+#[test]
+fn complete_alarm_example_preview_then_write_and_fixed_point() {
+    let fixture = Fixture::new();
+    let source = include_str!(
+        "../../../harness/experiments/textual-authoring-20260911/alarm-response.arcadia"
+    );
+    fixture.put("project.arcadia", source);
+    let (code, check) = fixture.cli(&["check"]);
+    assert_eq!(code, 0);
+    assert_eq!(check["diagnostics"], serde_json::json!([]));
+    let (code, preview) = fixture.cli(&["stabilize"]);
+    assert_eq!(code, 0);
+    assert_eq!(preview["identities_to_stabilize"], 40);
+    assert_eq!(preview["status"], "preview");
+    assert_eq!(fixture.read("project.arcadia"), source);
+    assert!(
+        preview["changes"][0]["diff"]
+            .as_str()
+            .unwrap()
+            .contains("+project alarm_response")
+    );
+    let (code, written) = fixture.cli(&["stabilize", "--write"]);
+    assert_eq!(code, 0);
+    let saved = fixture.read("project.arcadia");
+    assert_eq!(written["changes"][0]["after"], saved);
+    let project = fixture.model();
+    assert_eq!(project.identities().len(), 40);
+    let mut stripped = saved.clone();
+    for (id, _) in project.identities() {
+        stripped = stripped.replace(&format!(" id \"{id}\""), "");
+    }
+    assert_eq!(stripped, source, "only identity clauses may be inserted");
+    let (code, again) = fixture.cli(&["stabilize", "--write"]);
+    assert_eq!(code, 0);
+    assert_eq!(again["changes"], serde_json::json!([]));
+    assert_eq!(again["status"], "unchanged");
+    assert_eq!(fixture.model(), project);
+    assert_eq!(fixture.read("project.arcadia"), saved);
+}
+
+#[test]
+fn captured_candidate_exact_write_preserves_crlf_comments_and_noop_metadata() {
+    let fixture = Fixture::new();
+    fixture.put("project.arcadia", SIMPLE);
+    let candidate = fixture.prepare(Operation::Stabilize);
+    let expected = candidate.report().changes[0].after.clone();
+    assert_eq!(candidate.report().identities_to_stabilize, 2);
+    assert_eq!(fixture.read("project.arcadia"), SIMPLE);
+    assert_eq!(candidate.write().exit_code, 0);
+    assert_eq!(fixture.read("project.arcadia"), expected);
+    assert!(expected.contains("// 雨: authored defaults stay omitted\r\n"));
+    assert!(!expected.contains("description"));
+    let metadata = fs::metadata(fixture.entry()).unwrap().modified().unwrap();
+    let report = fixture.prepare(Operation::Stabilize).write();
+    assert_eq!(report.status, "unchanged");
+    assert!(!report.written);
+    assert_eq!(
+        fs::metadata(fixture.entry()).unwrap().modified().unwrap(),
+        metadata
+    );
+    assert_eq!(fs::read_dir(&fixture.0).unwrap().count(), 1);
+}
+
+#[test]
+fn alias_rename_across_modules_changes_only_live_tokens_and_retains_all_identity() {
+    let fixture = Fixture::new();
+    fixture.put("project.arcadia", "arcadia 7; project rescue \"Rescue\" { include \"participants.arcadia\"; include \"work.arcadia\"; }\n");
+    fixture.put(
+        "participants.arcadia",
+        "// @team is quoted documentation\noa_entity team \"Team @team\" {}\n",
+    );
+    fixture.put("work.arcadia", "oa_activity assess \"Assess\" {}\noa_activity report \"Report\" {}\nallocation assigned \"Assigned\" { source @team; target @assess; }\ninteraction transfer \"Transfer\" { source @assess; target @report; }\n");
+    assert_eq!(fixture.prepare(Operation::Stabilize).write().exit_code, 0);
+    let before = fixture.model();
+    let original: BTreeMap<_, _> = ["project.arcadia", "participants.arcadia", "work.arcadia"]
+        .into_iter()
+        .map(|p| (p, fixture.read(p)))
+        .collect();
+    let team = before
+        .identities()
+        .into_iter()
+        .find(|(_, alias)| *alias == "team")
+        .unwrap()
+        .0;
+    let candidate = fixture.prepare(Operation::RenameAlias {
+        old: "team".into(),
+        new: "rescue_team".into(),
+    });
+    assert_eq!(candidate.report().changes.len(), 2);
+    assert_eq!(fixture.model(), before, "preview cannot mutate");
+    assert_eq!(candidate.write().exit_code, 0);
+    let mut expected = before;
+    expected.elements.get_mut(&team).unwrap().alias = "rescue_team".into();
+    assert_eq!(fixture.model(), expected);
+    assert_eq!(fixture.read("project.arcadia"), original["project.arcadia"]);
+    assert_eq!(
+        fixture.read("participants.arcadia"),
+        original["participants.arcadia"].replacen("oa_entity team ", "oa_entity rescue_team ", 1)
+    );
+    assert_eq!(
+        fixture.read("work.arcadia"),
+        original["work.arcadia"].replace("source @team;", "source @rescue_team;")
+    );
+}
+
+#[test]
+fn invalid_unicode_raw_edit_is_located_and_never_stabilized_or_written() {
+    let fixture = Fixture::new();
+    let raw = "arcadia 7; project p \"雨\" {\n oa_activity a \"A\" {}\n allocation alloc \"Alloc\" { source @missing; target @a; }\n}\n";
+    fixture.put("project.arcadia", raw);
+    for command in [
+        vec!["check"],
+        vec!["stabilize", "--write"],
+        vec!["rename-alias", "a", "b", "--write"],
+    ] {
+        let (code, report) = fixture.cli(&command);
+        assert_eq!(code, 1);
+        assert_eq!(fixture.read("project.arcadia"), raw);
+        let diagnostics = report["diagnostics"].as_array().unwrap();
+        assert!(!diagnostics.is_empty());
+        for d in diagnostics {
+            assert_eq!(d["coordinate_space"], "input");
+            let at = &d["location"];
+            let start = at["start"].as_u64().unwrap() as usize;
+            assert!(raw.is_char_boundary(start));
+            assert_eq!(
+                at["line"].as_u64().unwrap() as usize,
+                raw[..start].bytes().filter(|b| *b == b'\n').count() + 1
+            );
+            let line = raw[..start]
+                .rsplit_once('\n')
+                .map_or(&raw[..start], |(_, tail)| tail);
+            assert_eq!(
+                at["column"].as_u64().unwrap() as usize,
+                line.chars().count() + 1
+            );
+        }
+    }
+}
+
+#[test]
+fn missing_id_warning_uses_raw_location_and_never_exposes_ephemeral_lint_id() {
+    let fixture = Fixture::new();
+    let raw = "arcadia 7;\nproject p \"雨\" {\n    oa_activity work \"Work\" {}\n}\n";
+    fixture.put("project.arcadia", raw);
+    let (code, result) = fixture.cli(&["lint"]);
+    assert_eq!(code, 0, "engineering warnings do not reject admission");
+    let warning = result["diagnostics"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .find(|d| d["code"] == "work_without_behavior_context")
+        .unwrap();
+    assert_eq!(warning["severity"], "warning");
+    assert_eq!(
+        warning["location"]["start"],
+        raw.find("oa_activity").unwrap()
+    );
+    assert_eq!(warning["location"]["line"], 3);
+    assert_eq!(warning["location"]["column"], 5);
+    assert!(warning["object_id"].is_null());
+    assert_eq!(fixture.read("project.arcadia"), raw);
+}
+
+#[test]
+fn captured_dependency_change_refuses_all_writes_even_on_noop() {
+    let fixture = Fixture::new();
+    fixture.put("project.arcadia", SIMPLE);
+    let pending = fixture.prepare(Operation::Stabilize);
+    let external = format!("{SIMPLE}// editor changed this\n");
+    fixture.put("project.arcadia", &external);
+    let result = pending.write();
+    assert_eq!(result.exit_code, 3);
+    assert_eq!(result.diagnostics.last().unwrap().code, "external_change");
+    assert_eq!(fixture.read("project.arcadia"), external);
+    assert_eq!(fixture.prepare(Operation::Stabilize).write().exit_code, 0);
+    let noop = fixture.prepare(Operation::Stabilize);
+    assert!(noop.report().changes.is_empty());
+    let latest = format!("{}// another edit\n", fixture.read("project.arcadia"));
+    fixture.put("project.arcadia", &latest);
+    assert_eq!(noop.write().exit_code, 3);
+    assert_eq!(fixture.read("project.arcadia"), latest);
+}
+
+#[test]
+fn pending_journal_refuses_read_preview_and_write_without_recovery() {
+    let fixture = Fixture::new();
+    fixture.put("project.arcadia", SIMPLE);
+    assert_eq!(fixture.prepare(Operation::Stabilize).write().exit_code, 0);
+    let noop = fixture.prepare(Operation::Stabilize);
+    let source = fixture.read("project.arcadia");
+    // An opaque incomplete journal must never be interpreted/recovered by CLI.
+    let journal = fixture.0.join(".arcadia-save-project.arcadia.journal");
+    fs::create_dir(&journal).unwrap();
+    fs::write(journal.join("sentinel"), b"retain").unwrap();
+    for op in [Operation::Check, Operation::Stabilize] {
+        let report = prepare(&fixture.entry(), op).err().unwrap();
+        assert_eq!(report.exit_code, 3);
+        assert!(report.diagnostics.iter().any(|d| d.code == "pending_save"));
+    }
+    assert_eq!(
+        noop.write().exit_code,
+        3,
+        "saver must recheck after preview"
+    );
+    assert_eq!(fixture.read("project.arcadia"), source);
+    assert_eq!(fs::read(journal.join("sentinel")).unwrap(), b"retain");
+}
+
+#[test]
+fn rejected_alias_and_same_alias_preserve_source() {
+    let fixture = Fixture::new();
+    fixture.put("project.arcadia", SIMPLE);
+    assert_eq!(fixture.prepare(Operation::Stabilize).write().exit_code, 0);
+    let source = fixture.read("project.arcadia");
+    for (old, new) in [
+        ("team", "rescue"),
+        ("team", "invalid alias"),
+        ("absent", "valid"),
+    ] {
+        let (code, result) = fixture.cli(&["rename-alias", old, new, "--write"]);
+        assert_eq!(code, 1);
+        assert_eq!(result["status"], "rejected");
+        assert_eq!(fixture.read("project.arcadia"), source);
+    }
+    let (code, result) = fixture.cli(&["rename-alias", "team", "team", "--write"]);
+    assert_eq!(code, 0);
+    assert_eq!(result["status"], "unchanged");
+    assert_eq!(fixture.read("project.arcadia"), source);
+}
+
+#[test]
+fn rename_shows_missing_identity_and_separate_source_migration() {
+    let fixture = Fixture::new();
+    let old = "// retain\narcadia 5; project p \"P\" { oa_entity team \"Team\" {} }\n";
+    fixture.put("project.arcadia", old);
+    let candidate = fixture.prepare(Operation::RenameAlias {
+        old: "team".into(),
+        new: "crew".into(),
+    });
+    let report = candidate.report();
+    assert_eq!(report.identities_to_stabilize, 2);
+    assert_eq!(report.migration.as_ref().unwrap().from_schema, 5);
+    assert_eq!(report.migration.as_ref().unwrap().to_schema, 7);
+    assert!(report.changes[0].diff.contains("-arcadia 5;"));
+    assert!(report.changes[0].diff.contains("+arcadia 7;"));
+    assert!(report.changes[0].after.contains("oa_entity crew"));
+    assert_eq!(fixture.read("project.arcadia"), old);
+    assert_eq!(candidate.write().exit_code, 0);
+}
+
+#[test]
+fn entry_is_explicit_and_machine_readable_usage_errors_do_not_write() {
+    let fixture = Fixture::new();
+    fixture.put("project.arcadia", SIMPLE);
+    let output = Command::new(env!("CARGO_BIN_EXE_arcadia"))
+        .current_dir(&fixture.0)
+        .args(["check", "--json"])
+        .output()
+        .unwrap();
+    assert_eq!(output.status.code(), Some(2));
+    let error: Value = serde_json::from_slice(&output.stdout).unwrap();
+    assert_eq!(error["diagnostics"][0]["code"], "usage");
+    assert_eq!(fixture.read("project.arcadia"), SIMPLE);
+    let (code, _) = fixture.cli(&["check", "--write"]);
+    assert_eq!(code, 2);
+    assert!(Path::new(env!("CARGO_BIN_EXE_arcadia")).is_file());
+}
+
+#[test]
+fn loader_encoding_missing_dependency_and_invalid_old_source_keep_original_bytes() {
+    let fixture = Fixture::new();
+    let entry = "arcadia 7; project p \"P\" { include \"part.arcadia\"; }";
+    fixture.put("project.arcadia", entry);
+    let (code, report) = fixture.cli(&["stabilize", "--write"]);
+    assert_eq!(code, 3, "a disk dependency could not be read");
+    assert!(
+        report["diagnostics"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .any(|d| d["code"] == "missing_include")
+    );
+    fs::write(fixture.0.join("part.arcadia"), [0xff, 0xfe]).unwrap();
+    let (code, report) = fixture.cli(&["stabilize", "--write"]);
+    assert_eq!(code, 1, "invalid encoding is invalid raw source");
+    assert!(
+        report["diagnostics"]
+            .as_array()
+            .unwrap()
+            .iter()
+            .any(|d| d["code"] == "source_encoding")
+    );
+    assert_eq!(fixture.read("project.arcadia"), entry);
+    assert_eq!(
+        fs::read(fixture.0.join("part.arcadia")).unwrap(),
+        [0xff, 0xfe]
+    );
+    for raw in [
+        "arcadia 5; project p \"P\" { oa_entity a \"A\" { ??? } }",
+        "arcadia 2; project p \"P\" {}",
+    ] {
+        fixture.put("project.arcadia", raw);
+        let (code, _) = fixture.cli(&["stabilize", "--write"]);
+        assert_eq!(code, 1);
+        assert_eq!(fixture.read("project.arcadia"), raw);
+    }
+}
+
+#[test]
+fn non_element_alias_detached_file_and_unchanged_dependency_conflict() {
+    let fixture = Fixture::new();
+    fixture.put("project.arcadia", "arcadia 7; project p \"P\" { include \"part.arcadia\"; oa_activity a \"A\" {} allocation responsible \"Responsible\" { source @ // keep edge comment\nteam; target @a; } }");
+    fixture.put("part.arcadia", "oa_entity team \"Team\" {}");
+    fixture.put(
+        "detached.arcadia",
+        "invalid detached draft must stay exact 雨",
+    );
+    assert_eq!(fixture.prepare(Operation::Stabilize).write().exit_code, 0);
+    let before = fixture.model();
+    let relation = before
+        .identities()
+        .into_iter()
+        .find(|(_, alias)| *alias == "responsible")
+        .unwrap()
+        .0;
+    let (code, _) = fixture.cli(&["rename-alias", "responsible", "performs", "--write"]);
+    assert_eq!(code, 0);
+    let mut expected = before;
+    expected.relations.get_mut(&relation).unwrap().alias = "performs".into();
+    assert_eq!(fixture.model(), expected);
+    assert!(
+        fixture
+            .read("project.arcadia")
+            .contains("@ // keep edge comment\nteam")
+    );
+    let captured = fixture.prepare(Operation::RenameAlias {
+        old: "p".into(),
+        new: "rescue".into(),
+    });
+    assert!(
+        captured
+            .report()
+            .changes
+            .iter()
+            .all(|c| c.path != "part.arcadia")
+    );
+    let root_before = fixture.read("project.arcadia");
+    fixture.put("part.arcadia", "// external unchanged-dependency edit\n");
+    assert_eq!(captured.write().exit_code, 3);
+    assert_eq!(fixture.read("project.arcadia"), root_before);
+    assert_eq!(
+        fixture.read("part.arcadia"),
+        "// external unchanged-dependency edit\n"
+    );
+    assert_eq!(
+        fixture.read("detached.arcadia"),
+        "invalid detached draft must stay exact 雨"
+    );
+}

crates/oa-core/examples/release_dense_views.rs

@@ -230,7 +230,7 @@ fn fixture() -> (Project, Id, Vec<Id>, Vec<Id>, Vec<Id>) {
             )
         })
         .collect();
-    p.diagrams.insert(diagram, Diagram { id: diagram, alias: "forty_exchange_view".into(), name: "Forty service exchanges · all concerns".into(), description: "Start with All. Compare first category, overlapping concerns, global coverage and chosen processes. No hand-routed edges.".into(), layer: Layer::Oa, projection: ProjectionKind::FunctionalDataflow, view_options: ViewOptions::default(), nodes, routes: vec![] });
+    p.diagrams.insert(diagram, Diagram { id: diagram, alias: "forty_exchange_view".into(), name: "Forty service exchanges · all concerns".into(), description: "Start with All. Compare first category, overlapping concerns, global coverage and chosen processes. No hand-routed edges.".into(), layer: Layer::Oa, projection: ProjectionKind::FunctionalDataflow, view_options: ViewOptions::default(), nodes, layout: None, routes: vec![] });
     (p, diagram, exchanges, categories, contexts)
 }
 

crates/oa-core/src/demo.rs

@@ -81,6 +81,7 @@ fn diagram(
             projection,
             view_options: Default::default(),
             nodes: BTreeMap::new(),
+            layout: None,
             routes: vec![],
         },
     );

crates/oa-core/src/language.rs

@@ -142,12 +142,87 @@ pub struct Analysis {
     pub declarations: Vec<DeclarationSpan>,
 }
 
+/// Check the decoded spelling required by declaration-header UUID clauses.
+/// This is the shared 36-byte/hyphen shape rule, not a hexadecimal parser:
+/// callers must additionally parse the UUID. Uppercase hex and JSON escapes
+/// that decode to this spelling remain accepted. URN/braced/compact forms do not.
+pub fn has_uuid_header_shape(decoded: &str) -> bool {
+    decoded.len() == 36
+        && [8, 13, 18, 23]
+            .into_iter()
+            .all(|index| decoded.as_bytes()[index] == b'-')
+}
+
+/// Budgets for one original source buffer. Policy is caller-owned; these
+/// limits do not change the grammar or perform model admission.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct OutlineLimits {
+    pub max_source_bytes: usize,
+    pub max_tokens: usize,
+    pub max_declarations: usize,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum OutlineResource {
+    SourceBytes,
+    Tokens,
+    Declarations,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct OutlineLimit {
+    pub resource: OutlineResource,
+    pub limit: usize,
+    pub observed_at_least: usize,
+    /// Original byte offset where admission stopped; never a rewritten offset.
+    pub offset: usize,
+}
+
+/// Roles discovered by the existing tolerant declaration walk. Keeping the
+/// wrapper preserves DeclarationSpan and Analysis as existing public APIs.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct OutlineDeclaration {
+    pub declaration: DeclarationSpan,
+    pub kind_span: Span,
+    pub alias_span: Span,
+    /// Whole quoted header ID token, even if it is not a valid UUID. In that
+    /// case declaration.id is None. Missing/non-string ID values have no span.
+    pub id_literal_span: Option<Span>,
+}
+
+/// A full-file tolerant scan, not a successful parse or validated model. Invalid
+/// text remains available. Lexical errors and unmatched braces are facts only:
+/// their absence does not establish syntactic or semantic validity.
+///
+/// A budget failure returns Err and no partial Outline. Include reachability,
+/// project completeness and editor revision are intentionally not inferred here.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Outline<'a> {
+    pub source: &'a str,
+    pub tokens: Vec<TokenSpan>,
+    pub declarations: Vec<OutlineDeclaration>,
+    pub has_lexical_errors: bool,
+    pub has_unmatched_braces: bool,
+}
+
 /// Tolerant highlighting tokens cover the whole input, including incomplete
 /// strings and unexpected characters. No model is created or modified.
 pub fn tokenize(source: &str) -> Vec<TokenSpan> {
+    tokenize_with_limit(source, usize::MAX).expect("unlimited token scan")
+}
+
+fn tokenize_with_limit(source: &str, max_tokens: usize) -> Result<Vec<TokenSpan>, OutlineLimit> {
     let mut tokens = Vec::new();
     let mut cursor = 0;
     while cursor < source.len() {
+        if tokens.len() == max_tokens {
+            return Err(OutlineLimit {
+                resource: OutlineResource::Tokens,
+                limit: max_tokens,
+                observed_at_least: tokens.len().saturating_add(1),
+                offset: cursor,
+            });
+        }
         let start = cursor;
         let ch = source[cursor..].chars().next().expect("in bounds");
         let class = if matches!(ch, ' ' | '\t' | '\r' | '\n') {
@@ -224,7 +299,7 @@ pub fn tokenize(source: &str) -> Vec<TokenSpan> {
             span: Span { start, end: cursor },
         });
     }
-    tokens
+    Ok(tokens)
 }
 
 pub fn lint(source: &str) -> Vec<Diagnostic> {
@@ -1230,11 +1305,7 @@ impl Parser<'_> {
         self.cursor += 1;
         let offset = self.current().span.start;
         let value = self.quoted()?;
-        if value.len() != 36
-            || ![8, 13, 18, 23]
-                .into_iter()
-                .all(|i| value.as_bytes()[i] == b'-')
-        {
+        if !has_uuid_header_shape(&value) {
             return Err(Error {
                 code: "invalid_source",
                 offset,
@@ -1752,7 +1823,7 @@ pub(crate) fn resolve_declarations(
                         return Err(conversion_error(std::format!("Unknown diagram field '{key}' in the frozen pre6 contract.")));
                     }
                     let defaults =
-                        serde_json::json!({"description":"","layer":"Oa","projection":"Overview","routes":[],"view_options":crate::view_options::ViewOptions::default()});
+                        serde_json::json!({"description":"","layer":"Oa","projection":"Overview","routes":[],"view_options":crate::view_options::ViewOptions::default(),"layout":null});
                     let mut record = merge_fields(defaults.as_object().unwrap().clone(), fields)
                         .map_err(&conversion_error)?;
                     header(&mut record, d, true);
@@ -1962,8 +2033,49 @@ fn take_required_id(fields: &mut Map<String, Value>, key: &str) -> Result<Id, St
 
 /// Analyze an incomplete source buffer without adopting a candidate. Declaration
 /// spans remain available even when a later declaration contains errors.
+/// Invalid compact/braced/URN header IDs retain no authored identity, matching
+/// the declaration parser rather than the UUID crate's broader accepted forms.
 pub fn analyze(source: &str) -> Analysis {
     let tokens = tokenize(source);
+    let (declarations, _) =
+        declaration_outline(source, &tokens, usize::MAX).expect("unlimited declaration walk");
+    Analysis {
+        tokens,
+        diagnostics: lint(source),
+        declarations: declarations.into_iter().map(|d| d.declaration).collect(),
+    }
+}
+
+/// Read exact current text without lint, parsing a model, stabilization or I/O.
+/// Source bytes are admitted before token allocation; token/declaration limits
+/// are checked before lexing the next token or materializing the next record.
+pub fn outline(source: &str, limits: OutlineLimits) -> Result<Outline<'_>, OutlineLimit> {
+    if source.len() > limits.max_source_bytes {
+        return Err(OutlineLimit {
+            resource: OutlineResource::SourceBytes,
+            limit: limits.max_source_bytes,
+            observed_at_least: source.len(),
+            offset: 0,
+        });
+    }
+    let tokens = tokenize_with_limit(source, limits.max_tokens)?;
+    let has_lexical_errors = tokens.iter().any(|token| token.class == TokenClass::Error);
+    let (declarations, has_unmatched_braces) =
+        declaration_outline(source, &tokens, limits.max_declarations)?;
+    Ok(Outline {
+        source,
+        tokens,
+        declarations,
+        has_lexical_errors,
+        has_unmatched_braces,
+    })
+}
+
+fn declaration_outline(
+    source: &str,
+    tokens: &[TokenSpan],
+    max_declarations: usize,
+) -> Result<(Vec<OutlineDeclaration>, bool), OutlineLimit> {
     let significant = tokens
         .iter()
         .filter(|t| !matches!(t.class, TokenClass::Whitespace | TokenClass::Comment))
@@ -1972,17 +2084,21 @@ pub fn analyze(source: &str) -> Analysis {
     // again would make tolerant navigation quadratic on deeply nested drafts.
     let mut body_ends = vec![None; significant.len()];
     let mut bodies = Vec::new();
+    let mut unmatched_close = false;
     for (index, token) in significant.iter().enumerate() {
         match &source[token.span.start..token.span.end] {
             "{" => bodies.push(index),
             "}" => {
                 if let Some(open) = bodies.pop() {
                     body_ends[open] = Some(token.span.end);
+                } else {
+                    unmatched_close = true;
                 }
             }
             _ => {}
         }
     }
+    let has_unmatched_braces = unmatched_close || !bodies.is_empty();
     let mut declarations = Vec::new();
     for (i, t) in significant.iter().enumerate() {
         let word = &source[t.span.start..t.span.end];
@@ -2007,7 +2123,16 @@ pub fn analyze(source: &str) -> Analysis {
             }
             j += 1;
         }
+        if declarations.len() == max_declarations {
+            return Err(OutlineLimit {
+                resource: OutlineResource::Declarations,
+                limit: max_declarations,
+                observed_at_least: declarations.len().saturating_add(1),
+                offset: t.span.start,
+            });
+        }
         let mut id = None;
+        let mut id_literal_span = None;
         if significant
             .get(j)
             .is_some_and(|t| &source[t.span.start..t.span.end] == "id")
@@ -2015,39 +2140,51 @@ pub fn analyze(source: &str) -> Analysis {
             if let Some(value) = significant.get(j + 1)
                 && value.class == TokenClass::String
             {
+                id_literal_span = Some(value.span);
                 let text =
                     serde_json::from_str::<String>(&source[value.span.start..value.span.end])
                         .unwrap();
-                id = Id::parse_str(&text).ok();
+                if has_uuid_header_shape(&text) {
+                    id = Id::parse_str(&text).ok();
+                }
             }
             j += 2;
         }
-        let mut end = significant
-            .get(j)
-            .map_or(alias_token.span.end, |t| t.span.end);
+        // A recognized header ID at EOF must remain inside the whole span.
+        // Keep the old next-token/body behavior; only the EOF fallback changes.
+        let header_end = significant
+            .get(j.saturating_sub(1))
+            .or_else(|| significant.last())
+            .map_or(alias_token.span.end, |token| token.span.end);
+        let mut end = significant.get(j).map_or(header_end, |t| t.span.end);
         if significant
             .get(j)
             .is_some_and(|t| &source[t.span.start..t.span.end] == "{")
         {
             end = body_ends[j].unwrap_or(source.len());
         }
-        declarations.push(DeclarationSpan {
-            alias: alias.into(),
-            id,
-            kind: word.into(),
-            span: Span {
-                start: t.span.start,
-                end,
+        declarations.push(OutlineDeclaration {
+            declaration: DeclarationSpan {
+                alias: alias.into(),
+                id,
+                kind: word.into(),
+                span: Span {
+                    start: t.span.start,
+                    end,
+                },
             },
+            kind_span: t.span,
+            alias_span: alias_token.span,
+            id_literal_span,
         });
     }
-    Analysis {
-        tokens,
-        diagnostics: lint(source),
-        declarations,
-    }
+    Ok((declarations, has_unmatched_braces))
 }
 
+#[cfg(test)]
+#[path = "language_outline_tests.rs"]
+mod outline_tests;
+
 #[cfg(test)]
 #[path = "language_nesting_tests.rs"]
 mod nesting_tests;
@@ -2442,11 +2579,7 @@ pub(crate) mod legacy {
             let value = self.quoted()?;
             // Require the portable 8-4-4-4-12 spelling, not the UUID crate's URN,
             // braces, or compact alternatives. Uppercase hexadecimal is accepted.
-            if value.len() != 36
-                || ![8, 13, 18, 23]
-                    .into_iter()
-                    .all(|index| value.as_bytes()[index] == b'-')
-            {
+            if !super::has_uuid_header_shape(&value) {
                 return Err(Error {
                     code: "invalid_source",
                     offset,

crates/oa-core/src/language_outline_tests.rs

@@ -0,0 +1,386 @@
+//! Prepared outline tests. Explicit compatibility tests additionally exercise
+//! the existing parsers/analyze; the outline entry itself never calls them.
+use super::*;
+
+fn limits() -> OutlineLimits {
+    OutlineLimits {
+        max_source_bytes: 1024 * 1024,
+        max_tokens: 100_000,
+        max_declarations: 1_000,
+    }
+}
+
+fn declaration<'a>(result: &'a Outline<'_>, alias: &str) -> &'a OutlineDeclaration {
+    result
+        .declarations
+        .iter()
+        .find(|d| d.declaration.alias == alias)
+        .unwrap()
+}
+
+fn text(source: &str, span: Span) -> &str {
+    &source[span.start..span.end]
+}
+
+#[test]
+fn outline_roles_preserve_unicode_crlf_and_exact_escaped_uuid_literal() {
+    let source = "// 検査 🚒\r\noa_actor responder \"救助\" id \"\\u00300000000-0000-0000-0000-000000000001\" {}\r\nsource @ // 使用\r\n responder;";
+    let before = source.as_bytes().to_vec();
+    let result = outline(source, limits()).unwrap();
+    assert_eq!(result.source.as_bytes(), before);
+    assert_eq!(result.source.as_ptr(), source.as_ptr());
+    let d = declaration(&result, "responder");
+    assert_eq!(text(source, d.kind_span), "oa_actor");
+    assert_eq!(text(source, d.alias_span), "responder");
+    assert_eq!(
+        text(source, d.id_literal_span.unwrap()),
+        "\"\\u00300000000-0000-0000-0000-000000000001\""
+    );
+    assert_eq!(d.declaration.id, Some(Id::from_u128(1)));
+    assert_eq!(d.declaration.span.start, source.find("oa_actor").unwrap());
+    assert_eq!(d.declaration.span.end, source.find("{}\r\n").unwrap() + 2);
+    let mut end = 0;
+    for token in &result.tokens {
+        assert_eq!(token.span.start, end);
+        assert!(token.span.start < token.span.end);
+        assert!(source.is_char_boundary(token.span.start));
+        assert!(source.is_char_boundary(token.span.end));
+        end = token.span.end;
+    }
+    assert_eq!(end, source.len());
+    assert!(!result.has_lexical_errors);
+    assert!(!result.has_unmatched_braces);
+}
+
+#[test]
+fn closed_id_at_eof_is_inside_the_declaration_extent() {
+    for source in [
+        "oa_actor a \"Actor\" id \"00000000-0000-0000-0000-000000000001\"",
+        "node placed id \"00000000-0000-0000-0000-000000000001\"",
+    ] {
+        let result = outline(source, limits()).unwrap();
+        let d = &result.declarations[0];
+        let literal = d.id_literal_span.unwrap();
+        assert_eq!(d.declaration.id, Some(Id::from_u128(1)));
+        assert_eq!(d.declaration.span.end, source.len());
+        assert!(d.declaration.span.start <= literal.start);
+        assert!(literal.end <= d.declaration.span.end);
+    }
+    for source in ["oa_actor a \"Actor\"", "oa_actor a \"Actor\" id"] {
+        let result = outline(source, limits()).unwrap();
+        let d = &result.declarations[0];
+        assert_eq!(d.declaration.span.end, source.len());
+        assert_eq!(d.declaration.id, None);
+        assert_eq!(d.id_literal_span, None);
+    }
+}
+
+#[test]
+fn missing_bad_and_historical_ids_never_allocate_authored_identity() {
+    let source = "oa_actor missing \"No ID\" {}\noa_actor bad \"Bad ID\" id \"not-a-uuid\" {}\noa_actor historical \"00000000-0000-0000-0000-000000000001\" { history uuid \"00000000-0000-0000-0000-000000000001\"; }";
+    let first = outline(source, limits()).unwrap();
+    let second = outline(source, limits()).unwrap();
+    assert_eq!(first, second);
+    assert!(
+        first
+            .declarations
+            .iter()
+            .all(|d| d.declaration.id.is_none())
+    );
+    assert_eq!(declaration(&first, "missing").id_literal_span, None);
+    assert_eq!(declaration(&first, "historical").id_literal_span, None);
+    assert_eq!(
+        text(source, declaration(&first, "bad").id_literal_span.unwrap()),
+        "\"not-a-uuid\""
+    );
+    // Balanced tokens are not a successful syntax/semantic validation claim.
+    assert!(!first.has_lexical_errors);
+    assert!(!first.has_unmatched_braces);
+}
+
+#[test]
+fn invalid_full_scan_keeps_closed_children_and_reports_lexical_body_facts() {
+    let source = "oa_entity outer \"Outer\" {\n oa_actor ready \"Ready\" { description \"} stays text\"; }\n oa_actor pending \"Pending\" { description \"unfinished 🌊";
+    let result = outline(source, limits()).unwrap();
+    assert_eq!(result.source, source);
+    assert_eq!(result.tokens.last().unwrap().span.end, source.len());
+    assert!(result.has_lexical_errors);
+    assert!(result.has_unmatched_braces);
+    let ready = declaration(&result, "ready");
+    assert_eq!(
+        text(source, ready.declaration.span),
+        "oa_actor ready \"Ready\" { description \"} stays text\"; }"
+    );
+    assert_eq!(
+        declaration(&result, "outer").declaration.span.end,
+        source.len()
+    );
+    assert_eq!(
+        declaration(&result, "pending").declaration.span.end,
+        source.len()
+    );
+    let unmatched_close = outline("}\n// brace in comment {\n", limits()).unwrap();
+    assert!(unmatched_close.has_unmatched_braces);
+    assert!(!unmatched_close.has_lexical_errors);
+}
+
+#[test]
+fn missing_body_syntax_is_unchecked_even_when_known_error_flags_are_clear() {
+    let source = "oa_actor a \"A\" id \"00000000-0000-0000-0000-000000000001\"";
+    let result = outline(source, limits()).unwrap();
+    assert_eq!(result.declarations.len(), 1);
+    assert!(!result.has_lexical_errors);
+    assert!(!result.has_unmatched_braces);
+    // There is deliberately no `valid` flag: the known-complete fact is scanning
+    // these bytes, not the missing body becoming legal or the draft being applied.
+    assert_eq!(result.source, source);
+}
+
+#[test]
+fn keyword_alias_and_collisions_keep_every_source_ordered_header() {
+    let source = "project root_model \"Model\" {\n oa_actor oa_activity \"First\" id \"00000000-0000-0000-0000-000000000001\" {}\n oa_actor oa_activity \"Second\" id \"00000000-0000-0000-0000-000000000001\" {}\n diagram view_one \"View\" {}\n node placement { diagram @view_one; }\n}";
+    let result = outline(source, limits()).unwrap();
+    assert_eq!(result.declarations.len(), 5);
+    let duplicates: Vec<_> = result
+        .declarations
+        .iter()
+        .filter(|d| d.declaration.alias == "oa_activity")
+        .collect();
+    assert_eq!(duplicates.len(), 2);
+    assert!(duplicates[0].alias_span.start < duplicates[1].alias_span.start);
+    assert_eq!(duplicates[0].declaration.id, duplicates[1].declaration.id);
+    assert!(
+        result
+            .tokens
+            .iter()
+            .any(|t| t.span == duplicates[0].alias_span && t.class == TokenClass::Keyword)
+    );
+    assert_eq!(
+        text(source, declaration(&result, "placement").kind_span),
+        "node"
+    );
+    assert_eq!(declaration(&result, "placement").declaration.id, None);
+}
+
+#[test]
+fn bounds_refuse_before_returning_a_partial_outline() {
+    let source = "oa_actor a \"A\" {}\noa_actor b \"B\" {}";
+    let admitted = outline(source, limits()).unwrap();
+    let exact = OutlineLimits {
+        max_source_bytes: source.len(),
+        max_tokens: admitted.tokens.len(),
+        max_declarations: 2,
+    };
+    assert_eq!(outline(source, exact).unwrap(), admitted);
+    for resource in [
+        OutlineResource::SourceBytes,
+        OutlineResource::Tokens,
+        OutlineResource::Declarations,
+    ] {
+        let mut lower = exact;
+        match resource {
+            OutlineResource::SourceBytes => lower.max_source_bytes -= 1,
+            OutlineResource::Tokens => lower.max_tokens -= 1,
+            OutlineResource::Declarations => lower.max_declarations -= 1,
+        }
+        let error = outline(source, lower).unwrap_err();
+        assert_eq!(error.resource, resource);
+        assert!(error.observed_at_least > error.limit);
+        assert!(source.is_char_boundary(error.offset));
+        if resource == OutlineResource::Declarations {
+            assert_eq!(error.offset, source.find("oa_actor b").unwrap());
+        }
+    }
+    let empty = outline(
+        "",
+        OutlineLimits {
+            max_source_bytes: 0,
+            max_tokens: 0,
+            max_declarations: 0,
+        },
+    )
+    .unwrap();
+    assert!(empty.tokens.is_empty() && empty.declarations.is_empty());
+    let unicode = "// 🌊\r\noa_actor a \"A\" {}";
+    let error = outline(
+        unicode,
+        OutlineLimits {
+            max_source_bytes: 4,
+            ..limits()
+        },
+    )
+    .unwrap_err();
+    assert_eq!(error.resource, OutlineResource::SourceBytes);
+    assert_eq!(error.offset, 0);
+    let error = outline(
+        unicode,
+        OutlineLimits {
+            max_tokens: 1,
+            ..limits()
+        },
+    )
+    .unwrap_err();
+    assert_eq!(error.resource, OutlineResource::Tokens);
+    assert_eq!(error.offset, unicode.find('\n').unwrap());
+}
+
+#[test]
+fn outline_ranges_follow_current_bytes_without_identity_stabilization() {
+    let old = "oa_actor a \"A\" {}\nsource @a;";
+    let current = format!("// 航海 🚒\r\n{old}");
+    let old_outline = outline(old, limits()).unwrap();
+    let current_outline = outline(&current, limits()).unwrap();
+    let shift = current.len() - old.len();
+    let old_role = &old_outline.declarations[0];
+    let current_role = &current_outline.declarations[0];
+    assert_eq!(
+        current_role.alias_span.start,
+        old_role.alias_span.start + shift
+    );
+    assert_eq!(
+        current_role.kind_span.start,
+        old_role.kind_span.start + shift
+    );
+    assert_eq!(
+        current_role.declaration.span.end,
+        old_role.declaration.span.end + shift
+    );
+    assert_eq!(current_outline.source, current);
+    assert_eq!(old_outline.source, old);
+    assert_eq!(current_role.declaration.id, None);
+    assert!(!current_outline.source.contains(" id "));
+    // Workspace revision/stale-handle rejection belongs to the query/adapter,
+    // not a claim that an old owned span can be applied to any other string.
+}
+
+#[test]
+fn deeply_nested_bounds_use_the_same_iterative_walk_and_declaration_budget() {
+    let mut source = String::new();
+    for index in 0..600 {
+        source.push_str(&format!("oa_activity work_{index} \"Work\" {{\n"));
+    }
+    source.push_str(&"}\n".repeat(600));
+    let result = outline(&source, limits()).unwrap();
+    assert_eq!(result.declarations.len(), 600);
+    assert!(!result.has_unmatched_braces);
+    assert_eq!(
+        result.declarations[0].declaration.span.end,
+        source.len() - 1
+    );
+    let error = outline(
+        &source,
+        OutlineLimits {
+            max_declarations: 599,
+            ..limits()
+        },
+    )
+    .unwrap_err();
+    assert_eq!(error.resource, OutlineResource::Declarations);
+    assert_eq!(error.observed_at_least, 600);
+    assert_eq!(error.offset, source.find("oa_activity work_599").unwrap());
+}
+
+#[test]
+fn noncanonical_uuid_spellings_have_no_outline_or_analysis_identity() {
+    for raw in [
+        "00000000000000000000000000000001",
+        "{00000000-0000-0000-0000-000000000001}",
+        "urn:uuid:00000000-0000-0000-0000-000000000001",
+    ] {
+        assert!(
+            Id::parse_str(raw).is_ok(),
+            "The UUID crate alone is too permissive"
+        );
+        assert!(!has_uuid_header_shape(raw));
+        let literal = format!("\"{raw}\"");
+        let modern = format!("arcadia 7; project model \"Model\" id {literal} {{}}");
+        let before = modern.clone();
+        let result = outline(&modern, limits()).unwrap();
+        let d = declaration(&result, "model");
+        assert_eq!(d.declaration.id, None);
+        assert_eq!(text(&modern, d.id_literal_span.unwrap()), literal);
+        assert_eq!(modern, before);
+        let errors = parse(&modern).unwrap_err();
+        assert!(
+            errors
+                .iter()
+                .any(|error| error.message.contains("8-4-4-4-12")
+                    && error.span.start == modern.find(&literal).unwrap())
+        );
+        // Intentional compatibility correction: old analyze yielded Some(Id(1))
+        // here despite lint rejecting the header. It now shares outline's None.
+        let analysis = analyze(&modern);
+        assert_eq!(
+            analysis
+                .declarations
+                .iter()
+                .find(|d| d.alias == "model")
+                .unwrap()
+                .id,
+            None
+        );
+        assert!(
+            analysis
+                .diagnostics
+                .iter()
+                .any(|error| error.message.contains("8-4-4-4-12"))
+        );
+        let legacy_source = format!("arcadia 1; project \"Legacy\" id {literal} {{}}");
+        let legacy_errors = legacy::parse(&legacy_source).unwrap_err();
+        assert!(
+            legacy_errors
+                .iter()
+                .any(|error| error.message.contains("8-4-4-4-12"))
+        );
+    }
+}
+
+#[test]
+fn uppercase_and_json_escaped_header_ids_survive_both_parsers_and_outline() {
+    let expected = Id::from_u128(0xabcdef);
+    let canonical = expected.to_string();
+    let uppercase = canonical.to_uppercase();
+    assert_ne!(uppercase, canonical);
+    for raw in [uppercase.clone(), format!("\\u0030{}", &uppercase[1..])] {
+        let literal = format!("\"{raw}\"");
+        let decoded: String = serde_json::from_str(&literal).unwrap();
+        assert!(has_uuid_header_shape(&decoded));
+        let modern = format!("arcadia 7; project model \"Model\" id {literal} {{}}");
+        let result = outline(&modern, limits()).unwrap();
+        let d = declaration(&result, "model");
+        assert_eq!(d.declaration.id, Some(expected));
+        assert_eq!(text(&modern, d.id_literal_span.unwrap()), literal);
+        assert_eq!(result.source.as_bytes(), modern.as_bytes());
+        assert_eq!(parse(&modern).unwrap().id, expected);
+        let analysis = analyze(&modern);
+        assert_eq!(analysis.declarations[0].id, Some(expected));
+        assert!(
+            !analysis
+                .diagnostics
+                .iter()
+                .any(|error| error.severity == crate::validation::Severity::Error)
+        );
+        let legacy_source = format!("arcadia 1; project \"Legacy\" id {literal} {{}}");
+        assert_eq!(legacy::parse(&legacy_source).unwrap().id, expected);
+    }
+}
+
+#[test]
+fn header_shape_still_requires_valid_hexadecimal_uuid_data() {
+    let raw = "00000000-0000-0000-0000-00000000000Z";
+    assert!(has_uuid_header_shape(raw));
+    assert!(Id::parse_str(raw).is_err());
+    let literal = format!("\"{raw}\"");
+    let source = format!("arcadia 7; project model \"Model\" id {literal} {{}}");
+    let result = outline(&source, limits()).unwrap();
+    let d = declaration(&result, "model");
+    assert_eq!(d.declaration.id, None);
+    assert_eq!(text(&source, d.id_literal_span.unwrap()), literal);
+    assert!(
+        parse(&source)
+            .unwrap_err()
+            .iter()
+            .any(|error| error.message == "Invalid UUID identity.")
+    );
+    assert_eq!(analyze(&source).declarations[0].id, None);
+}

crates/oa-core/src/lib.rs

@@ -8,6 +8,7 @@ pub mod ports;
 pub mod projection;
 pub mod references;
 pub mod routing;
+pub mod scenario_layout;
 pub mod semantic;
 pub mod session;
 pub mod source_files;
@@ -18,6 +19,9 @@ pub mod validation;
 pub mod view_options;
 pub use model::*;
 pub use ports::*;
+pub use scenario_layout::{
+    DiagramLayout, ScenarioLanePosition, ScenarioLayout, ScenarioMessagePosition,
+};
 pub use semantic::*;
 pub use session::*;
 mod demo;

crates/oa-core/src/model.rs

@@ -1436,6 +1436,7 @@ pub enum ProjectionKind {
     FunctionalDataflow,
     Capabilities,
     StateMachine { machine: Id },
+    Scenario { scenario: Id },
 }
 impl ProjectionKind {
     pub fn state_machine(self) -> Option<Id> {
@@ -1445,8 +1446,30 @@ impl ProjectionKind {
         }
     }
 
+    /// The semantic owner of a saved Scenario representation.
+    pub fn scenario(self) -> Option<Id> {
+        match self {
+            Self::Scenario { scenario } => Some(scenario),
+            _ => None,
+        }
+    }
+
+    /// Explicitly classify architecture views; absence of a state machine is insufficient.
+    pub fn is_architecture(self) -> bool {
+        match self {
+            Self::Overview
+            | Self::Decomposition
+            | Self::Allocation
+            | Self::Traceability
+            | Self::FunctionalDataflow
+            | Self::Capabilities => true,
+            Self::StateMachine { .. } | Self::Scenario { .. } => false,
+        }
+    }
+
     pub fn includes(self, kind: Kind) -> bool {
         match self {
+            Self::Scenario { .. } => false,
             Self::StateMachine { .. } => {
                 matches!(kind, Kind::StateMachine | Kind::Region) || kind.is_state()
             }
@@ -1471,6 +1494,7 @@ impl std::fmt::Display for ProjectionKind {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         f.write_str(match self {
             Self::StateMachine { .. } => "State machine",
+            Self::Scenario { .. } => "Scenario",
             Self::Allocation => "Architecture · allocated work",
             Self::FunctionalDataflow => "Functional dataflow",
             Self::Capabilities => "Missions & capabilities",
@@ -1495,6 +1519,8 @@ pub struct Diagram {
     pub nodes: BTreeMap<Id, NodePlacement>,
     #[serde(default)]
     pub routes: Vec<EdgeRoute>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub layout: Option<crate::scenario_layout::DiagramLayout>,
 }
 /// Authored presentation for one existing relation or trace in one diagram.
 /// Computed endpoints and automatic routing elbows are never persisted here.
@@ -1921,6 +1947,7 @@ impl Project {
                 view_options: crate::view_options::ViewOptions::default(),
                 nodes: BTreeMap::new(),
                 routes: vec![],
+                layout: None,
             },
         );
         id

crates/oa-core/src/projection.rs

@@ -278,6 +278,11 @@ fn project_diagram_impl(
     mut availability: Option<&mut BTreeMap<Id, crate::view_options::EdgeAvailability>>,
     index: Option<&crate::view_options::ViewIndex>,
 ) -> ProjectedView {
+    // Saved Scenario layout is not an architecture/state projection. Its dedicated
+    // renderer is not wired yet; never interpret its payload through this fallback.
+    if d.projection.scenario().is_some() {
+        return ProjectedView::default();
+    }
     let parents = parents(p, d);
     let mut nodes = Vec::new();
     for n in d.nodes.values() {
@@ -394,6 +399,7 @@ fn project_diagram_impl(
             continue;
         }
         let included = match d.projection {
+            ProjectionKind::Scenario { .. } => false,
             ProjectionKind::StateMachine { machine } => matches!(&r.body,
                 RelationBody::StateTransition { transition_kind, .. }
                     if *transition_kind != TransitionKind::Internal

crates/oa-core/src/references.rs

@@ -203,7 +203,81 @@ pub fn visit_relation_refs(r: &mut Relation, mut visit: impl FnMut(&mut Id)) {
         _ => {}
     }
 }
-pub fn remap_references(p: &mut Project, old: Id, new: Id) {
+/// Every semantic/presentation reference in a diagram, excluding its own identities.
+pub fn diagram_references(d: &Diagram) -> Vec<Id> {
+    let mut copy = d.clone();
+    let mut refs = Vec::new();
+    visit_diagram_refs(&mut copy, |id| refs.push(*id));
+    refs
+}
+
+pub fn visit_diagram_refs(d: &mut Diagram, mut visit: impl FnMut(&mut Id)) {
+    d.view_options.visit_references(&mut visit);
+    match &mut d.projection {
+        ProjectionKind::StateMachine { machine } => visit(machine),
+        ProjectionKind::Scenario { scenario } => visit(scenario),
+        _ => {}
+    }
+    if let Some(layout) = &mut d.layout {
+        layout.visit_references(&mut visit);
+    }
+    for route in &mut d.routes {
+        visit(&mut route.edge);
+    }
+    for node in d.nodes.values_mut() {
+        for anchor in &mut node.port_anchors {
+            visit(&mut anchor.port);
+        }
+        visit(&mut node.element);
+    }
+}
+
+/// Preflight reference-key collisions before the caller changes object identities.
+/// Fresh targets are allowed. This is not whole-project admission: unrelated
+/// invalid records remain repairable within a transaction. Future typed reference
+/// domains must compose their own preflight here before any remap mutation.
+pub fn check_remap(p: &Project, old: Id, new: Id) -> Result<(), ModelError> {
+    if old == new {
+        return Ok(());
+    }
+    let remap = |id: Id| if id == old { new } else { id };
+    for diagram in p.diagrams.values() {
+        let Some(DiagramLayout::Scenario(layout)) = &diagram.layout else {
+            continue;
+        };
+        let mut lanes = std::collections::BTreeMap::new();
+        for lane in &layout.lanes {
+            let affected = lane.lifeline == old;
+            if let Some(previous_affected) = lanes.insert(remap(lane.lifeline), affected)
+                && (affected || previous_affected)
+            {
+                return Err(ModelError(
+                    "Identity remap would collide with a Scenario lane position.".into(),
+                ));
+            }
+        }
+        let mut messages = std::collections::BTreeMap::new();
+        for message in &layout.messages {
+            let mut address = message.address.clone();
+            let affected = address.occurrence == old || address.references.contains(&old);
+            address.occurrence = remap(address.occurrence);
+            for reference in &mut address.references {
+                *reference = remap(*reference);
+            }
+            if let Some(previous_affected) = messages.insert(address, affected)
+                && (affected || previous_affected)
+            {
+                return Err(ModelError(
+                    "Identity remap would collide with a Scenario message position.".into(),
+                ));
+            }
+        }
+    }
+    Ok(())
+}
+
+pub fn remap_references(p: &mut Project, old: Id, new: Id) -> Result<(), ModelError> {
+    check_remap(p, old, new)?;
     for e in p.elements.values_mut() {
         visit_element_refs(e, |id| {
             if *id == old {
@@ -219,31 +293,11 @@ pub fn remap_references(p: &mut Project, old: Id, new: Id) {
         });
     }
     for d in p.diagrams.values_mut() {
-        d.view_options.visit_references(|id| {
+        visit_diagram_refs(d, |id| {
             if *id == old {
                 *id = new;
             }
         });
-        if let ProjectionKind::StateMachine { machine } = &mut d.projection
-            && *machine == old
-        {
-            *machine = new;
-        }
-        for route in &mut d.routes {
-            if route.edge == old {
-                route.edge = new;
-            }
-        }
-        for n in d.nodes.values_mut() {
-            for anchor in &mut n.port_anchors {
-                if anchor.port == old {
-                    anchor.port = new;
-                }
-            }
-            if n.element == old {
-                n.element = new;
-            }
-        }
     }
     for a in p.artifact_links.values_mut() {
         if a.owner == old {
@@ -265,6 +319,7 @@ pub fn remap_references(p: &mut Project, old: Id, new: Id) {
             });
         }
     }
+    Ok(())
 }
 /// IDs removed by a cascade. Cross-layer traced counterparts are never included.
 pub fn deletion_impact(p: &Project, id: Id) -> BTreeSet<Id> {
@@ -339,7 +394,8 @@ fn deletion_impact_inner(p: &Project, id: Id, defer_exchange_allocations: bool)
         for d in p.diagrams.values() {
             if d.projection
                 .state_machine()
-                .is_some_and(|machine| removed.contains(&machine))
+                .or_else(|| d.projection.scenario())
+                .is_some_and(|owner| removed.contains(&owner))
             {
                 removed.insert(d.id);
             }
@@ -412,6 +468,7 @@ fn remove_objects(p: &mut Project, removed: BTreeSet<Id>) {
     p.artifact_links.retain(|id, _| !removed.contains(id));
     for d in p.diagrams.values_mut() {
         d.view_options.retain_references(|id| !removed.contains(id));
+        crate::scenario_layout::prune_deleted(d, &removed);
         d.nodes.retain(|id, _| !removed.contains(id));
         d.routes.retain(|route| !removed.contains(&route.edge));
         for node in d.nodes.values_mut() {
@@ -589,3 +646,7 @@ fn remove_objects(p: &mut Project, removed: BTreeSet<Id>) {
         }
     }
 }
+
+#[cfg(test)]
+#[path = "references/scenario_layout_tests.rs"]
+mod scenario_layout_tests;

crates/oa-core/src/references/scenario_layout_tests.rs

@@ -0,0 +1,388 @@
+use super::*;
+use std::collections::BTreeMap;
+
+struct Fixture {
+    project: Project,
+    owner: Id,
+    lanes: [Id; 2],
+    messages: [Id; 2],
+    views: [Id; 2],
+}
+
+fn address(occurrence: Id) -> OccurrenceEndpoint {
+    OccurrenceEndpoint {
+        references: vec![],
+        occurrence,
+    }
+}
+
+fn layout(project: &Project, view: Id) -> &ScenarioLayout {
+    let Some(DiagramLayout::Scenario(layout)) = &project.diagrams[&view].layout else {
+        panic!("expected authored Scenario positions")
+    };
+    layout
+}
+
+fn layout_mut(project: &mut Project, view: Id) -> &mut ScenarioLayout {
+    let Some(DiagramLayout::Scenario(layout)) =
+        &mut project.diagrams.get_mut(&view).unwrap().layout
+    else {
+        panic!("expected authored Scenario positions")
+    };
+    layout
+}
+
+fn admitted(project: &Project) {
+    let errors: Vec<_> = crate::validation::validate(project)
+        .into_iter()
+        .filter(|issue| issue.severity == crate::validation::Severity::Error)
+        .collect();
+    assert!(errors.is_empty(), "{errors:?}");
+}
+
+fn fixture() -> Fixture {
+    let mut project = Project::empty();
+    let owner = project
+        .add_element(Kind::Scenario, Layer::Oa, "Delivery", None)
+        .unwrap();
+    let lanes = ["Sender", "Receiver"].map(|name| {
+        project
+            .add_element(Kind::Lifeline, Layer::Oa, name, Some(owner))
+            .unwrap()
+    });
+    let messages = ["First message", "Second message"].map(|name| {
+        let id = project
+            .add_element(Kind::Occurrence, Layer::Oa, name, Some(owner))
+            .unwrap();
+        *project.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange {
+                exchange: None,
+                sender: Some(lanes[0]),
+                receiver: Some(lanes[1]),
+                message_kind: MessageKind::Asynchronous,
+                reply_to: None,
+                values: vec![],
+                operation: None,
+            },
+            precondition: String::new(),
+            postcondition: String::new(),
+        };
+        id
+    });
+    *project
+        .elements
+        .get_mut(&owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap() = messages.to_vec();
+    let views = ["delivery_view", "review_view"].map(|alias| {
+        let id = Id::new_v4();
+        project.diagrams.insert(
+            id,
+            Diagram {
+                id,
+                alias: alias.into(),
+                name: alias.into(),
+                description: String::new(),
+                layer: Layer::Oa,
+                projection: ProjectionKind::Scenario { scenario: owner },
+                view_options: Default::default(),
+                nodes: BTreeMap::new(),
+                routes: vec![],
+                layout: Some(DiagramLayout::Scenario(ScenarioLayout {
+                    lanes: vec![
+                        ScenarioLanePosition {
+                            lifeline: lanes[0],
+                            x: 120.,
+                        },
+                        ScenarioLanePosition {
+                            lifeline: lanes[1],
+                            x: 420.,
+                        },
+                    ],
+                    messages: vec![
+                        ScenarioMessagePosition {
+                            address: address(messages[0]),
+                            send_y: 220.,
+                        },
+                        ScenarioMessagePosition {
+                            address: address(messages[1]),
+                            send_y: 360.,
+                        },
+                    ],
+                })),
+            },
+        );
+        id
+    });
+    admitted(&project);
+    Fixture {
+        project,
+        owner,
+        lanes,
+        messages,
+        views,
+    }
+}
+
+#[test]
+fn fresh_identity_swap_preserves_coordinates_and_semantic_sequence() {
+    let mut f = fixture();
+    let before = f.project.clone();
+    let temporary = Id::new_v4();
+    for ids in [f.lanes, f.messages] {
+        f.project = crate::execute_batch(
+            &f.project,
+            &[
+                Command::Reidentify(ids[0], temporary),
+                Command::Reidentify(ids[1], ids[0]),
+                Command::Reidentify(temporary, ids[1]),
+            ],
+        )
+        .unwrap();
+    }
+    admitted(&f.project);
+    assert_eq!(
+        f.project.elements[&f.owner].steps().unwrap(),
+        &vec![f.messages[1], f.messages[0]]
+    );
+    for view in f.views {
+        let rows = layout(&f.project, view);
+        assert_eq!(
+            rows.lanes,
+            vec![
+                ScenarioLanePosition {
+                    lifeline: f.lanes[1],
+                    x: 120.
+                },
+                ScenarioLanePosition {
+                    lifeline: f.lanes[0],
+                    x: 420.
+                }
+            ]
+        );
+        assert_eq!(
+            rows.messages,
+            vec![
+                ScenarioMessagePosition {
+                    address: address(f.messages[1]),
+                    send_y: 220.
+                },
+                ScenarioMessagePosition {
+                    address: address(f.messages[0]),
+                    send_y: 360.
+                }
+            ]
+        );
+    }
+    // Reverse the swaps: no values or identities other than those requested drift.
+    for ids in [f.lanes, f.messages] {
+        f.project = crate::execute_batch(
+            &f.project,
+            &[
+                Command::Reidentify(ids[0], temporary),
+                Command::Reidentify(ids[1], ids[0]),
+                Command::Reidentify(temporary, ids[1]),
+            ],
+        )
+        .unwrap();
+    }
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn colliding_lane_or_message_remap_rejects_before_any_reference_changes() {
+    for message in [false, true] {
+        let mut f = fixture();
+        let [old, new] = if message { f.messages } else { f.lanes };
+        let before = f.project.clone();
+        assert!(check_remap(&f.project, old, new).is_err());
+        assert!(remap_references(&mut f.project, old, new).is_err());
+        assert_eq!(f.project, before);
+    }
+}
+
+#[test]
+fn reidentify_preflight_precedes_object_map_mutation_for_fresh_colliding_target() {
+    let mut f = fixture();
+    let fresh = Id::new_v4();
+    // A repair candidate can already have a dangling coordinate key. It must not
+    // silently merge with the live lane, even though the destination ID is vacant.
+    layout_mut(&mut f.project, f.views[0]).lanes[1].lifeline = fresh;
+    let before = f.project.clone();
+    assert!(crate::session::reidentify(&mut f.project, f.lanes[0], fresh).is_err());
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn full_address_paths_are_walked_and_collision_checked_without_admitting_expansion() {
+    let mut f = fixture();
+    let [old, new] = [Id::new_v4(), Id::new_v4()];
+    let rows = layout_mut(&mut f.project, f.views[0]);
+    // Future/invalid expanded candidates still participate in reference safety.
+    rows.messages[0].address.references = vec![old];
+    rows.messages[1].address = OccurrenceEndpoint {
+        references: vec![new],
+        occurrence: f.messages[0],
+    };
+    let refs = diagram_references(&f.project.diagrams[&f.views[0]]);
+    assert!(refs.contains(&f.owner) && refs.contains(&old) && refs.contains(&new));
+    let before = f.project.clone();
+    assert!(remap_references(&mut f.project, old, new).is_err());
+    assert_eq!(f.project, before);
+    let fresh = Id::new_v4();
+    remap_references(&mut f.project, old, fresh).unwrap();
+    let rows = layout(&f.project, f.views[0]);
+    assert_eq!(rows.messages[0].address.references, vec![fresh]);
+    assert_eq!(rows.messages[0].address.occurrence, f.messages[0]);
+    assert_eq!(rows.messages[1].address.references, vec![new]);
+}
+
+#[test]
+fn owner_reidentify_and_delete_cover_all_saved_views_without_deleting_other_owners() {
+    let mut f = fixture();
+    let other_owner = f
+        .project
+        .add_element(Kind::Scenario, Layer::Oa, "Independent", None)
+        .unwrap();
+    let mut other_view = f.project.diagrams[&f.views[0]].clone();
+    other_view.id = Id::new_v4();
+    other_view.alias = "independent_view".into();
+    other_view.projection = ProjectionKind::Scenario {
+        scenario: other_owner,
+    };
+    other_view.layout = None;
+    f.project.diagrams.insert(other_view.id, other_view.clone());
+    admitted(&f.project);
+    let fresh_owner = Id::new_v4();
+    f.project = crate::prepare_command(&f.project, &Command::Reidentify(f.owner, fresh_owner))
+        .unwrap()
+        .project;
+    for view in f.views {
+        assert_eq!(
+            f.project.diagrams[&view].projection.scenario(),
+            Some(fresh_owner)
+        );
+    }
+    let impact = deletion_impact(&f.project, fresh_owner);
+    assert!(
+        f.views
+            .iter()
+            .chain(&f.lanes)
+            .chain(&f.messages)
+            .all(|id| impact.contains(id))
+    );
+    assert!(!impact.contains(&other_owner) && !impact.contains(&other_view.id));
+    delete_cascade(&mut f.project, fresh_owner);
+    assert_eq!(f.project.diagrams[&other_view.id], other_view);
+    assert!(
+        f.views
+            .iter()
+            .all(|id| !f.project.diagrams.contains_key(id))
+    );
+    admitted(&f.project);
+}
+
+#[test]
+fn deletion_then_recreation_never_resurrects_lane_or_message_coordinates() {
+    let mut f = fixture();
+    let lane = f.project.elements[&f.lanes[0]].clone();
+    let message = f.project.elements[&f.messages[0]].clone();
+    delete_cascade(&mut f.project, lane.id);
+    for view in f.views {
+        let rows = layout(&f.project, view);
+        assert_eq!(rows.lanes.len(), 1);
+        assert_eq!(rows.lanes[0].lifeline, f.lanes[1]);
+        // Missing endpoint assignment does not erase a still-live message's spacing.
+        assert_eq!(rows.messages.len(), 2);
+    }
+    let mut pending = BTreeSet::new();
+    delete_cascade_deferred(&mut f.project, message.id, &mut pending);
+    // Pruning happens during deletion, before later batch commands can recreate IDs.
+    assert!(
+        layout(&f.project, f.views[0])
+            .messages
+            .iter()
+            .all(|row| row.address.occurrence != message.id)
+    );
+    f.project.elements.insert(lane.id, lane);
+    f.project.elements.insert(message.id, message);
+    f.project
+        .elements
+        .get_mut(&f.owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap()
+        .insert(0, f.messages[0]);
+    finish_deletions(&mut f.project, &pending);
+    for view in f.views {
+        let rows = layout(&f.project, view);
+        assert_eq!(rows.lanes.len(), 1);
+        assert_eq!(
+            rows.messages,
+            vec![ScenarioMessagePosition {
+                address: address(f.messages[1]),
+                send_y: 360.
+            }]
+        );
+    }
+    admitted(&f.project);
+}
+
+#[test]
+fn unrelated_invalid_records_do_not_block_scoped_remap_or_get_repaired_implicitly() {
+    let mut f = fixture();
+    let unrelated = Id::new_v4();
+    let rows = layout_mut(&mut f.project, f.views[1]);
+    let invalid = ScenarioLanePosition {
+        lifeline: unrelated,
+        x: MAX_COORDINATE * 2.,
+    };
+    rows.lanes.extend([invalid.clone(), invalid]);
+    let fresh = Id::new_v4();
+    let untouched = f.project.diagrams[&f.views[1]].clone();
+    let before = f.project.clone();
+    remap_references(&mut f.project, f.owner, f.owner).unwrap();
+    assert_eq!(f.project, before);
+    // The duplicate lane records do not involve the remapped message identity.
+    remap_references(&mut f.project, f.messages[0], fresh).unwrap();
+    assert_eq!(
+        layout(&f.project, f.views[1]).lanes,
+        layout_from(&untouched).lanes
+    );
+    assert_eq!(
+        layout(&f.project, f.views[1]).messages[0]
+            .address
+            .occurrence,
+        fresh
+    );
+    assert_eq!(layout(&f.project, f.views[1]).messages[0].send_y, 220.);
+}
+
+fn layout_from(diagram: &Diagram) -> &ScenarioLayout {
+    let Some(DiagramLayout::Scenario(layout)) = &diagram.layout else {
+        panic!("missing layout")
+    };
+    layout
+}
+
+#[test]
+fn deletion_prunes_an_explicit_address_path_without_pruning_other_message_rows() {
+    let mut f = fixture();
+    // Expanded addresses are not admitted in this slice, but deleting their
+    // explicit references must still make an intermediate repair candidate safe.
+    layout_mut(&mut f.project, f.views[0]).messages[0]
+        .address
+        .references = vec![f.lanes[0]];
+    delete_cascade(&mut f.project, f.lanes[0]);
+    assert_eq!(
+        layout(&f.project, f.views[0]).messages,
+        vec![ScenarioMessagePosition {
+            address: address(f.messages[1]),
+            send_y: 360.
+        }]
+    );
+    assert_eq!(layout(&f.project, f.views[1]).messages.len(), 2);
+    assert!(f.project.elements.contains_key(&f.messages[0]));
+    admitted(&f.project);
+}

crates/oa-core/src/scenario_layout.rs

@@ -0,0 +1,429 @@
+//! Authored Scenario presentation. Structural admission never changes event order.
+use crate::{
+    Diagram, Id, Kind, Layer, MAX_COORDINATE, ModelError, OccurrenceBody, OccurrenceEndpoint,
+    Project, SharedBody, validation,
+};
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeSet;
+
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub enum DiagramLayout {
+    Scenario(ScenarioLayout),
+}
+
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Default)]
+#[serde(deny_unknown_fields)]
+pub struct ScenarioLayout {
+    #[serde(default)]
+    pub lanes: Vec<ScenarioLanePosition>,
+    #[serde(default)]
+    pub messages: Vec<ScenarioMessagePosition>,
+}
+
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct ScenarioLanePosition {
+    pub lifeline: Id,
+    pub x: f32,
+}
+
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct ScenarioMessagePosition {
+    pub address: OccurrenceEndpoint,
+    /// Actual send endpoint, not the renderer's receive-oriented lifecycle row.
+    pub send_y: f32,
+}
+
+impl DiagramLayout {
+    /// Visit every explicit reference, including unsupported paths in a candidate.
+    /// The caller owns remap preflight and final atomic validation.
+    pub fn visit_references(&mut self, mut visit: impl FnMut(&mut Id)) {
+        match self {
+            Self::Scenario(layout) => {
+                for lane in &mut layout.lanes {
+                    visit(&mut lane.lifeline);
+                }
+                for message in &mut layout.messages {
+                    for reference in &mut message.address.references {
+                        visit(reference);
+                    }
+                    visit(&mut message.address.occurrence);
+                }
+            }
+        }
+    }
+}
+
+/// Proposed aggregate accounting contribution; the shared admission owner applies it.
+/// One payload plus one record per lane/message. No graph objects are introduced.
+pub fn record_count(diagram: &Diagram) -> usize {
+    match &diagram.layout {
+        None => 0,
+        Some(DiagramLayout::Scenario(layout)) => 1usize
+            .saturating_add(layout.lanes.len())
+            .saturating_add(layout.messages.len()),
+    }
+}
+
+fn coordinate(value: f32) -> bool {
+    value.is_finite() && value.abs() <= MAX_COORDINATE
+}
+
+fn owner(p: &Project, diagram: &Diagram) -> Result<Id, ModelError> {
+    let scenario = diagram
+        .projection
+        .scenario()
+        .ok_or_else(|| ModelError("Scenario layout requires a Scenario projection.".into()))?;
+    if !p
+        .elements
+        .get(&scenario)
+        .is_some_and(|element| element.kind() == Kind::Scenario && element.layer() == diagram.layer)
+    {
+        return Err(ModelError(
+            "Scenario projection requires an existing Scenario in the diagram layer.".into(),
+        ));
+    }
+    Ok(scenario)
+}
+
+fn lane_member(p: &Project, owner: Id, layer: Layer, lifeline: Id) -> bool {
+    p.elements.get(&lifeline).is_some_and(|element| {
+        element.kind() == Kind::Lifeline
+            && element.parent == Some(owner)
+            && element.layer() == layer
+    })
+}
+
+/// Only actual steps of this Scenario and its own Fragment/Branch sequences.
+/// ScenarioUse/SequenceReference are deliberately never expanded. Invalid graph
+/// cycles terminate, and malformed parent/step links do not manufacture membership.
+fn direct_messages(p: &Project, owner: Id, layer: Layer) -> BTreeSet<Id> {
+    let mut messages = BTreeSet::new();
+    let mut visited = BTreeSet::new();
+    let mut pending = vec![owner];
+    while let Some(scope) = pending.pop() {
+        if !visited.insert(scope) {
+            continue;
+        }
+        let Some(element) = p.elements.get(&scope) else {
+            continue;
+        };
+        for id in element.steps().into_iter().flatten() {
+            let Some(item) = p.elements.get(id) else {
+                continue;
+            };
+            if item.parent != Some(scope) || item.layer() != layer {
+                continue;
+            }
+            match item.shared() {
+                Some(SharedBody::Occurrence {
+                    body: OccurrenceBody::Exchange { .. },
+                    ..
+                }) => {
+                    messages.insert(*id);
+                }
+                Some(SharedBody::Occurrence {
+                    body: OccurrenceBody::Fragment { branches, .. },
+                    ..
+                }) => {
+                    for branch in branches {
+                        if p.elements.get(branch).is_some_and(|operand| {
+                            operand.parent == Some(*id)
+                                && operand.layer() == layer
+                                && matches!(
+                                    operand.shared(),
+                                    Some(SharedBody::Occurrence {
+                                        body: OccurrenceBody::Branch { .. },
+                                        ..
+                                    })
+                                )
+                        }) {
+                            pending.push(*branch);
+                        }
+                    }
+                }
+                _ => {}
+            }
+        }
+    }
+    messages
+}
+
+pub(crate) fn validate_diagram(p: &Project, diagram: &Diagram, out: &mut Vec<validation::Issue>) {
+    if diagram.projection.scenario().is_none() {
+        if diagram.layout.is_some() {
+            validation::error(
+                out,
+                diagram.id,
+                "scenario_layout_projection",
+                "layout",
+                "Only a Scenario projection accepts a Scenario layout, including an empty payload.",
+            );
+        }
+        return;
+    }
+    let scenario = match owner(p, diagram) {
+        Ok(owner) => owner,
+        Err(error) => {
+            validation::error(
+                out,
+                diagram.id,
+                "scenario_diagram_context",
+                "projection",
+                error.0,
+            );
+            return;
+        }
+    };
+    if !diagram.nodes.is_empty() || !diagram.routes.is_empty() {
+        validation::error(
+            out,
+            diagram.id,
+            "scenario_diagram_content",
+            "layout",
+            "Scenario views do not accept architecture node placements or edge routes.",
+        );
+    }
+    let Some(DiagramLayout::Scenario(layout)) = &diagram.layout else {
+        return;
+    };
+    let mut lanes = BTreeSet::new();
+    for lane in &layout.lanes {
+        if !lanes.insert(lane.lifeline) {
+            validation::error(
+                out,
+                diagram.id,
+                "duplicate_scenario_lane",
+                "layout",
+                "A Scenario layout has at most one position per lifeline.",
+            );
+        }
+        if !lane_member(p, scenario, diagram.layer, lane.lifeline) {
+            validation::error(
+                out,
+                diagram.id,
+                "scenario_layout_lifeline",
+                "layout",
+                "Lane positions reference a Lifeline directly owned by the projected Scenario.",
+            );
+        }
+        if !coordinate(lane.x) {
+            validation::error(
+                out,
+                diagram.id,
+                "scenario_layout_coordinate",
+                "layout",
+                "Scenario positions must be finite and within the shared coordinate bounds.",
+            );
+        }
+    }
+    let members = direct_messages(p, scenario, diagram.layer);
+    let mut addresses = BTreeSet::new();
+    for message in &layout.messages {
+        // Reject expanded paths without cloning or indexing their potentially large contents.
+        if !message.address.references.is_empty() {
+            validation::error(
+                out,
+                diagram.id,
+                "scenario_layout_address",
+                "layout",
+                "Expanded-reference message positions are not supported; references must be empty.",
+            );
+        } else if !addresses.insert(message.address.occurrence) {
+            validation::error(
+                out,
+                diagram.id,
+                "duplicate_scenario_message",
+                "layout",
+                "A Scenario layout has at most one position per message address.",
+            );
+        }
+        if !members.contains(&message.address.occurrence) {
+            validation::error(
+                out,
+                diagram.id,
+                "scenario_layout_message",
+                "layout",
+                "Message positions reference Exchange occurrences in the Scenario's own ordered sequence tree.",
+            );
+        }
+        if !coordinate(message.send_y) {
+            validation::error(
+                out,
+                diagram.id,
+                "scenario_layout_coordinate",
+                "layout",
+                "Scenario positions must be finite and within the shared coordinate bounds.",
+            );
+        }
+    }
+}
+
+fn editable(p: &Project, id: Id) -> Result<(&Diagram, Id), ModelError> {
+    let diagram = p
+        .diagrams
+        .get(&id)
+        .ok_or_else(|| ModelError("Scenario diagram does not exist.".into()))?;
+    let scenario = owner(p, diagram)?;
+    if !diagram.nodes.is_empty() || !diagram.routes.is_empty() {
+        return Err(ModelError(
+            "Scenario views do not accept architecture node placements or edge routes.".into(),
+        ));
+    }
+    Ok((diagram, scenario))
+}
+
+fn check_message(
+    p: &Project,
+    diagram: &Diagram,
+    owner: Id,
+    address: &OccurrenceEndpoint,
+) -> Result<(), ModelError> {
+    if !address.references.is_empty() {
+        return Err(ModelError(
+            "Expanded-reference message positions are not supported; references must be empty."
+                .into(),
+        ));
+    }
+    if !direct_messages(p, owner, diagram.layer).contains(&address.occurrence) {
+        return Err(ModelError("Message position requires an Exchange occurrence in the Scenario's own ordered sequence tree.".into()));
+    }
+    Ok(())
+}
+
+fn payload(diagram: &mut Diagram) -> &mut ScenarioLayout {
+    let DiagramLayout::Scenario(layout) = diagram
+        .layout
+        .get_or_insert_with(|| DiagramLayout::Scenario(ScenarioLayout::default()));
+    layout
+}
+
+/// Target-scoped preparation, not whole-project or whole-layout validation.
+/// Unrelated intermediate errors remain repairable by later commands in a batch.
+pub fn set_lane(
+    p: &Project,
+    diagram: Id,
+    position: ScenarioLanePosition,
+) -> Result<Diagram, ModelError> {
+    let (current, owner) = editable(p, diagram)?;
+    if !lane_member(p, owner, current.layer, position.lifeline) || !coordinate(position.x) {
+        return Err(ModelError(
+            "Lane position requires an owned Lifeline and a finite bounded x coordinate.".into(),
+        ));
+    }
+    let mut result = current.clone();
+    let layout = payload(&mut result);
+    if layout
+        .lanes
+        .iter()
+        .filter(|row| row.lifeline == position.lifeline)
+        .count()
+        > 1
+    {
+        return Err(ModelError(
+            "Cannot set an ambiguous duplicate lane position.".into(),
+        ));
+    }
+    if let Some(existing) = layout
+        .lanes
+        .iter_mut()
+        .find(|row| row.lifeline == position.lifeline)
+    {
+        if existing.x != position.x {
+            *existing = position;
+        }
+    } else {
+        layout.lanes.push(position);
+    }
+    Ok(result)
+}
+
+pub fn remove_lane(p: &Project, diagram: Id, lifeline: Id) -> Result<Diagram, ModelError> {
+    let (current, owner) = editable(p, diagram)?;
+    if !lane_member(p, owner, current.layer, lifeline) {
+        return Err(ModelError(
+            "Removing a lane position requires an owned Lifeline.".into(),
+        ));
+    }
+    let mut result = current.clone();
+    if let Some(DiagramLayout::Scenario(layout)) = &mut result.layout {
+        layout.lanes.retain(|row| row.lifeline != lifeline);
+    }
+    Ok(result)
+}
+
+pub fn set_message(
+    p: &Project,
+    diagram: Id,
+    position: ScenarioMessagePosition,
+) -> Result<Diagram, ModelError> {
+    let (current, owner) = editable(p, diagram)?;
+    check_message(p, current, owner, &position.address)?;
+    if !coordinate(position.send_y) {
+        return Err(ModelError(
+            "Message position requires a finite bounded send_y coordinate.".into(),
+        ));
+    }
+    let mut result = current.clone();
+    let layout = payload(&mut result);
+    if layout
+        .messages
+        .iter()
+        .filter(|row| row.address == position.address)
+        .count()
+        > 1
+    {
+        return Err(ModelError(
+            "Cannot set an ambiguous duplicate message position.".into(),
+        ));
+    }
+    if let Some(existing) = layout
+        .messages
+        .iter_mut()
+        .find(|row| row.address == position.address)
+    {
+        if existing.send_y != position.send_y {
+            *existing = position;
+        }
+    } else {
+        layout.messages.push(position);
+    }
+    Ok(result)
+}
+
+pub fn remove_message(
+    p: &Project,
+    diagram: Id,
+    address: &OccurrenceEndpoint,
+) -> Result<Diagram, ModelError> {
+    let (current, owner) = editable(p, diagram)?;
+    check_message(p, current, owner, address)?;
+    let mut result = current.clone();
+    if let Some(DiagramLayout::Scenario(layout)) = &mut result.layout {
+        layout.messages.retain(|row| &row.address != address);
+    }
+    Ok(result)
+}
+
+/// Prune only identities in the caller's actual deletion closure, never visibility
+/// or missing endpoint assignments. Owner-view cascade remains the caller's job.
+pub fn prune_deleted(diagram: &mut Diagram, deleted: &BTreeSet<Id>) {
+    if let Some(DiagramLayout::Scenario(layout)) = &mut diagram.layout {
+        layout
+            .lanes
+            .retain(|lane| !deleted.contains(&lane.lifeline));
+        layout.messages.retain(|message| {
+            !deleted.contains(&message.address.occurrence)
+                && !message
+                    .address
+                    .references
+                    .iter()
+                    .any(|id| deleted.contains(id))
+        });
+    }
+}
+
+#[cfg(test)]
+mod tests;

crates/oa-core/src/scenario_layout/tests.rs

@@ -0,0 +1,800 @@
+use super::*;
+use crate::{
+    Element, FragmentOperator, MessageKind, ProjectionKind, Relation, RelationBody, RelationKind,
+    ScenarioViewpoint,
+};
+use std::collections::BTreeMap;
+
+struct Fixture {
+    project: Project,
+    owner: Id,
+    performer: Id,
+    lane: Id,
+    repeated_lane: Id,
+    first: Id,
+    second: Id,
+    nested: Id,
+    fragment: Id,
+    branch: Id,
+    view: Id,
+    other_view: Id,
+    exchange: Id,
+}
+
+fn set_body(element: &mut Element, body: OccurrenceBody) {
+    *element.shared_mut().unwrap() = SharedBody::Occurrence {
+        body,
+        precondition: String::new(),
+        postcondition: String::new(),
+    };
+}
+fn address(occurrence: Id) -> OccurrenceEndpoint {
+    OccurrenceEndpoint {
+        references: vec![],
+        occurrence,
+    }
+}
+fn diagram(owner: Id, alias: &str) -> Diagram {
+    Diagram {
+        id: Id::new_v4(),
+        alias: alias.into(),
+        name: alias.into(),
+        description: String::new(),
+        layer: Layer::Oa,
+        projection: ProjectionKind::Scenario { scenario: owner },
+        view_options: Default::default(),
+        nodes: BTreeMap::new(),
+        routes: vec![],
+        layout: None,
+    }
+}
+fn assert_admitted(project: &Project) {
+    let errors: Vec<_> = validation::validate(project)
+        .into_iter()
+        .filter(|issue| issue.severity == validation::Severity::Error)
+        .collect();
+    assert!(errors.is_empty(), "{errors:?}");
+}
+fn has_code(project: &Project, code: &str) -> bool {
+    validation::validate(project)
+        .iter()
+        .any(|issue| issue.code == code)
+}
+fn layout(diagram: &Diagram) -> &ScenarioLayout {
+    let Some(DiagramLayout::Scenario(layout)) = &diagram.layout else {
+        panic!("expected saved payload")
+    };
+    layout
+}
+fn save(project: &mut Project, replacement: Diagram) {
+    project.diagrams.insert(replacement.id, replacement);
+}
+fn fixture() -> Fixture {
+    let mut project = Project::empty();
+    let owner = project
+        .add_element(Kind::Scenario, Layer::Oa, "Nominal", None)
+        .unwrap();
+    let Some(SharedBody::Scenario { viewpoint, .. }) =
+        project.elements.get_mut(&owner).unwrap().shared_mut()
+    else {
+        panic!("Scenario fixture body");
+    };
+    *viewpoint = ScenarioViewpoint::ParticipantInteraction;
+    let performer = project
+        .add_element(Kind::Entity, Layer::Oa, "Controller", None)
+        .unwrap();
+    let receiver = project
+        .add_element(Kind::Entity, Layer::Oa, "Provider", None)
+        .unwrap();
+    let lane = project
+        .add_element(Kind::Lifeline, Layer::Oa, "Controller lane", Some(owner))
+        .unwrap();
+    let repeated_lane = project
+        .add_element(
+            Kind::Lifeline,
+            Layer::Oa,
+            "Controller review lane",
+            Some(owner),
+        )
+        .unwrap();
+    let receiver_lane = project
+        .add_element(Kind::Lifeline, Layer::Oa, "Provider lane", Some(owner))
+        .unwrap();
+    for (id, represented) in [
+        (lane, performer),
+        (repeated_lane, performer),
+        (receiver_lane, receiver),
+    ] {
+        *project.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Lifeline {
+            represented: Some(represented),
+        };
+    }
+    let exchange = Id::new_v4();
+    project.relations.insert(
+        exchange,
+        Relation {
+            id: exchange,
+            alias: "delivery_channel".into(),
+            name: "Delivery".into(),
+            description: String::new(),
+            body: RelationBody::new(RelationKind::CommunicationMean, performer, receiver),
+        },
+    );
+    let first = project
+        .add_element(Kind::Occurrence, Layer::Oa, "First delivery", Some(owner))
+        .unwrap();
+    let second = project
+        .add_element(Kind::Occurrence, Layer::Oa, "Second delivery", Some(owner))
+        .unwrap();
+    for (id, sender) in [(first, lane), (second, repeated_lane)] {
+        set_body(
+            project.elements.get_mut(&id).unwrap(),
+            OccurrenceBody::Exchange {
+                exchange: Some(exchange),
+                sender: Some(sender),
+                receiver: Some(receiver_lane),
+                message_kind: MessageKind::Asynchronous,
+                reply_to: None,
+                values: vec![],
+                operation: None,
+            },
+        );
+    }
+    let fragment = project
+        .add_element(
+            Kind::Occurrence,
+            Layer::Oa,
+            "Optional delivery",
+            Some(owner),
+        )
+        .unwrap();
+    set_body(
+        project.elements.get_mut(&fragment).unwrap(),
+        OccurrenceBody::Fragment {
+            operator: FragmentOperator::Optional,
+            branches: vec![],
+        },
+    );
+    let branch = project
+        .add_element(Kind::Occurrence, Layer::Oa, "Option body", Some(fragment))
+        .unwrap();
+    let nested = project
+        .add_element(
+            Kind::Occurrence,
+            Layer::Oa,
+            "Unfinished nested delivery",
+            Some(branch),
+        )
+        .unwrap();
+    set_body(
+        project.elements.get_mut(&nested).unwrap(),
+        OccurrenceBody::Exchange {
+            exchange: None,
+            sender: None,
+            receiver: None,
+            message_kind: MessageKind::Asynchronous,
+            reply_to: None,
+            values: vec![],
+            operation: None,
+        },
+    );
+    set_body(
+        project.elements.get_mut(&branch).unwrap(),
+        OccurrenceBody::Branch {
+            guard: "requested".into(),
+            occurrences: vec![nested],
+        },
+    );
+    set_body(
+        project.elements.get_mut(&fragment).unwrap(),
+        OccurrenceBody::Fragment {
+            operator: FragmentOperator::Optional,
+            branches: vec![branch],
+        },
+    );
+    *project
+        .elements
+        .get_mut(&owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap() = vec![first, second, fragment];
+    let view_record = diagram(owner, "nominal_view");
+    let other_record = diagram(owner, "review_view");
+    let view = view_record.id;
+    let other_view = other_record.id;
+    save(&mut project, view_record);
+    save(&mut project, other_record);
+    assert_admitted(&project);
+    Fixture {
+        project,
+        owner,
+        performer,
+        lane,
+        repeated_lane,
+        first,
+        second,
+        nested,
+        fragment,
+        branch,
+        view,
+        other_view,
+        exchange,
+    }
+}
+
+#[test]
+fn two_views_and_repeated_semantic_definitions_keep_independent_overrides() {
+    let mut f = fixture();
+    let semantics = (f.project.elements.clone(), f.project.relations.clone());
+    for (view, line, x) in [
+        (f.view, f.lane, 420.),
+        (f.view, f.repeated_lane, 680.),
+        (f.other_view, f.lane, 900.),
+    ] {
+        let result =
+            set_lane(&f.project, view, ScenarioLanePosition { lifeline: line, x }).unwrap();
+        save(&mut f.project, result);
+    }
+    for (view, id, y) in [
+        (f.view, f.first, 200.),
+        (f.view, f.second, 350.),
+        (f.other_view, f.first, 260.),
+    ] {
+        let result = set_message(
+            &f.project,
+            view,
+            ScenarioMessagePosition {
+                address: address(id),
+                send_y: y,
+            },
+        )
+        .unwrap();
+        save(&mut f.project, result);
+    }
+    assert_eq!(
+        layout(&f.project.diagrams[&f.view]).lanes,
+        vec![
+            ScenarioLanePosition {
+                lifeline: f.lane,
+                x: 420.
+            },
+            ScenarioLanePosition {
+                lifeline: f.repeated_lane,
+                x: 680.
+            },
+        ]
+    );
+    assert_eq!(
+        layout(&f.project.diagrams[&f.view])
+            .messages
+            .iter()
+            .map(|r| (r.address.occurrence, r.send_y))
+            .collect::<Vec<_>>(),
+        vec![(f.first, 200.), (f.second, 350.)]
+    );
+    assert_eq!(
+        layout(&f.project.diagrams[&f.other_view]).messages[0].send_y,
+        260.
+    );
+    assert_eq!(layout(&f.project.diagrams[&f.other_view]).lanes[0].x, 900.);
+    assert_eq!(
+        (f.project.elements.clone(), f.project.relations.clone()),
+        semantics
+    );
+    assert_admitted(&f.project);
+}
+
+#[test]
+fn own_nested_unfinished_message_is_admitted_but_expansion_is_not() {
+    let mut f = fixture();
+    let result = set_message(
+        &f.project,
+        f.view,
+        ScenarioMessagePosition {
+            address: address(f.nested),
+            send_y: -80.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    assert_admitted(&f.project);
+    let before = f.project.clone();
+    let expanded = OccurrenceEndpoint {
+        references: vec![f.fragment],
+        occurrence: f.nested,
+    };
+    assert!(
+        set_message(
+            &f.project,
+            f.view,
+            ScenarioMessagePosition {
+                address: expanded.clone(),
+                send_y: 400.
+            }
+        )
+        .is_err()
+    );
+    assert!(remove_message(&f.project, f.view, &expanded).is_err());
+    assert_eq!(f.project, before);
+    payload(f.project.diagrams.get_mut(&f.view).unwrap()).messages[0].address = expanded;
+    assert!(has_code(&f.project, "scenario_layout_address"));
+}
+
+#[test]
+fn only_ordered_message_appearances_and_owned_lifelines_are_targets() {
+    let mut f = fixture();
+    assert!(
+        set_lane(
+            &f.project,
+            f.view,
+            ScenarioLanePosition {
+                lifeline: f.performer,
+                x: 10.
+            }
+        )
+        .is_err()
+    );
+    for id in [f.exchange, f.fragment, f.branch, f.owner, Id::new_v4()] {
+        assert!(
+            set_message(
+                &f.project,
+                f.view,
+                ScenarioMessagePosition {
+                    address: address(id),
+                    send_y: 100.
+                }
+            )
+            .is_err()
+        );
+    }
+    let foreign = f
+        .project
+        .add_element(Kind::Scenario, Layer::Oa, "Foreign", None)
+        .unwrap();
+    let foreign_lane = f
+        .project
+        .add_element(Kind::Lifeline, Layer::Oa, "Foreign lane", Some(foreign))
+        .unwrap();
+    assert!(remove_lane(&f.project, f.view, foreign_lane).is_err());
+    f.project.elements.get_mut(&f.first).unwrap().parent = Some(foreign);
+    assert!(
+        set_message(
+            &f.project,
+            f.view,
+            ScenarioMessagePosition {
+                address: address(f.first),
+                send_y: 100.
+            }
+        )
+        .is_err()
+    );
+    f.project.elements.get_mut(&f.first).unwrap().parent = Some(f.owner);
+    f.project
+        .elements
+        .get_mut(&f.owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap()
+        .retain(|id| *id != f.first);
+    assert!(
+        set_message(
+            &f.project,
+            f.view,
+            ScenarioMessagePosition {
+                address: address(f.first),
+                send_y: 100.
+            }
+        )
+        .is_err()
+    );
+}
+
+#[test]
+fn duplicate_positions_reject_even_when_values_match() {
+    let mut f = fixture();
+    let lane = ScenarioLanePosition {
+        lifeline: f.lane,
+        x: 10.,
+    };
+    let message = ScenarioMessagePosition {
+        address: address(f.first),
+        send_y: 100.,
+    };
+    let entries = payload(f.project.diagrams.get_mut(&f.view).unwrap());
+    entries.lanes = vec![lane.clone(), lane.clone()];
+    entries.messages = vec![message.clone(), message.clone()];
+    assert!(has_code(&f.project, "duplicate_scenario_lane"));
+    assert!(has_code(&f.project, "duplicate_scenario_message"));
+    assert!(set_lane(&f.project, f.view, lane).is_err());
+    assert!(set_message(&f.project, f.view, message).is_err());
+    // Explicit removal can repair all duplicates of the targeted identity.
+    let result = remove_lane(&f.project, f.view, f.lane).unwrap();
+    save(&mut f.project, result);
+    let result = remove_message(&f.project, f.view, &address(f.first)).unwrap();
+    save(&mut f.project, result);
+    assert_admitted(&f.project);
+}
+
+#[test]
+fn sparse_absence_empty_payload_and_signed_zero_are_preserved() {
+    let mut f = fixture();
+    let absent = f.project.diagrams[&f.view].clone();
+    assert_eq!(remove_lane(&f.project, f.view, f.lane).unwrap(), absent);
+    assert_eq!(
+        remove_message(&f.project, f.view, &address(f.first)).unwrap(),
+        absent
+    );
+    assert!(
+        serde_json::to_value(&absent)
+            .unwrap()
+            .get("layout")
+            .is_none()
+    );
+    let result = set_lane(
+        &f.project,
+        f.view,
+        ScenarioLanePosition {
+            lifeline: f.lane,
+            x: -0.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    let result = set_message(
+        &f.project,
+        f.view,
+        ScenarioMessagePosition {
+            address: address(f.first),
+            send_y: -0.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    let result = set_lane(
+        &f.project,
+        f.view,
+        ScenarioLanePosition {
+            lifeline: f.lane,
+            x: 0.,
+        },
+    )
+    .unwrap();
+    assert_eq!(layout(&result).lanes[0].x.to_bits(), (-0.0_f32).to_bits());
+    let result = set_message(
+        &f.project,
+        f.view,
+        ScenarioMessagePosition {
+            address: address(f.first),
+            send_y: 0.,
+        },
+    )
+    .unwrap();
+    assert_eq!(
+        layout(&result).messages[0].send_y.to_bits(),
+        (-0.0_f32).to_bits()
+    );
+    assert_eq!(
+        serde_json::to_string(&result).unwrap(),
+        serde_json::to_string(&f.project.diagrams[&f.view]).unwrap()
+    );
+    let result = remove_lane(&f.project, f.view, f.lane).unwrap();
+    save(&mut f.project, result);
+    let result = remove_message(&f.project, f.view, &address(f.first)).unwrap();
+    assert_eq!(
+        result.layout,
+        Some(DiagramLayout::Scenario(ScenarioLayout::default()))
+    );
+    assert_ne!(result, absent);
+}
+
+#[test]
+fn bounds_are_structural_and_rejected_helpers_do_not_mutate_project() {
+    let mut f = fixture();
+    for value in [-MAX_COORDINATE, MAX_COORDINATE, -7., 0.] {
+        let result = set_lane(
+            &f.project,
+            f.view,
+            ScenarioLanePosition {
+                lifeline: f.lane,
+                x: value,
+            },
+        )
+        .unwrap();
+        save(&mut f.project, result);
+        let result = set_message(
+            &f.project,
+            f.view,
+            ScenarioMessagePosition {
+                address: address(f.first),
+                send_y: value,
+            },
+        )
+        .unwrap();
+        save(&mut f.project, result);
+        assert_admitted(&f.project);
+    }
+    let before = serde_json::to_string(&f.project).unwrap();
+    for value in [
+        f32::NAN,
+        f32::INFINITY,
+        f32::NEG_INFINITY,
+        MAX_COORDINATE + 1.,
+    ] {
+        assert!(
+            set_lane(
+                &f.project,
+                f.view,
+                ScenarioLanePosition {
+                    lifeline: f.lane,
+                    x: value
+                }
+            )
+            .is_err()
+        );
+        assert!(
+            set_message(
+                &f.project,
+                f.view,
+                ScenarioMessagePosition {
+                    address: address(f.first),
+                    send_y: value
+                }
+            )
+            .is_err()
+        );
+    }
+    assert_eq!(serde_json::to_string(&f.project).unwrap(), before);
+    payload(f.project.diagrams.get_mut(&f.view).unwrap()).messages[0].send_y = f32::NAN;
+    assert!(has_code(&f.project, "scenario_layout_coordinate"));
+}
+
+#[test]
+fn helpers_do_not_validate_unrelated_transient_records_in_repair_batches() {
+    let mut f = fixture();
+    payload(f.project.diagrams.get_mut(&f.view).unwrap())
+        .messages
+        .push(ScenarioMessagePosition {
+            address: address(f.second),
+            send_y: f32::INFINITY,
+        });
+    let result = set_lane(
+        &f.project,
+        f.view,
+        ScenarioLanePosition {
+            lifeline: f.lane,
+            x: 420.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    assert!(has_code(&f.project, "scenario_layout_coordinate"));
+    let result = set_message(
+        &f.project,
+        f.view,
+        ScenarioMessagePosition {
+            address: address(f.second),
+            send_y: 300.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    assert_admitted(&f.project);
+}
+
+#[test]
+fn projection_context_and_architecture_payloads_are_explicitly_separate() {
+    let mut f = fixture();
+    let scenario = f.project.diagrams[&f.view].projection;
+    assert_eq!(scenario.scenario(), Some(f.owner));
+    assert!(!scenario.is_architecture());
+    assert!(!scenario.includes(Kind::Lifeline));
+    assert!(ProjectionKind::Overview.is_architecture());
+    assert!(!ProjectionKind::StateMachine { machine: f.owner }.is_architecture());
+    f.project.diagrams.get_mut(&f.view).unwrap().layer = Layer::Sa;
+    assert!(has_code(&f.project, "scenario_diagram_context"));
+    assert!(remove_lane(&f.project, f.view, f.lane).is_err());
+    f.project.diagrams.get_mut(&f.view).unwrap().layer = Layer::Oa;
+    f.project
+        .diagrams
+        .get_mut(&f.view)
+        .unwrap()
+        .routes
+        .push(crate::EdgeRoute {
+            edge: f.exchange,
+            waypoints: vec![],
+            label: None,
+        });
+    assert!(has_code(&f.project, "scenario_diagram_content"));
+    f.project.diagrams.get_mut(&f.view).unwrap().routes.clear();
+    payload(f.project.diagrams.get_mut(&f.view).unwrap());
+    f.project.diagrams.get_mut(&f.view).unwrap().projection = ProjectionKind::Overview;
+    assert!(has_code(&f.project, "scenario_layout_projection"));
+    assert!(
+        set_lane(
+            &f.project,
+            f.view,
+            ScenarioLanePosition {
+                lifeline: f.lane,
+                x: 10.
+            }
+        )
+        .is_err()
+    );
+}
+
+#[test]
+fn typed_json_records_round_trip_and_reject_unknown_or_missing_fields() {
+    let mut f = fixture();
+    let result = set_message(
+        &f.project,
+        f.view,
+        ScenarioMessagePosition {
+            address: address(f.first),
+            send_y: 200.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    let encoded = serde_json::to_value(&f.project.diagrams[&f.view]).unwrap();
+    assert_eq!(
+        serde_json::from_value::<Diagram>(encoded.clone()).unwrap(),
+        f.project.diagrams[&f.view]
+    );
+    assert_eq!(
+        encoded["layout"]["Scenario"]["messages"][0]["address"]["occurrence"],
+        serde_json::json!(f.first)
+    );
+    let mut unknown = encoded.clone();
+    unknown["layout"]["Scenario"]["messages"][0]["extra"] = serde_json::json!(1);
+    assert!(serde_json::from_value::<Diagram>(unknown).is_err());
+    let mut missing = encoded;
+    missing["layout"]["Scenario"]["messages"][0]["address"]
+        .as_object_mut()
+        .unwrap()
+        .remove("references");
+    assert!(serde_json::from_value::<Diagram>(missing).is_err());
+}
+
+#[test]
+fn deleting_only_actual_ids_preserves_latent_message_positions_and_other_views() {
+    let mut f = fixture();
+    let result = set_lane(
+        &f.project,
+        f.view,
+        ScenarioLanePosition {
+            lifeline: f.lane,
+            x: 420.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    let result = set_message(
+        &f.project,
+        f.view,
+        ScenarioMessagePosition {
+            address: address(f.first),
+            send_y: 200.,
+        },
+    )
+    .unwrap();
+    save(&mut f.project, result);
+    let mut copied = f.project.diagrams[&f.view].clone();
+    copied.id = f.other_view;
+    copied.alias = "review_view".into();
+    copied.name = "Review view".into();
+    save(&mut f.project, copied.clone());
+    assert_admitted(&f.project);
+    assert_eq!(layout(&copied).messages[0].address.occurrence, f.first);
+    let mut candidate = f.project.diagrams[&f.view].clone();
+    prune_deleted(&mut candidate, &BTreeSet::from([f.lane, f.exchange]));
+    assert!(layout(&candidate).lanes.is_empty());
+    assert_eq!(layout(&candidate).messages.len(), 1);
+    prune_deleted(&mut candidate, &BTreeSet::from([f.first]));
+    assert!(layout(&candidate).messages.is_empty());
+    assert!(candidate.layout.is_some());
+    assert_eq!(f.project.diagrams[&f.other_view], copied);
+}
+
+#[test]
+fn reference_visitor_and_record_count_cover_explicit_rows() {
+    let f = fixture();
+    let mut d = f.project.diagrams[&f.view].clone();
+    assert_eq!(record_count(&d), 0);
+    let rows = payload(&mut d);
+    rows.lanes.push(ScenarioLanePosition {
+        lifeline: f.lane,
+        x: 50.,
+    });
+    rows.messages.push(ScenarioMessagePosition {
+        address: address(f.first),
+        send_y: 100.,
+    });
+    assert_eq!(record_count(&d), 3);
+    let replacement = Id::new_v4();
+    d.layout.as_mut().unwrap().visit_references(|id| {
+        if *id == f.first {
+            *id = replacement;
+        }
+    });
+    assert_eq!(layout(&d).messages[0].address.occurrence, replacement);
+    assert_eq!(layout(&d).messages[0].send_y, 100.);
+    assert_eq!(layout(&d).lanes[0].lifeline, f.lane);
+}
+
+#[test]
+fn a_real_scenario_use_never_imports_its_called_message_as_a_direct_target() {
+    let mut f = fixture();
+    let called = f
+        .project
+        .add_element(Kind::Scenario, Layer::Oa, "Called sequence", None)
+        .unwrap();
+    let Some(SharedBody::Scenario { viewpoint, .. }) =
+        f.project.elements.get_mut(&called).unwrap().shared_mut()
+    else {
+        panic!("Called Scenario fixture body");
+    };
+    *viewpoint = ScenarioViewpoint::ParticipantInteraction;
+    let called_message = f
+        .project
+        .add_element(Kind::Occurrence, Layer::Oa, "Called delivery", Some(called))
+        .unwrap();
+    set_body(
+        f.project.elements.get_mut(&called_message).unwrap(),
+        OccurrenceBody::Exchange {
+            exchange: None,
+            sender: None,
+            receiver: None,
+            message_kind: MessageKind::Asynchronous,
+            reply_to: None,
+            values: vec![],
+            operation: None,
+        },
+    );
+    *f.project
+        .elements
+        .get_mut(&called)
+        .unwrap()
+        .steps_mut()
+        .unwrap() = vec![called_message];
+    let usage = f
+        .project
+        .add_element(Kind::Occurrence, Layer::Oa, "Call sequence", Some(f.owner))
+        .unwrap();
+    set_body(
+        f.project.elements.get_mut(&usage).unwrap(),
+        OccurrenceBody::ScenarioUse {
+            scenario: Some(called),
+            bindings: vec![],
+        },
+    );
+    f.project
+        .elements
+        .get_mut(&f.owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap()
+        .push(usage);
+    assert_admitted(&f.project);
+    for target in [
+        address(called_message),
+        address(usage),
+        OccurrenceEndpoint {
+            references: vec![usage],
+            occurrence: called_message,
+        },
+    ] {
+        assert!(
+            set_message(
+                &f.project,
+                f.view,
+                ScenarioMessagePosition {
+                    address: target,
+                    send_y: 200.
+                }
+            )
+            .is_err()
+        );
+    }
+}
+
+mod source_lifecycle;

crates/oa-core/src/scenario_layout/tests/source_lifecycle.rs

@@ -0,0 +1,245 @@
+//! Source/command lifecycle checks for the candidate payload. Public version
+//! assignment remains the coordinated codec integration gate.
+use super::*;
+use crate::{Command, Session, language, prepare_command, source_project::*};
+
+fn authored(f: &Fixture) -> CompiledSourceProject {
+    let mut bundle = format_bundle(&f.project);
+    let initial = compile_bundle(&bundle, ProjectLimits::default()).unwrap();
+    let location = &initial.index.declarations[&f.view];
+    let source = bundle.files.get_mut(&location.path).unwrap();
+    let text = format!(
+        r#"diagram nominal_view "Nominal review" id "{}" {{
+ projection {{ Scenario {{ scenario @{}; }}; }};
+ layout {{ Scenario {{
+  lanes [
+   // Controller spacing rationale.
+   {{ lifeline @ // first lane identity
+      {}; x 4.20e2; }},
+   // Repeated performer has its own lane.
+   {{ lifeline @{}; x 680; }}
+  ];
+  messages [
+   // First delivery timing rationale.
+   {{ address {{ references []; occurrence @{}; }}; send_y 2.00e2; }},
+   // Second delivery timing rationale.
+   {{ address {{ references []; occurrence @{}; }}; send_y 350; }}
+  ];
+ }}; }};
+}}
+"#,
+        f.view,
+        f.project.elements[&f.owner].alias,
+        f.project.elements[&f.lane].alias,
+        f.project.elements[&f.repeated_lane].alias,
+        f.project.elements[&f.first].alias,
+        f.project.elements[&f.second].alias
+    );
+    source.replace_range(location.span.start..location.span.end, &text);
+    compile_bundle(&bundle, ProjectLimits::default()).unwrap()
+}
+
+#[test]
+fn source_rows_follow_identity_order_and_keep_comments_numeric_spelling_and_file_ownership() {
+    let f = fixture();
+    let original = authored(&f);
+    let mut changed = original.decoded.project.clone();
+    let rows = payload(changed.diagrams.get_mut(&f.view).unwrap());
+    rows.lanes.swap(0, 1);
+    rows.messages.swap(0, 1);
+    rows.messages[0].send_y = 390.;
+    changed.elements.get_mut(&f.lane).unwrap().alias = "renamed_controller_lane".into();
+    let updated = update_bundle(&original, &changed, ProjectLimits::default()).unwrap();
+    assert_eq!(updated.decoded.project, changed);
+    let path = &original.index.declarations[&f.view].path;
+    assert_eq!(&updated.index.declarations[&f.view].path, path);
+    let text = &updated.bundle.files[path];
+    assert!(
+        text.find("// Repeated performer").unwrap() < text.find("// Controller spacing").unwrap(),
+        "{text}"
+    );
+    assert!(
+        text.find("// Second delivery").unwrap() < text.find("// First delivery").unwrap(),
+        "{text}"
+    );
+    assert!(
+        text.contains(
+            "lifeline @ // first lane identity\n      renamed_controller_lane; x 4.20e2;"
+        ),
+        "{text}"
+    );
+    assert!(text.contains("send_y 2.00e2"), "{text}");
+    assert!(text.contains("send_y 390"), "{text}");
+    for (other, bytes) in &original.bundle.files {
+        if other != path && !bytes.contains(&f.project.elements[&f.lane].alias) {
+            assert_eq!(&updated.bundle.files[other], bytes);
+        }
+    }
+    assert_eq!(
+        compile_bundle(&updated.bundle, ProjectLimits::default())
+            .unwrap()
+            .decoded
+            .project,
+        changed
+    );
+}
+
+#[test]
+fn source_identity_swap_keeps_each_coordinate_comment_with_its_original_object() {
+    let f = fixture();
+    let original = authored(&f);
+    let temporary = Id::new_v4();
+    let command = Command::Batch(vec![
+        Command::Reidentify(f.first, temporary),
+        Command::Reidentify(f.second, f.first),
+        Command::Reidentify(temporary, f.second),
+    ]);
+    let prepared = prepare_command(&original.decoded.project, &command).unwrap();
+    let mut changed = prepared.project;
+    payload(changed.diagrams.get_mut(&f.view).unwrap())
+        .messages
+        .swap(0, 1);
+    let updated = update_bundle_with_identity_map(
+        &original,
+        &changed,
+        &prepared.identity_map,
+        ProjectLimits::default(),
+    )
+    .unwrap();
+    assert_eq!(updated.decoded.project, changed);
+    let path = &original.index.declarations[&f.view].path;
+    let text = &updated.bundle.files[path];
+    assert!(
+        text.find("// Second delivery").unwrap() < text.find("// First delivery").unwrap(),
+        "{text}"
+    );
+    let first_comment = text.find("// First delivery").unwrap();
+    assert!(text[first_comment..].contains(&format!(
+        "occurrence @{}",
+        changed.elements[&f.second].alias
+    )));
+    assert!(text[first_comment..].contains("send_y 2.00e2"));
+}
+
+#[test]
+fn coordinate_batch_is_one_undo_and_numeric_noop_keeps_source_exact() {
+    let f = fixture();
+    let original = authored(&f);
+    let mut session = Session::new(original.decoded.project.clone());
+    session
+        .execute(Command::Batch(vec![
+            Command::SetScenarioLanePosition {
+                diagram: f.view,
+                position: ScenarioLanePosition {
+                    lifeline: f.lane,
+                    x: 510.,
+                },
+            },
+            Command::SetScenarioMessagePosition {
+                diagram: f.view,
+                position: ScenarioMessagePosition {
+                    address: address(f.second),
+                    send_y: 430.,
+                },
+            },
+        ]))
+        .unwrap();
+    let changed = session.project().clone();
+    assert_eq!(session.revision(), 1);
+    assert_eq!(changed.elements, original.decoded.project.elements);
+    assert_eq!(changed.relations, original.decoded.project.relations);
+    let updated = update_bundle(&original, &changed, ProjectLimits::default()).unwrap();
+    session.undo();
+    assert_eq!(session.project(), &original.decoded.project);
+    assert!(!session.can_undo());
+    session.redo();
+    assert_eq!(session.project(), &changed);
+    session
+        .execute(Command::SetScenarioMessagePosition {
+            diagram: f.view,
+            position: ScenarioMessagePosition {
+                address: address(f.second),
+                send_y: 430.,
+            },
+        })
+        .unwrap();
+    assert_eq!(session.revision(), 3);
+    let noop = update_bundle(&updated, session.project(), ProjectLimits::default()).unwrap();
+    assert_eq!(noop.bundle, updated.bundle);
+}
+
+#[test]
+fn absent_and_empty_payload_round_trip_distinctly_and_remove_does_not_materialize_absence() {
+    let f = fixture();
+    let before = language::format(&f.project);
+    let mut session = Session::new(f.project.clone());
+    session
+        .execute(Command::RemoveScenarioLanePosition {
+            diagram: f.view,
+            lifeline: f.lane,
+        })
+        .unwrap();
+    assert_eq!(session.project(), &f.project);
+    assert!(!session.can_undo());
+    assert_eq!(language::format(session.project()), before);
+    let mut present = f.project.clone();
+    present.diagrams.get_mut(&f.view).unwrap().layout =
+        Some(DiagramLayout::Scenario(ScenarioLayout::default()));
+    let text = language::format(&present);
+    assert_ne!(text, before);
+    assert_eq!(language::parse(&text).unwrap(), present);
+    assert_eq!(language::parse(&before).unwrap(), f.project);
+}
+
+#[test]
+fn invalid_layout_source_rejects_without_changing_last_compiled_workspace() {
+    let f = fixture();
+    let original = authored(&f);
+    let before = original.bundle.clone();
+    let path = original.index.declarations[&f.view].path.clone();
+    for replacement in ["x 1e30", "x not_a_number"] {
+        let mut candidate = before.clone();
+        let source = candidate.files.get_mut(&path).unwrap();
+        *source = source.replace("x 4.20e2", replacement);
+        assert!(compile_bundle(&candidate, ProjectLimits::default()).is_err());
+        assert_eq!(original.bundle, before);
+    }
+    let mut candidate = before.clone();
+    let source = candidate.files.get_mut(&path).unwrap();
+    *source = source.replace(
+        &format!("occurrence @{}", f.project.elements[&f.first].alias),
+        &format!("occurrence @{}", f.project.elements[&f.performer].alias),
+    );
+    assert!(compile_bundle(&candidate, ProjectLimits::default()).is_err());
+    assert_eq!(original.bundle, before);
+}
+
+#[test]
+fn explicit_none_survives_other_edits_while_real_payload_clear_removes_values() {
+    let f = fixture();
+    let mut bundle = format_bundle(&f.project);
+    let compiled = compile_bundle(&bundle, ProjectLimits::default()).unwrap();
+    let location = &compiled.index.declarations[&f.view];
+    let path = location.path.clone();
+    bundle.files.get_mut(&path).unwrap().insert_str(
+        location.span.end - 1,
+        "\n layout // explicitly automatic\n none;\n",
+    );
+    let original = compile_bundle(&bundle, ProjectLimits::default()).unwrap();
+    let mut described = original.decoded.project.clone();
+    described.diagrams.get_mut(&f.view).unwrap().description =
+        "Review spacing independently".into();
+    let updated = update_bundle(&original, &described, ProjectLimits::default()).unwrap();
+    assert!(updated.bundle.files[&path].contains("layout // explicitly automatic\n none;"));
+    assert_eq!(updated.decoded.project, described);
+    let mut empty = described.clone();
+    empty.diagrams.get_mut(&f.view).unwrap().layout =
+        Some(DiagramLayout::Scenario(ScenarioLayout::default()));
+    let present = update_bundle(&updated, &empty, ProjectLimits::default()).unwrap();
+    assert_eq!(present.decoded.project, empty);
+    assert!(present.bundle.files[&path].contains("// explicitly automatic"));
+    let cleared = update_bundle(&present, &described, ProjectLimits::default()).unwrap();
+    assert_eq!(cleared.decoded.project, described);
+    assert!(!cleared.bundle.files[&path].contains("layout"));
+    assert!(cleared.bundle.files[&path].contains("// explicitly automatic"));
+}

crates/oa-core/src/session.rs

@@ -23,6 +23,22 @@ pub enum Command {
     EditRelation(Id, Relation),
     CreateDiagram(Diagram),
     EditDiagram(Id, Diagram),
+    SetScenarioLanePosition {
+        diagram: Id,
+        position: ScenarioLanePosition,
+    },
+    RemoveScenarioLanePosition {
+        diagram: Id,
+        lifeline: Id,
+    },
+    SetScenarioMessagePosition {
+        diagram: Id,
+        position: ScenarioMessagePosition,
+    },
+    RemoveScenarioMessagePosition {
+        diagram: Id,
+        address: OccurrenceEndpoint,
+    },
     CreateArtifact(ArtifactLink),
     EditArtifact(Id, ArtifactLink),
     CreateTrace(Trace),
@@ -488,6 +504,26 @@ fn apply_command(
             reidentify_tracked(p, *old, value.id, provenance)?;
             Some(value.id)
         }
+        Command::SetScenarioLanePosition { diagram, position } => {
+            let replacement = crate::scenario_layout::set_lane(p, *diagram, position.clone())?;
+            p.diagrams.insert(*diagram, replacement);
+            Some(*diagram)
+        }
+        Command::RemoveScenarioLanePosition { diagram, lifeline } => {
+            let replacement = crate::scenario_layout::remove_lane(p, *diagram, *lifeline)?;
+            p.diagrams.insert(*diagram, replacement);
+            Some(*diagram)
+        }
+        Command::SetScenarioMessagePosition { diagram, position } => {
+            let replacement = crate::scenario_layout::set_message(p, *diagram, position.clone())?;
+            p.diagrams.insert(*diagram, replacement);
+            Some(*diagram)
+        }
+        Command::RemoveScenarioMessagePosition { diagram, address } => {
+            let replacement = crate::scenario_layout::remove_message(p, *diagram, address)?;
+            p.diagrams.insert(*diagram, replacement);
+            Some(*diagram)
+        }
         Command::CreateArtifact(value) => {
             vacant(p, value.id)?;
             p.artifact_links.insert(value.id, value.clone());
@@ -878,6 +914,7 @@ pub fn reidentify(p: &mut Project, old: Id, new: Id) -> Result<(), ModelError> {
         return Ok(());
     }
     vacant(p, new)?;
+    crate::references::check_remap(p, old, new)?;
     if p.id == old {
         p.id = new;
     } else if let Some(mut v) = p.elements.remove(&old) {
@@ -904,12 +941,17 @@ pub fn reidentify(p: &mut Project, old: Id, new: Id) -> Result<(), ModelError> {
             }
         }
     }
-    crate::references::remap_references(p, old, new);
+    crate::references::remap_references(p, old, new)?;
     Ok(())
 }
 fn layout(p: &mut Project, diagram: Id) -> Result<(), ModelError> {
     use std::collections::{BTreeMap, BTreeSet};
     let d = p.diagrams.get(&diagram).ok_or_else(missing)?;
+    if d.projection.scenario().is_some() {
+        return Err(ModelError(
+            "Scenario layout requires the Scenario geometry operation.".into(),
+        ));
+    }
     let parents = crate::projection::parents(p, d);
     let mut children: BTreeMap<Option<Id>, Vec<Id>> = BTreeMap::new();
     for (id, parent) in &parents {

crates/oa-core/src/source_project.rs

@@ -930,7 +930,18 @@ pub fn update_bundle_with_identity_map(
             };
             let local = edits.entry(path.clone()).or_default();
             update.header(&actual.header, &previous.header, &next.header, local);
-            update.value(&actual.fields, Some(&previous.fields), &next.fields, local);
+            let context = if old.diagrams.contains_key(&id) {
+                EditContext::Diagram
+            } else {
+                EditContext::Other
+            };
+            update.value(
+                &actual.fields,
+                Some(&previous.fields),
+                &next.fields,
+                context,
+                local,
+            );
         }
     }
     if old.id != project.id || old.alias != project.alias || old.name != project.name {
@@ -1119,6 +1130,29 @@ fn inserted_value(text: &str, indent: &str, source: &str) -> String {
     output
 }
 
+// Schema context is explicit: similarly named fields in arbitrary records must
+// never acquire Scenario row identity or move their authored trivia.
+#[derive(Clone, Copy)]
+enum EditContext {
+    Other,
+    Diagram,
+    Layout,
+    Scenario,
+    Lanes,
+    Messages,
+}
+impl EditContext {
+    fn field(self, name: &str) -> Self {
+        match (self, name) {
+            (Self::Diagram, "layout") => Self::Layout,
+            (Self::Layout, "Scenario") => Self::Scenario,
+            (Self::Scenario, "lanes") => Self::Lanes,
+            (Self::Scenario, "messages") => Self::Messages,
+            _ => Self::Other,
+        }
+    }
+}
+
 struct SyntaxUpdate<'a> {
     source: &'a str,
     before: &'a str,
@@ -1185,6 +1219,7 @@ impl SyntaxUpdate<'_> {
         actual: &language::EditValue,
         before: Option<&language::EditValue>,
         after: &language::EditValue,
+        context: EditContext,
         edits: &mut LocalEdits,
     ) {
         use language::EditKind;
@@ -1200,7 +1235,7 @@ impl SyntaxUpdate<'_> {
                         None
                     }
                 });
-                self.record(actual.span, fields, previous, next, edits);
+                self.record(actual.span, fields, previous, next, context, edits);
             }
             (EditKind::List(items), EditKind::List(next)) => {
                 let previous = before.and_then(|old| {
@@ -1210,7 +1245,7 @@ impl SyntaxUpdate<'_> {
                         None
                     }
                 });
-                self.list(actual.span, items, previous, next, edits);
+                self.list(actual.span, items, previous, next, context, edits);
             }
             (EditKind::Reference(_), EditKind::Reference(alias)) => {
                 let token = significant(&self.source[actual.span.start..actual.span.end])
@@ -1263,6 +1298,7 @@ impl SyntaxUpdate<'_> {
         actual: &BTreeMap<String, language::EditField>,
         before: Option<&BTreeMap<String, language::EditField>>,
         after: &BTreeMap<String, language::EditField>,
+        context: EditContext,
         edits: &mut LocalEdits,
     ) {
         // A typed constructor tag change retains shared fields and their trivia.
@@ -1286,7 +1322,13 @@ impl SyntaxUpdate<'_> {
                     },
                     new_key.clone(),
                 ));
-                self.value(&field.value, Some(&old.value), &new.value, edits);
+                self.value(
+                    &field.value,
+                    Some(&old.value),
+                    &new.value,
+                    context.field(new_key),
+                    edits,
+                );
                 return;
             }
         }
@@ -1298,9 +1340,16 @@ impl SyntaxUpdate<'_> {
                         .and_then(|fields| fields.get(key))
                         .map(|field| &field.value),
                     &next.value,
+                    context.field(key),
                     edits,
                 );
-            } else {
+            } else if !(matches!(context, EditContext::Diagram)
+                && key == "layout"
+                && before.is_some_and(|fields| !fields.contains_key(key)))
+            {
+                // Canonical None omits layout. Preserve an authored explicit
+                // none while another field changes; a real Some->None clear
+                // still removes the former payload and retains its trivia.
                 erase_syntax(self.source, field.span, edits);
             }
         }
@@ -1355,6 +1404,7 @@ impl SyntaxUpdate<'_> {
         actual: &[language::EditValue],
         before: Option<&[language::EditValue]>,
         after: &[language::EditValue],
+        context: EditContext,
         edits: &mut LocalEdits,
     ) {
         let previous = before.unwrap_or(&[]);
@@ -1367,6 +1417,7 @@ impl SyntaxUpdate<'_> {
                     self.old_aliases,
                     self.legacy_value_paths,
                     None,
+                    context,
                 )
             })
             .collect();
@@ -1379,6 +1430,7 @@ impl SyntaxUpdate<'_> {
                     self.new_aliases,
                     self.legacy_value_paths,
                     self.identity_origins,
+                    context,
                 )
             })
             .collect();
@@ -1407,7 +1459,7 @@ impl SyntaxUpdate<'_> {
                 .all(|(i, source)| *source == Some(i))
         {
             for (i, (current, next)) in actual.iter().zip(after).enumerate() {
-                self.value(current, previous.get(i), next, edits);
+                self.value(current, previous.get(i), next, EditContext::Other, edits);
             }
             return;
         }
@@ -1440,7 +1492,13 @@ impl SyntaxUpdate<'_> {
                 let chunk = chunks[index];
                 text.push_str(&self.source[chunk.start..current.span.start]);
                 let mut local = Vec::new();
-                self.value(current, previous.get(index), next, &mut local);
+                self.value(
+                    current,
+                    previous.get(index),
+                    next,
+                    EditContext::Other,
+                    &mut local,
+                );
                 text.push_str(&changed_text(self.source, current.span, local));
                 suffix = &self.source[current.span.end..chunk.end];
             } else {
@@ -1483,14 +1541,58 @@ impl SyntaxUpdate<'_> {
     }
 }
 
+fn scenario_item_key(
+    value: &language::EditValue,
+    aliases: &BTreeMap<String, String>,
+    context: EditContext,
+) -> Option<String> {
+    use language::EditKind;
+    let EditKind::Record(fields) = &value.kind else {
+        return None;
+    };
+    let reference = |value: &language::EditValue| {
+        if let EditKind::Reference(alias) = &value.kind {
+            aliases.get(alias).cloned()
+        } else {
+            None
+        }
+    };
+    match context {
+        EditContext::Lanes => {
+            reference(&fields.get("lifeline")?.value).map(|id| format!("scenario-lane:{id}"))
+        }
+        EditContext::Messages => {
+            let EditKind::Record(address) = &fields.get("address")?.value.kind else {
+                return None;
+            };
+            let occurrence = reference(&address.get("occurrence")?.value)?;
+            let path: Vec<_> = match address.get("references") {
+                None => Vec::new(),
+                Some(field) => {
+                    let EditKind::List(path) = &field.value.kind else {
+                        return None;
+                    };
+                    path.iter().map(reference).collect::<Option<Vec<_>>>()?
+                }
+            };
+            Some(format!("scenario-message:{}:{occurrence}", path.join("/")))
+        }
+        _ => None,
+    }
+}
+
 fn item_key(
     value: &language::EditValue,
     source: &str,
     aliases: &BTreeMap<String, String>,
     legacy_value_paths: bool,
     origins: Option<&BTreeMap<Id, Id>>,
+    context: EditContext,
 ) -> Option<String> {
     use language::EditKind;
+    if matches!(context, EditContext::Lanes | EditContext::Messages) {
+        return scenario_item_key(value, aliases, context);
+    }
     if matches!(value.kind, EditKind::Record(_))
         && let Some(key) = language::semantic_row_key(
             &source[value.span.start..value.span.end],

crates/oa-core/src/source_project/source_migration.rs

@@ -68,6 +68,11 @@ pub(super) fn upgrade(
                 &actual.fields,
                 Some(&actual.fields),
                 &next.fields,
+                if project.diagrams.contains_key(&id) {
+                    EditContext::Diagram
+                } else {
+                    EditContext::Other
+                },
                 edits.entry(path.clone()).or_default(),
             );
         }

crates/oa-core/src/validation.rs

@@ -619,6 +619,7 @@ pub fn validate(p: &Project) -> Vec<Issue> {
         }
         text(&mut out, d.id, "name", &d.name);
         text(&mut out, d.id, "description", &d.description);
+        crate::scenario_layout::validate_diagram(p, d, &mut out);
         let option_issues = if d.projection == ProjectionKind::Traceability {
             crate::view_options::validate_options_cross_layer(p, &d.view_options)
         } else {

crates/oa-core/tests/release_routing.rs

@@ -41,6 +41,7 @@ fn fixture() -> Fixture {
             projection: ProjectionKind::Overview,
             view_options: Default::default(),
             nodes: BTreeMap::new(),
+            layout: None,
             routes: vec![],
         },
     );

crates/oa-core/tests/source7_contract.rs

@@ -261,7 +261,7 @@ fn source7_context_lifecycle_source_history_and_closed_admission() {
     assert_eq!(session.project(), &after);
     let fresh = Id::new_v4();
     let mut reidentified = after.clone();
-    references::remap_references(&mut reidentified, f.r1, fresh);
+    references::remap_references(&mut reidentified, f.r1, fresh).unwrap();
     let mut e = reidentified.elements.remove(&f.r1).unwrap();
     e.id = fresh;
     reidentified.elements.insert(fresh, e);

crates/oa-core/tests/state_diagrams.rs

@@ -20,6 +20,7 @@ fn view(p: &mut Project, machine: Id, alias: &str) -> Id {
             projection: ProjectionKind::StateMachine { machine },
             view_options: Default::default(),
             nodes: BTreeMap::new(),
+            layout: None,
             routes: vec![],
         },
     );

crates/oa-desktop/Cargo.toml

@@ -18,6 +18,7 @@ serde_json.workspace = true
 reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }
 tokio = { version = "1", features = ["rt", "time"] }
 tempfile = "3"
+unicode-segmentation = "1.13.3"
 
 [dev-dependencies]
 iced_runtime = "0.14"

crates/oa-desktop/src/app/architecture_authoring.rs

@@ -138,7 +138,7 @@ pub fn validate_saved(p: &Project, s: &Saved) -> Result<(), String> {
         .diagrams
         .get(&s.diagram)
         .ok_or("The creation draft's diagram is missing.")?;
-    if matches!(d.projection, ProjectionKind::StateMachine { .. })
+    if !d.projection.is_architecture()
         || s.query.len() > 16384
         || s.page > 1_000_000
         || s.point
@@ -180,7 +180,7 @@ pub fn validate_saved(p: &Project, s: &Saved) -> Result<(), String> {
 }
 fn context_kinds(p: &Project, d: &Diagram) -> Vec<Kind> {
     let mut values = match (d.layer, d.projection) {
-        (_, ProjectionKind::StateMachine { .. }) => vec![],
+        (_, ProjectionKind::StateMachine { .. } | ProjectionKind::Scenario { .. }) => vec![],
         (Layer::Oa, ProjectionKind::FunctionalDataflow) => vec![Kind::Activity],
         (Layer::Sa, ProjectionKind::FunctionalDataflow) => vec![Kind::Function],
         (Layer::Oa, ProjectionKind::Capabilities) => vec![
@@ -208,11 +208,12 @@ pub fn kinds(app: &App) -> Vec<Kind> {
         .unwrap_or_default()
 }
 fn compatible(p: &Project, d: &Diagram, id: Id) -> bool {
-    p.elements.get(&id).is_some_and(|e| {
-        e.kind() != Kind::Port
-            && d.projection.includes(e.kind())
-            && (e.layer() == d.layer || d.projection == ProjectionKind::Traceability)
-    })
+    d.projection.is_architecture()
+        && p.elements.get(&id).is_some_and(|e| {
+            e.kind() != Kind::Port
+                && d.projection.includes(e.kind())
+                && (e.layer() == d.layer || d.projection == ProjectionKind::Traceability)
+        })
 }
 fn suggested(p: &Project, d: &Diagram, kind: Kind) -> bool {
     // Existing System remains a useful choice even when the singleton exists.
@@ -257,6 +258,17 @@ pub fn candidates(app: &App) -> Vec<(Id, String, bool)> {
 }
 impl App {
     pub(super) fn architecture_event(&mut self, event: Event) -> Task<Message> {
+        if matches!(
+            &event,
+            Event::Start(..) | Event::Allocate(..) | Event::Existing(..)
+        ) && !self
+            .active_diagram
+            .and_then(|id| self.project().diagrams.get(&id))
+            .is_some_and(|d| d.projection.is_architecture())
+        {
+            self.status = "Choose an architecture view before adding architecture content.".into();
+            return Task::none();
+        }
         match event {
             Event::Start(_, point) | Event::Allocate(_, _, point) | Event::Existing(point) => {
                 if self.architecture.is_some() {

crates/oa-desktop/src/app/architecture_authoring/tests.rs

@@ -70,6 +70,7 @@ fn architecture_f2_routes_selected_node_to_inline_rename_and_exact_undo() {
         view_index: None,
         diagram: app.active_diagram.unwrap(),
         selected: element,
+        navigation_focus: None,
         zoom: app.zoom,
         pan: app.pan,
         context: app.route_context().unwrap(),

crates/oa-desktop/src/app/architecture_authoring_tests.rs

@@ -225,6 +225,7 @@ fn architecture_canvas_left_click_uses_world_coordinate_once_at_zoom_and_pan() {
         view_index: None,
         diagram: app.active_diagram.unwrap(),
         selected: app.selected,
+        navigation_focus: None,
         zoom: app.zoom,
         pan: app.pan,
         context: app.route_context().unwrap(),
@@ -299,6 +300,7 @@ fn architecture_f2_rename_preserves_identity_placement_and_atomic_history() {
         view_index: None,
         diagram: app.active_diagram.unwrap(),
         selected: element,
+        navigation_focus: None,
         zoom: app.zoom,
         pan: app.pan,
         context: app.route_context().unwrap(),

crates/oa-desktop/src/app/checkpoints.rs

@@ -214,6 +214,11 @@ impl App {
             .is_some_and(architecture_authoring::State::inline)
         {
             Task::batch([lint, iced::widget::operation::focus("architecture-name")])
+        } else if self.page == Page::Behavior && self.behavior.source_open() {
+            Task::batch([
+                lint,
+                iced::widget::operation::focus(behavior::source_draft::NAME_INPUT),
+            ])
         } else if self.page == Page::Behavior && self.behavior.creation.created().is_some() {
             Task::batch([
                 lint,

crates/oa-desktop/src/app/diagram_reveal.rs

@@ -0,0 +1,146 @@
+//! Complete a navigation camera after the destination reports its real viewport.
+use super::*;
+use crate::diagram_usage::{Context, Surface};
+#[cfg(test)]
+mod tests;
+
+impl App {
+    pub(super) fn is_diagram_viewport(message: &Message) -> bool {
+        matches!(
+            message,
+            Message::CanvasResized(_)
+                | Message::DiagramRevealViewport(..)
+                | Message::TopologyCanvas(behavior::topology::CanvasEvent::Viewport(..))
+                | Message::ScenarioCanvas(behavior::scenario::CanvasEvent::Viewport(..))
+                | Message::StateDiagram(behavior::state_edit::Event::Viewport(..))
+        )
+    }
+    pub(crate) fn architecture_reveal_stamp(&self, diagram: Id) -> Option<(Context, u64)> {
+        self.pending_diagram_reveal
+            .as_ref()
+            .filter(|(_, u, _)| u.surface == Surface::Saved(diagram))
+            .map(|(context, _, epoch)| (*context, *epoch))
+    }
+
+    pub(super) fn diagram_reveal_viewport(&self, message: &Message) -> Option<Surface> {
+        let (context, usage, epoch) = self.pending_diagram_reveal.as_ref()?;
+        if context.document != self.canvas_document
+            || context.revision != self.document.revision()
+            || *epoch != self.canvas_epoch
+        {
+            return None;
+        }
+        let (surface, size, valid) = match message {
+            Message::DiagramRevealViewport(c, e, size) => (
+                usage.surface,
+                *size,
+                c == context
+                    && e == epoch
+                    && self.page == Page::Diagram
+                    && Some(usage.surface.id()) == self.active_diagram,
+            ),
+            Message::TopologyCanvas(behavior::topology::CanvasEvent::Viewport(c, size)) => (
+                Surface::Process(c.owner),
+                *size,
+                c.document == context.document
+                    && c.revision == context.revision
+                    && c.epoch == *epoch,
+            ),
+            Message::ScenarioCanvas(behavior::scenario::CanvasEvent::Viewport(c, size)) => (
+                Surface::Scenario(c.scenario),
+                *size,
+                c.document == context.document
+                    && c.revision == context.revision
+                    && c.epoch == *epoch,
+            ),
+            Message::StateDiagram(behavior::state_edit::Event::Viewport(c, size)) => (
+                Surface::Saved(c.diagram),
+                *size,
+                c.document == context.document
+                    && c.revision == context.revision
+                    && c.epoch == *epoch,
+            ),
+            _ => return None,
+        };
+        (valid
+            && surface == usage.surface
+            && size.width.is_finite()
+            && size.height.is_finite()
+            && size.width > 0.
+            && size.height > 0.)
+            .then_some(surface)
+    }
+
+    pub(super) fn reconcile_pending_diagram_reveal(&mut self, message: &Message) {
+        if !matches!(
+            message,
+            Message::CheckpointTick
+                | Message::CheckpointWritten(..)
+                | Message::Lint(_)
+                | Message::Linted(..)
+                | Message::SourceViewport(_)
+                | Message::WindowResized(_)
+                | Message::CanvasResized(_)
+                | Message::DiagramRevealViewport(..)
+                | Message::DiagramUsage(_)
+                | Message::DiagramUsagesReady(_)
+                | Message::SourceSymbolsReady(_)
+                | Message::SourceRenameReady(_)
+                | Message::TopologyCanvas(behavior::topology::CanvasEvent::Viewport(..))
+                | Message::ScenarioCanvas(behavior::scenario::CanvasEvent::Viewport(..))
+                | Message::StateDiagram(behavior::state_edit::Event::Viewport(..))
+        ) {
+            self.pending_diagram_reveal = None;
+            if !Self::is_navigation_camera(message) {
+                self.diagram_navigation_focus = None;
+            }
+        }
+    }
+
+    fn is_navigation_camera(message: &Message) -> bool {
+        if let Message::BehaviorControl(intent) = message {
+            return Self::is_navigation_camera(&intent.message);
+        }
+        matches!(
+            message,
+            Message::Pan(_)
+                | Message::Zoom(_)
+                | Message::Fit
+                | Message::TopologyCanvas(
+                    behavior::topology::CanvasEvent::Camera(..)
+                        | behavior::topology::CanvasEvent::Zoom(..)
+                        | behavior::topology::CanvasEvent::Scrolled(..)
+                        | behavior::topology::CanvasEvent::Focus(..)
+                )
+                | Message::ScenarioCanvas(
+                    behavior::scenario::CanvasEvent::Camera(..)
+                        | behavior::scenario::CanvasEvent::Zoom(..)
+                        | behavior::scenario::CanvasEvent::Scrolled(..)
+                        | behavior::scenario::CanvasEvent::Focus(..)
+                )
+                | Message::StateDiagram(
+                    behavior::state_edit::Event::Pan(..)
+                        | behavior::state_edit::Event::Zoom(..)
+                        | behavior::state_edit::Event::Fit(..)
+                )
+        )
+    }
+
+    pub(super) fn finish_diagram_reveal(&mut self, surface: Surface) {
+        let Some((context, usage, _)) = self.pending_diagram_reveal.take() else {
+            return;
+        };
+        if context.document == self.canvas_document
+            && context.revision == self.document.revision()
+            && usage.surface == surface
+            && !self.draft_dirty()
+            && !self.source_dirty()
+            && !self.behavior.has_pending()
+        {
+            // The normal viewport handler has now stored the measured size.
+            // Target identity was validated for this revision before navigation.
+            self.reveal_diagram_usage(&usage);
+        }
+        self.pending_diagram_reveal = None;
+    }
+}

crates/oa-desktop/src/app/diagram_reveal/tests.rs

@@ -0,0 +1,404 @@
+//! Independent first-layout navigation oracles, through the real App boundary.
+use super::*;
+use crate::diagram_usage::{self as usage, Target, Usage};
+use iced::{Size, Vector};
+use std::collections::BTreeMap;
+
+#[derive(Clone, Copy, Debug)]
+enum Canvas {
+    Architecture,
+    Process,
+    Scenario,
+    State,
+}
+const CANVASES: [Canvas; 4] = [
+    Canvas::Architecture,
+    Canvas::Process,
+    Canvas::Scenario,
+    Canvas::State,
+];
+const WIDE: Size = Size::new(1200., 700.);
+const ACTUAL: Size = Size::new(500., 300.);
+
+fn send(app: &mut App, message: Message) {
+    let _ = app.update(message);
+}
+
+fn fixture(canvas: Canvas) -> (App, Usage) {
+    let mut p = Project::empty();
+    let work = p
+        .add_element(Kind::Activity, Layer::Oa, "Respond", None)
+        .unwrap();
+    let (surface, subject) = match canvas {
+        Canvas::Architecture => {
+            let diagram = p.ensure_diagram(Layer::Oa);
+            p.place(
+                diagram,
+                work,
+                Position {
+                    x: 12_000.,
+                    y: 9_000.,
+                },
+            );
+            (Surface::Saved(diagram), work)
+        }
+        Canvas::Process | Canvas::Scenario => {
+            let kind = if matches!(canvas, Canvas::Process) {
+                Kind::Process
+            } else {
+                Kind::Scenario
+            };
+            let owner = p.add_element(kind, Layer::Oa, "Response", None).unwrap();
+            let occurrence = p
+                .add_element(Kind::Occurrence, Layer::Oa, "Respond here", Some(owner))
+                .unwrap();
+            *p.elements
+                .get_mut(&occurrence)
+                .unwrap()
+                .shared_mut()
+                .unwrap() = SharedBody::Occurrence {
+                body: OccurrenceBody::Action {
+                    action: Some(work),
+                    lifeline: None,
+                },
+                precondition: String::new(),
+                postcondition: String::new(),
+            };
+            let steps = p.elements.get_mut(&owner).unwrap().steps_mut().unwrap();
+            if !steps.contains(&occurrence) {
+                steps.push(occurrence);
+            }
+            (
+                if matches!(canvas, Canvas::Process) {
+                    Surface::Process(owner)
+                } else {
+                    Surface::Scenario(owner)
+                },
+                occurrence,
+            )
+        }
+        Canvas::State => {
+            let machine = p
+                .add_element(Kind::StateMachine, Layer::Oa, "Modes", None)
+                .unwrap();
+            let region = p
+                .add_element(Kind::Region, Layer::Oa, "Main", Some(machine))
+                .unwrap();
+            let state = p
+                .add_element(Kind::State, Layer::Oa, "Ready", Some(region))
+                .unwrap();
+            let diagram = Id::new_v4();
+            p.diagrams.insert(
+                diagram,
+                Diagram {
+                    id: diagram,
+                    alias: "ready_view".into(),
+                    name: "Ready view".into(),
+                    description: String::new(),
+                    layer: Layer::Oa,
+                    projection: ProjectionKind::StateMachine { machine },
+                    nodes: BTreeMap::new(),
+                    layout: None,
+                    routes: vec![],
+                    view_options: Default::default(),
+                },
+            );
+            p.place(
+                diagram,
+                state,
+                Position {
+                    x: 8_000.,
+                    y: 11_000.,
+                },
+            );
+            (Surface::Saved(diagram), state)
+        }
+    };
+    let mut app = App::with_project(p);
+    let found = usage::collect(
+        app.project(),
+        subject,
+        &app.behavior.topology,
+        &app.behavior.scenario,
+    )
+    .into_iter()
+    .find(|u| u.surface == surface && u.target != Target::Whole)
+    .unwrap();
+    app.canvas_size = Some(WIDE);
+    app.behavior.diagram.viewport = Some(WIDE);
+    if let Surface::Process(owner) = surface {
+        app.behavior.topology.enter(app.canvas_document, owner);
+        app.behavior.topology.viewport(WIDE);
+    }
+    if let Surface::Scenario(owner) = surface {
+        app.behavior.scenario.enter(app.canvas_document, owner);
+        app.behavior.scenario.viewport(WIDE);
+    }
+    app.page = Page::Text;
+    (app, found)
+}
+
+fn measurement(
+    canvas: Canvas,
+    context: Context,
+    epoch: u64,
+    surface: Surface,
+    size: Size,
+) -> Message {
+    match canvas {
+        Canvas::Architecture => Message::DiagramRevealViewport(context, epoch, size),
+        Canvas::Process => Message::TopologyCanvas(behavior::topology::CanvasEvent::Viewport(
+            behavior::topology::Context {
+                document: context.document,
+                owner: surface.id(),
+                revision: context.revision,
+                epoch,
+            },
+            size,
+        )),
+        Canvas::Scenario => Message::ScenarioCanvas(behavior::scenario::CanvasEvent::Viewport(
+            behavior::scenario::Context {
+                document: context.document,
+                scenario: surface.id(),
+                revision: context.revision,
+                epoch,
+            },
+            size,
+        )),
+        Canvas::State => Message::StateDiagram(behavior::state_edit::Event::Viewport(
+            behavior::state_edit::Context {
+                document: context.document,
+                diagram: surface.id(),
+                revision: context.revision,
+                epoch,
+            },
+            size,
+        )),
+    }
+}
+
+fn stamp(app: &App) -> (Context, u64) {
+    let (context, _, epoch) = app
+        .pending_diagram_reveal
+        .as_ref()
+        .expect("reveal awaits measured destination");
+    (*context, *epoch)
+}
+
+fn assert_centered(app: &App, canvas: Canvas, target: &Usage) {
+    // All independently authored fixture targets fit ACTUAL at the readable cap.
+    // This oracle does not call the production camera/reveal implementation.
+    let zoom = 1.25;
+    let pan = Vector::new(
+        250. - target.bounds.center_x() * zoom,
+        150. - target.bounds.center_y() * zoom,
+    );
+    match canvas {
+        Canvas::Architecture => {
+            assert_eq!(app.canvas_size, Some(ACTUAL));
+            assert_eq!(app.zoom, zoom);
+            assert_eq!(app.pan, pan);
+            assert!(!app.fit_to_view);
+        }
+        Canvas::State => {
+            assert_eq!(app.behavior.diagram.viewport, Some(ACTUAL));
+            assert_eq!(app.behavior.diagram.zoom, zoom);
+            assert_eq!(app.behavior.diagram.pan, pan);
+            assert!(!app.behavior.diagram.fit);
+        }
+        Canvas::Process => {
+            let mut expected = behavior::topology::State::default();
+            expected.enter(app.canvas_document, target.surface.id());
+            expected.viewport(ACTUAL);
+            expected.zoom(Some(zoom));
+            expected.camera(behavior::canvas_workspace::Event::Pan(pan));
+            assert!(app.behavior.topology.camera_boundary() == expected.camera_boundary());
+        }
+        Canvas::Scenario => {
+            let mut expected = behavior::scenario::State::default();
+            expected.enter(app.canvas_document, target.surface.id());
+            expected.choose_tool(target.surface.id(), behavior::scenario::CanvasTool::Select);
+            expected.viewport(ACTUAL);
+            expected.zoom(Some(zoom));
+            expected.camera(behavior::canvas_workspace::Event::Pan(pan));
+            assert!(app.behavior.scenario.camera_boundary() == expected.camera_boundary());
+        }
+    }
+}
+
+#[test]
+fn all_reveal_surfaces_recenter_once_after_the_real_viewport_and_preserve_authored_state() {
+    for canvas in CANVASES {
+        let (mut app, target) = fixture(canvas);
+        let accepted = app.document.snapshot();
+        let drafts = app.source_workspace.bundle();
+        let revision = app.document.revision();
+        let history = (
+            app.document.can_undo(),
+            app.document.can_redo(),
+            app.document.dirty(),
+        );
+        assert!(app.reveal_diagram_usage(&target));
+        let (context, epoch) = stamp(&app);
+        send(
+            &mut app,
+            measurement(canvas, context, epoch, target.surface, ACTUAL),
+        );
+        assert!(app.pending_diagram_reveal.is_none());
+        assert_centered(&app, canvas, &target);
+        assert!(Arc::ptr_eq(&accepted, &app.document.snapshot()));
+        assert_eq!(app.source_workspace.bundle(), drafts);
+        assert_eq!(app.document.revision(), revision);
+        assert_eq!(
+            (
+                app.document.can_undo(),
+                app.document.can_redo(),
+                app.document.dirty()
+            ),
+            history
+        );
+        // The exact delivered callback is a replay after the one-shot is consumed.
+        let camera = app.camera_boundary();
+        send(
+            &mut app,
+            measurement(canvas, context, epoch, target.surface, ACTUAL),
+        );
+        assert!(app.pending_diagram_reveal.is_none());
+        assert!(app.camera_boundary() == camera);
+        assert_centered(&app, canvas, &target);
+    }
+}
+
+#[test]
+fn malformed_or_wrong_stamp_measurements_cannot_poison_a_pending_reveal() {
+    for canvas in CANVASES {
+        for invalid in 0..6 {
+            let (mut app, target) = fixture(canvas);
+            assert!(app.reveal_diagram_usage(&target));
+            let (context, epoch) = stamp(&app);
+            let camera = app.camera_boundary();
+            let mut stale = context;
+            let mut wrong_epoch = epoch;
+            let mut size = Size::new(111., 122.);
+            match invalid {
+                0 => stale.document = Id::new_v4(),
+                1 => stale.revision = stale.revision.wrapping_add(1),
+                2 => wrong_epoch = wrong_epoch.wrapping_add(1),
+                3 => size.width = f32::NAN,
+                4 => size.height = f32::INFINITY,
+                _ => size.width = 0.,
+            }
+            send(
+                &mut app,
+                measurement(canvas, stale, wrong_epoch, target.surface, size),
+            );
+            assert!(
+                app.pending_diagram_reveal.is_some(),
+                "{canvas:?} invalid case {invalid}"
+            );
+            assert_eq!(stamp(&app), (context, epoch));
+            assert_eq!(app.canvas_epoch, epoch);
+            assert!(
+                app.camera_boundary() == camera,
+                "{canvas:?} invalid case {invalid}"
+            );
+            send(
+                &mut app,
+                measurement(canvas, context, epoch, target.surface, ACTUAL),
+            );
+            assert!(app.pending_diagram_reveal.is_none());
+            assert_centered(&app, canvas, &target);
+        }
+    }
+}
+
+#[test]
+fn actual_window_resize_before_first_measurement_retains_focus_for_the_new_context() {
+    for canvas in CANVASES {
+        let (mut app, target) = fixture(canvas);
+        let accepted = app.document.snapshot();
+        assert!(app.reveal_diagram_usage(&target));
+        let (context, old_epoch) = stamp(&app);
+        send(&mut app, Message::WindowResized(Size::new(1100., 700.)));
+        let (current, epoch) = stamp(&app);
+        assert_eq!(current, context);
+        assert_eq!(epoch, app.canvas_epoch);
+        if matches!(canvas, Canvas::Process | Canvas::Scenario) {
+            assert_ne!(epoch, old_epoch);
+            let camera = app.camera_boundary();
+            send(
+                &mut app,
+                measurement(canvas, context, old_epoch, target.surface, ACTUAL),
+            );
+            assert_eq!(stamp(&app), (current, epoch));
+            assert!(app.camera_boundary() == camera);
+        }
+        send(
+            &mut app,
+            measurement(canvas, current, epoch, target.surface, ACTUAL),
+        );
+        assert!(app.pending_diagram_reveal.is_none());
+        assert_centered(&app, canvas, &target);
+        assert!(Arc::ptr_eq(&accepted, &app.document.snapshot()));
+    }
+}
+
+#[test]
+fn user_camera_edit_and_navigation_cancel_deferred_focus_without_late_snapping() {
+    for canvas in CANVASES {
+        for action in 0..3 {
+            let (mut app, target) = fixture(canvas);
+            let accepted = app.document.snapshot();
+            assert!(app.reveal_diagram_usage(&target));
+            let (context, epoch) = stamp(&app);
+            let event = match action {
+                0 => match canvas {
+                    Canvas::Architecture => Message::Pan(Vector::new(31., -17.)),
+                    Canvas::State => Message::StateDiagram(behavior::state_edit::Event::Pan(
+                        app.state_context().unwrap(),
+                        Vector::new(31., -17.),
+                    )),
+                    Canvas::Process => {
+                        Message::TopologyCanvas(behavior::topology::CanvasEvent::Camera(
+                            app.topology_context().unwrap(),
+                            app.camera_epoch,
+                            behavior::canvas_workspace::Event::Pan(Vector::new(31., -17.)),
+                        ))
+                    }
+                    Canvas::Scenario => {
+                        Message::ScenarioCanvas(behavior::scenario::CanvasEvent::Camera(
+                            app.scenario_context().unwrap(),
+                            app.camera_epoch,
+                            behavior::canvas_workspace::Event::Pan(Vector::new(31., -17.)),
+                        ))
+                    }
+                },
+                1 => Message::Field("/name".into(), "Pending title edit".into()),
+                _ => Message::Page(Page::Catalog),
+            };
+            send(&mut app, event);
+            assert!(
+                app.pending_diagram_reveal.is_none(),
+                "{canvas:?} action {action}"
+            );
+            let camera = app.camera_boundary();
+            let page = app.page;
+            // A stale layout callback at the already retained size cannot
+            // restore the old navigation camera after deliberate user input.
+            send(
+                &mut app,
+                measurement(canvas, context, epoch, target.surface, WIDE),
+            );
+            assert!(app.pending_diagram_reveal.is_none());
+            assert!(
+                app.camera_boundary() == camera,
+                "{canvas:?} action {action}"
+            );
+            assert_eq!(app.page, page);
+            assert!(Arc::ptr_eq(&accepted, &app.document.snapshot()));
+            if action == 1 {
+                assert!(app.draft_dirty());
+            }
+        }
+    }
+}

crates/oa-desktop/src/app/diagram_usages.rs

@@ -0,0 +1,454 @@
+//! Navigation-only adapter: validates destinations before changing presentation.
+use super::*;
+use crate::diagram_usage::{self as usage, Context, Event, Panel, Surface, Target, Usage};
+#[cfg(test)]
+mod tests;
+
+impl App {
+    pub(crate) fn diagram_usage_message(&self, subject: Id) -> Message {
+        Message::DiagramUsage(Event::Open(Context {
+            document: self.canvas_document,
+            revision: self.document.revision(),
+            subject,
+        }))
+    }
+
+    fn usage_navigation_available(&self) -> bool {
+        !self.busy
+            && !self.source_rename.open()
+            && self.pending.is_none()
+            && self.file_prompt.is_none()
+            && !self.delete_pending
+            && self.workflow.is_none()
+            && !self.hosted.visible
+            && self.architecture.is_none()
+            && !self.reference_input_active()
+            && !self.behavior.has_pending()
+            && !self.draft_dirty()
+            && !self.source_dirty()
+    }
+
+    /// Admit at most one expensive lookup, including one accepted Project clone.
+    /// A replacement panel waits for the previous worker's exact completion.
+    fn start_diagram_lookup(&mut self) -> Task<Message> {
+        let Some(panel) = self.diagram_usages.as_ref() else {
+            return Task::none();
+        };
+        if !panel.loading || self.diagram_lookup_in_flight.is_some() {
+            return Task::none();
+        }
+        let (token, context) = (panel.token, panel.context);
+        if context.document != self.canvas_document
+            || context.revision != self.document.revision()
+            || !self.usage_navigation_available()
+        {
+            let panel = self.diagram_usages.as_mut().unwrap();
+            panel.loading = false;
+            panel.notice = Some(
+                "The model or pending edits changed. Reopen diagram navigation when ready.".into(),
+            );
+            return Task::none();
+        }
+        let project = self.project().clone();
+        let presentation = self.behavior.topology.usage_snapshot();
+        self.diagram_lookup_in_flight = Some(token);
+        Task::perform(
+            async move {
+                let result = tokio::task::spawn_blocking(move || {
+                    let process = presentation.into_query_state();
+                    let scenario = behavior::scenario::State::default();
+                    usage::collect(&project, context.subject, &process, &scenario)
+                        .into_iter()
+                        .filter(|row| !matches!(row.surface, Surface::Saved(id)
+                            if project.diagrams.get(&id).is_some_and(|d| d.projection.scenario().is_some())))
+                        .collect()
+                })
+                .await
+                .map_err(|error| format!("Diagram lookup failed: {error}. Close and try again."));
+                usage::Completion {
+                    token,
+                    context,
+                    result,
+                }
+            },
+            Message::DiagramUsagesReady,
+        )
+    }
+
+    fn refresh_diagram_lookup(&mut self, notice: &str) -> Task<Message> {
+        let Some(panel) = self.diagram_usages.as_mut() else {
+            return Task::none();
+        };
+        panel.token = Id::new_v4();
+        panel.context.revision = self.document.revision();
+        panel.usages.clear();
+        panel.loading = true;
+        panel.page = 0;
+        panel.cursor = 0;
+        panel.destination = None;
+        panel.notice = Some(notice.into());
+        self.start_diagram_lookup()
+    }
+
+    /// Must run before modal/input dispatch. A closed or replaced panel still
+    /// owns its worker slot until this exact completion arrives.
+    pub(super) fn diagram_usages_ready(&mut self, completion: usage::Completion) -> Task<Message> {
+        if self.diagram_lookup_in_flight != Some(completion.token) {
+            return Task::none();
+        }
+        self.diagram_lookup_in_flight = None;
+        let Some(panel) = self.diagram_usages.as_ref() else {
+            return Task::none();
+        };
+        if panel.context.document != self.canvas_document {
+            self.diagram_usages = None;
+            return Task::none();
+        }
+        if panel.context.revision != self.document.revision() {
+            return self
+                .refresh_diagram_lookup("The model changed. Review the refreshed destinations.");
+        }
+        if panel.token != completion.token {
+            // A newer Open/refresh waited without cloning or spawning a second job.
+            return self.start_diagram_lookup();
+        }
+        let panel = self.diagram_usages.as_mut().unwrap();
+        if panel.context != completion.context || !panel.loading {
+            panel.loading = false;
+            panel.notice = Some(
+                "This lookup no longer matches the requested model. Close and try again.".into(),
+            );
+            return Task::none();
+        }
+        panel.loading = false;
+        match completion.result {
+            Ok(usages) => panel.usages = usages,
+            Err(error) => panel.notice = Some(error),
+        }
+        Task::none()
+    }
+
+    /// Selection validates one destination only; opening the chooser does the
+    /// whole-project scan on its worker, never on the GUI thread.
+    fn current_surface_usages(&self, subject: Id, surface: Surface) -> Vec<Usage> {
+        match surface {
+            Surface::Saved(diagram) => {
+                usage::saved_usages_for(self.project(), subject, Some(diagram))
+            }
+            Surface::Process(owner) => {
+                self.behavior
+                    .topology
+                    .diagram_usages(self.project(), owner, subject)
+            }
+            Surface::Scenario(owner) => {
+                self.behavior
+                    .scenario
+                    .diagram_usages(self.project(), owner, subject)
+            }
+        }
+    }
+
+    pub(super) fn diagram_usage_event(&mut self, event: Event) -> Task<Message> {
+        if let Event::Open(context) = event {
+            if context.document != self.canvas_document
+                || context.revision != self.document.revision()
+                || !self.project().contains(context.subject)
+            {
+                return Task::none();
+            }
+            if !self.usage_navigation_available() {
+                self.status = "Apply or revert pending edits before opening diagram navigation. Your inputs are retained.".into();
+                return Task::none();
+            }
+            let mut panel = Panel::new(context, Vec::new());
+            panel.loading = true;
+            let filter_id = format!("diagram-usage-filter-{}", panel.token);
+            self.diagram_usages = Some(panel);
+            self.model_menu = None;
+            // Only an accepted new chooser supersedes the previous reveal.
+            // Rejected/stale panel envelopes leave its first measurement intact.
+            self.pending_diagram_reveal = None;
+            self.diagram_navigation_focus = None;
+            self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+            return Task::batch([
+                self.start_diagram_lookup(),
+                iced::widget::operation::focus(filter_id),
+            ]);
+        }
+        let token = match &event {
+            Event::Open(_) => unreachable!(),
+            Event::Close(t)
+            | Event::Search(t, _)
+            | Event::Page(t, _)
+            | Event::Move(t, _)
+            | Event::Activate(t)
+            | Event::Destination(t, _)
+            | Event::Choose(t, _) => *t,
+        };
+        let Some(panel) = &self.diagram_usages else {
+            return Task::none();
+        };
+        if panel.token != token {
+            return Task::none();
+        }
+        if matches!(event, Event::Close(_)) {
+            self.diagram_usages = None;
+            if self.page == Page::Text {
+                self.restore_source_editor_focus();
+            }
+            return Task::none();
+        }
+        if panel.context.document != self.canvas_document {
+            self.diagram_usages = None;
+            return Task::none();
+        }
+        if panel.context.revision != self.document.revision() {
+            return self
+                .refresh_diagram_lookup("The model changed. Review the refreshed destinations.");
+        }
+        if panel.loading {
+            // Search and Close remain useful while loading; queued activation
+            // must not perform a synchronous fallback or choose an old row.
+            if let Event::Search(_, query) = event {
+                self.diagram_usages.as_mut().unwrap().search = query;
+            }
+            return Task::none();
+        }
+        match event {
+            Event::Move(_, direction) => {
+                let panel = self.diagram_usages.as_ref().unwrap();
+                let count = panel.choices(self.project()).len();
+                let panel = self.diagram_usages.as_mut().unwrap();
+                if count > 0 {
+                    panel.cursor = if direction < 0 {
+                        (panel.cursor + count - 1) % count
+                    } else {
+                        (panel.cursor + 1) % count
+                    };
+                    panel.page = panel.cursor / 6;
+                }
+            }
+            Event::Activate(_) => {
+                let panel = self.diagram_usages.as_ref().unwrap();
+                if let Some(event) = panel.choices(self.project()).get(panel.cursor).cloned() {
+                    return self.diagram_usage_event(event);
+                }
+            }
+            Event::Search(_, query) => {
+                let panel = self.diagram_usages.as_mut().unwrap();
+                panel.search = query;
+                panel.page = 0;
+                panel.cursor = 0;
+            }
+            Event::Page(_, page) => {
+                let panel = self.diagram_usages.as_mut().unwrap();
+                panel.page = page;
+                panel.cursor = page.saturating_mul(6);
+            }
+            Event::Destination(_, surface) => {
+                let panel = self.diagram_usages.as_mut().unwrap();
+                if surface.is_none() || panel.usages.iter().any(|u| Some(u.surface) == surface) {
+                    panel.destination = surface;
+                    panel.page = 0;
+                    panel.cursor = 0;
+                }
+            }
+            Event::Choose(_, requested) => {
+                if !self.usage_navigation_available() {
+                    return Task::none();
+                }
+                let subject = self.diagram_usages.as_ref().unwrap().context.subject;
+                let fresh = self
+                    .current_surface_usages(subject, requested.surface)
+                    .into_iter()
+                    .find(|u| u.subject == requested.subject && u.target == requested.target);
+                let Some(fresh) = fresh else {
+                    return self.refresh_diagram_lookup(
+                        "This representation changed. Review the refreshed destinations.",
+                    );
+                };
+                if self.reveal_diagram_usage(&fresh) {
+                    self.diagram_usages = None;
+                    self.status = format!(
+                        "{} · {} in {}",
+                        self.project().named(subject),
+                        fresh.role,
+                        self.project().named(fresh.surface.id())
+                    );
+                    return Task::batch(["model-explorer", "model-browser", "inspector"].map(
+                        |id| {
+                            iced::widget::operation::snap_to(
+                                id,
+                                iced::widget::scrollable::RelativeOffset::START,
+                            )
+                        },
+                    ));
+                }
+            }
+            Event::Open(_) | Event::Close(_) => unreachable!(),
+        }
+        Task::none()
+    }
+
+    pub(super) fn reveal_diagram_usage(&mut self, usage: &Usage) -> bool {
+        if !self.usage_navigation_available() {
+            return false;
+        }
+        if matches!(usage.surface, Surface::Saved(id) if self.saved_scenario_diagram(id)) {
+            return false;
+        }
+        let previous_layer = self.layer;
+        let p = self.document.project();
+        let (selected, placement) = match &usage.target {
+            Target::Whole => (usage.surface.id(), None),
+            Target::Placement(id) => {
+                let Some(node) = p
+                    .diagrams
+                    .get(&usage.surface.id())
+                    .and_then(|d| d.nodes.get(id))
+                else {
+                    return false;
+                };
+                (node.element, Some(*id))
+            }
+            Target::Port { port, placement } => (*port, Some(*placement)),
+            Target::StateRow {
+                placement,
+                relation,
+            } => (*relation, Some(*placement)),
+            Target::Edge(id)
+            | Target::ProcessLink(id)
+            | Target::ScenarioObject(id)
+            | Target::AllocationGrouping { relation: id, .. }
+            | Target::ProcessPreviewLink { relation: id, .. } => (*id, None),
+            Target::ProcessOccurrence(endpoint) => (
+                endpoint
+                    .references
+                    .first()
+                    .copied()
+                    .unwrap_or(endpoint.occurrence),
+                None,
+            ),
+        };
+        match usage.surface {
+            Surface::Saved(id) => {
+                let Some(diagram) = p.diagrams.get(&id) else {
+                    return false;
+                };
+                self.layer = diagram.layer;
+                self.active_diagram = Some(id);
+                if let Some(machine) = diagram.projection.state_machine() {
+                    let viewport = self.behavior.diagram.viewport.unwrap_or(iced::Size::new(
+                        (self.window_size.width - 610.).max(280.),
+                        (self.window_size.height - 320.).max(240.),
+                    ));
+                    let (zoom, pan) = usage::camera_for(&usage.target, usage.bounds, viewport);
+                    self.behavior.diagram = behavior::state_view::State {
+                        diagram: Some(id),
+                        placement,
+                        viewport: Some(viewport),
+                        zoom,
+                        pan,
+                        fit: false,
+                        ..Default::default()
+                    };
+                    self.behavior.active_owner = Some(machine);
+                    self.page = Page::Behavior;
+                } else {
+                    let viewport = self.canvas_size.unwrap_or(iced::Size::new(
+                        (self.window_size.width - 550.).max(280.),
+                        (self.window_size.height - 284.).max(240.),
+                    ));
+                    (self.zoom, self.pan) =
+                        usage::camera_for(&usage.target, usage.bounds, viewport);
+                    self.fit_to_view = false;
+                    self.page = Page::Diagram;
+                }
+            }
+            Surface::Process(owner) => {
+                if !self.behavior.topology.reveal_usage(
+                    p,
+                    self.canvas_document,
+                    owner,
+                    &usage.target,
+                ) {
+                    return false;
+                }
+                self.layer = p.elements[&owner].layer();
+                self.behavior.active_owner = Some(owner);
+                self.page = Page::Behavior;
+            }
+            Surface::Scenario(owner) => {
+                if !self.behavior.scenario.reveal_usage(
+                    p,
+                    self.canvas_document,
+                    owner,
+                    &usage.target,
+                ) {
+                    return false;
+                }
+                self.layer = p.elements[&owner].layer();
+                self.behavior.active_owner = Some(owner);
+                self.page = Page::Behavior;
+            }
+        }
+        self.selected = selected;
+        self.selected_node = placement;
+        self.model_menu = None;
+        self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+        self.selected_bend = None;
+        self.connection = None;
+        self.last_workspace_page = self.page;
+        if previous_layer != self.layer {
+            self.data_state = Default::default();
+            self.explorer_index = crate::explorer::Index::new(self.project(), self.layer);
+            self.explorer_focus = None;
+            self.explorer_group = None;
+            self.explorer_page = 0;
+        }
+        self.normalize_creation();
+        self.reveal_explorer_selection();
+        self.refresh_draft();
+        self.diagram_navigation_focus = Some(usage::Focus {
+            context: Context {
+                document: self.canvas_document,
+                revision: self.document.revision(),
+                subject: usage.subject,
+            },
+            usage: usage.clone(),
+            selected,
+        });
+        self.pending_diagram_reveal = Some((
+            Context {
+                document: self.canvas_document,
+                revision: self.document.revision(),
+                subject: usage.subject,
+            },
+            usage.clone(),
+            self.canvas_epoch,
+        ));
+        true
+    }
+
+    /// Validated presentation identity. Edit selection and Delete capture remain
+    /// semantic; a port owner or allocation work box is only a visual marker.
+    pub(crate) fn diagram_focus(&self, surface: Surface) -> Option<&Usage> {
+        let focus = self.diagram_navigation_focus.as_ref()?;
+        let current_surface = match surface {
+            Surface::Saved(id) => {
+                self.active_diagram == Some(id)
+                    && !self.saved_scenario_diagram(id)
+                    && matches!(self.page, Page::Diagram | Page::Behavior)
+            }
+            Surface::Process(owner) | Surface::Scenario(owner) => {
+                self.page == Page::Behavior && self.behavior.active_owner == Some(owner)
+            }
+        };
+        (current_surface
+            && focus.usage.surface == surface
+            && focus.context.document == self.canvas_document
+            && focus.context.revision == self.document.revision()
+            && focus.selected == self.selected)
+            .then_some(&focus.usage)
+    }
+}

crates/oa-desktop/src/app/hosted.rs

@@ -213,6 +213,14 @@ impl App {
             self.pending = None;
             return Task::none();
         }
+        if self.path.is_some()
+            || self.hosted.session.as_ref().is_none_or(|session| {
+                session.resource_id != remote.resource_id
+                    || session.connection.base() != request.connection.base()
+            })
+        {
+            self.source_workspace.reset_navigation_session();
+        }
         self.hosted.session = Some(Session {
             connection: request.connection.clone(),
             resource_id: remote.resource_id,
@@ -345,6 +353,14 @@ impl App {
                         match self.document.apply_compiled((*remote.compiled).clone()) {
                             Ok(_) => {
                                 self.document.mark_saved(remote.compiled.clone());
+                                if self.path.is_some()
+                                    || self.hosted.session.as_ref().is_none_or(|session| {
+                                        session.resource_id != remote.resource_id
+                                            || session.connection.base() != connection.base()
+                                    })
+                                {
+                                    self.source_workspace.reset_navigation_session();
+                                }
                                 self.hosted.session = Some(Session {
                                     connection,
                                     resource_id: remote.resource_id,

crates/oa-desktop/src/app/process_canvas.rs

@@ -15,18 +15,15 @@ impl App {
             epoch: self.canvas_epoch,
         })
     }
-    pub(super) fn reveal_process_selection(&self) -> Task<Message> {
-        let Some(context) = self.topology_context() else {
-            return Task::none();
-        };
-        let Some(offset) =
-            self.behavior
-                .topology
-                .selection_offset(self.project(), context.owner, self.selected)
-        else {
-            return Task::none();
-        };
-        iced::widget::operation::scroll_to("process-canvas", offset)
+    pub(super) fn reveal_process_selection(&mut self) -> Task<Message> {
+        if let Some(context) = self.topology_context() {
+            let mut state = std::mem::take(&mut self.behavior.topology);
+            if state.reveal_selection(self.project(), context.owner, self.selected) {
+                self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+            }
+            self.behavior.topology = state;
+        }
+        Task::none()
     }
     pub(super) fn edit_process_canvas(&mut self, event: CanvasEvent) -> Task<Message> {
         let context = event.context();
@@ -52,6 +49,47 @@ impl App {
             }
             return Task::none();
         }
+        if let CanvasEvent::Camera(_, lifetime, input) = event {
+            use crate::behavior::canvas_workspace::{self, Event};
+            if lifetime != self.camera_epoch
+                || !self.topology_context().is_some_and(|c| {
+                    c.document == context.document
+                        && c.owner == context.owner
+                        && c.revision == context.revision
+                })
+            {
+                return Task::none();
+            }
+            let scope = canvas_workspace::Scope {
+                document: context.document,
+                owner: context.owner,
+                revision: context.revision,
+                epoch: lifetime,
+            };
+            if self.behavior.has_pending()
+                || self.draft_dirty()
+                || self.source_dirty()
+                || !canvas_workspace::keyboard_enabled(self)
+            {
+                return Task::none();
+            }
+            match input {
+                Event::Focus
+                | Event::Traverse(_)
+                | Event::ControlFocus(_)
+                | Event::ToggleFocus
+                | Event::Leave => {
+                    return canvas_workspace::focus_task(scope, input);
+                }
+                Event::CancelGesture => self.canvas_epoch = self.canvas_epoch.wrapping_add(1),
+                input => {
+                    if self.behavior.topology.camera(input) {
+                        self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+                    }
+                }
+            }
+            return Task::none();
+        }
         if self.topology_context() != Some(context) {
             return Task::none();
         }
@@ -81,6 +119,7 @@ impl App {
                             .first()
                             .copied()
                             .unwrap_or(endpoint.occurrence),
+                        resolved.defining_sequence,
                     );
                     self.behavior.active_owner = Some(resolved.defining_sequence);
                     self.select(endpoint.occurrence);
@@ -118,14 +157,18 @@ impl App {
                 }
             }
             CanvasEvent::Choose(_, tool) => {
-                if self.behavior.has_pending() || !self.apply() {
+                if self.behavior.has_pending() || self.draft_dirty() || self.source_dirty() {
+                    self.status =
+                        "Apply or cancel pending edits before choosing a process tool.".into();
                     return Task::none();
                 }
                 self.behavior.topology.choose(tool);
                 self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
             }
             CanvasEvent::Zoom(_, zoom) => {
-                self.behavior.topology.zoom(zoom);
+                let mut state = std::mem::take(&mut self.behavior.topology);
+                state.camera_zoom(self.project(), context.owner, zoom);
+                self.behavior.topology = state;
                 self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
             }
             CanvasEvent::Expand(_, id) => {
@@ -149,7 +192,9 @@ impl App {
                         .get(&target)
                         .is_some_and(|e| matches!(e.kind(), Kind::Process | Kind::FunctionalChain))
                     {
-                        self.behavior.topology.remember(context.owner, occurrence);
+                        self.behavior
+                            .topology
+                            .remember(context.owner, occurrence, target);
                         self.behavior.active_owner = Some(target);
                     }
                     self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
@@ -524,32 +569,30 @@ mod tests {
         assert!(!app.behavior.has_pending());
     }
     #[test]
-    fn direct_process_app_save_scroll_resize_and_passive_geometry_keep_drafts_and_current_origin() {
+    fn direct_process_app_save_details_resize_and_passive_geometry_keep_drafts_and_camera() {
         let (mut app, f) = setup();
         let context = app.topology_context().unwrap();
+        let _ = app.update(Message::TopologyCanvas(CanvasEvent::Camera(
+            context,
+            app.camera_epoch,
+            behavior::canvas_workspace::Event::Pan(iced::Vector::new(25., 100.)),
+        )));
+        let context = app.topology_context().unwrap();
         let original = app.document.snapshot();
         app.busy = true;
-        for (area, offset) in [
-            (
-                behavior::scenario::ScrollArea::Canvas,
-                iced::Vector::new(25., 100.),
-            ),
-            (
-                behavior::scenario::ScrollArea::Page,
-                iced::Vector::new(0., 40.),
-            ),
-        ] {
-            let _ = app.update(Message::TopologyCanvas(CanvasEvent::Scrolled(
-                context, area, offset,
-            )));
-        }
+        let _ = app.update(Message::TopologyCanvas(CanvasEvent::Scrolled(
+            context,
+            behavior::scenario::ScrollArea::Page,
+            iced::Vector::new(0., 40.),
+        )));
         let _ = app.update(Message::TopologyCanvas(CanvasEvent::Viewport(
             context,
             iced::Size::new(500., 300.),
         )));
+        let camera = app.behavior.topology.camera_boundary();
         assert_eq!(
-            app.behavior.topology.scroll_offset(),
-            iced::Vector::new(25., 140.)
+            app.behavior.topology.details_offset(),
+            iced::Vector::new(0., 40.)
         );
         assert_ne!(app.topology_context(), Some(context));
         assert!(app.busy);
@@ -557,12 +600,12 @@ mod tests {
         stale.document = Id::new_v4();
         let _ = app.update(Message::TopologyCanvas(CanvasEvent::Scrolled(
             stale,
-            behavior::scenario::ScrollArea::Canvas,
+            behavior::scenario::ScrollArea::Page,
             iced::Vector::new(0., 900.),
         )));
         assert_eq!(
-            app.behavior.topology.scroll_offset(),
-            iced::Vector::new(25., 140.)
+            app.behavior.topology.details_offset(),
+            iced::Vector::new(0., 40.)
         );
         let root = PathBuf::from("process-scroll-save-fixture");
         let receipt = FileSnapshot {
@@ -582,6 +625,7 @@ mod tests {
         assert!(!app.busy);
         assert!(!app.document.can_undo());
         assert_eq!(app.project(), &f.p);
+        assert!(app.behavior.topology.camera_boundary() == camera);
         let context = app.topology_context().unwrap();
         let size = app.window_size;
         let _ = app.update(Message::WindowResized(size));

crates/oa-desktop/src/app/reference_authoring.rs

@@ -0,0 +1,304 @@
+//! One transient chooser for the currently mounted Inspector or review field.
+//! Browsing never calls a draft setter or semantic planner.
+use super::{App, Message, Page, Pending};
+use crate::{
+    forms::{
+        Draft,
+        reference_chooser::{self as chooser, Action, Close, Outcome, adapter, trigger},
+    },
+    navigation::InspectorTab,
+    semantic_review::{self, RowAddress, RowEvent},
+    workflow,
+};
+use iced::{Element, Rectangle, Task};
+use oa_core::{FacetSelector, Id, Layer};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+enum Host {
+    Inspector,
+    Review {
+        address: Option<RowAddress>,
+        facet: FacetSelector,
+    },
+}
+impl Host {
+    fn message(&self, event: chooser::Event) -> Message {
+        match self {
+            Self::Inspector => Message::FieldReferenceEvent(event),
+            Self::Review { address, facet } => {
+                Message::Workflow(workflow::Event::semantic(semantic_review::Event::Row {
+                    address: *address,
+                    facet: Some(facet.clone()),
+                    event: RowEvent::ReferenceEvent(event),
+                }))
+            }
+        }
+    }
+}
+struct Opened {
+    host: Host,
+    request: adapter::Open,
+    document_session: Id,
+    page: Page,
+    layer: Layer,
+    chooser: chooser::State,
+}
+#[derive(Default)]
+pub(super) struct State {
+    opened: Option<Opened>,
+}
+
+impl App {
+    pub(crate) fn reference_input_active(&self) -> bool {
+        self.reference_authoring.opened.is_some()
+    }
+
+    fn reference_draft(&self, host: &Host, path: &str) -> Option<&Draft> {
+        match host {
+            Host::Inspector
+                if self.workflow.is_none() && self.inspector_tab == InspectorTab::Properties =>
+            {
+                self.draft.as_ref()
+            }
+            Host::Review { address, facet } => match self.workflow.as_ref()? {
+                workflow::Workflow::Semantic(state) => {
+                    state.reference_draft(self.project(), *address, facet, path)
+                }
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+    fn reference_available(&self) -> bool {
+        !self.busy
+            && !self.hosted.visible
+            && self.architecture.is_none()
+            && self.model_menu.is_none()
+            && self.file_prompt.is_none()
+            && !self.delete_pending
+            && self.pending.is_none()
+            && !self.source_dirty()
+            && !self.behavior.has_pending()
+            && !matches!(self.page, Page::Home | Page::Guide | Page::Text)
+    }
+    fn reference_valid(&self, opened: &Opened) -> bool {
+        self.reference_available()
+            && self.canvas_document == opened.document_session
+            && self.page == opened.page
+            && self.layer == opened.layer
+            && self.document.revision() == opened.chooser.stamp().context.revision
+            && self.project().id == opened.request.document
+            && self
+                .reference_draft(&opened.host, &opened.request.path)
+                .is_some_and(|draft| draft.reference_matches(&opened.request))
+    }
+    pub(super) fn reconcile_reference_chooser(&mut self) {
+        if self
+            .reference_authoring
+            .opened
+            .as_ref()
+            .is_some_and(|opened| !self.reference_valid(opened))
+        {
+            self.reference_authoring
+                .opened
+                .as_mut()
+                .unwrap()
+                .chooser
+                .invalidate();
+            self.reference_authoring.opened = None;
+        }
+    }
+    fn open_reference(&mut self, host: Host, request: adapter::Open) -> Task<Message> {
+        if !self.reference_available() {
+            return Task::none();
+        }
+        let Some(draft) = self.reference_draft(&host, &request.path) else {
+            return Task::none();
+        };
+        let Ok(chooser) =
+            draft.reference_catalog(self.project(), &request, self.document.revision())
+        else {
+            return Task::none();
+        };
+        self.reference_authoring.opened = Some(Opened {
+            host,
+            request,
+            document_session: self.canvas_document,
+            page: self.page,
+            layer: self.layer,
+            chooser,
+        });
+        Task::none()
+    }
+    fn reference_event(&mut self, host: Host, event: chooser::Event) -> Task<Message> {
+        let Some(mut opened) = self.reference_authoring.opened.take() else {
+            return Task::none();
+        };
+        if !self.reference_valid(&opened) {
+            return Task::none();
+        }
+        if opened.host != host {
+            self.reference_authoring.opened = Some(opened);
+            return Task::none();
+        }
+        match opened.chooser.update(event) {
+            Outcome::Ignored | Outcome::Browsed => {
+                self.reference_authoring.opened = Some(opened);
+                Task::none()
+            }
+            Outcome::Closed(reason) => self.reference_focus(
+                &opened,
+                match reason {
+                    Close::Escape => Some(0),
+                    Close::Tab { backwards } => Some(if backwards { -1 } else { 1 }),
+                    Close::Outside | Close::WindowChanged => None,
+                },
+            ),
+            Outcome::Write { context, value } => {
+                let intent = adapter::Set {
+                    context,
+                    generation: opened.request.generation,
+                    value,
+                };
+                let result = match &opened.host {
+                    Host::Inspector => self
+                        .draft
+                        .as_mut()
+                        .ok_or_else(|| "The property editor closed.".to_owned())
+                        .and_then(|draft| draft.reference_set(self.document.project(), &intent)),
+                    Host::Review { address, facet } => match self.workflow.as_mut() {
+                        Some(workflow::Workflow::Semantic(state)) => {
+                            state.set_reference(self.document.project(), *address, facet, intent)
+                        }
+                        _ => Err("The review editor closed.".into()),
+                    },
+                };
+                if let Err(error) = result {
+                    self.status = error;
+                }
+                // A scoped write rotates field generation. The task targets the
+                // newly rendered field, while a later structural edit makes it inert.
+                self.reference_focus(&opened, Some(0))
+            }
+        }
+    }
+    fn reference_focus(&self, opened: &Opened, step: Option<i32>) -> Task<Message> {
+        let Some(step) = step else {
+            return Task::none();
+        };
+        let Some(draft) = self.reference_draft(&opened.host, &opened.request.path) else {
+            return Task::none();
+        };
+        if draft.reference_session() != opened.request.session {
+            return Task::none();
+        }
+        trigger::focus(
+            draft.reference_session(),
+            draft.reference_generation(),
+            &opened.request.path,
+            step,
+        )
+    }
+    /// Called before generic modal dispatch: the review owns a modal, and this
+    /// chooser owns only its active field. All browser events stop here.
+    pub(super) fn reference_message(&mut self, message: &Message) -> Option<Task<Message>> {
+        self.reconcile_reference_chooser();
+        match message {
+            Message::FieldReferenceOpen(request) => {
+                Some(self.open_reference(Host::Inspector, request.clone()))
+            }
+            Message::FieldReferenceEvent(event) => {
+                Some(self.reference_event(Host::Inspector, event.clone()))
+            }
+            Message::Workflow(workflow::Event::Semantic(review_event)) => {
+                let semantic_review::Event::Row {
+                    address,
+                    facet: Some(facet),
+                    event,
+                } = review_event.as_ref()
+                else {
+                    return None;
+                };
+                let host = Host::Review {
+                    address: *address,
+                    facet: facet.clone(),
+                };
+                match event {
+                    RowEvent::ReferenceOpen(request) => {
+                        Some(self.open_reference(host, request.clone()))
+                    }
+                    RowEvent::ReferenceEvent(event) => {
+                        Some(self.reference_event(host, event.clone()))
+                    }
+                    _ => None,
+                }
+            }
+            Message::Escape | Message::Request(Pending::Close(_))
+                if self.reference_authoring.opened.is_some() =>
+            {
+                let opened = self.reference_authoring.opened.as_ref().unwrap();
+                let host = opened.host.clone();
+                let event = opened.chooser.event(Action::Close(Close::Escape));
+                Some(self.reference_event(host, event))
+            }
+            // Global shortcuts are also emitted for keys captured by the search
+            // input. They must not apply drafts, navigate, or undo the model.
+            Message::Save(_)
+            | Message::ShortcutUndo(_)
+            | Message::Request(Pending::Open | Pending::New)
+            | Message::SourceNavigation(_)
+            | Message::Page(Page::Guide)
+                if self.reference_authoring.opened.is_some() =>
+            {
+                Some(Task::none())
+            }
+            _ => None,
+        }
+    }
+    pub(super) fn reference_overlay<
+        'a,
+        R: iced::advanced::text::Renderer<Font = iced::Font> + 'a,
+    >(
+        &'a self,
+        content: Element<'a, Message, iced::Theme, R>,
+    ) -> Element<'a, Message, iced::Theme, R> {
+        let opened = self
+            .reference_authoring
+            .opened
+            .as_ref()
+            .filter(|opened| self.reference_valid(opened));
+        let host = opened
+            .map(|opened| opened.host.clone())
+            .unwrap_or(Host::Inspector);
+        let focus_scope = if self.reference_available() {
+            match self.workflow.as_ref() {
+                None if self.inspector_tab == InspectorTab::Properties => {
+                    self.draft.as_ref().map(|draft| trigger::FormScope {
+                        session: draft.reference_session(),
+                        modal: false,
+                    })
+                }
+                Some(workflow::Workflow::Semantic(state)) => state
+                    .reference_form(self.project())
+                    .map(|draft| trigger::FormScope {
+                        session: draft.reference_session(),
+                        modal: true,
+                    }),
+                _ => None,
+            }
+        } else {
+            None
+        };
+        chooser::widget::Popup::new(
+            content,
+            opened.map(|opened| &opened.chooser),
+            opened.map_or(Rectangle::default(), |opened| opened.request.anchor),
+            move |event| host.message(event),
+        )
+        .focus_scope(focus_scope)
+        .into()
+    }
+}
+
+#[cfg(test)]
+mod tests;

crates/oa-desktop/src/app/reference_authoring/tests.rs

@@ -0,0 +1,586 @@
+use super::*;
+use crate::forms::Draft;
+use oa_core::*;
+use serde_json::{Value, json};
+
+const OWNER: Id = Id::from_u128(100);
+const BASE: u128 = 10_000;
+const PATH: &str = "/body/Oa/Shared/DataType/definition/Record/supertype";
+
+fn element(p: &mut Project, id: Id, kind: Kind, layer: Layer, name: &str, parent: Option<Id>) {
+    let generated = p.add_element(kind, layer, name, parent).unwrap();
+    let mut element = p.elements.remove(&generated).unwrap();
+    element.id = id;
+    element.alias = format!("object_{}", id.as_u128());
+    if let Some(SharedBody::DataType { definition, .. }) = element.shared_mut() {
+        *definition = DataTypeDefinition::Record { supertype: None };
+    }
+    p.elements.insert(id, element);
+}
+fn catalog() -> Project {
+    let mut p = Project::empty();
+    p.id = Id::from_u128(1);
+    p.name = "Reference catalog".into();
+    element(
+        &mut p,
+        OWNER,
+        Kind::DataType,
+        Layer::Oa,
+        "Edited record",
+        None,
+    );
+    for n in (0..1_000).rev() {
+        let id = Id::from_u128(BASE + n);
+        element(&mut p, id, Kind::DataType, Layer::Oa, "Controller", None);
+        p.elements.get_mut(&id).unwrap().alias = format!("controller_{n:04}");
+    }
+    element(
+        &mut p,
+        Id::from_u128(200),
+        Kind::DataType,
+        Layer::Sa,
+        "Controller",
+        None,
+    );
+    element(
+        &mut p,
+        Id::from_u128(201),
+        Kind::Activity,
+        Layer::Oa,
+        "Controller",
+        None,
+    );
+    p
+}
+fn inspector(p: Project, selected: Id) -> App {
+    let mut app = App::with_project(p);
+    let _ = app.update(Message::Select(selected));
+    app
+}
+fn request(app: &App, host: &Host, path: &str) -> adapter::Open {
+    app.reference_draft(host, path).unwrap().reference_open(
+        app.project(),
+        path,
+        Rectangle {
+            x: 790.,
+            y: 640.,
+            width: 278.,
+            height: 32.,
+        },
+    )
+}
+fn open(app: &mut App, host: &Host, path: &str) {
+    let request = request(app, host, path);
+    let message = match host {
+        Host::Inspector => Message::FieldReferenceOpen(request),
+        Host::Review { address, facet } => {
+            Message::Workflow(workflow::Event::semantic(semantic_review::Event::Row {
+                address: *address,
+                facet: Some(facet.clone()),
+                event: RowEvent::ReferenceOpen(request),
+            }))
+        }
+    };
+    let _ = app.update(message);
+    assert!(
+        app.reference_authoring.opened.is_some(),
+        "field must open: {}",
+        app.status
+    );
+}
+fn event(app: &App, action: Action) -> Message {
+    let opened = app.reference_authoring.opened.as_ref().unwrap();
+    opened.host.message(opened.chooser.event(action))
+}
+fn search(app: &mut App, query: &str) {
+    let serial = app
+        .reference_authoring
+        .opened
+        .as_ref()
+        .unwrap()
+        .chooser
+        .query_serial()
+        + 1;
+    let event = event(
+        app,
+        Action::Query {
+            text: query.into(),
+            serial,
+        },
+    );
+    let _ = app.update(event);
+}
+fn choose(app: &mut App, id: Id) {
+    let event = event(app, Action::Choose(id));
+    let _ = app.update(event);
+}
+fn raw(app: &App) -> Value {
+    serde_json::to_value(app.draft.as_ref().unwrap().recovery_snapshot()).unwrap()
+}
+fn review(app: &App) -> &semantic_review::State {
+    let Some(workflow::Workflow::Semantic(state)) = app.workflow.as_ref() else {
+        panic!("Review is open")
+    };
+    state
+}
+fn send_review(app: &mut App, event: RowEvent) {
+    let addressed = review(app).address_event(event);
+    let _ = app.update(Message::Workflow(workflow::Event::semantic(addressed)));
+}
+fn review_host(app: &App) -> Host {
+    let semantic_review::Event::Row {
+        address,
+        facet: Some(facet),
+        ..
+    } = review(app).address_event(RowEvent::Preview)
+    else {
+        panic!("Active facet")
+    };
+    Host::Review { address, facet }
+}
+fn trace(p: &mut Project, id: Id, oa: Id, sa: Id) {
+    p.traces.insert(
+        id,
+        Trace {
+            id,
+            alias: format!("trace_{}", id.as_u128()),
+            name: "Rationale".into(),
+            description: String::new(),
+            oa,
+            sa,
+            kind: TraceKind::Manual,
+            baseline: None,
+        },
+    );
+}
+
+#[test]
+fn inspector_reference_browse_is_read_only_then_one_scoped_value_applies_with_exact_undo_redo() {
+    let p = catalog();
+    let mut app = inspector(p.clone(), OWNER);
+    let before = app.document.bundle().clone();
+    let revision = app.document.revision();
+    // Malformed escaped text is unrelated to the selected reference. Browsing
+    // and the scoped write must keep its exact spelling and inactive payload.
+    app.draft.as_mut().unwrap().set_exact(true).unwrap();
+    let _ = app.update(Message::Field("/name".into(), "\"unfinished".into()));
+    let raw_before = raw(&app);
+    open(&mut app, &Host::Inspector, PATH);
+    assert_eq!(
+        app.reference_authoring
+            .opened
+            .as_ref()
+            .unwrap()
+            .chooser
+            .count(),
+        1_000
+    );
+    search(&mut app, "controller @controller_0720 OA");
+    let picker = &app.reference_authoring.opened.as_ref().unwrap().chooser;
+    assert_eq!(picker.count(), 1);
+    assert_eq!(picker.highlighted().unwrap().id, Id::from_u128(BASE + 720));
+    assert_eq!(raw(&app), raw_before);
+    assert_eq!(app.document.bundle(), &before);
+    assert_eq!(app.document.revision(), revision);
+    assert!(!app.document.can_undo());
+    // Captured search shortcuts cannot accidentally save/apply or undo a model.
+    let _ = app.update(Message::Save(false));
+    let _ = app.update(Message::ShortcutUndo(false));
+    assert_eq!(raw(&app), raw_before);
+    assert_eq!(app.document.bundle(), &before);
+    choose(&mut app, Id::from_u128(BASE + 720));
+    let mut expected_raw = raw_before;
+    *expected_raw["value"].pointer_mut(PATH).unwrap() = json!(Id::from_u128(BASE + 720));
+    expected_raw["inputs"][PATH] = json!(Id::from_u128(BASE + 720).to_string());
+    assert_eq!(raw(&app), expected_raw);
+    assert_eq!(app.document.bundle(), &before);
+    assert!(!app.document.can_undo());
+    let _ = app.update(Message::Apply);
+    assert_eq!(
+        app.document.bundle(),
+        &before,
+        "Unrelated invalid text remains an Apply error"
+    );
+    let _ = app.update(Message::Field("/name".into(), "\"Edited record\"".into()));
+    let _ = app.update(Message::Apply);
+    let mut expected = p;
+    if let Some(SharedBody::DataType { definition, .. }) =
+        expected.elements.get_mut(&OWNER).unwrap().shared_mut()
+    {
+        *definition = DataTypeDefinition::Record {
+            supertype: Some(Id::from_u128(BASE + 720)),
+        };
+    }
+    assert_eq!(app.project(), &expected);
+    let accepted = app.document.bundle().clone();
+    assert_ne!(accepted, before);
+    let _ = app.update(Message::Undo);
+    assert_eq!(app.document.bundle(), &before);
+    let _ = app.update(Message::Redo);
+    assert_eq!(app.document.bundle(), &accepted);
+    assert_eq!(app.project(), &expected);
+}
+
+#[test]
+fn inspector_reference_retains_invalid_missing_and_incompatible_current_until_explicit_clear() {
+    for (raw_id, expected) in [
+        ("-".into(), "invalid"),
+        (Id::from_u128(999).to_string(), "missing"),
+        (Id::from_u128(200).to_string(), "incompatible"),
+    ] {
+        let mut app = inspector(catalog(), OWNER);
+        app.draft
+            .as_mut()
+            .unwrap()
+            .shape_scoped(PATH, json!(raw_id))
+            .unwrap();
+        let original = raw(&app);
+        let accepted = app.document.bundle().clone();
+        open(&mut app, &Host::Inspector, PATH);
+        let current = &app
+            .reference_authoring
+            .opened
+            .as_ref()
+            .unwrap()
+            .chooser
+            .current;
+        assert!(matches!(
+            (expected, current),
+            ("invalid", chooser::Current::InvalidRaw(_))
+                | ("missing", chooser::Current::Missing(_))
+                | ("incompatible", chooser::Current::Incompatible(_))
+        ));
+        let _ = app.update(Message::Escape);
+        assert_eq!(raw(&app), original);
+        open(&mut app, &Host::Inspector, PATH);
+        let clear = event(&app, Action::Clear);
+        let _ = app.update(clear);
+        assert!(
+            app.draft
+                .as_ref()
+                .unwrap()
+                .value
+                .pointer(PATH)
+                .unwrap()
+                .is_null()
+        );
+        assert_eq!(app.document.bundle(), &accepted);
+        assert!(!app.document.can_undo());
+    }
+}
+
+#[test]
+fn chooser_rejects_old_results_after_context_recovery_reload_or_modal_and_keeps_history_text_out() {
+    for change in 0..7 {
+        let mut app = inspector(catalog(), OWNER);
+        open(&mut app, &Host::Inspector, PATH);
+        let delayed = event(&app, Action::Choose(Id::from_u128(BASE + 1)));
+        match change {
+            0 => {
+                app.draft
+                    .as_mut()
+                    .unwrap()
+                    .shape_scoped(PATH, json!(Id::from_u128(BASE + 2)))
+                    .unwrap();
+            }
+            1 => {
+                let saved = app.draft.as_ref().unwrap().recovery_snapshot();
+                app.draft = Some(Draft::from_recovery(app.project(), saved).unwrap());
+            }
+            2 => {
+                app.canvas_document = Id::new_v4();
+            }
+            3 => {
+                app.hosted.visible = true;
+            }
+            4 => {
+                app.draft
+                    .as_mut()
+                    .unwrap()
+                    .set_context(Some(json!({"different":"scope"})));
+            }
+            5 => {
+                let _ = app.update(Message::Command(Command::Rename(
+                    Id::from_u128(BASE + 3),
+                    "Changed model".into(),
+                )));
+            }
+            _ => {
+                app.source_workspace.edit(
+                    "unfinished source".into(),
+                    iced::widget::text_editor::Cursor {
+                        position: iced::widget::text_editor::Position { line: 0, column: 0 },
+                        selection: None,
+                    },
+                );
+            }
+        }
+        let expected = raw(&app);
+        let source = app.document.bundle().clone();
+        let _ = app.update(delayed);
+        assert!(app.reference_authoring.opened.is_none());
+        assert_eq!(raw(&app), expected);
+        assert_eq!(app.document.bundle(), &source);
+    }
+    let mut p = catalog();
+    trace(&mut p, Id::from_u128(300), OWNER, Id::from_u128(200));
+    let app = inspector(p, Id::from_u128(300));
+    let draft = app.draft.as_ref().unwrap();
+    let request = draft.reference_open(
+        app.project(),
+        "/baseline/semantic/facets/0/references/0/target",
+        Rectangle::default(),
+    );
+    assert!(draft.reference_catalog(app.project(), &request, 0).is_err());
+}
+
+#[test]
+fn reference_array_row_reorder_and_constructor_switch_invalidate_exact_old_field() {
+    let mut p = Project::empty();
+    for n in 0..3 {
+        element(
+            &mut p,
+            Id::from_u128(BASE + n),
+            Kind::ExchangeItem,
+            Layer::Oa,
+            "Signal item",
+            None,
+        );
+    }
+    element(&mut p, OWNER, Kind::Event, Layer::Oa, "Signal", None);
+    *p.elements.get_mut(&OWNER).unwrap().shared_mut().unwrap() = SharedBody::Event {
+        body: EventBody::Signal {
+            items: vec![Id::from_u128(BASE), Id::from_u128(BASE + 1)],
+        },
+    };
+    let mut app = inspector(p, OWNER);
+    let list = "/body/Oa/Shared/Event/body/Signal/items";
+    let path = format!("{list}/0");
+    open(&mut app, &Host::Inspector, &path);
+    let delayed = event(&app, Action::Choose(Id::from_u128(BASE + 2)));
+    let _ = app.update(Message::FieldArray(list.into(), Some(0), 1));
+    let expected = raw(&app);
+    assert_eq!(
+        app.draft.as_ref().unwrap().value.pointer(list),
+        Some(&json!([Id::from_u128(BASE + 1), Id::from_u128(BASE)]))
+    );
+    let _ = app.update(delayed);
+    assert_eq!(raw(&app), expected);
+    open(&mut app, &Host::Inspector, &path);
+    let delayed = event(&app, Action::Choose(Id::from_u128(BASE + 2)));
+    let _ = app.update(Message::FieldVariant(
+        "/body/Oa/Shared/Event/body".into(),
+        json!({"Change":{"expression":"unfinished"}}),
+    ));
+    let expected = raw(&app);
+    let _ = app.update(delayed);
+    assert_eq!(raw(&app), expected);
+    assert!(!app.document.can_undo());
+}
+
+#[test]
+fn review_reference_facets_groups_and_attachment_hosts_browse_without_replanning_and_reject_old_facet()
+ {
+    for mode in 0..3 {
+        let mut p = Project::empty();
+        p.id = Id::from_u128(1);
+        for (id, layer, parent) in [
+            (100, Layer::Oa, None),
+            (101, Layer::Sa, None),
+            (102, Layer::Sa, None),
+            (103, Layer::Oa, Some(Id::from_u128(100))),
+            (104, Layer::Sa, Some(Id::from_u128(101))),
+        ] {
+            element(
+                &mut p,
+                Id::from_u128(id),
+                if parent.is_some() {
+                    Kind::DataField
+                } else {
+                    Kind::DataType
+                },
+                layer,
+                "Record",
+                parent,
+            );
+        }
+        trace(
+            &mut p,
+            Id::from_u128(300),
+            Id::from_u128(100),
+            Id::from_u128(101),
+        );
+        let facet = match mode {
+            0 => FacetSelector::Data(DataFacet::RecordSupertype),
+            1 => FacetSelector::Data(DataFacet::Constructor),
+            _ => FacetSelector::Child(KeyPair {
+                oa: Some(Id::from_u128(103)),
+                sa: Some(Id::from_u128(104)),
+            }),
+        };
+        let path = if mode == 2 {
+            "/parent"
+        } else {
+            "/body/Sa/Shared/DataType/definition/Record/supertype"
+        };
+        let mut app = App::with_project(p.clone());
+        let _ = app.update(Message::StartSemanticReview(Id::from_u128(100)));
+        if mode == 2 {
+            // A paired attachment is a real catalog facet only after explicit
+            // correspondence; selecting an unstaged synthetic pair is rejected.
+            for (id, oa) in [(103, true), (104, false)] {
+                let choice = crate::app::Choice {
+                    id: Id::from_u128(id),
+                    label: format!("Record · @object_{id}"),
+                };
+                send_review(
+                    &mut app,
+                    if oa {
+                        RowEvent::ReferenceOa(choice)
+                    } else {
+                        RowEvent::ReferenceSa(choice)
+                    },
+                );
+            }
+            send_review(&mut app, RowEvent::AddReference);
+        }
+        send_review(&mut app, RowEvent::Select(facet.clone()));
+        send_review(
+            &mut app,
+            RowEvent::Decide(facet.clone(), Some(SemanticDecision::Candidate)),
+        );
+        let host = review_host(&app);
+        let record = if mode == 2 {
+            Id::from_u128(104)
+        } else {
+            Id::from_u128(101)
+        };
+        assert_eq!(
+            app.reference_draft(&host, path)
+                .unwrap_or_else(|| {
+                    panic!(
+                        "Reference fixture mode={mode}, facet={facet:?}, selected={:?}, decisions={:?}, error={:?}",
+                        review(&app).selected,
+                        review(&app).decisions,
+                        review(&app).error
+                    )
+                })
+                .original,
+            record
+        );
+        let before = review(&app).recovery_snapshot().unwrap();
+        let plan = serde_json::to_value(&review(&app).plan).unwrap();
+        let proposed = review(&app).proposed.clone();
+        let source = app.document.bundle().clone();
+        open(&mut app, &host, path);
+        search(&mut app, "@object_102 SA");
+        assert_eq!(
+            app.reference_authoring
+                .opened
+                .as_ref()
+                .unwrap()
+                .chooser
+                .count(),
+            1
+        );
+        assert_eq!(review(&app).recovery_snapshot().unwrap(), before);
+        assert_eq!(serde_json::to_value(&review(&app).plan).unwrap(), plan);
+        assert_eq!(review(&app).proposed, proposed);
+        assert_eq!(app.document.bundle(), &source);
+        let old = event(&app, Action::Choose(Id::from_u128(102)));
+        send_review(
+            &mut app,
+            RowEvent::Select(FacetSelector::Header(HeaderFacet::Name)),
+        );
+        let switched = review(&app).recovery_snapshot().unwrap();
+        let _ = app.update(old);
+        assert_eq!(review(&app).recovery_snapshot().unwrap(), switched);
+        send_review(&mut app, RowEvent::Select(facet));
+        open(&mut app, &host, path);
+        choose(&mut app, Id::from_u128(102));
+        let draft = app.reference_draft(&host, path).unwrap();
+        let mut expected_record = serde_json::to_value(&p.elements[&record]).unwrap();
+        *expected_record.pointer_mut(path).unwrap() = json!(Id::from_u128(102));
+        assert_eq!(draft.materialize().unwrap(), expected_record);
+        assert_eq!(app.document.bundle(), &source);
+        assert!(
+            !app.document.can_undo(),
+            "A choice only stages the active review candidate"
+        );
+    }
+}
+
+mod mounted;
+
+#[test]
+fn review_reference_cannot_reopen_or_write_a_banked_row_after_another_row_takes_focus() {
+    let mut p = Project::empty();
+    for (id, layer) in [
+        (100, Layer::Oa),
+        (101, Layer::Sa),
+        (102, Layer::Sa),
+        (110, Layer::Oa),
+        (111, Layer::Sa),
+    ] {
+        element(
+            &mut p,
+            Id::from_u128(id),
+            Kind::DataType,
+            layer,
+            "Record",
+            None,
+        );
+    }
+    trace(
+        &mut p,
+        Id::from_u128(300),
+        Id::from_u128(100),
+        Id::from_u128(101),
+    );
+    trace(
+        &mut p,
+        Id::from_u128(310),
+        Id::from_u128(110),
+        Id::from_u128(111),
+    );
+    let mut app = App::with_project(p);
+    let _ = app.update(Message::StartSemanticReview(Id::from_u128(300)));
+    let facet = FacetSelector::Data(DataFacet::RecordSupertype);
+    send_review(&mut app, RowEvent::Select(facet.clone()));
+    send_review(
+        &mut app,
+        RowEvent::Decide(facet, Some(SemanticDecision::Candidate)),
+    );
+    let host = review_host(&app);
+    let path = "/body/Sa/Shared/DataType/definition/Record/supertype";
+    let old_open = request(&app, &host, path);
+    open(&mut app, &host, path);
+    let old_choice = event(&app, Action::Choose(Id::from_u128(102)));
+    for event in [
+        semantic_review::Event::ChooseTrace(crate::app::Choice {
+            id: Id::from_u128(310),
+            label: "Second exact trace".into(),
+        }),
+        semantic_review::Event::OpenTrace,
+    ] {
+        let _ = app.update(Message::Workflow(workflow::Event::semantic(event)));
+    }
+    assert_eq!(review(&app).target(app.project()), Some(Id::from_u128(111)));
+    let expected = review(&app).recovery_snapshot().unwrap();
+    let source = app.document.bundle().clone();
+    let _ = app.update(old_choice);
+    let Host::Review { address, facet } = host else {
+        unreachable!()
+    };
+    let _ = app.update(Message::Workflow(workflow::Event::semantic(
+        semantic_review::Event::Row {
+            address,
+            facet: Some(facet),
+            event: RowEvent::ReferenceOpen(old_open),
+        },
+    )));
+    assert!(app.reference_authoring.opened.is_none());
+    assert_eq!(review(&app).recovery_snapshot().unwrap(), expected);
+    assert_eq!(app.document.bundle(), &source);
+    assert!(!app.document.can_undo());
+}

crates/oa-desktop/src/app/reference_authoring/tests/mounted.rs

@@ -0,0 +1,910 @@
+//! Real field + app-root overlay interaction. The null text renderer lets the
+//! same retained widget tree exercise focus and geometry without a GPU/window.
+use super::*;
+use iced::futures::StreamExt;
+use iced::{
+    Element, Event as Input, Point, Size, Theme, Vector,
+    advanced::{
+        Layout, Shell, layout,
+        widget::{Id as WidgetId, Operation, Tree, operation},
+    },
+    keyboard, mouse,
+    widget::{Space, column, container, opaque, scrollable, stack, text_input},
+};
+use oa_core::transitions::TransitionDirection;
+
+#[derive(Default)]
+struct Clipboard;
+impl iced::advanced::Clipboard for Clipboard {
+    fn read(&self, _: iced::advanced::clipboard::Kind) -> Option<String> {
+        None
+    }
+    fn write(&mut self, _: iced::advanced::clipboard::Kind, _: String) {}
+}
+#[derive(Default)]
+struct Fields {
+    values: Vec<(WidgetId, Rectangle, bool)>,
+    scrolls: Vec<(Rectangle, Vector)>,
+}
+impl Operation for Fields {
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn Operation)) {
+        visit(self);
+    }
+    fn focusable(
+        &mut self,
+        id: Option<&WidgetId>,
+        bounds: Rectangle,
+        state: &mut dyn operation::Focusable,
+    ) {
+        if let Some(id) = id {
+            self.values.push((id.clone(), bounds, state.is_focused()));
+        }
+    }
+    fn scrollable(
+        &mut self,
+        _: Option<&WidgetId>,
+        bounds: Rectangle,
+        _: Rectangle,
+        translation: Vector,
+        _: &mut dyn operation::Scrollable,
+    ) {
+        self.scrolls.push((bounds, translation));
+    }
+}
+impl Fields {
+    fn field(&self, id: &WidgetId) -> (Rectangle, bool) {
+        self.values
+            .iter()
+            .find(|(actual, _, _)| actual == id)
+            .map(|(_, bounds, focused)| (*bounds, *focused))
+            .expect("Mounted field identity")
+    }
+}
+fn view(
+    app: &App,
+    scrolled: bool,
+    nested: bool,
+    show_review: bool,
+) -> Element<'_, Message, Theme, ()> {
+    let draft = app.draft.as_ref().unwrap();
+    let form = column![
+        text_input("Name", &draft.inputs["/name"].raw)
+            .id("before-reference")
+            .on_input(|raw| Message::Field("/name".into(), raw)),
+        adapter::field(draft, app.project(), PATH),
+        text_input("Description", &draft.inputs["/description"].raw)
+            .id("after-reference")
+            .on_input(|raw| Message::Field("/description".into(), raw)),
+    ]
+    .spacing(9);
+    let form = trigger::scope(form, draft.reference_session());
+    let base: Element<'_, Message, Theme, ()> = if scrolled {
+        container(
+            scrollable(column![Space::new().height(500), form])
+                .id("reference-scroll")
+                .height(180),
+        )
+        .width(300)
+        .into()
+    } else {
+        container(form).width(300).height(iced::Fill).into()
+    };
+    let base: Element<'_, Message, Theme, ()> = if nested {
+        scrollable(column![Space::new().height(400), base])
+            .id("outer-reference-scroll")
+            .height(180)
+            .width(300)
+            .into()
+    } else {
+        base
+    };
+    let base = if show_review {
+        let review: Element<'_, Message, Theme, ()> = match app.workflow.as_ref() {
+            Some(workflow::Workflow::Semantic(state)) => {
+                match state.reference_form(app.project()) {
+                    Some(draft) => {
+                        let mut content = column![];
+                        if let Some(raw) = &state.operation_omission {
+                            content = content.push(
+                                text_input("Required engineering rationale", raw)
+                                    .id("review-rationale")
+                                    .on_input(|raw| {
+                                        Message::Workflow(workflow::Event::semantic(
+                                            state.address_event(RowEvent::OperationRationale(raw)),
+                                        ))
+                                    }),
+                            );
+                        }
+                        content = content.push(trigger::scope(
+                            adapter::field(draft, app.project(), "/parent").map(|message| {
+                                match message {
+                                    Message::FieldReferenceOpen(request) => {
+                                        Message::Workflow(workflow::Event::semantic(
+                                            state.address_event(RowEvent::ReferenceOpen(request)),
+                                        ))
+                                    }
+                                    other => other,
+                                }
+                            }),
+                            draft.reference_session(),
+                        ));
+                        opaque(container(trigger::modal(content)).width(300).height(180))
+                    }
+                    None => Space::new().into(),
+                }
+            }
+            _ => Space::new().into(),
+        };
+        stack![base, review].into()
+    } else {
+        base
+    };
+    app.reference_overlay(base)
+}
+struct Mount {
+    tree: Option<Tree>,
+    size: Size,
+    scrolled: bool,
+    nested: bool,
+    show_review: bool,
+}
+impl Default for Mount {
+    fn default() -> Self {
+        Self {
+            tree: None,
+            size: Size::new(360., 320.),
+            scrolled: false,
+            nested: false,
+            show_review: false,
+        }
+    }
+}
+impl Mount {
+    fn frame(
+        &mut self,
+        app: &App,
+        events: &[(Input, Option<Point>)],
+    ) -> (Vec<Message>, Fields, Option<Rectangle>) {
+        let mut view = view(app, self.scrolled, self.nested, self.show_review);
+        let tree = self.tree.get_or_insert_with(|| Tree::new(view.as_widget()));
+        view.as_widget().diff(tree);
+        let node =
+            view.as_widget_mut()
+                .layout(tree, &(), &layout::Limits::new(Size::ZERO, self.size));
+        let viewport = Rectangle::with_size(self.size);
+        let overlay_node = view
+            .as_widget_mut()
+            .overlay(tree, Layout::new(&node), &(), &viewport, Vector::ZERO)
+            .map(|mut overlay| overlay.as_overlay_mut().layout(&(), self.size));
+        let mut messages = Vec::new();
+        for (input, point) in events {
+            let mut shell = Shell::new(&mut messages);
+            let cursor = point.map_or(mouse::Cursor::Unavailable, mouse::Cursor::Available);
+            if let Some(overlay_node) = &overlay_node {
+                let mut overlay = view
+                    .as_widget_mut()
+                    .overlay(tree, Layout::new(&node), &(), &viewport, Vector::ZERO)
+                    .unwrap();
+                overlay.as_overlay_mut().update(
+                    input,
+                    Layout::new(overlay_node),
+                    cursor,
+                    &(),
+                    &mut Clipboard,
+                    &mut shell,
+                );
+                assert!(shell.is_event_captured());
+            } else {
+                view.as_widget_mut().update(
+                    tree,
+                    input,
+                    Layout::new(&node),
+                    cursor,
+                    &(),
+                    &mut Clipboard,
+                    &mut shell,
+                    &viewport,
+                );
+            }
+        }
+        let mut fields = Fields::default();
+        view.as_widget_mut()
+            .operate(tree, Layout::new(&node), &(), &mut fields);
+        (
+            messages,
+            fields,
+            overlay_node.map(|node| node.children()[0].bounds()),
+        )
+    }
+    fn click(&mut self, app: &App, point: Point) -> Vec<Message> {
+        self.frame(
+            app,
+            &[
+                (
+                    Input::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)),
+                    Some(point),
+                ),
+                (
+                    Input::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left)),
+                    Some(point),
+                ),
+            ],
+        )
+        .0
+    }
+    async fn perform(&mut self, app: &App, task: Task<Message>) {
+        let Some(mut stream) = iced_runtime::task::into_stream(task) else {
+            return;
+        };
+        while let Some(action) = stream.next().await {
+            let iced_runtime::Action::Widget(mut operation) = action else {
+                panic!("Chooser only requests scoped widget focus")
+            };
+            let mut view = view(app, self.scrolled, self.nested, self.show_review);
+            let tree = self.tree.get_or_insert_with(|| Tree::new(view.as_widget()));
+            view.as_widget().diff(tree);
+            let node =
+                view.as_widget_mut()
+                    .layout(tree, &(), &layout::Limits::new(Size::ZERO, self.size));
+            loop {
+                view.as_widget_mut()
+                    .operate(tree, Layout::new(&node), &(), operation.as_mut());
+                match operation.finish() {
+                    operation::Outcome::Chain(next) => operation = next,
+                    _ => break,
+                }
+            }
+        }
+    }
+    async fn dispatch(&mut self, app: &mut App, messages: Vec<Message>) {
+        for message in messages {
+            let task = app.update(message);
+            self.perform(app, task).await;
+        }
+    }
+}
+fn key(key: keyboard::key::Named, shift: bool) -> Input {
+    Input::Keyboard(keyboard::Event::KeyPressed {
+        key: keyboard::Key::Named(key),
+        modified_key: keyboard::Key::Named(key),
+        physical_key: keyboard::key::Physical::Code(keyboard::key::Code::Space),
+        location: keyboard::Location::Standard,
+        modifiers: if shift {
+            keyboard::Modifiers::SHIFT
+        } else {
+            keyboard::Modifiers::empty()
+        },
+        text: None,
+        repeat: false,
+    })
+}
+fn typing(raw: &str) -> Vec<(Input, Option<Point>)> {
+    raw.chars()
+        .map(|character| {
+            let raw = character.to_string();
+            (
+                Input::Keyboard(keyboard::Event::KeyPressed {
+                    key: keyboard::Key::Character(raw.clone().into()),
+                    modified_key: keyboard::Key::Character(raw.clone().into()),
+                    physical_key: keyboard::key::Physical::Code(keyboard::key::Code::KeyA),
+                    location: keyboard::Location::Standard,
+                    modifiers: keyboard::Modifiers::empty(),
+                    text: Some(raw.into()),
+                    repeat: false,
+                }),
+                None,
+            )
+        })
+        .collect()
+}
+
+#[tokio::test]
+async fn mounted_reference_trigger_tabs_to_root_popup_search_escape_and_exact_adjacent_fields() {
+    let mut app = inspector(catalog(), OWNER);
+    let accepted = app.document.bundle().clone();
+    let original = raw(&app);
+    let mut mount = Mount::default();
+    let fields = mount.frame(&app, &[]).1;
+    let messages = mount.click(
+        &app,
+        fields.field(&WidgetId::new("before-reference")).0.center(),
+    );
+    mount.dispatch(&mut app, messages).await;
+    let (_, fields, _) = mount.frame(&app, &[(key(keyboard::key::Named::Tab, false), None)]);
+    let id = trigger::field_id(app.draft.as_ref().unwrap().reference_generation(), PATH);
+    assert!(
+        fields.field(&id).1,
+        "Tab reaches the real reference trigger"
+    );
+    let messages = mount
+        .frame(&app, &[(key(keyboard::key::Named::Enter, false), None)])
+        .0;
+    assert_eq!(messages.len(), 1, "One keyboard activation opens one field");
+    mount.dispatch(&mut app, messages).await;
+    let popup = mount
+        .frame(&app, &[])
+        .2
+        .expect("App root overlay is mounted");
+    assert!(
+        popup.x >= 0.
+            && popup.y >= 0.
+            && popup.x + popup.width <= 360.
+            && popup.y + popup.height <= 320.
+    );
+    let mut inputs = typing("@controller_0720");
+    inputs.push((key(keyboard::key::Named::Escape, false), None));
+    let messages = mount.frame(&app, &inputs).0;
+    mount.dispatch(&mut app, messages).await;
+    let (_, fields, popup) = mount.frame(&app, &[]);
+    assert!(popup.is_none());
+    assert!(
+        fields.field(&id).1,
+        "Escape returns to its exact reference field"
+    );
+    assert_eq!(raw(&app), original);
+    assert_eq!(app.document.bundle(), &accepted);
+    for (backwards, expected) in [(false, "after-reference"), (true, "before-reference")] {
+        let messages = mount.click(&app, fields.field(&id).0.center());
+        mount.dispatch(&mut app, messages).await;
+        let messages = mount
+            .frame(&app, &[(key(keyboard::key::Named::Tab, backwards), None)])
+            .0;
+        mount.dispatch(&mut app, messages).await;
+        let (_, fields, popup) = mount.frame(&app, &[]);
+        assert!(popup.is_none());
+        assert!(
+            fields.field(&WidgetId::new(expected)).1,
+            "Chooser Tab stays within the originating form"
+        );
+    }
+    assert_eq!(app.document.bundle(), &accepted);
+}
+
+#[tokio::test]
+async fn mounted_reference_choice_stages_literal_identity_and_delayed_focus_cannot_hit_replacement_field()
+ {
+    let mut app = inspector(catalog(), OWNER);
+    let accepted = app.document.bundle().clone();
+    let mut mount = Mount::default();
+    let id = trigger::field_id(app.draft.as_ref().unwrap().reference_generation(), PATH);
+    let fields = mount.frame(&app, &[]).1;
+    let messages = mount.click(&app, fields.field(&id).0.center());
+    mount.dispatch(&mut app, messages).await;
+    let messages = mount.frame(&app, &typing("@controller_0720")).0;
+    mount.dispatch(&mut app, messages).await;
+    assert_eq!(
+        app.reference_authoring
+            .opened
+            .as_ref()
+            .unwrap()
+            .chooser
+            .count(),
+        1
+    );
+    let messages = mount
+        .frame(&app, &[(key(keyboard::key::Named::Enter, false), None)])
+        .0;
+    assert_eq!(messages.len(), 1);
+    let delayed_focus = app.update(messages.into_iter().next().unwrap());
+    assert_eq!(
+        app.draft.as_ref().unwrap().value.pointer(PATH),
+        Some(&json!(Id::from_u128(BASE + 720)))
+    );
+    assert_eq!(app.document.bundle(), &accepted);
+    // A structural edit occurs after Choose but before its asynchronous focus.
+    app.draft
+        .as_mut()
+        .unwrap()
+        .shape_scoped(PATH, Value::Null)
+        .unwrap();
+    let fields = mount.frame(&app, &[]).1;
+    let messages = mount.click(
+        &app,
+        fields.field(&WidgetId::new("after-reference")).0.center(),
+    );
+    mount.dispatch(&mut app, messages).await;
+    mount.perform(&app, delayed_focus).await;
+    let fields = mount.frame(&app, &[]).1;
+    assert!(
+        fields.field(&WidgetId::new("after-reference")).1,
+        "A missing old field target makes no focus changes"
+    );
+    assert!(
+        !fields
+            .field(&trigger::field_id(
+                app.draft.as_ref().unwrap().reference_generation(),
+                PATH
+            ))
+            .1
+    );
+    assert_eq!(app.document.bundle(), &accepted);
+}
+
+#[tokio::test]
+async fn mounted_scrolled_reference_anchor_uses_window_geometry_for_pointer_and_keyboard() {
+    let mut app = inspector(catalog(), OWNER);
+    let mut mount = Mount {
+        scrolled: true,
+        ..Default::default()
+    };
+    mount.frame(&app, &[]);
+    mount
+        .perform(
+            &app,
+            iced::widget::operation::snap_to("reference-scroll", scrollable::RelativeOffset::END),
+        )
+        .await;
+    let fields = mount.frame(&app, &[]).1;
+    let id = trigger::field_id(app.draft.as_ref().unwrap().reference_generation(), PATH);
+    let content = fields.field(&id).0;
+    let (viewport, offset) = fields.scrolls[0];
+    assert!(offset.y > 400., "Fixture is genuinely scrolled");
+    let expected = Rectangle {
+        x: content.x - offset.x,
+        y: content.y - offset.y,
+        ..content
+    }
+    .intersection(&viewport)
+    .unwrap();
+    let messages = mount.click(&app, expected.center());
+    let [Message::FieldReferenceOpen(request)] = messages.as_slice() else {
+        panic!("Scrolled field should emit one actual Open")
+    };
+    assert_eq!(request.anchor, expected);
+    mount.dispatch(&mut app, messages).await;
+    let close = app.update(Message::Escape);
+    mount.perform(&app, close).await;
+    let messages = mount
+        .frame(&app, &[(key(keyboard::key::Named::Enter, false), None)])
+        .0;
+    let [Message::FieldReferenceOpen(request)] = messages.as_slice() else {
+        panic!("Focused scrolled field opens without a pointer")
+    };
+    assert_eq!(request.anchor, expected);
+}
+
+#[tokio::test]
+async fn mounted_fresh_tab_reveals_offscreen_reference_and_return_reveals_it_again() {
+    for nested in [false, true] {
+        let mut app = inspector(catalog(), OWNER);
+        let original = raw(&app);
+        let source = app.document.bundle().clone();
+        let mut mount = Mount {
+            scrolled: true,
+            nested,
+            ..Default::default()
+        };
+        let fields = mount.frame(&app, &[]).1;
+        assert!(
+            fields
+                .scrolls
+                .iter()
+                .all(|(_, offset)| *offset == Vector::ZERO)
+        );
+        assert!(fields.field(&WidgetId::new("before-reference")).0.y > 180.);
+        let messages = mount
+            .frame(&app, &[(key(keyboard::key::Named::Tab, false), None)])
+            .0;
+        assert!(
+            messages.is_empty(),
+            "Keyboard reveal must not author any input"
+        );
+        let fields = mount.frame(&app, &[]).1;
+        assert!(fields.field(&WidgetId::new("before-reference")).1);
+        assert!(
+            fields.scrolls.iter().all(|(_, offset)| offset.y > 0.),
+            "Every enclosing viewport reveals fresh focus"
+        );
+        let id = trigger::field_id(app.draft.as_ref().unwrap().reference_generation(), PATH);
+        let offset: f32 = fields.scrolls.iter().map(|(_, offset)| offset.y).sum();
+        assert!(
+            fields.field(&id).0.y - offset >= 180.,
+            "The next reference starts below the fold"
+        );
+        let messages = mount
+            .frame(&app, &[(key(keyboard::key::Named::Tab, false), None)])
+            .0;
+        assert!(messages.is_empty());
+        let fields = mount.frame(&app, &[]).1;
+        let offset: f32 = fields.scrolls.iter().map(|(_, offset)| offset.y).sum();
+        let (bounds, focused) = fields.field(&id);
+        assert!(focused);
+        assert!(bounds.y - offset >= -0.01 && bounds.y + bounds.height - offset <= 180.01);
+        let messages = mount
+            .frame(&app, &[(key(keyboard::key::Named::Enter, false), None)])
+            .0;
+        assert_eq!(
+            messages.len(),
+            1,
+            "A newly revealed field opens through Enter"
+        );
+        mount.dispatch(&mut app, messages).await;
+        let return_focus = app.update(Message::Escape);
+        mount
+            .perform(
+                &app,
+                iced::widget::operation::snap_to(
+                    "reference-scroll",
+                    scrollable::RelativeOffset::START,
+                ),
+            )
+            .await;
+        if nested {
+            mount
+                .perform(
+                    &app,
+                    iced::widget::operation::snap_to(
+                        "outer-reference-scroll",
+                        scrollable::RelativeOffset::START,
+                    ),
+                )
+                .await;
+        }
+        assert!(
+            mount
+                .frame(&app, &[])
+                .1
+                .scrolls
+                .iter()
+                .all(|(_, offset)| *offset == Vector::ZERO)
+        );
+        mount.perform(&app, return_focus).await;
+        let fields = mount.frame(&app, &[]).1;
+        let offset: f32 = fields.scrolls.iter().map(|(_, offset)| offset.y).sum();
+        let (bounds, focused) = fields.field(&id);
+        assert!(
+            focused && bounds.y - offset >= -0.01 && bounds.y + bounds.height - offset <= 180.01
+        );
+        assert_eq!(raw(&app), original);
+        assert_eq!(app.document.bundle(), &source);
+    }
+}
+
+#[tokio::test]
+async fn mounted_form_tab_enters_in_both_directions_and_cycles_boundaries_without_losing_focus() {
+    for backwards in [false, true] {
+        let app = inspector(catalog(), OWNER);
+        let original = raw(&app);
+        let mut mount = Mount::default();
+        let reference = trigger::field_id(app.draft.as_ref().unwrap().reference_generation(), PATH);
+        let forward = [
+            WidgetId::new("before-reference"),
+            reference.clone(),
+            WidgetId::new("after-reference"),
+        ];
+        let reverse = [
+            WidgetId::new("after-reference"),
+            reference,
+            WidgetId::new("before-reference"),
+        ];
+        let expected = if backwards { &reverse } else { &forward };
+        for n in 0..7 {
+            let (messages, fields, popup) =
+                mount.frame(&app, &[(key(keyboard::key::Named::Tab, backwards), None)]);
+            assert!(messages.is_empty() && popup.is_none());
+            assert!(fields.field(&expected[n % 3]).1);
+            assert_eq!(
+                fields
+                    .values
+                    .iter()
+                    .filter(|(_, _, focused)| *focused)
+                    .count(),
+                1
+            );
+        }
+        assert_eq!(raw(&app), original);
+        assert!(!app.document.can_undo());
+    }
+}
+
+#[tokio::test]
+async fn mounted_delayed_return_cannot_focus_under_review_and_fresh_modal_tab_owns_its_form() {
+    let mut p = catalog();
+    trace(&mut p, Id::from_u128(300), OWNER, Id::from_u128(200));
+    let mut app = inspector(p, OWNER);
+    let source = app.document.bundle().clone();
+    let original = raw(&app);
+    let mut mount = Mount {
+        show_review: true,
+        ..Default::default()
+    };
+    let id = trigger::field_id(app.draft.as_ref().unwrap().reference_generation(), PATH);
+    let session = app.draft.as_ref().unwrap().reference_session();
+    let fields = mount.frame(&app, &[]).1;
+    let messages = mount.click(&app, fields.field(&id).0.center());
+    mount.dispatch(&mut app, messages).await;
+    let return_focus = app.update(Message::Escape);
+    let fields = mount.frame(&app, &[]).1;
+    let messages = mount.click(
+        &app,
+        fields.field(&WidgetId::new("after-reference")).0.center(),
+    );
+    mount.dispatch(&mut app, messages).await;
+    let _ = app.update(Message::StartSemanticReview(Id::from_u128(300)));
+    let facet = FacetSelector::Header(HeaderFacet::Parent);
+    send_review(&mut app, RowEvent::Select(facet.clone()));
+    send_review(
+        &mut app,
+        RowEvent::Decide(facet, Some(SemanticDecision::Candidate)),
+    );
+    assert_eq!(
+        app.draft.as_ref().unwrap().reference_session(),
+        session,
+        "Old Inspector really remains mounted"
+    );
+    assert_eq!(
+        trigger::field_id(app.draft.as_ref().unwrap().reference_generation(), PATH),
+        id
+    );
+    let review_before = review(&app).recovery_snapshot().unwrap();
+    let review_field = trigger::field_id(
+        review(&app)
+            .reference_form(app.project())
+            .unwrap()
+            .reference_generation(),
+        "/parent",
+    );
+    mount.perform(&app, return_focus).await;
+    let fields = mount.frame(&app, &[]).1;
+    assert!(
+        !fields.field(&id).1,
+        "A live old field underneath a modal cannot receive the stale focus task"
+    );
+    assert!(fields.field(&WidgetId::new("after-reference")).1);
+    assert!(!fields.field(&review_field).1);
+    let (messages, fields, _) = mount.frame(&app, &[(key(keyboard::key::Named::Tab, false), None)]);
+    assert!(messages.is_empty());
+    assert!(
+        fields.field(&review_field).1,
+        "Review entry ignores retained focus under its modal"
+    );
+    assert!(
+        !fields.field(&WidgetId::new("after-reference")).1,
+        "Modal focus acquisition deactivates background inputs"
+    );
+    let messages = mount.frame(&app, &typing("x")).0;
+    assert!(
+        messages.is_empty(),
+        "A character at the focused Review trigger cannot type into the Inspector below it"
+    );
+    let (messages, fields, _) = mount.frame(&app, &[(key(keyboard::key::Named::Tab, true), None)]);
+    assert!(messages.is_empty());
+    assert!(fields.field(&review_field).1);
+    assert!(!fields.field(&id).1);
+    assert_eq!(review(&app).recovery_snapshot().unwrap(), review_before);
+    assert_eq!(raw(&app), original);
+    assert_eq!(app.document.bundle(), &source);
+}
+
+#[tokio::test]
+async fn mounted_review_pointer_open_and_outside_dismissal_keep_background_input_inactive() {
+    let mut p = catalog();
+    trace(&mut p, Id::from_u128(300), OWNER, Id::from_u128(200));
+    let mut app = inspector(p, OWNER);
+    let original = raw(&app);
+    let source = app.document.bundle().clone();
+    let mut mount = Mount {
+        show_review: true,
+        ..Default::default()
+    };
+    let fields = mount.frame(&app, &[]).1;
+    let messages = mount.click(
+        &app,
+        fields.field(&WidgetId::new("after-reference")).0.center(),
+    );
+    mount.dispatch(&mut app, messages).await;
+    let _ = app.update(Message::StartSemanticReview(Id::from_u128(300)));
+    let facet = FacetSelector::Header(HeaderFacet::Parent);
+    send_review(&mut app, RowEvent::Select(facet.clone()));
+    send_review(
+        &mut app,
+        RowEvent::Decide(facet, Some(SemanticDecision::Candidate)),
+    );
+    let saved = review(&app).recovery_snapshot().unwrap();
+    let id = trigger::field_id(
+        review(&app)
+            .reference_form(app.project())
+            .unwrap()
+            .reference_generation(),
+        "/parent",
+    );
+    let fields = mount.frame(&app, &[]).1;
+    assert!(
+        fields.field(&WidgetId::new("after-reference")).1,
+        "Fixture retains Inspector focus before the modal receives input"
+    );
+    let messages = mount.click(&app, fields.field(&id).0.center());
+    mount.dispatch(&mut app, messages).await;
+    assert!(matches!(
+        &app.reference_authoring.opened.as_ref().unwrap().host,
+        Host::Review { .. }
+    ));
+    let fields = mount.frame(&app, &[]).1;
+    assert!(!fields.field(&WidgetId::new("after-reference")).1);
+    let messages = mount.click(&app, Point::new(359., 319.));
+    assert!(matches!(
+        messages.as_slice(),
+        [Message::Workflow(workflow::Event::Semantic(event))] if matches!(event.as_ref(),
+            semantic_review::Event::Row {
+                event: RowEvent::ReferenceEvent(chooser::Event {
+                    action: Action::Close(Close::Outside),
+                    ..
+                }),
+                ..
+            }
+        )
+    ));
+    for message in messages {
+        let task = app.update(message);
+        assert!(
+            iced_runtime::task::into_stream(task).is_none(),
+            "Outside dismissal must not request focus or apply"
+        );
+    }
+    let (messages, fields, popup) = mount.frame(&app, &typing("x"));
+    assert!(messages.is_empty() && popup.is_none());
+    assert!(!fields.field(&WidgetId::new("after-reference")).1);
+    assert_eq!(review(&app).recovery_snapshot().unwrap(), saved);
+    assert_eq!(raw(&app), original);
+    assert_eq!(app.document.bundle(), &source);
+}
+
+#[tokio::test]
+async fn mounted_reverse_review_required_rationale_remains_editable_beside_candidate_reference_form()
+ {
+    let mut p = persistence::decode(include_bytes!(concat!(
+        env!("CARGO_MANIFEST_DIR"),
+        "/../../harness/fixtures/interface-operation-probe/output/boundary-only.json"
+    )))
+    .unwrap();
+    let sa = p
+        .elements
+        .values()
+        .find(|element| element.alias == "operation_probe_43")
+        .unwrap()
+        .id;
+    let allocation = p
+        .relations
+        .values()
+        .find(|relation| relation.alias == "operation_probe_30")
+        .unwrap()
+        .id;
+    // The boundary fixture deliberately has no selected operation. Author one
+    // through the validated command path before testing reverse omission.
+    let mut message = p.elements[&sa].clone();
+    let Some(SharedBody::Occurrence {
+        body: OccurrenceBody::Exchange { operation, .. },
+        ..
+    }) = message.shared_mut()
+    else {
+        panic!("The operation fixture must contain an Exchange call")
+    };
+    *operation = Some(OperationUse {
+        allocation: Some(allocation),
+    });
+    p = execute_batch(&p, &[Command::EditElement(sa, message)]).unwrap();
+    assert!(matches!(
+        oa_core::operations::resolve(&p, sa).unwrap(),
+        oa_core::operations::OperationResolution::Selected(value)
+            if value.allocation == allocation
+    ));
+    let inspector_id = Id::new_v4();
+    element(
+        &mut p,
+        inspector_id,
+        Kind::DataType,
+        Layer::Oa,
+        "Inspector record",
+        None,
+    );
+    let scenario = p
+        .add_element(Kind::Scenario, Layer::Oa, "Operational counterpart", None)
+        .unwrap();
+    let oa = p
+        .add_element(
+            Kind::Occurrence,
+            Layer::Oa,
+            "Operational message",
+            Some(scenario),
+        )
+        .unwrap();
+    *p.elements.get_mut(&oa).unwrap().shared_mut().unwrap() = SharedBody::Occurrence {
+        body: OccurrenceBody::Exchange {
+            exchange: None,
+            sender: None,
+            receiver: None,
+            message_kind: MessageKind::Asynchronous,
+            reply_to: None,
+            values: vec![],
+            operation: None,
+        },
+        precondition: String::new(),
+        postcondition: String::new(),
+    };
+    p.elements
+        .get_mut(&scenario)
+        .unwrap()
+        .steps_mut()
+        .unwrap()
+        .push(oa);
+    let trace_id = Id::new_v4();
+    trace(&mut p, trace_id, oa, sa);
+    let mut app = inspector(p, inspector_id);
+    let source = app.document.bundle().clone();
+    let inspector_raw = raw(&app);
+    let _ = app.update(Message::StartSemanticReview(trace_id));
+    let _ = app.update(Message::Workflow(workflow::Event::semantic(
+        semantic_review::Event::Direction(TransitionDirection::SaToOa),
+    )));
+    let facet = FacetSelector::Header(HeaderFacet::Parent);
+    send_review(&mut app, RowEvent::Select(facet.clone()));
+    send_review(
+        &mut app,
+        RowEvent::Decide(facet, Some(SemanticDecision::Candidate)),
+    );
+    send_review(&mut app, RowEvent::OperationOmission(true));
+    assert_eq!(review(&app).direction, TransitionDirection::SaToOa);
+    assert_eq!(review(&app).operation_omission.as_deref(), Some(""));
+    let candidate = serde_json::to_value(
+        review(&app)
+            .reference_form(app.project())
+            .unwrap_or_else(|| {
+                panic!(
+                    "Reverse review candidate: selected={:?}, decisions={:?}, error={:?}",
+                    review(&app).selected,
+                    review(&app).decisions,
+                    review(&app).error
+                )
+            })
+            .recovery_snapshot(),
+    )
+    .unwrap();
+    let mut mount = Mount {
+        show_review: true,
+        ..Default::default()
+    };
+    let fields = mount.frame(&app, &[]).1;
+    let messages = mount.click(
+        &app,
+        fields.field(&WidgetId::new("review-rationale")).0.center(),
+    );
+    mount.dispatch(&mut app, messages).await;
+    let messages = mount.frame(&app, &typing("Engineering reason")).0;
+    assert_eq!(
+        messages.len(),
+        "Engineering reason".chars().count(),
+        "Every key reaches the legitimate sibling inside Review"
+    );
+    assert!(messages.iter().all(|message| matches!(
+        message,
+        Message::Workflow(workflow::Event::Semantic(event)) if matches!(event.as_ref(), semantic_review::Event::Row {
+            event: RowEvent::OperationRationale(_),
+            ..
+        })
+    )));
+    mount.dispatch(&mut app, messages).await;
+    assert_eq!(
+        review(&app).operation_omission.as_deref(),
+        Some("Engineering reason")
+    );
+    assert!(
+        mount
+            .frame(&app, &[])
+            .1
+            .field(&WidgetId::new("review-rationale"))
+            .1
+    );
+    assert_eq!(
+        serde_json::to_value(
+            review(&app)
+                .reference_form(app.project())
+                .unwrap()
+                .recovery_snapshot()
+        )
+        .unwrap(),
+        candidate
+    );
+    assert_eq!(raw(&app), inspector_raw);
+    assert_eq!(app.document.bundle(), &source);
+    assert!(!app.document.can_undo());
+}

crates/oa-desktop/src/app/repair_save_state_tests.rs

@@ -0,0 +1,263 @@
+use super::*;
+
+const VALID: &str = concat!(
+    "arcadia 7;\r\n",
+    "project repair \"Repair 救援\" id \"9e8f0000-0000-4000-8000-000000000001\" {\r\n",
+    "    oa_activity assess \"Assess\" id \"9e8f0000-0000-4000-8000-000000000002\" {}\r\n",
+    "}\r\n",
+);
+
+fn open(app: &mut App, path: &std::path::Path) {
+    let _ = app.update(Message::Loaded(Ok(Some(
+        read_snapshot(path.to_owned()).unwrap(),
+    ))));
+}
+
+fn edit(app: &mut App, text: &str) {
+    let _ = app.update(Message::SourceEdit(text_editor::Action::SelectAll));
+    let _ = app.update(Message::SourceEdit(text_editor::Action::Edit(
+        text_editor::Edit::Paste(Arc::new(text.into())),
+    )));
+}
+
+fn save(app: &mut App, path: &std::path::Path) {
+    let receipt = write_snapshot(
+        app.canvas_document,
+        app.document.revision(),
+        app.document.snapshot(),
+        path.to_owned(),
+        app.disk_project.clone(),
+    )
+    .unwrap();
+    let _ = app.update(Message::Saved(Ok(Some(receipt))));
+}
+
+#[test]
+fn repair_to_previous_saved_bytes_requires_save_at_new_destination_and_guards_close() {
+    for extra in [
+        "    include \"missing.arcadia\";\r\n",
+        "    oa_activity assess \"Duplicate\" id \"9e8f0000-0000-4000-8000-000000000003\" {}\r\n",
+    ] {
+        let first = tempfile::tempdir().unwrap();
+        let second = tempfile::tempdir().unwrap();
+        let first_path = first.path().canonicalize().unwrap().join("project.arcadia");
+        let second_path = second
+            .path()
+            .canonicalize()
+            .unwrap()
+            .join("project.arcadia");
+        let invalid = VALID.strip_suffix("}\r\n").unwrap().to_owned() + extra + "}\r\n";
+        std::fs::write(&first_path, VALID).unwrap();
+        std::fs::write(&second_path, &invalid).unwrap();
+        let mut app = App::with_project(Project::empty());
+        open(&mut app, &first_path);
+        assert!(!app.dirty());
+        let before = app.document.snapshot();
+        let revision = app.document.revision();
+        open(&mut app, &second_path);
+        assert!(!app.source_workspace.applied);
+        assert!(Arc::ptr_eq(&before, &app.document.snapshot()));
+        edit(&mut app, VALID);
+        assert!(app.apply_source(), "{}", app.status);
+        assert!(app.source_workspace.applied);
+        assert!(!app.source_dirty());
+        assert_eq!(app.document.bundle(), &before.bundle);
+        assert_eq!(app.project(), &before.decoded.project);
+        assert_eq!(app.document.revision(), revision);
+        assert!(
+            !app.document.can_undo(),
+            "Equal content creates no history step"
+        );
+        assert!(app.document.dirty());
+        assert_eq!(app.hosted_label(), "Unsaved changes");
+        assert_eq!(std::fs::read(&second_path).unwrap(), invalid.as_bytes());
+        assert_eq!(std::fs::read(&first_path).unwrap(), VALID.as_bytes());
+        let close = window::Id::unique();
+        let task = app.update(Message::Request(Pending::Close(close)));
+        assert!(iced_runtime::task::into_stream(task).is_none());
+        assert!(matches!(app.pending, Some(Pending::Close(id)) if id == close));
+        let _ = app.update(Message::Cancel);
+        save(&mut app, &second_path);
+        assert!(!app.dirty());
+        assert_eq!(app.hosted_label(), "All changes saved");
+        assert_eq!(std::fs::read(&second_path).unwrap(), VALID.as_bytes());
+        assert_eq!(std::fs::read(&first_path).unwrap(), VALID.as_bytes());
+    }
+}
+
+#[test]
+fn repair_history_compares_to_new_disk_baseline_and_then_successful_save() {
+    let directory = tempfile::tempdir().unwrap();
+    let path = directory
+        .path()
+        .canonicalize()
+        .unwrap()
+        .join("project.arcadia");
+    std::fs::write(&path, VALID).unwrap();
+    let mut app = App::with_project(Project::empty());
+    open(&mut app, &path);
+    let before = app.document.snapshot();
+    let invalid = format!("{VALID} unfinished {{");
+    std::fs::write(&path, &invalid).unwrap();
+    open(&mut app, &path);
+    let repaired = format!("{VALID}// Repaired rationale\r\n");
+    edit(&mut app, &repaired);
+    assert!(app.apply_source());
+    assert!(app.dirty());
+    let _ = app.update(Message::Undo);
+    assert_eq!(app.document.bundle(), &before.bundle);
+    assert!(
+        app.dirty(),
+        "Old saved bytes are not saved at the repair destination"
+    );
+    let _ = app.update(Message::Redo);
+    assert!(app.dirty());
+    assert_eq!(std::fs::read(&path).unwrap(), invalid.as_bytes());
+
+    std::fs::write(&path, "external edit").unwrap();
+    let failed = write_snapshot(
+        app.canvas_document,
+        app.document.revision(),
+        app.document.snapshot(),
+        path.clone(),
+        app.disk_project.clone(),
+    )
+    .unwrap_err();
+    let _ = app.update(Message::Saved(Err(failed)));
+    assert!(app.dirty());
+    assert_eq!(std::fs::read(&path).unwrap(), b"external edit");
+    std::fs::write(&path, &invalid).unwrap();
+    save(&mut app, &path);
+    assert!(!app.dirty());
+    let _ = app.update(Message::Undo);
+    assert!(app.dirty());
+    assert_eq!(app.document.bundle(), &before.bundle);
+    let _ = app.update(Message::Redo);
+    assert!(!app.dirty(), "Redo to the new saved snapshot is clean");
+    assert_eq!(std::fs::read(&path).unwrap(), repaired.as_bytes());
+}
+
+#[test]
+fn valid_equal_content_at_distinct_destinations_stays_clean() {
+    let first = tempfile::tempdir().unwrap();
+    let second = tempfile::tempdir().unwrap();
+    let first_path = first.path().canonicalize().unwrap().join("project.arcadia");
+    let second_path = second
+        .path()
+        .canonicalize()
+        .unwrap()
+        .join("project.arcadia");
+    std::fs::write(&first_path, VALID).unwrap();
+    std::fs::write(&second_path, VALID).unwrap();
+    let mut app = App::with_project(Project::empty());
+    open(&mut app, &first_path);
+    let before = app.document.bundle().clone();
+    open(&mut app, &second_path);
+    assert_eq!(app.document.bundle(), &before);
+    assert_eq!(app.path.as_ref(), Some(&second_path));
+    assert!(!app.dirty());
+    assert_eq!(app.hosted_label(), "All changes saved");
+}
+
+#[test]
+fn recovering_applied_repair_rebinds_rolled_back_disk_bytes_without_changing_model() {
+    let first = tempfile::tempdir().unwrap();
+    let second = tempfile::tempdir().unwrap();
+    let first_path = first.path().canonicalize().unwrap().join("project.arcadia");
+    let root = second.path().canonicalize().unwrap();
+    let path = root.join("project.arcadia");
+    let before = VALID.replace("Repair 救援", "Before 救援");
+    std::fs::write(&first_path, VALID).unwrap();
+    std::fs::write(&path, VALID).unwrap();
+    let journal = root.join(".arcadia-save-project.arcadia.journal");
+    std::fs::create_dir(&journal).unwrap();
+    std::fs::write(
+        journal.join("journal.json"),
+        br#"{"version":1,"entry":"project.arcadia","files":[{"path":"project.arcadia","before":true,"write":true}]}"#,
+    )
+    .unwrap();
+    std::fs::write(journal.join("0.before"), &before).unwrap();
+    std::fs::write(journal.join("0.after"), VALID).unwrap();
+    let mut app = App::with_project(Project::empty());
+    open(&mut app, &first_path);
+    let accepted = app.document.snapshot();
+    open(&mut app, &path);
+    assert_eq!(app.pending_recovery.as_ref(), Some(&path));
+    assert!(!app.source_workspace.applied);
+    assert!(app.apply_source());
+    assert!(
+        !app.dirty(),
+        "Current bytes still match disk before rollback"
+    );
+    let _ = app.update(Message::SourceRecovered(recover_snapshot(path.clone())));
+    assert!(app.pending_recovery.is_none());
+    assert!(!journal.exists());
+    assert_eq!(std::fs::read(&path).unwrap(), before.as_bytes());
+    assert!(Arc::ptr_eq(&accepted, &app.document.snapshot()));
+    assert!(!app.source_dirty());
+    assert!(app.dirty(), "Recovery changed disk, not the accepted model");
+    assert_eq!(app.hosted_label(), "Unsaved changes");
+    save(&mut app, &path);
+    assert!(!app.dirty());
+    assert_eq!(std::fs::read(&path).unwrap(), VALID.as_bytes());
+}
+
+#[test]
+fn recovery_missing_entry_or_failed_reload_preserves_current_destination_save_authority() {
+    for (current_destination, failed_reload) in
+        [(true, false), (false, false), (true, true), (false, true)]
+    {
+        let directory = tempfile::tempdir().unwrap();
+        let root = directory.path().canonicalize().unwrap();
+        let path = root.join("project.arcadia");
+        std::fs::write(&path, VALID).unwrap();
+        let mut app = App::with_project(Project::empty());
+        open(&mut app, &path);
+        let accepted = app.document.snapshot();
+        let journal = root.join(".arcadia-save-project.arcadia.journal");
+        std::fs::create_dir(&journal).unwrap();
+        std::fs::write(
+            journal.join("journal.json"),
+            br#"{"version":1,"entry":"project.arcadia","files":[{"path":"project.arcadia","before":false,"write":true}]}"#,
+        )
+        .unwrap();
+        std::fs::write(journal.join("0.after"), VALID).unwrap();
+        open(&mut app, &path);
+        assert!(app.apply_source());
+        assert!(!app.dirty());
+        let destination = tempfile::tempdir().unwrap();
+        let saved_elsewhere = destination
+            .path()
+            .canonicalize()
+            .unwrap()
+            .join("project.arcadia");
+        if !current_destination {
+            save(&mut app, &saved_elsewhere);
+            assert_eq!(app.path.as_ref(), Some(&saved_elsewhere));
+            assert_eq!(app.pending_recovery.as_ref(), Some(&path));
+        }
+        let mut receipt = recover_snapshot(path.clone()).unwrap();
+        assert!(
+            receipt.disk.as_ref().unwrap().bundle.files.is_empty(),
+            "Missing entry reloads as an empty repair workspace"
+        );
+        if failed_reload {
+            // Separately exercise the adapter's successful-recovery/failed-read
+            // boundary; first-save rollback itself does not cause a read error.
+            receipt.disk = Err("Injected post-recovery reload failure".into());
+        }
+        let _ = app.update(Message::SourceRecovered(Ok(receipt)));
+        assert!(!path.exists());
+        assert!(!journal.exists());
+        assert!(app.pending_recovery.is_none());
+        assert!(Arc::ptr_eq(&accepted, &app.document.snapshot()));
+        assert_eq!(app.dirty(), current_destination);
+        if current_destination {
+            let _ = app.update(Message::Request(Pending::New));
+            assert!(matches!(app.pending, Some(Pending::New)));
+        } else {
+            assert_eq!(app.path.as_ref(), Some(&saved_elsewhere));
+            assert_eq!(std::fs::read(&saved_elsewhere).unwrap(), VALID.as_bytes());
+        }
+    }
+}

crates/oa-desktop/src/app/review_navigation_tests.rs

@@ -16,7 +16,7 @@ fn state(app: &App) -> &State {
 }
 fn row_event(app: &mut App, event: RowEvent) {
     let event = state(app).address_event(event);
-    send(app, Message::Workflow(Event::Semantic(event)));
+    send(app, Message::Workflow(Event::semantic(event)));
 }
 fn fixture(reverse: bool, destination_view: bool) -> (App, Id, Id, Id, Option<Id>) {
     let mut p = Project::empty();

crates/oa-desktop/src/app/source_rename/alias_input.rs

@@ -0,0 +1,219 @@
+//! Keep Iced's single-line input from silently filtering pasted control bytes.
+//! Only the alias field uses this adapter. The child retains editing and focus.
+use iced::advanced::{
+    Clipboard, Layout, Shell, Widget, clipboard, layout, overlay, renderer, text, widget,
+};
+use iced::{Element, Event, Length, Rectangle, Size, Vector, keyboard, mouse};
+
+pub(super) fn guard<'a, Message: Clone + 'a, Theme: 'a, R: text::Renderer + 'a>(
+    input: Element<'a, Message, Theme, R>,
+    rejected: Option<Message>,
+) -> Element<'a, Message, Theme, R> {
+    Element::new(AliasInput { input, rejected })
+}
+
+struct AliasInput<'a, Message, Theme, R> {
+    input: Element<'a, Message, Theme, R>,
+    rejected: Option<Message>,
+}
+
+#[derive(Default)]
+struct State {
+    modifiers: keyboard::Modifiers,
+}
+
+// Each fresh child clipboard read uses the checked snapshot. Iced may reuse its
+// previously admitted paste while V is held, until KeyReleased clears that cache.
+struct CapturedClipboard<'a> {
+    content: Option<String>,
+    original: &'a mut dyn Clipboard,
+}
+impl Clipboard for CapturedClipboard<'_> {
+    fn read(&self, kind: clipboard::Kind) -> Option<String> {
+        if kind == clipboard::Kind::Standard {
+            self.content.clone()
+        } else {
+            self.original.read(kind)
+        }
+    }
+    fn write(&mut self, kind: clipboard::Kind, contents: String) {
+        self.original.write(kind, contents);
+    }
+}
+
+impl<Message: Clone, Theme, R: text::Renderer> Widget<Message, Theme, R>
+    for AliasInput<'_, Message, Theme, R>
+{
+    fn size(&self) -> Size<Length> {
+        self.input.as_widget().size()
+    }
+    fn size_hint(&self) -> Size<Length> {
+        self.input.as_widget().size_hint()
+    }
+    fn tag(&self) -> widget::tree::Tag {
+        widget::tree::Tag::of::<State>()
+    }
+    fn state(&self) -> widget::tree::State {
+        widget::tree::State::new(State::default())
+    }
+    fn children(&self) -> Vec<widget::Tree> {
+        vec![widget::Tree::new(self.input.as_widget())]
+    }
+    fn diff(&self, tree: &mut widget::Tree) {
+        tree.diff_children(std::slice::from_ref(&self.input));
+    }
+    fn layout(
+        &mut self,
+        tree: &mut widget::Tree,
+        renderer: &R,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        self.input
+            .as_widget_mut()
+            .layout(&mut tree.children[0], renderer, limits)
+    }
+    fn draw(
+        &self,
+        tree: &widget::Tree,
+        renderer: &mut R,
+        theme: &Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+    ) {
+        self.input.as_widget().draw(
+            &tree.children[0],
+            renderer,
+            theme,
+            style,
+            layout,
+            cursor,
+            viewport,
+        );
+    }
+    fn operate(
+        &mut self,
+        tree: &mut widget::Tree,
+        layout: Layout<'_>,
+        renderer: &R,
+        operation: &mut dyn widget::Operation,
+    ) {
+        self.input
+            .as_widget_mut()
+            .operate(&mut tree.children[0], layout, renderer, operation);
+    }
+    fn update(
+        &mut self,
+        tree: &mut widget::Tree,
+        event: &Event,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        renderer: &R,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        viewport: &Rectangle,
+    ) {
+        let focused = tree.children[0]
+            .state
+            .downcast_ref::<iced::widget::text_input::State<R::Paragraph>>()
+            .is_focused();
+        let state = tree.state.downcast_mut::<State>();
+        // Iced 0.14.2 uses stored ModifiersChanged state, not KeyPressed.modifiers.
+        // Mirror its Escape reset and its Latin/physical-key paste shortcut.
+        if let Event::Keyboard(keyboard::Event::ModifiersChanged(modifiers)) = event {
+            state.modifiers = *modifiers;
+        }
+        let paste = matches!(event,
+            Event::Keyboard(keyboard::Event::KeyPressed { key, physical_key, .. })
+                if key.to_latin(*physical_key) == Some('v')
+                    && state.modifiers.command() && !state.modifiers.alt());
+        if focused
+            && paste
+            && let Some(rejected) = &self.rejected
+        {
+            let content = clipboard.read(clipboard::Kind::Standard);
+            if content
+                .as_ref()
+                .is_some_and(|value| value.chars().any(char::is_control))
+            {
+                // Do not invoke the child: even an empty replacement would erase
+                // its selection. Approval invalidation is an explicit App event.
+                shell.publish(rejected.clone());
+                shell.capture_event();
+                return;
+            }
+            self.input.as_widget_mut().update(
+                &mut tree.children[0],
+                event,
+                layout,
+                cursor,
+                renderer,
+                &mut CapturedClipboard {
+                    content,
+                    original: clipboard,
+                },
+                shell,
+                viewport,
+            );
+            return;
+        }
+        self.input.as_widget_mut().update(
+            &mut tree.children[0],
+            event,
+            layout,
+            cursor,
+            renderer,
+            clipboard,
+            shell,
+            viewport,
+        );
+        // In Iced 0.14.2 the only KeyPressed branch that removes focus is its
+        // Escape branch, which also resets stored modifiers. Observe that branch
+        // after its text/shortcut early returns and effective-key conversion.
+        if focused
+            && matches!(event, Event::Keyboard(keyboard::Event::KeyPressed { .. }))
+            && !tree.children[0]
+                .state
+                .downcast_ref::<iced::widget::text_input::State<R::Paragraph>>()
+                .is_focused()
+        {
+            tree.state.downcast_mut::<State>().modifiers = keyboard::Modifiers::default();
+        }
+    }
+    fn mouse_interaction(
+        &self,
+        tree: &widget::Tree,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+        renderer: &R,
+    ) -> mouse::Interaction {
+        self.input.as_widget().mouse_interaction(
+            &tree.children[0],
+            layout,
+            cursor,
+            viewport,
+            renderer,
+        )
+    }
+    fn overlay<'a>(
+        &'a mut self,
+        tree: &'a mut widget::Tree,
+        layout: Layout<'a>,
+        renderer: &R,
+        viewport: &Rectangle,
+        translation: Vector,
+    ) -> Option<overlay::Element<'a, Message, Theme, R>> {
+        self.input.as_widget_mut().overlay(
+            &mut tree.children[0],
+            layout,
+            renderer,
+            viewport,
+            translation,
+        )
+    }
+}
+
+#[cfg(all(test, debug_assertions))]
+mod tests;

crates/oa-desktop/src/app/source_rename/alias_input/tests.rs

@@ -0,0 +1,220 @@
+use super::*;
+use crate::views::source_tests::FontLayout;
+use iced::keyboard::{
+    Key, Modifiers,
+    key::{Code, Named, Physical},
+};
+use std::cell::Cell;
+
+#[derive(Debug, Clone, PartialEq)]
+enum Signal {
+    Input(String),
+    Rejected,
+}
+
+struct ClipboardText {
+    text: String,
+    reads: Cell<usize>,
+}
+impl Clipboard for ClipboardText {
+    fn read(&self, _: clipboard::Kind) -> Option<String> {
+        self.reads.set(self.reads.get() + 1);
+        Some(self.text.clone())
+    }
+    fn write(&mut self, _: clipboard::Kind, _: String) {}
+}
+type InputState = iced::widget::text_input::State<<FontLayout as text::Renderer>::Paragraph>;
+
+struct Mounted {
+    input: Element<'static, Signal, iced::Theme, FontLayout>,
+    tree: widget::Tree,
+    node: layout::Node,
+    clipboard: ClipboardText,
+    messages: Vec<Signal>,
+}
+impl Mounted {
+    fn new(focused: bool, enabled: bool, modifiers: Modifiers) -> Self {
+        let mut child = iced::widget::text_input("Alias", "send_water");
+        if enabled {
+            child = child.on_input(Signal::Input);
+        }
+        let mut input = guard(child.into(), enabled.then_some(Signal::Rejected));
+        let mut tree = widget::Tree::new(input.as_widget());
+        let node = input.as_widget_mut().layout(
+            &mut tree,
+            &FontLayout,
+            &layout::Limits::new(Size::ZERO, Size::new(500., 40.)),
+        );
+        if focused {
+            let state = tree.children[0].state.downcast_mut::<InputState>();
+            state.focus();
+            state.select_range(0, 10);
+        }
+        let mut mounted = Self {
+            input,
+            tree,
+            node,
+            clipboard: ClipboardText {
+                text: "foo\nbar".into(),
+                reads: Cell::new(0),
+            },
+            messages: vec![],
+        };
+        mounted.event(Event::Keyboard(keyboard::Event::ModifiersChanged(
+            modifiers,
+        )));
+        mounted
+    }
+    fn state(&self) -> &InputState {
+        self.tree.children[0].state.downcast_ref::<InputState>()
+    }
+    fn event(&mut self, event: Event) -> bool {
+        let mut shell = Shell::new(&mut self.messages);
+        self.input.as_widget_mut().update(
+            &mut self.tree,
+            &event,
+            Layout::new(&self.node),
+            mouse::Cursor::Unavailable,
+            &FontLayout,
+            &mut self.clipboard,
+            &mut shell,
+            &Rectangle::new(iced::Point::ORIGIN, Size::new(500., 40.)),
+        );
+        shell.is_event_captured()
+    }
+}
+fn key(key: Key, modified_key: Key, code: Code) -> Event {
+    Event::Keyboard(keyboard::Event::KeyPressed {
+        key,
+        modified_key,
+        physical_key: Physical::Code(code),
+        location: keyboard::Location::Standard,
+        modifiers: Modifiers::empty(),
+        text: None,
+        repeat: false,
+    })
+}
+fn paste() -> Event {
+    key(
+        Key::Character("v".into()),
+        Key::Character("v".into()),
+        Code::KeyV,
+    )
+}
+
+#[test]
+fn paste_refusal_matches_child_focus_enabled_and_stored_modifier_protocol() {
+    for focused in [false, true] {
+        for enabled in [false, true] {
+            for modifiers in [
+                Modifiers::empty(),
+                Modifiers::SHIFT,
+                Modifiers::COMMAND,
+                Modifiers::COMMAND | Modifiers::ALT,
+                Modifiers::COMMAND | Modifiers::SHIFT,
+            ] {
+                let mut mounted = Mounted::new(focused, enabled, modifiers);
+                let before = mounted.state().cursor();
+                let expected = focused && enabled && modifiers.command() && !modifiers.alt();
+                let captured = mounted.event(paste());
+                assert_eq!(
+                    mounted.messages,
+                    if expected {
+                        vec![Signal::Rejected]
+                    } else {
+                        vec![]
+                    }
+                );
+                assert_eq!(mounted.clipboard.reads.get(), usize::from(expected));
+                assert_eq!(mounted.state().cursor(), before);
+                if expected {
+                    assert!(captured);
+                }
+            }
+        }
+    }
+}
+
+#[test]
+fn effective_escape_reset_follows_child_after_early_returns() {
+    // Raw Escape mapped to Home must not clear only the guard's Command state.
+    let mut mounted = Mounted::new(true, true, Modifiers::COMMAND);
+    mounted.event(key(
+        Key::Named(Named::Escape),
+        Key::Named(Named::Home),
+        Code::Escape,
+    ));
+    assert!(mounted.state().is_focused());
+    assert!(mounted.event(paste()));
+    assert_eq!(mounted.messages, vec![Signal::Rejected]);
+
+    // Effective Escape clears both states; a later focus operation does not
+    // invent a new ModifiersChanged event or revive the previous Command state.
+    let mut mounted = Mounted::new(true, true, Modifiers::COMMAND);
+    mounted.event(key(
+        Key::Named(Named::Home),
+        Key::Named(Named::Escape),
+        Code::Home,
+    ));
+    assert!(!mounted.state().is_focused());
+    mounted.tree.children[0]
+        .state
+        .downcast_mut::<InputState>()
+        .focus();
+    mounted.event(paste());
+    assert!(mounted.messages.is_empty());
+    assert_eq!(mounted.clipboard.reads.get(), 0);
+
+    // Printable text returns before effective Escape and leaves modifiers live.
+    let mut mounted = Mounted::new(true, true, Modifiers::COMMAND);
+    let mut event = key(
+        Key::Named(Named::Home),
+        Key::Named(Named::Escape),
+        Code::Home,
+    );
+    if let Event::Keyboard(keyboard::Event::KeyPressed { text, .. }) = &mut event {
+        *text = Some("x".into());
+    }
+    mounted.event(event);
+    assert!(mounted.state().is_focused());
+    assert_eq!(mounted.messages, vec![Signal::Input("x".into())]);
+    mounted.messages.clear();
+    mounted.event(paste());
+    assert_eq!(mounted.messages, vec![Signal::Rejected]);
+}
+
+#[test]
+fn held_paste_cache_contains_only_previously_admitted_text() {
+    let mut mounted = Mounted::new(true, true, Modifiers::COMMAND);
+    mounted.clipboard.text = "water".into();
+    mounted.event(paste());
+    assert_eq!(mounted.messages, vec![Signal::Input("water".into())]);
+    mounted.messages.clear();
+    mounted.clipboard.text = "other".into();
+    mounted.event(paste());
+    assert_eq!(
+        mounted.messages,
+        vec![Signal::Input("waterwater".into())],
+        "Iced reuses its first admitted paste while the key is held"
+    );
+    mounted.messages.clear();
+    let before = mounted.state().cursor();
+    mounted.clipboard.text = "bad\tvalue".into();
+    mounted.event(paste());
+    assert_eq!(mounted.messages, vec![Signal::Rejected]);
+    assert_eq!(mounted.state().cursor(), before);
+    mounted.messages.clear();
+    mounted.event(Event::Keyboard(keyboard::Event::KeyReleased {
+        key: Key::Character("v".into()),
+        modified_key: Key::Character("v".into()),
+        physical_key: Physical::Code(Code::KeyV),
+        location: keyboard::Location::Standard,
+        modifiers: Modifiers::empty(),
+    }));
+    mounted.clipboard.text = "later".into();
+    mounted.event(paste());
+    assert_eq!(
+        mounted.messages,
+        vec![Signal::Input("waterwaterlater".into())]
+    );
+}

crates/oa-desktop/src/app/source_rename/editor_patch.rs

@@ -0,0 +1,303 @@
+//! Display-only reuse after a guarded alias rename. This is not model authority.
+use iced::{advanced::text::Renderer, widget::text_editor};
+use std::sync::Arc;
+
+/// Replace exact, unchanged-line-count source in an existing editor.
+///
+/// The caller must first authorize/commit the model change and must reconstruct
+/// from accepted source on false. Preflight failures do not mutate the editor;
+/// a failed final readback can leave it changed. On changing success the cursor
+/// is at 0:0 without selection; the caller restores its approved origin/reveal.
+/// Direct Content actions deliberately bypass App draft edits and Undo history.
+pub(super) fn replace<R: Renderer>(
+    editor: &mut text_editor::Content<R>,
+    before: &str,
+    after: &str,
+) -> bool {
+    if editor.text() != before {
+        return false;
+    }
+    let Some(old_lines) = lines(before) else {
+        return false;
+    };
+    let Some(new_lines) = lines(after) else {
+        return false;
+    };
+    if old_lines.len() != new_lines.len() || old_lines.len() != editor.line_count() {
+        return false;
+    }
+    let mut patches = Vec::new();
+    for (line, ((old, old_ending), (new, new_ending))) in
+        old_lines.into_iter().zip(new_lines).enumerate()
+    {
+        let Some(actual) = editor.line(line) else {
+            return false;
+        };
+        // Cosmic also recognizes bare CR and LFCR. Comparing the actual lines
+        // catches its greedy LFCR interpretation of e.g. "x\n\r\ny" too.
+        if old_ending != new_ending || actual.text != old || actual.ending != old_ending {
+            return false;
+        }
+        if old == new {
+            continue;
+        }
+        let mut start = old
+            .bytes()
+            .zip(new.bytes())
+            .take_while(|(a, b)| a == b)
+            .count();
+        while !old.is_char_boundary(start) || !new.is_char_boundary(start) {
+            start -= 1;
+        }
+        let mut suffix = old[start..]
+            .bytes()
+            .rev()
+            .zip(new[start..].bytes().rev())
+            .take_while(|(a, b)| a == b)
+            .count();
+        while !old.is_char_boundary(old.len() - suffix) || !new.is_char_boundary(new.len() - suffix)
+        {
+            suffix -= 1;
+        }
+        // All positions and owned payloads are prepared before the first edit.
+        patches.push((
+            line,
+            start,
+            old.len() - suffix,
+            Arc::new(new[start..new.len() - suffix].to_owned()),
+        ));
+    }
+    if patches.is_empty() {
+        return true;
+    }
+    let empty = Arc::new(String::new());
+    for (line, start, end, replacement) in patches.into_iter().rev() {
+        select(editor, line, start, end);
+        editor.perform(text_editor::Action::Edit(text_editor::Edit::Paste(
+            replacement,
+        )));
+    }
+    // Iced overwrites its earliest-change marker on each Edit. An explicit
+    // zero-width selection + empty Paste changes no bytes, but marks line zero.
+    // This also refreshes previously unhighlighted lines before the first patch.
+    // It resets only line zero's text cache; other unchanged lines retain theirs.
+    select(editor, 0, 0, 0);
+    editor.perform(text_editor::Action::Edit(text_editor::Edit::Paste(empty)));
+    editor.text() == after
+}
+
+fn select<R: Renderer>(
+    editor: &mut text_editor::Content<R>,
+    line: usize,
+    start: usize,
+    end: usize,
+) {
+    editor.move_to(text_editor::Cursor {
+        position: text_editor::Position {
+            line,
+            column: start,
+        },
+        // move_to(None) does not clear a previous selection in this Iced version.
+        selection: Some(text_editor::Position { line, column: end }),
+    });
+}
+
+fn lines(source: &str) -> Option<Vec<(&str, text_editor::LineEnding)>> {
+    use text_editor::LineEnding;
+    let mut result = Vec::new();
+    let mut parts = source.split('\n').peekable();
+    while let Some(part) = parts.next() {
+        let (text, ending) = if parts.peek().is_none() {
+            (part, LineEnding::None)
+        } else if let Some(text) = part.strip_suffix('\r') {
+            (text, LineEnding::CrLf)
+        } else {
+            (part, LineEnding::Lf)
+        };
+        if text.contains('\r')
+            || (text.is_empty()
+                && ending == LineEnding::CrLf
+                && result
+                    .last()
+                    .is_some_and(|(_, previous)| *previous == LineEnding::Lf))
+        {
+            return None;
+        }
+        result.push((text, ending));
+    }
+    Some(result)
+}
+
+#[cfg(all(test, debug_assertions))]
+mod tests {
+    use super::*;
+    use crate::views::source_tests::FontLayout;
+    use iced::advanced::{layout, text::Highlighter, widget::Tree};
+    use iced::{Element, Font, Length, Size};
+    use std::{cell::RefCell, ops::Range};
+
+    #[test]
+    fn exact_text_matrix_and_reverse_preserve_endings() {
+        for (before, after) in [
+            ("", ""),
+            ("", "alias"),
+            ("alias", ""),
+            ("same", "same"),
+            ("a\n", "alias\n"),
+            ("a\r\n", "alias\r\n"),
+            ("\r\na\r\n\r\n", "\r\nlong_alias\r\n\r\n"),
+            ("\na\n\n", "\nlong_alias\n\n"),
+            ("a\r\nb\nc", "long_a\r\nlong_b\nlong_c"),
+            (
+                "雨🙂 e\u{301} @a @a // a",
+                "雨🙂 e\u{301} @a_long @a_long // a",
+            ),
+            ("@abc", "@abcdef"),
+            ("@abcdef", "@abc"),
+            ("@abc_suffix", "@def_suffix"),
+            ("@none", "@identifier"),
+            // Shared prefix/suffix bytes inside distinct UTF-8 codepoints must
+            // not be used as String split positions, even outside alias scope.
+            ("雨xé", "雪xê"),
+            ("é", "©"),
+            (
+                "unchanged\n@a\nunchanged\n@a\n",
+                "unchanged\n@long\nunchanged\n@long\n",
+            ),
+        ] {
+            let mut editor = text_editor::Content::<FontLayout>::with_text(before);
+            assert!(
+                replace(&mut editor, before, after),
+                "{before:?} -> {after:?}"
+            );
+            assert_eq!(editor.text(), after);
+            let expected = text_editor::Content::<FontLayout>::with_text(after);
+            assert_eq!(editor.line_count(), expected.line_count());
+            for (actual, expected) in editor.lines().zip(expected.lines()) {
+                assert_eq!(actual.text, expected.text);
+                assert_eq!(actual.ending, expected.ending);
+            }
+            if before != after {
+                assert_eq!(
+                    editor.cursor().position,
+                    text_editor::Position { line: 0, column: 0 }
+                );
+                assert_eq!(editor.cursor().selection, None);
+            }
+            assert!(replace(&mut editor, after, before));
+            assert_eq!(editor.text(), before);
+        }
+    }
+
+    #[test]
+    fn all_preflight_refusals_leave_text_cursor_and_selection_unchanged() {
+        for (actual, before, after) in [
+            ("live", "stale", "changed"),
+            ("a\nb", "a\nb", "long\nb\nc"),
+            ("a\nb", "a\nb", "long\r\nb"),
+            // Refusal on a later line must not apply the earlier planned edit.
+            ("a\nb\r\n", "a\nb\r\n", "long\nb\n"),
+            ("a\rb", "a\rb", "long\rb"),
+            ("a\n\rb", "a\n\rb", "long\n\rb"),
+            ("a\n\r\nb", "a\n\r\nb", "long\n\r\nb"),
+            // The replacement must not introduce a greedy LFCR boundary either.
+            ("a\nx\r\n", "a\nx\r\n", "a\n\r\n"),
+            ("a", "a", "long\r"),
+        ] {
+            let mut editor = text_editor::Content::<FontLayout>::with_text(actual);
+            select(&mut editor, 0, 0, 1);
+            let cursor = editor.cursor();
+            let selection = editor.selection();
+            assert!(
+                !replace(&mut editor, before, after),
+                "{before:?} -> {after:?}"
+            );
+            assert_eq!(editor.text(), actual);
+            assert_eq!(editor.cursor(), cursor);
+            assert_eq!(editor.selection(), selection);
+        }
+    }
+
+    #[test]
+    fn unchanged_content_preserves_selection_and_next_direct_edit_works() {
+        let mut editor = text_editor::Content::<FontLayout>::with_text("@a");
+        select(&mut editor, 0, 1, 2);
+        let cursor = editor.cursor();
+        assert!(replace(&mut editor, "@a", "@a"));
+        assert_eq!(editor.cursor(), cursor);
+        assert!(replace(&mut editor, "@a", "@long"));
+        editor.move_to(text_editor::Cursor {
+            position: text_editor::Position { line: 0, column: 5 },
+            selection: None,
+        });
+        editor.perform(text_editor::Action::Edit(text_editor::Edit::Insert('!')));
+        assert_eq!(editor.text(), "@long!");
+    }
+
+    thread_local! {
+        static CHANGES: RefCell<Vec<usize>> = const { RefCell::new(Vec::new()) };
+    }
+
+    struct Tracked(crate::highlight::ArcadiaHighlighter);
+    impl Highlighter for Tracked {
+        type Settings = Arc<str>;
+        type Highlight = oa_core::language::TokenClass;
+        type Iterator<'a> = std::vec::IntoIter<(Range<usize>, Self::Highlight)>;
+        fn new(settings: &Self::Settings) -> Self {
+            Self(crate::highlight::ArcadiaHighlighter::new(settings))
+        }
+        fn update(&mut self, settings: &Self::Settings) {
+            self.0.update(settings);
+        }
+        fn change_line(&mut self, line: usize) {
+            CHANGES.with(|changes| changes.borrow_mut().push(line));
+            self.0.change_line(line);
+        }
+        fn highlight_line(&mut self, line: &str) -> Self::Iterator<'_> {
+            self.0.highlight_line(line)
+        }
+        fn current_line(&self) -> usize {
+            self.0.current_line()
+        }
+    }
+
+    fn view(
+        editor: &text_editor::Content<FontLayout>,
+        source: Arc<str>,
+    ) -> Element<'_, (), iced::Theme, FontLayout> {
+        text_editor(editor)
+            .font(Font::MONOSPACE)
+            .size(14)
+            .height(Length::Fill)
+            .highlight_with::<Tracked>(source, crate::highlight::format)
+            .into()
+    }
+
+    #[test]
+    fn already_laid_out_editor_notifies_highlighter_from_zero_after_later_line_patch() {
+        let before = "// earlier\n// unmodified\n@a";
+        let after = "// earlier\n// unmodified\n@none";
+        let mut editor = text_editor::Content::<FontLayout>::with_text(before);
+        let limits = layout::Limits::new(Size::ZERO, Size::new(400., 60.));
+        let mut tree = {
+            let mut widget = view(&editor, Arc::from(before));
+            let mut tree = Tree::new(widget.as_widget());
+            let _ = widget
+                .as_widget_mut()
+                .layout(&mut tree, &FontLayout, &limits);
+            tree
+        };
+        CHANGES.with(|changes| changes.borrow_mut().clear());
+        assert!(replace(&mut editor, before, after));
+        {
+            let mut widget = view(&editor, Arc::from(after));
+            let _ = widget
+                .as_widget_mut()
+                .layout(&mut tree, &FontLayout, &limits);
+        }
+        // Font/metrics/bounds are already stable. This notification must come
+        // from the helper's empty edit, not a fresh renderer initialization.
+        CHANGES.with(|changes| assert_eq!(*changes.borrow(), [0]));
+        assert_eq!(editor.text(), after);
+    }
+}

crates/oa-desktop/src/app/source_rename/navigation_union_tests.rs

@@ -0,0 +1,448 @@
+//! Combined App-boundary oracles: the workers are completed independently and
+//! no returned Task is polled. Rendering measurements use the real reveal path.
+use super::*;
+use crate::diagram_usage::{self as usage, Surface, Target as UsageTarget, Usage};
+use iced::{Size, Vector};
+
+fn model_id(number: u8) -> Id {
+    Id::parse_str(&format!("00000000-0000-0000-0000-{number:012}")).unwrap()
+}
+
+fn navigation_fixture() -> App {
+    let mut source = bundle();
+    let entry = source.files.get_mut("project.arcadia").unwrap();
+    *entry = entry.replace(
+        "include \"uses.arcadia\";",
+        "include \"uses.arcadia\"; include \"views.arcadia\";",
+    );
+    source.files.insert(
+        "views.arcadia".into(),
+        concat!(
+            "// Keep @pump and the exact distant placement.\r\n",
+            "diagram overview \"Pump overview\" id \"00000000-0000-0000-0000-000000000008\" { layer Oa; }\r\n",
+            "node placed_pump id \"00000000-0000-0000-0000-000000000009\" { diagram @overview; element @pump; position { x 12000; y 9000; }; size { width 260; height 94; }; }\r\n",
+        ).into(),
+    );
+    let mut app = fixture();
+    app.document = Document::from_bundle(source.clone(), LIMITS).unwrap();
+    assert_eq!(app.document.bundle(), &source);
+    assert!(
+        !validate(app.project())
+            .iter()
+            .any(|issue| issue.severity == validation::Severity::Error)
+    );
+    app.source_workspace = Workspace::new(app.document.bundle(), true);
+    app.selected = app.project().id;
+    app.refresh_draft();
+    app.source_workspace.active = "uses.arcadia".into();
+    app.show_source_file(false);
+    seek_pump(&mut app);
+    app.canvas_size = Some(Size::new(1200., 700.));
+    app.zoom = 0.8;
+    app.pan = Vector::new(31., 47.);
+    app
+}
+
+fn seek_pump(app: &mut App) {
+    let source = app.source_workspace.text();
+    let offset = source.rfind("pump;").unwrap();
+    app.source_editor
+        .move_to(cursor(source, offset, offset + 4));
+}
+
+fn source_completion(app: &App, request: nav::Request) -> nav::Completion {
+    let snapshot = Arc::new(
+        app.with_source_input(|input| query::capture(input, query::Limits::default()).unwrap()),
+    );
+    let results = snapshot
+        .query(query::Query {
+            stamp: request.stamp,
+            path: &request.path,
+            byte_offset: request.offset,
+            action: request.action,
+        })
+        .unwrap();
+    nav::Completion {
+        request,
+        result: Ok((snapshot, Arc::new(results))),
+    }
+}
+
+fn diagram_completion(app: &App) -> usage::Completion {
+    let panel = app.diagram_usages.as_ref().unwrap();
+    let process = app.behavior.topology.usage_snapshot().into_query_state();
+    usage::Completion {
+        token: panel.token,
+        context: panel.context,
+        result: Ok(usage::collect(
+            app.project(),
+            panel.context.subject,
+            &process,
+            &behavior::scenario::State::default(),
+        )),
+    }
+}
+
+fn finish_lookup(app: &mut App) -> (Id, Usage) {
+    let completion = diagram_completion(app);
+    send(app, Message::DiagramUsagesReady(completion));
+    let panel = app.diagram_usages.as_ref().unwrap();
+    assert!(!panel.loading);
+    assert!(app.diagram_lookup_in_flight.is_none());
+    let found = panel
+        .usages
+        .iter()
+        .find(|u| {
+            u.surface == Surface::Saved(model_id(8))
+                && u.target == UsageTarget::Placement(model_id(9))
+        })
+        .expect("the exact placed pump is represented")
+        .clone();
+    assert_eq!(found.subject, model_id(2));
+    assert_eq!((found.bounds.x, found.bounds.y), (12000., 9000.));
+    (panel.token, found)
+}
+
+fn navigate(app: &mut App) -> Usage {
+    let message = app.diagram_usage_message(model_id(2));
+    send(app, message);
+    let (token, found) = finish_lookup(app);
+    send(
+        app,
+        Message::DiagramUsage(usage::Event::Choose(token, found.clone())),
+    );
+    assert_eq!(app.page, Page::Diagram);
+    assert_eq!(app.active_diagram, Some(model_id(8)));
+    assert_eq!(app.selected, model_id(2));
+    assert_eq!(app.selected_node, Some(model_id(9)));
+    assert!(app.diagram_usages.is_none());
+    assert!(app.pending_diagram_reveal.is_some());
+    assert!(app.diagram_focus(found.surface).is_some());
+    found
+}
+
+#[derive(Debug, PartialEq)]
+struct Navigation {
+    page: Page,
+    selected: Id,
+    placement: Option<Id>,
+    diagram: Option<Id>,
+    zoom: f32,
+    pan: Vector,
+    pending: Option<(usage::Context, Usage, u64)>,
+    focus: Option<(usage::Context, Usage, Id)>,
+    canvas_epoch: u64,
+    camera_epoch: u64,
+    source_interaction: Id,
+    source_reveal: Option<Id>,
+}
+
+fn navigation(app: &App) -> Navigation {
+    Navigation {
+        page: app.page,
+        selected: app.selected,
+        placement: app.selected_node,
+        diagram: app.active_diagram,
+        zoom: app.zoom,
+        pan: app.pan,
+        pending: app.pending_diagram_reveal.clone(),
+        focus: app
+            .diagram_navigation_focus
+            .as_ref()
+            .map(|f| (f.context, f.usage.clone(), f.selected)),
+        canvas_epoch: app.canvas_epoch,
+        camera_epoch: app.camera_epoch,
+        source_interaction: app.source_symbols.interaction,
+        source_reveal: app.source_reveal_ticket(),
+    }
+}
+
+fn first_measurement(app: &mut App, found: &Usage) {
+    let (context, _, epoch) = app.pending_diagram_reveal.as_ref().unwrap();
+    let (context, epoch) = (*context, *epoch);
+    let actual = Size::new(500., 300.);
+    send(app, Message::DiagramRevealViewport(context, epoch, actual));
+    assert!(app.pending_diagram_reveal.is_none());
+    assert_eq!(app.canvas_size, Some(actual));
+    assert!((found.bounds.center_x() * app.zoom + app.pan.x - 250.).abs() < 0.05);
+    assert!((found.bounds.center_y() * app.zoom + app.pan.y - 150.).abs() < 0.05);
+    assert_eq!(app.selected, model_id(2));
+    assert_eq!(app.selected_node, Some(model_id(9)));
+    assert!(app.diagram_focus(found.surface).is_some());
+}
+
+#[test]
+fn rename_modal_rejects_queued_diagram_and_source_navigation_without_losing_approval() {
+    let mut app = navigation_fixture();
+    let original = evidence(&app);
+    let snapshot = app.document.snapshot();
+    let queued = app.diagram_usage_message(model_id(2));
+    begin(&mut app);
+    input(&mut app, "send_water");
+    let confirm = preview(&mut app);
+    let form = app.source_rename.form.as_ref().unwrap();
+    let approved = (
+        form.invocation,
+        form.generation,
+        form.approval.as_ref().unwrap().id,
+    );
+    send(&mut app, queued);
+    let source = app.source_symbol_message(nav::SymbolEvent::DiagramUsages);
+    send(&mut app, source);
+    let definition = app.source_symbol_message(nav::SymbolEvent::Query(query::Action::Definition));
+    send(&mut app, definition);
+    assert!(app.diagram_usages.is_none());
+    assert!(app.diagram_lookup_in_flight.is_none());
+    assert!(app.source_symbols.in_flight.is_none());
+    assert!(!app.source_navigation_available());
+    let form = app.source_rename.form.as_ref().unwrap();
+    assert_eq!(
+        (
+            form.invocation,
+            form.generation,
+            form.approval.as_ref().unwrap().id
+        ),
+        approved
+    );
+    assert_eq!(form.replacement, "send_water");
+    assert_eq!(evidence(&app), original);
+    assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+    send(&mut app, Message::Escape);
+    send(&mut app, confirm);
+    assert!(!app.source_rename.open());
+    assert_eq!(evidence(&app), original);
+}
+
+#[test]
+fn loading_and_ready_diagram_choosers_reject_a_previously_captured_rename_begin() {
+    for finish in [false, true] {
+        let mut app = navigation_fixture();
+        let before = evidence(&app);
+        let queued_rename = app.source_rename_message();
+        let open = app.diagram_usage_message(model_id(2));
+        send(&mut app, open);
+        if finish {
+            finish_lookup(&mut app);
+        }
+        let panel = app.diagram_usages.as_ref().unwrap();
+        let token = panel.token;
+        let loading = panel.loading;
+        assert!(app.rename_admission().is_err());
+        assert!(!app.source_navigation_available());
+        send(&mut app, queued_rename);
+        assert!(!app.source_rename.open());
+        assert!(app.source_rename.in_flight.is_none());
+        let panel = app.diagram_usages.as_ref().unwrap();
+        assert_eq!((panel.token, panel.loading), (token, loading));
+        assert_eq!(evidence(&app), before);
+        send(&mut app, Message::DiagramUsage(usage::Event::Close(token)));
+        let rename = app.source_rename_message();
+        send(&mut app, rename);
+        assert!(
+            app.source_rename.open(),
+            "the dismissed chooser no longer owns input"
+        );
+    }
+}
+
+#[test]
+fn late_target_and_preview_results_release_only_their_slot_and_preserve_first_camera_measurement() {
+    for preview_pending in [false, true] {
+        let mut app = navigation_fixture();
+        let before = evidence(&app);
+        let completion = if preview_pending {
+            begin(&mut app);
+            input(&mut app, "send_water");
+            let job = start_preview(&mut app);
+            preview_completion(&app, job)
+        } else {
+            let rename = app.source_rename_message();
+            send(&mut app, rename);
+            target_completion(&app, current_job(&app))
+        };
+        let occupied = completion.job.id;
+        event(&mut app, Event::Close(completion.job.invocation));
+        assert_eq!(app.source_rename.in_flight, Some(occupied));
+        let found = navigate(&mut app);
+        let location = navigation(&app);
+        assert_eq!(evidence(&app), before);
+        let mut forged = completion.clone();
+        forged.job.id = Id::new_v4();
+        send(&mut app, Message::SourceRenameReady(forged));
+        assert_eq!(app.source_rename.in_flight, Some(occupied));
+        assert_eq!(navigation(&app), location);
+        send(&mut app, Message::SourceRenameReady(completion.clone()));
+        assert!(app.source_rename.in_flight.is_none());
+        assert!(!app.source_rename.open());
+        assert_eq!(navigation(&app), location);
+        assert_eq!(evidence(&app), before);
+        send(&mut app, Message::SourceRenameReady(completion));
+        assert_eq!(
+            navigation(&app),
+            location,
+            "duplicate completion is passive too"
+        );
+        first_measurement(&mut app, &found);
+        assert_eq!(evidence(&app), before);
+    }
+}
+
+#[test]
+fn stale_begin_close_and_actual_confirm_leave_new_diagram_focus_and_pending_measurement_unchanged()
+{
+    let mut app = navigation_fixture();
+    let before = evidence(&app);
+    let snapshot = app.document.snapshot();
+    let queued_begin = app.source_rename_message();
+    begin(&mut app);
+    input(&mut app, "send_water");
+    let confirm = preview(&mut app);
+    let invocation = app.source_rename.form.as_ref().unwrap().invocation;
+    event(&mut app, Event::Close(invocation));
+    let found = navigate(&mut app);
+    let location = navigation(&app);
+    for stale in [
+        queued_begin,
+        Message::SourceRename(Event::Close(invocation)),
+        confirm,
+    ] {
+        send(&mut app, stale);
+        assert_eq!(navigation(&app), location);
+        assert_eq!(evidence(&app), before);
+        assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+    }
+    first_measurement(&mut app, &found);
+}
+
+#[test]
+fn document_reset_retains_all_three_worker_slots_until_their_exact_results_arrive() {
+    let mut app = navigation_fixture();
+    let source = app.source_symbol_message(nav::SymbolEvent::Query(query::Action::Definition));
+    send(&mut app, source);
+    let request = app.source_symbols.request.clone().unwrap();
+    let source_ready = source_completion(&app, request.clone());
+    let rename = app.source_rename_message();
+    send(&mut app, rename);
+    let rename_ready = target_completion(&app, current_job(&app));
+    let rename_job = rename_ready.job.id;
+    event(&mut app, Event::Close(rename_ready.job.invocation));
+    let open = app.diagram_usage_message(model_id(2));
+    send(&mut app, open);
+    let old_diagram = diagram_completion(&app);
+    let diagram_job = old_diagram.token;
+    let old_document = app.canvas_document;
+    let project = app.project().clone();
+    app.reset(project, None);
+    assert_ne!(app.canvas_document, old_document);
+    assert_eq!(app.source_symbols.in_flight, Some(request.job));
+    assert_eq!(app.source_rename.in_flight, Some(rename_job));
+    assert_eq!(app.diagram_lookup_in_flight, Some(diagram_job));
+    assert!(!app.source_rename.open());
+    assert!(app.diagram_usages.is_none());
+    let before = evidence(&app);
+    let snapshot = app.document.snapshot();
+    let new_open = app.diagram_usage_message(model_id(2));
+    send(&mut app, new_open);
+    let new_token = app.diagram_usages.as_ref().unwrap().token;
+    assert_ne!(new_token, diagram_job);
+    assert_eq!(
+        app.diagram_lookup_in_flight,
+        Some(diagram_job),
+        "replacement waits for old worker"
+    );
+    send(&mut app, Message::SourceRenameReady(rename_ready));
+    assert!(app.source_rename.in_flight.is_none());
+    assert_eq!(app.source_symbols.in_flight, Some(request.job));
+    assert_eq!(app.diagram_lookup_in_flight, Some(diagram_job));
+    send(&mut app, Message::SourceSymbolsReady(source_ready));
+    assert!(app.source_symbols.in_flight.is_none());
+    assert!(!app.source_symbols.open);
+    send(&mut app, Message::DiagramUsagesReady(old_diagram));
+    assert_eq!(app.diagram_lookup_in_flight, Some(new_token));
+    assert!(app.diagram_usages.as_ref().unwrap().loading);
+    finish_lookup(&mut app);
+    assert_eq!(evidence(&app), before);
+    assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+    assert!(!app.source_rename.open());
+}
+
+#[test]
+fn rename_then_exact_caret_diagram_navigation_preserves_complete_model_undo_redo_history() {
+    let mut app = navigation_fixture();
+    let baseline = app.document.snapshot();
+    let project = app.project().id;
+    app.document
+        .execute(Command::Rename(project, "Previously accepted name".into()))
+        .unwrap();
+    app.sync_source();
+    app.refresh_draft();
+    seek_pump(&mut app);
+    let before = app.document.snapshot();
+    let mut expected_project = app.project().clone();
+    expected_project
+        .elements
+        .get_mut(&model_id(2))
+        .unwrap()
+        .alias = "send_water".into();
+    let mut expected_source = app.document.bundle().clone();
+    let defs = expected_source.files.get_mut("defs.arcadia").unwrap();
+    *defs = defs.replace("oa_activity pump ", "oa_activity send_water ");
+    let uses = expected_source.files.get_mut("uses.arcadia").unwrap();
+    *uses = uses
+        .replace("source @pump;", "source @send_water;")
+        .replace("// keep @pump\r\n pump;", "// keep @pump\r\n send_water;");
+    let views = expected_source.files.get_mut("views.arcadia").unwrap();
+    *views = views.replace("element @pump;", "element @send_water;");
+    begin(&mut app);
+    input(&mut app, "send_water");
+    let confirm = preview(&mut app);
+    send(&mut app, confirm);
+    assert_eq!(app.project(), &expected_project);
+    assert_eq!(app.document.bundle(), &expected_source);
+    let renamed = app.document.snapshot();
+    let accepted = evidence(&app);
+    let queued_undo_rename = app
+        .source_rename_undo_message()
+        .expect("fresh rename offers its guarded undo");
+    let message = app.source_symbol_message(nav::SymbolEvent::DiagramUsages);
+    send(&mut app, message);
+    let request = app
+        .source_symbols
+        .request
+        .clone()
+        .expect("renamed exact caret remains queryable");
+    let ready = source_completion(&app, request);
+    send(&mut app, Message::SourceSymbolsReady(ready));
+    let (token, found) = finish_lookup(&mut app);
+    send(
+        &mut app,
+        Message::DiagramUsage(usage::Event::Choose(token, found.clone())),
+    );
+    assert_eq!(app.selected, model_id(2));
+    assert_eq!(app.selected_node, Some(model_id(9)));
+    let destination = navigation(&app);
+    send(&mut app, queued_undo_rename);
+    assert_eq!(navigation(&app), destination);
+    assert_eq!(evidence(&app), accepted);
+    first_measurement(&mut app, &found);
+    assert_eq!(evidence(&app), accepted);
+    assert!(Arc::ptr_eq(&renamed, &app.document.snapshot()));
+    for (message, expected) in [
+        (Message::Undo, before.clone()),
+        (Message::Redo, renamed.clone()),
+        (Message::Undo, before.clone()),
+        (Message::Undo, baseline.clone()),
+        (Message::Redo, before),
+        (Message::Redo, renamed),
+    ] {
+        send(&mut app, message);
+        assert!(
+            Arc::ptr_eq(&expected, &app.document.snapshot()),
+            "exact history entry restored"
+        );
+        assert_eq!(app.project(), &expected.decoded.project);
+        assert_eq!(app.document.bundle(), &expected.bundle);
+        assert_eq!(app.source_workspace.bundle(), expected.bundle);
+        assert!(!app.source_dirty());
+    }
+}

crates/oa-desktop/src/app/source_rename/preview_glyph_tests.rs

@@ -0,0 +1,449 @@
+//! Real paragraph advances and clipping through the actual preview dialog.
+//! Native screenshots additionally check raster ink and the platform renderer.
+use super::*;
+use crate::views::source_tests::FontLayout;
+use iced::advanced::{Layout, layout, renderer, text as shaped, widget};
+use iced::{Background, Color, Font, Pixels, Point, Rectangle, Size, Transformation, Vector};
+use std::collections::{BTreeMap, BTreeSet};
+
+struct Glyph {
+    text: String,
+    paragraph_y: u32,
+    line: usize,
+    bytes: std::ops::Range<usize>,
+    bounds: Rectangle,
+    clip: Rectangle,
+}
+
+struct GlyphRecorder {
+    wanted: BTreeSet<String>,
+    transforms: Vec<Transformation>,
+    clips: Vec<Rectangle>,
+    glyphs: Vec<Glyph>,
+    quads: Vec<Rectangle>,
+}
+impl GlyphRecorder {
+    fn new(wanted: BTreeSet<String>, viewport: Rectangle) -> Self {
+        Self {
+            wanted,
+            transforms: vec![Transformation::IDENTITY],
+            clips: vec![viewport],
+            glyphs: vec![],
+            quads: vec![],
+        }
+    }
+    fn transform(&self) -> Transformation {
+        *self.transforms.last().unwrap()
+    }
+    fn clip(&self, bounds: Rectangle) -> Rectangle {
+        self.clips
+            .last()
+            .unwrap()
+            .intersection(&(bounds * self.transform()))
+            .unwrap_or(Rectangle::with_size(Size::ZERO))
+    }
+}
+impl renderer::Renderer for GlyphRecorder {
+    fn start_layer(&mut self, bounds: Rectangle) {
+        self.clips.push(self.clip(bounds));
+    }
+    fn end_layer(&mut self) {
+        self.clips.pop().unwrap();
+    }
+    fn start_transformation(&mut self, transform: Transformation) {
+        self.transforms.push(self.transform() * transform);
+    }
+    fn end_transformation(&mut self) {
+        self.transforms.pop().unwrap();
+    }
+    fn reset(&mut self, bounds: Rectangle) {
+        self.transforms = vec![Transformation::IDENTITY];
+        self.clips = vec![bounds];
+        self.glyphs.clear();
+        self.quads.clear();
+    }
+    fn fill_quad(&mut self, quad: renderer::Quad, _: impl Into<Background>) {
+        self.quads.push(quad.bounds * self.transform());
+    }
+    fn allocate_image(
+        &mut self,
+        handle: &iced::advanced::image::Handle,
+        callback: impl FnOnce(Result<iced::advanced::image::Allocation, iced::advanced::image::Error>)
+        + Send
+        + 'static,
+    ) {
+        renderer::Renderer::allocate_image(&mut FontLayout, handle, callback);
+    }
+}
+impl shaped::Renderer for GlyphRecorder {
+    type Font = Font;
+    type Paragraph = <FontLayout as shaped::Renderer>::Paragraph;
+    type Editor = <FontLayout as shaped::Renderer>::Editor;
+    const ICON_FONT: Font = <FontLayout as shaped::Renderer>::ICON_FONT;
+    const CHECKMARK_ICON: char = <FontLayout as shaped::Renderer>::CHECKMARK_ICON;
+    const ARROW_DOWN_ICON: char = <FontLayout as shaped::Renderer>::ARROW_DOWN_ICON;
+    const SCROLL_UP_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_UP_ICON;
+    const SCROLL_DOWN_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_DOWN_ICON;
+    const SCROLL_LEFT_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_LEFT_ICON;
+    const SCROLL_RIGHT_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_RIGHT_ICON;
+    const ICED_LOGO: char = <FontLayout as shaped::Renderer>::ICED_LOGO;
+    fn default_font(&self) -> Font {
+        shaped::Renderer::default_font(&FontLayout)
+    }
+    fn default_size(&self) -> Pixels {
+        shaped::Renderer::default_size(&FontLayout)
+    }
+    fn fill_paragraph(
+        &mut self,
+        paragraph: &Self::Paragraph,
+        position: Point,
+        _: Color,
+        clip: Rectangle,
+    ) {
+        let buffer = paragraph.buffer();
+        let text = buffer
+            .lines
+            .iter()
+            .map(|line| line.text())
+            .collect::<Vec<_>>()
+            .join("\n");
+        if !self.wanted.contains(&text) {
+            return;
+        }
+        let clip = self.clip(clip);
+        for run in buffer.layout_runs() {
+            for glyph in run.glyphs {
+                if run.text[glyph.start..glyph.end]
+                    .chars()
+                    .all(char::is_whitespace)
+                {
+                    continue;
+                }
+                let bounds = Rectangle {
+                    x: position.x + glyph.x + glyph.x_offset * glyph.font_size,
+                    y: position.y + run.line_top,
+                    width: glyph.w,
+                    height: run.line_height,
+                } * self.transform();
+                self.glyphs.push(Glyph {
+                    text: text.clone(),
+                    paragraph_y: position.y.to_bits(),
+                    line: run.line_i,
+                    bytes: glyph.start..glyph.end,
+                    bounds,
+                    clip,
+                });
+            }
+        }
+    }
+    fn fill_editor(
+        &mut self,
+        editor: &Self::Editor,
+        position: Point,
+        color: Color,
+        clip: Rectangle,
+    ) {
+        shaped::Renderer::fill_editor(&mut FontLayout, editor, position, color, clip);
+    }
+    fn fill_text(&mut self, text: shaped::Text, position: Point, color: Color, clip: Rectangle) {
+        shaped::Renderer::fill_text(&mut FontLayout, text, position, color, clip);
+    }
+}
+
+#[derive(Default)]
+struct ScrollGeometry {
+    id: Option<widget::Id>,
+    bounds: Option<Rectangle>,
+    content: Option<Rectangle>,
+    offset: Vector,
+}
+impl widget::Operation for ScrollGeometry {
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn widget::Operation)) {
+        visit(self);
+    }
+    fn scrollable(
+        &mut self,
+        id: Option<&widget::Id>,
+        bounds: Rectangle,
+        content: Rectangle,
+        offset: Vector,
+        _: &mut dyn widget::operation::Scrollable,
+    ) {
+        if id == self.id.as_ref() {
+            self.bounds = Some(bounds);
+            self.content = Some(content);
+            self.offset = offset;
+        }
+    }
+}
+fn normalized(text: &str) -> String {
+    text.replace("\r\n", "\n").replace('\r', "\n")
+}
+fn required_chars(text: &str) -> BTreeSet<(usize, usize)> {
+    text.split('\n')
+        .enumerate()
+        .flat_map(|(line, text)| {
+            text.char_indices()
+                .filter(|(_, ch)| !ch.is_whitespace())
+                .map(move |(byte, _)| (line, byte))
+        })
+        .collect()
+}
+
+fn declarations(long: bool) -> App {
+    let name = if long {
+        format!("Assess {} request", "界🚀".repeat(90))
+    } else {
+        "Assess 救援 request".into()
+    };
+    let source = SourceBundle { entry: "project.arcadia".into(), files: BTreeMap::from([
+        ("project.arcadia".into(), "arcadia 7;\r\nproject navigation_trial \"Navigation — 救援\" id \"9e8f0000-0000-4000-8000-000000000001\" {\r\n include \"救援/assess.arcadia\";\r\n}\r\n".into()),
+        ("救援/assess.arcadia".into(), format!("// Comment @assess must not be a lexical use.\r\noa_activity assess \"{name}\" id \"9e8f0000-0000-4000-8000-000000000002\" {{\r\n    description \"Keep @assess as prose, not a use.\";\r\n}}\r\n")),
+    ]) };
+    let mut app = fixture();
+    app.document = Document::from_bundle(source, LIMITS).unwrap();
+    app.source_workspace = Workspace::new(app.document.bundle(), true);
+    app.source_workspace.active = "救援/assess.arcadia".into();
+    app.selected = app.project().id;
+    app.refresh_draft();
+    app.show_source_file(false);
+    let start = app
+        .source_workspace
+        .text()
+        .find("oa_activity assess")
+        .unwrap()
+        + "oa_activity ".len();
+    app.source_editor.move_to(cursor(
+        app.source_workspace.text(),
+        start,
+        start + "assess".len(),
+    ));
+    begin(&mut app);
+    let replacement = if long {
+        "a".repeat(255)
+    } else {
+        "assess_damage".into()
+    };
+    input(&mut app, &replacement);
+    let _ = preview(&mut app);
+    app
+}
+
+fn assert_page_glyphs_visible(app: &App, host: Size) {
+    let form = app.source_rename.form.as_ref().unwrap();
+    let ready = form.approval.as_ref().unwrap();
+    let file = &ready.preview.files()[form.file];
+    let mut expected = BTreeMap::<String, usize>::new();
+    for line in file.hunks()[form.hunk]
+        .lines()
+        .iter()
+        .skip(form.line)
+        .take(LINES_PER_PAGE)
+    {
+        for source in [
+            line.before_text(&ready.prepared.before().bundle.files[file.path()])
+                .unwrap(),
+            line.after_text(&ready.prepared.after().bundle.files[file.path()])
+                .unwrap(),
+        ] {
+            if let Some(fragment) = preview::text_segment(source, form.segment) {
+                let text = normalized(fragment);
+                if !required_chars(&text).is_empty() {
+                    *expected.entry(text).or_default() += 1;
+                }
+            }
+        }
+    }
+    assert!(!expected.is_empty());
+    let viewport = Rectangle::new(Point::ORIGIN, host);
+    let mut renderer = GlyphRecorder::new(expected.keys().cloned().collect(), viewport);
+    let editor = text_editor::Content::<GlyphRecorder>::new();
+    let mut view = dialog_content(app, &editor);
+    let mut tree = widget::Tree::new(view.as_widget());
+    let node =
+        view.as_widget_mut()
+            .layout(&mut tree, &renderer, &layout::Limits::new(Size::ZERO, host));
+    let mut geometry = ScrollGeometry {
+        id: Some(preview_scroll_id(form, ready.id)),
+        ..ScrollGeometry::default()
+    };
+    view.as_widget_mut()
+        .operate(&mut tree, Layout::new(&node), &renderer, &mut geometry);
+    let bounds = geometry.bounds.unwrap();
+    let content = geometry.content.unwrap();
+    assert!(bounds.height >= 40.);
+    let maximum = (content.height - bounds.height).max(0.);
+    let steps = (maximum / (bounds.height * 0.5)).ceil() as usize;
+    let mut visible = BTreeMap::<(String, u32), BTreeSet<(usize, usize)>>::new();
+    let mut reserved_bar_gap = true;
+    for step in 0..=steps {
+        let offset = (step as f32 * bounds.height * 0.5).min(maximum);
+        view.as_widget_mut().operate(
+            &mut tree,
+            Layout::new(&node),
+            &renderer,
+            &mut widget::operation::scrollable::scroll_to(
+                preview_scroll_id(form, ready.id),
+                widget::operation::scrollable::AbsoluteOffset {
+                    x: None,
+                    y: Some(offset),
+                },
+            ),
+        );
+        view.as_widget_mut()
+            .operate(&mut tree, Layout::new(&node), &renderer, &mut geometry);
+        assert!(
+            (geometry.offset.y - offset).abs() <= 0.5,
+            "actual scroll operation reaches the requested source offset"
+        );
+        renderer::Renderer::reset(&mut renderer, viewport);
+        view.as_widget().draw(
+            &tree,
+            &mut renderer,
+            &iced::Theme::Light,
+            &renderer::Style::default(),
+            Layout::new(&node),
+            iced::mouse::Cursor::Unavailable,
+            &viewport,
+        );
+        // The vertical scrollbar's actual painted thumb fixes its excluded x
+        // region; the outer scroll clip alone cannot detect overpainting.
+        let scrollbar_left = renderer
+            .quads
+            .iter()
+            .filter(|quad| {
+                quad.width > 0.
+                    && quad.width <= 16.
+                    && quad.height > 0.
+                    && quad.x >= bounds.x + bounds.width - 18.
+                    && quad.x + quad.width <= bounds.x + bounds.width + 0.5
+                    && quad.y >= bounds.y - 0.5
+                    && quad.y + quad.height <= bounds.y + bounds.height + 0.5
+            })
+            .map(|quad| quad.x)
+            .min_by(f32::total_cmp);
+        if maximum > 0. {
+            let left = scrollbar_left.expect("overflowing actual preview must paint its scrollbar");
+            reserved_bar_gap &= content.x + content.width <= left - 7.5;
+        }
+        for glyph in &renderer.glyphs {
+            let right = glyph.bounds.x + glyph.bounds.width;
+            if let Some(left) = scrollbar_left {
+                assert!(
+                    right <= left - 0.5,
+                    "source glyph under scrollbar: text={:?} cluster={:?} glyph={:?} bar x={left}",
+                    glyph.text,
+                    glyph.bytes,
+                    glyph.bounds
+                );
+            }
+            assert!(
+                glyph.bounds.x >= content.x - 0.5 && right <= content.x + content.width + 0.5,
+                "source glyph escaped reserved width: {:?} {:?}",
+                glyph.text,
+                glyph.bounds
+            );
+            assert!(
+                glyph.bounds.x >= glyph.clip.x - 0.5
+                    && right <= glyph.clip.x + glyph.clip.width + 0.5,
+                "source glyph horizontally clipped: {:?} {:?} {:?}",
+                glyph.text,
+                glyph.bounds,
+                glyph.clip
+            );
+            if glyph.bounds.y >= glyph.clip.y - 0.5
+                && glyph.bounds.y + glyph.bounds.height <= glyph.clip.y + glyph.clip.height + 0.5
+            {
+                let logical_line = glyph.text.split('\n').nth(glyph.line).unwrap();
+                let chars = logical_line
+                    .char_indices()
+                    .filter(|(byte, ch)| glyph.bytes.contains(byte) && !ch.is_whitespace())
+                    .map(|(byte, _)| (glyph.line, byte));
+                visible
+                    .entry((glyph.text.clone(), glyph.paragraph_y))
+                    .or_default()
+                    .extend(chars);
+            }
+        }
+    }
+    assert!(
+        reserved_bar_gap,
+        "source content must reserve actual scrollbar width plus gap"
+    );
+    assert!(
+        bounds.width >= host.width - 30.,
+        "preview must use available dialog width: {bounds:?} / {host:?}"
+    );
+    for (text, count) in expected {
+        let required = required_chars(&text);
+        let instances: Vec<_> = visible
+            .iter()
+            .filter(|((value, _), _)| value == &text)
+            .collect();
+        assert_eq!(
+            instances.len(),
+            count,
+            "all before/after occurrences must be seen: {text:?}"
+        );
+        for (_, seen) in instances {
+            assert_eq!(
+                seen, &required,
+                "every non-whitespace source cluster must be fully visible at some vertical offset: {text:?}"
+            );
+        }
+    }
+}
+
+#[test]
+fn actual_preview_source_glyphs_clear_scrollbar_and_all_long_fragments_are_reachable() {
+    for long in [false, true] {
+        let mut app = declarations(long);
+        let ready = app
+            .source_rename
+            .form
+            .as_ref()
+            .unwrap()
+            .approval
+            .as_ref()
+            .unwrap()
+            .clone();
+        let invocation = app.source_rename.form.as_ref().unwrap().invocation;
+        let before = evidence(&app);
+        for (width, height) in [(1100., 700.), (580., 700.)] {
+            app.window_size = Size::new(width, height);
+            let host = Size::new((width - 84.).min(708.), height - 120.);
+            let total = segment_total(app.source_rename.form.as_ref().unwrap());
+            if long {
+                assert!(
+                    total >= 3,
+                    "include unbroken ASCII and wide Unicode across segments"
+                );
+            }
+            for segment in 0..total {
+                assert_page_glyphs_visible(&app, host);
+                if segment + 1 < total {
+                    event(&mut app, Event::Segment(invocation, ready.id, true));
+                }
+            }
+            for _ in 1..total {
+                event(&mut app, Event::Segment(invocation, ready.id, false));
+            }
+        }
+        assert_eq!(
+            evidence(&app),
+            before,
+            "preview geometry/paging cannot alter transaction inputs"
+        );
+        assert_eq!(
+            app.source_rename
+                .form
+                .as_ref()
+                .unwrap()
+                .approval
+                .as_ref()
+                .unwrap()
+                .id,
+            ready.id
+        );
+    }
+}

crates/oa-desktop/src/app/source_rename/preview_scroll_tests.rs

@@ -0,0 +1,385 @@
+//! Execute the controller's scroll operations on a retained, scrolled dialog.
+use super::*;
+use crate::views::source_tests::FontLayout;
+use iced::advanced::{Layout, layout, widget};
+use iced::futures::StreamExt;
+use iced::{Rectangle, Size, Vector};
+
+const HOST: Size = Size::new(720., 660.);
+
+fn paged_fixture() -> App {
+    let mut source = bundle();
+    let name = "Long engineering name 雨 ".repeat(18);
+    source.files.get_mut("defs.arcadia").unwrap().replace_range(
+        ..,
+        &format!(
+            "oa_activity pump \"{name}\" id \"00000000-0000-0000-0000-000000000002\" {{}}\r\n\
+            oa_activity backup \"Backup\" id \"00000000-0000-0000-0000-000000000004\" {{}}\r\n"
+        ),
+    );
+    let mut uses = String::new();
+    for index in 0..16 {
+        if index == 12 {
+            uses.push_str(&"// unchanged gap\r\n".repeat(10));
+        }
+        uses.push_str(&format!(
+            "interaction use_{index} \"{name}\" id \"00000000-0000-0000-0001-{index:012}\" {{ source @pump; target @backup; }}\r\n"
+        ));
+    }
+    source.files.insert("uses.arcadia".into(), uses);
+    let mut app = fixture();
+    app.window_size = HOST;
+    app.document = Document::from_bundle(source, LIMITS).unwrap();
+    app.source_workspace = Workspace::new(app.document.bundle(), true);
+    app.source_workspace.active = "uses.arcadia".into();
+    app.show_source_file(false);
+    let start = app.source_workspace.text().find("source @pump").unwrap() + "source @".len();
+    app.source_editor
+        .move_to(cursor(app.source_workspace.text(), start, start + 4));
+    begin(&mut app);
+    input(&mut app, "pump_long");
+    let _ = preview(&mut app);
+    app
+}
+
+fn scroll_id(app: &App) -> widget::Id {
+    let form = app.source_rename.form.as_ref().unwrap();
+    preview_scroll_id(form, form.approval.as_ref().unwrap().id)
+}
+
+struct Geometry {
+    id: widget::Id,
+    offset: Option<Vector>,
+}
+impl widget::Operation for Geometry {
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn widget::Operation)) {
+        visit(self);
+    }
+    fn scrollable(
+        &mut self,
+        id: Option<&widget::Id>,
+        _: Rectangle,
+        _: Rectangle,
+        offset: Vector,
+        _: &mut dyn widget::operation::Scrollable,
+    ) {
+        if id == Some(&self.id) {
+            self.offset = Some(offset);
+        }
+    }
+}
+
+struct Mounted {
+    editor: text_editor::Content<FontLayout>,
+    tree: widget::Tree,
+}
+impl Mounted {
+    fn new(app: &App) -> Self {
+        let editor = text_editor::Content::<FontLayout>::new();
+        let tree = widget::Tree::new(dialog_content(app, &editor).as_widget());
+        Self { editor, tree }
+    }
+    fn operate(&mut self, app: &App, operation: &mut dyn widget::Operation) {
+        let mut view = dialog_content(app, &self.editor);
+        // Preserve the actual scroll state across the new page's view diff.
+        self.tree.diff(view.as_widget());
+        let node = view.as_widget_mut().layout(
+            &mut self.tree,
+            &FontLayout,
+            &layout::Limits::new(Size::ZERO, HOST),
+        );
+        view.as_widget_mut()
+            .operate(&mut self.tree, Layout::new(&node), &FontLayout, operation);
+    }
+    fn offset(&mut self, app: &App) -> f32 {
+        let mut geometry = Geometry {
+            id: scroll_id(app),
+            offset: None,
+        };
+        self.operate(app, &mut geometry);
+        geometry.offset.expect("mounted preview scrollable").y
+    }
+    fn scroll_down(&mut self, app: &App) -> f32 {
+        self.operate(
+            app,
+            &mut widget::operation::scrollable::scroll_to(
+                scroll_id(app),
+                widget::operation::scrollable::AbsoluteOffset {
+                    x: None,
+                    y: Some(10_000.),
+                },
+            ),
+        );
+        let offset = self.offset(app);
+        assert!(offset > 10., "fixture must really be scrolled");
+        offset
+    }
+    async fn execute(&mut self, app: &App, task: Task<Message>) -> usize {
+        let mut count = 0;
+        if let Some(mut actions) = iced_runtime::task::into_stream(task) {
+            while let Some(action) = actions.next().await {
+                let iced_runtime::Action::Widget(mut operation) = action else {
+                    panic!("preview paging must only schedule a widget operation");
+                };
+                self.operate(app, operation.as_mut());
+                count += 1;
+            }
+        }
+        count
+    }
+}
+
+#[tokio::test]
+async fn explicit_navigation_resets_retained_scroll_but_id_change_alone_does_not() {
+    let mut app = paged_fixture();
+    let before = evidence(&app);
+    let form = app.source_rename.form.as_ref().unwrap();
+    let invocation = form.invocation;
+    let approval = form.approval.as_ref().unwrap().id;
+    let mut mounted = Mounted::new(&app);
+    mounted.scroll_down(&app);
+    let old_id = scroll_id(&app);
+    let task = app.update(Message::SourceRename(Event::File(
+        invocation, approval, true,
+    )));
+    assert_ne!(old_id, scroll_id(&app));
+    // Negative control: even after diff/layout with the new id and new file,
+    // Iced retains the previous offset until the returned operation executes.
+    assert!(mounted.offset(&app) > 10.);
+    assert_eq!(mounted.execute(&app, task).await, 1);
+    assert_eq!(mounted.offset(&app), 0.);
+
+    for navigation in [
+        Event::Line(invocation, approval, true),
+        Event::Segment(invocation, approval, true),
+        Event::Hunk(invocation, approval, true),
+        Event::File(invocation, approval, false),
+        Event::Search(invocation, "uses".into()),
+        Event::Search(invocation, "no-path-match".into()),
+        Event::Search(invocation, String::new()),
+    ] {
+        mounted.scroll_down(&app);
+        let task = app.update(Message::SourceRename(navigation));
+        assert_eq!(mounted.execute(&app, task).await, 1);
+        assert_eq!(mounted.offset(&app), 0.);
+        assert_eq!(evidence(&app), before);
+    }
+    // Passive redraw and unchanged filter input preserve deliberate scrolling.
+    let offset = mounted.scroll_down(&app);
+    assert_eq!(mounted.offset(&app), offset);
+    let task = app.update(Message::SourceRename(Event::Search(
+        invocation,
+        String::new(),
+    )));
+    assert_eq!(mounted.execute(&app, task).await, 0);
+    assert_eq!(mounted.offset(&app), offset);
+    let task = app.update(Message::SourceRename(Event::Input(
+        invocation,
+        "pump_long".into(),
+    )));
+    assert_eq!(mounted.execute(&app, task).await, 0);
+    assert_eq!(mounted.offset(&app), offset);
+    let task = app.update(Message::SourceRename(Event::File(
+        invocation, approval, false,
+    )));
+    assert_eq!(
+        mounted.execute(&app, task).await,
+        0,
+        "clamped first-page request is a no-op"
+    );
+    assert_eq!(mounted.offset(&app), offset);
+    assert_eq!(evidence(&app), before);
+}
+
+#[tokio::test]
+async fn delayed_page_and_approval_operations_cannot_reset_a_new_destination() {
+    let mut app = paged_fixture();
+    let before = evidence(&app);
+    let form = app.source_rename.form.as_ref().unwrap();
+    let invocation = form.invocation;
+    let old_approval = form.approval.as_ref().unwrap().id;
+    let mut mounted = Mounted::new(&app);
+    let old_page_task = app.update(Message::SourceRename(Event::File(
+        invocation,
+        old_approval,
+        true,
+    )));
+    let next_page_task = app.update(Message::SourceRename(Event::Line(
+        invocation,
+        old_approval,
+        true,
+    )));
+    assert_eq!(mounted.execute(&app, next_page_task).await, 1);
+    let offset = mounted.scroll_down(&app);
+    assert_eq!(mounted.execute(&app, old_page_task).await, 1);
+    assert_eq!(mounted.offset(&app), offset, "old page target is absent");
+
+    let old_approval_task = app.update(Message::SourceRename(Event::Search(
+        invocation,
+        "defs".into(),
+    )));
+    input(&mut app, "pump_new");
+    let _ = preview(&mut app); // Real new approval in the same invocation/page.
+    assert_ne!(
+        app.source_rename
+            .form
+            .as_ref()
+            .unwrap()
+            .approval
+            .as_ref()
+            .unwrap()
+            .id,
+        old_approval
+    );
+    let offset = mounted.scroll_down(&app);
+    assert_eq!(mounted.execute(&app, old_approval_task).await, 1);
+    assert_eq!(
+        mounted.offset(&app),
+        offset,
+        "old approval target is absent"
+    );
+    let task = app.update(Message::SourceRename(Event::File(
+        invocation,
+        old_approval,
+        true,
+    )));
+    assert_eq!(
+        mounted.execute(&app, task).await,
+        0,
+        "stale envelope is rejected before scheduling"
+    );
+    assert_eq!(mounted.offset(&app), offset);
+    assert_eq!(evidence(&app), before);
+}
+
+#[tokio::test]
+async fn repeated_page_visits_filters_and_fast_preview_completion_have_distinct_destinations() {
+    let mut app = paged_fixture();
+    let before = evidence(&app);
+    let form = app.source_rename.form.as_ref().unwrap();
+    let invocation = form.invocation;
+    let approval = form.approval.as_ref().unwrap().id;
+    let mut mounted = Mounted::new(&app);
+
+    let first_visit = app.update(Message::SourceRename(Event::File(
+        invocation, approval, true,
+    )));
+    let next_page = app.update(Message::SourceRename(Event::Line(
+        invocation, approval, true,
+    )));
+    assert_eq!(mounted.execute(&app, next_page).await, 1);
+    let return_visit = app.update(Message::SourceRename(Event::Line(
+        invocation, approval, false,
+    )));
+    assert_eq!(mounted.execute(&app, return_visit).await, 1);
+    let offset = mounted.scroll_down(&app);
+    assert_eq!(mounted.execute(&app, first_visit).await, 1);
+    assert_eq!(
+        mounted.offset(&app),
+        offset,
+        "old visit to the identical page is stale"
+    );
+
+    let old_filter = app.update(Message::SourceRename(Event::Search(
+        invocation,
+        "uses".into(),
+    )));
+    let new_filter = app.update(Message::SourceRename(Event::Search(
+        invocation,
+        "us".into(),
+    )));
+    assert_eq!(mounted.execute(&app, new_filter).await, 1);
+    let offset = mounted.scroll_down(&app);
+    assert_eq!(mounted.execute(&app, old_filter).await, 1);
+    assert_eq!(
+        mounted.offset(&app),
+        offset,
+        "old filter on the same page is stale"
+    );
+
+    input(&mut app, "pump_new");
+    let job = start_preview(&mut app);
+    let completion = preview_completion(&app, job);
+    // No intermediate frame mounts the temporary no-approval view. The old
+    // Scrollable survives even though the new approval has a different id.
+    let ready = app.update(Message::SourceRenameReady(completion));
+    assert!(mounted.offset(&app) > 10.);
+    assert_eq!(mounted.execute(&app, ready).await, 1);
+    assert_eq!(mounted.offset(&app), 0.);
+    assert_eq!(evidence(&app), before);
+}
+
+#[tokio::test]
+async fn details_round_trip_retires_held_reset_without_changing_page_or_repeated_visibility_scroll()
+{
+    // Exercise both an actually mounted Details view and a fast round trip
+    // between frames, where Iced retains the same preview Scrollable state.
+    for mount_details in [true, false] {
+        let mut app = paged_fixture();
+        let before = evidence(&app);
+        let form = app.source_rename.form.as_ref().unwrap();
+        let invocation = form.invocation;
+        let approval = form.approval.as_ref().unwrap().id;
+        let mut mounted = Mounted::new(&app);
+        mounted.scroll_down(&app);
+        let held_reset = app.update(Message::SourceRename(Event::File(
+            invocation, approval, true,
+        )));
+        let old_preview = scroll_id(&app);
+        let form = app.source_rename.form.as_ref().unwrap();
+        let page = (form.file, form.hunk, form.line, form.segment);
+
+        let show_details = app.update(Message::SourceRename(Event::Details(invocation, true)));
+        assert_eq!(mounted.execute(&app, show_details).await, 0);
+        let details_visit = scroll_id(&app);
+        assert_ne!(details_visit, old_preview);
+        if mount_details {
+            let mut hidden = Geometry {
+                id: old_preview.clone(),
+                offset: None,
+            };
+            mounted.operate(&app, &mut hidden);
+            assert!(
+                hidden.offset.is_none(),
+                "Details actually replaced the preview"
+            );
+        }
+        let repeat_details = app.update(Message::SourceRename(Event::Details(invocation, true)));
+        assert_eq!(mounted.execute(&app, repeat_details).await, 0);
+        assert_eq!(
+            scroll_id(&app),
+            details_visit,
+            "unchanged visibility keeps its visit"
+        );
+
+        let show_preview = app.update(Message::SourceRename(Event::Details(invocation, false)));
+        assert_eq!(
+            mounted.execute(&app, show_preview).await,
+            0,
+            "returning does not force a scroll reset"
+        );
+        let returned_visit = scroll_id(&app);
+        assert_ne!(returned_visit, old_preview);
+        assert_ne!(returned_visit, details_visit);
+        let form = app.source_rename.form.as_ref().unwrap();
+        assert_eq!((form.file, form.hunk, form.line, form.segment), page);
+        assert_eq!(form.approval.as_ref().unwrap().id, approval);
+
+        let offset = mounted.scroll_down(&app);
+        let repeat_preview = app.update(Message::SourceRename(Event::Details(invocation, false)));
+        assert_eq!(mounted.execute(&app, repeat_preview).await, 0);
+        assert_eq!(scroll_id(&app), returned_visit);
+        assert_eq!(
+            mounted.offset(&app),
+            offset,
+            "repeated Preview preserves deliberate scroll"
+        );
+        assert_eq!(mounted.execute(&app, held_reset).await, 1);
+        assert_eq!(
+            mounted.offset(&app),
+            offset,
+            "the previous visit cannot reset the returned preview"
+        );
+        assert_eq!(evidence(&app), before);
+    }
+}

crates/oa-desktop/src/app/source_rename_layout_timing_tests.rs

@@ -0,0 +1,313 @@
+//! Manual replacement + next-layout/highlight evaluator; no GPU or native paint.
+//! Child of source_rename_timing_tests, preserving the separate real App test.
+use super::*;
+use crate::{highlight, views::source_tests::FontLayout};
+use iced::advanced::widget::operation::Focusable;
+use iced::advanced::{Layout, graphics, layout, renderer, text as shaped, widget::Tree};
+use iced::{
+    Background, Color, Element, Font, Length, Pixels, Point, Rectangle, Size, Transformation,
+};
+
+// The same real Paragraph and Editor as FontLayout. During draw, retain only a
+// Weak and fixed geometry; inspect glyphs after timing, never in fill_editor.
+#[derive(Default)]
+struct ObservedFontLayout {
+    drawn: Option<(graphics::text::editor::Weak, Point, Rectangle)>,
+}
+impl renderer::Renderer for ObservedFontLayout {
+    fn start_layer(&mut self, _: Rectangle) {}
+    fn end_layer(&mut self) {}
+    fn start_transformation(&mut self, _: Transformation) {}
+    fn end_transformation(&mut self) {}
+    fn reset(&mut self, _: Rectangle) {
+        self.drawn = None;
+    }
+    fn fill_quad(&mut self, _: renderer::Quad, _: impl Into<Background>) {}
+    fn allocate_image(
+        &mut self,
+        handle: &iced::advanced::image::Handle,
+        callback: impl FnOnce(Result<iced::advanced::image::Allocation, iced::advanced::image::Error>)
+        + Send
+        + 'static,
+    ) {
+        renderer::Renderer::allocate_image(&mut FontLayout, handle, callback);
+    }
+}
+impl shaped::Renderer for ObservedFontLayout {
+    type Font = Font;
+    type Paragraph = <FontLayout as shaped::Renderer>::Paragraph;
+    type Editor = <FontLayout as shaped::Renderer>::Editor;
+    const ICON_FONT: Font = <FontLayout as shaped::Renderer>::ICON_FONT;
+    const CHECKMARK_ICON: char = <FontLayout as shaped::Renderer>::CHECKMARK_ICON;
+    const ARROW_DOWN_ICON: char = <FontLayout as shaped::Renderer>::ARROW_DOWN_ICON;
+    const SCROLL_UP_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_UP_ICON;
+    const SCROLL_DOWN_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_DOWN_ICON;
+    const SCROLL_LEFT_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_LEFT_ICON;
+    const SCROLL_RIGHT_ICON: char = <FontLayout as shaped::Renderer>::SCROLL_RIGHT_ICON;
+    const ICED_LOGO: char = <FontLayout as shaped::Renderer>::ICED_LOGO;
+    fn default_font(&self) -> Font {
+        shaped::Renderer::default_font(&FontLayout)
+    }
+    fn default_size(&self) -> Pixels {
+        shaped::Renderer::default_size(&FontLayout)
+    }
+    fn fill_paragraph(&mut self, _: &Self::Paragraph, _: Point, _: Color, _: Rectangle) {}
+    fn fill_editor(&mut self, editor: &Self::Editor, position: Point, _: Color, clip: Rectangle) {
+        self.drawn = Some((editor.downgrade(), position, clip));
+    }
+    fn fill_text(&mut self, _: shaped::Text, _: Point, _: Color, _: Rectangle) {}
+}
+
+type Content = text_editor::Content<ObservedFontLayout>;
+const HOST: Size = Size::new(640., 350.);
+
+fn view(editor: &Content, source: Arc<str>) -> Element<'_, (), iced::Theme, ObservedFontLayout> {
+    text_editor(editor)
+        .on_action(|_| ())
+        .font(Font::MONOSPACE)
+        .size(14)
+        .padding(16)
+        .height(Length::Fill)
+        .highlight_with::<highlight::ArcadiaHighlighter>(source, highlight::format)
+        .into()
+}
+
+fn check_text(editor: &Content, expected: &str, cursor: text_editor::Cursor) {
+    assert_eq!(editor.text(), expected);
+    assert_eq!(editor.cursor(), cursor);
+    let lines: Vec<_> = expected.split('\n').collect();
+    assert_eq!(editor.line_count(), lines.len());
+    for (index, part) in lines.iter().enumerate() {
+        let (text, ending) = if index + 1 == lines.len() {
+            (*part, text_editor::LineEnding::None)
+        } else if let Some(text) = part.strip_suffix('\r') {
+            (text, text_editor::LineEnding::CrLf)
+        } else {
+            (*part, text_editor::LineEnding::Lf)
+        };
+        let actual = editor.line(index).unwrap();
+        assert_eq!(actual.text, text);
+        assert_eq!(actual.ending, ending);
+    }
+}
+
+fn check_draw(renderer: &ObservedFontLayout, cursor: text_editor::Cursor, alias: &str) {
+    let (weak, position, clip) = renderer.drawn.as_ref().expect("real editor draw");
+    let editor = weak.upgrade().expect("drawn editor is still live");
+    let buffer = editor.buffer();
+    assert_eq!(weak.bounds, Size::new(608., 318.));
+    assert_eq!(buffer.size(), (Some(608.), Some(318.)));
+    assert_eq!(buffer.metrics().font_size, 14.);
+    assert_eq!(
+        buffer.scroll().horizontal,
+        0.,
+        "fixture origin fits the viewport"
+    );
+    let start = cursor.position;
+    let end = cursor.selection.expect("approved alias selection");
+    assert_eq!(start.line, end.line);
+    assert_eq!(end.column - start.column, alias.len());
+    let line = &buffer.lines[start.line];
+    assert_eq!(&line.text()[start.column..end.column], alias);
+    let color = graphics::text::to_color(Color::from_rgb8(20, 93, 139));
+    let font = graphics::text::to_attributes(Font::MONOSPACE);
+    for byte in start.column..end.column {
+        let attrs = line.attrs_list().get_span(byte);
+        assert_eq!(
+            attrs.color_opt,
+            Some(color),
+            "accepted alias syntax attributes"
+        );
+        assert_eq!(attrs.family, font.family);
+    }
+    let mut covered = vec![false; alias.len()];
+    for run in buffer.layout_runs().filter(|run| run.line_i == start.line) {
+        for glyph in run.glyphs {
+            let from = glyph.start.max(start.column);
+            let to = glyph.end.min(end.column);
+            if from >= to {
+                continue;
+            }
+            assert_eq!(glyph.color_opt, Some(color), "drawn alias glyph color");
+            let x = position.x + glyph.x + glyph.x_offset * glyph.font_size;
+            let y = position.y + run.line_top;
+            assert!(x >= clip.x - 0.5 && x + glyph.w <= clip.x + clip.width + 0.5);
+            assert!(y + run.line_height > clip.y && y < clip.y + clip.height);
+            covered[from - start.column..to - start.column].fill(true);
+        }
+    }
+    assert!(
+        covered.into_iter().all(|seen| seen),
+        "entire alias has visible shaped glyphs"
+    );
+    // This temporary strong upgrade is dropped before the next editor mutation.
+}
+
+#[derive(Clone, Copy)]
+enum Arm {
+    Constructor,
+    Reuse,
+}
+impl Arm {
+    fn name(self) -> &'static str {
+        match self {
+            Self::Constructor => "with_text",
+            Self::Reuse => "same_line_reuse",
+        }
+    }
+    fn phases(self) -> [&'static str; 4] {
+        match self {
+            Self::Constructor => [
+                "constructor_replace_origin",
+                "constructor_next_layout",
+                "constructor_highlight_draw",
+                "constructor_combined",
+            ],
+            Self::Reuse => [
+                "reuse_replace_origin",
+                "reuse_next_layout",
+                "reuse_highlight_draw",
+                "reuse_combined",
+            ],
+        }
+    }
+}
+
+fn trial(
+    fixture: &Fixture,
+    cursor: text_editor::Cursor,
+    arm: Arm,
+    trial: usize,
+    samples: &mut Samples,
+) {
+    let before = &fixture.bundle.files[ORIGIN];
+    let after = &fixture.expected_bundle.files[ORIGIN];
+    let mut editor = Content::with_text(before);
+    editor.move_to(fixture.cursor);
+    let mut renderer = ObservedFontLayout::default();
+    let theme = iced::Theme::Light;
+    let defaults = renderer::Style::default();
+    let viewport = Rectangle::with_size(HOST);
+    let limits = layout::Limits::new(Size::ZERO, HOST);
+    let mut tree = {
+        let mut widget = view(&editor, Arc::from(before.as_str()));
+        let mut tree = Tree::new(widget.as_widget());
+        let node = widget.as_widget_mut().layout(&mut tree, &renderer, &limits);
+        tree.state
+            .downcast_mut::<text_editor::State<highlight::ArcadiaHighlighter>>()
+            .focus();
+        widget.as_widget().draw(
+            &tree,
+            &mut renderer,
+            &theme,
+            &defaults,
+            Layout::new(&node),
+            iced::mouse::Cursor::Unavailable,
+            &viewport,
+        );
+        tree
+    };
+    check_text(&editor, before, fixture.cursor);
+    check_draw(&renderer, fixture.cursor, OLD);
+    // No recorder Weak/Strong from setup may perturb replacement ownership.
+    renderer.drawn = None;
+    let next_source: Arc<str> = Arc::from(after.as_str());
+
+    // Only normal operations and four timestamps occur between start and end.
+    // Source/model oracles, logging and recorder glyph inspection are outside.
+    let started = Instant::now();
+    let replaced = match arm {
+        Arm::Constructor => {
+            editor = Content::with_text(after);
+            true
+        }
+        Arm::Reuse => super::super::editor_patch::replace(&mut editor, before, after),
+    };
+    editor.move_to(cursor);
+    let replaced_at = Instant::now();
+    let mut widget = view(&editor, next_source);
+    let node = widget.as_widget_mut().layout(&mut tree, &renderer, &limits);
+    let laid_out_at = Instant::now();
+    widget.as_widget().draw(
+        &tree,
+        &mut renderer,
+        &theme,
+        &defaults,
+        Layout::new(&node),
+        iced::mouse::Cursor::Unavailable,
+        &viewport,
+    );
+    let drawn_at = Instant::now();
+    drop(widget);
+
+    assert!(replaced, "reuse must not silently time a fallback/refusal");
+    check_text(&editor, after, cursor);
+    check_draw(&renderer, cursor, NEW);
+    renderer.drawn = None;
+    for (phase, duration) in arm.phases().into_iter().zip([
+        replaced_at.duration_since(started),
+        laid_out_at.duration_since(replaced_at),
+        drawn_at.duration_since(laid_out_at),
+        drawn_at.duration_since(started),
+    ]) {
+        println!(
+            "{}",
+            serde_json::json!({
+                "record": "editor_layout_timing", "arm": arm.name(), "phase": phase,
+                "trial": trial, "warmup": trial == 0,
+                "elapsed_ns": duration.as_nanos().to_string(),
+                "elapsed_ms": duration.as_secs_f64() * 1000.0,
+            })
+        );
+        if trial != 0 {
+            samples.0.entry(phase).or_default().push(duration);
+        }
+    }
+}
+
+#[test]
+#[ignore = "manual Windows dev/debug editor replacement + layout/highlight trial; run alone with --ignored --nocapture --test-threads=1"]
+fn accepted_release1_constructor_vs_reuse_through_next_highlight() {
+    let fixture = Fixture::load();
+    // Resolve the exact production approval and verify full Project/source once,
+    // outside all intervals. The actual App Confirm evaluator remains separate.
+    let cursor = {
+        let app = fixture.app();
+        let target = resolve(&app, &app.rename_context());
+        let prepared = app
+            .document
+            .alias_rename_request(target.id, NEW.into())
+            .unwrap()
+            .prepare()
+            .unwrap();
+        fixture.check_candidate(&prepared);
+        prepare_approval(prepared, &target, ORIGIN).unwrap().cursor
+    };
+    println!(
+        "{}",
+        serde_json::json!({
+            "record": "editor_layout_fixture", "host_width": HOST.width, "host_height": HOST.height,
+            "font": "MONOSPACE", "font_size": 14, "padding": 16, "height": "Fill",
+            "active_file": ORIGIN, "before_bytes": fixture.bundle.files[ORIGIN].len(),
+            "after_bytes": fixture.expected_bundle.files[ORIGIN].len(), "warmups_per_arm": 1,
+            "measured_trials_per_arm": 5, "debug_assertions": cfg!(debug_assertions),
+            "scope": "real editor replacement, retained Tree layout and Widget draw/highlight; no GPU, native paint or App Confirm",
+        })
+    );
+    let mut samples = Samples::default();
+    for index in 0..=5 {
+        let arms = if index % 2 == 0 {
+            [Arm::Constructor, Arm::Reuse]
+        } else {
+            [Arm::Reuse, Arm::Constructor]
+        };
+        println!(
+            "{}",
+            serde_json::json!({"record": "editor_layout_order", "trial": index, "first": arms[0].name()})
+        );
+        for arm in arms {
+            trial(&fixture, cursor, arm, index, &mut samples);
+        }
+    }
+    samples.report();
+}

crates/oa-desktop/src/app/source_rename_timing_tests.rs

@@ -0,0 +1,347 @@
+//! Manual timing through the real Document and App paths. No disk writes,
+//! executor polling, layout, GPU work or first-paint measurement occurs here.
+//! Register as a test child of app::source_rename to use its actual worker helpers.
+use super::*;
+use crate::source_workspace::Workspace;
+use oa_core::source_project::SourceBundle;
+use std::{
+    collections::BTreeMap,
+    path::PathBuf,
+    time::{Duration, Instant},
+};
+
+#[cfg(debug_assertions)]
+#[path = "source_rename_layout_timing_tests.rs"]
+mod layout_timing_tests;
+
+const OLD: &str = "oa_restore_work";
+const NEW: &str = "oa_restore_pressure";
+const DECLARATIONS: &str = "oa/activities/activity_oa_restore_work.arcadia";
+const ORIGIN: &str = "traceability.arcadia";
+
+struct Fixture {
+    bundle: SourceBundle,
+    project: Project,
+    expected_bundle: SourceBundle,
+    expected_project: Project,
+    target: Id,
+    cursor: text_editor::Cursor,
+}
+
+impl Fixture {
+    fn load() -> Self {
+        // The optional entry selects a parent-pinned copy of this exact fixture,
+        // not an arbitrary performance generator or a mutable GUI destination.
+        let entry = std::env::var_os("ARCADIA_RENAME_TIMING_ENTRY")
+            .map(PathBuf::from)
+            .unwrap_or_else(|| {
+                PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+                    .join("../../examples/release1/project.arcadia")
+            });
+        let loaded = oa_core::source_files::load_project(&entry, LIMITS).unwrap();
+        let bundle = loaded.reachable_bundle();
+        assert_eq!(
+            bundle.files.len(),
+            30,
+            "use the preserved release1 walkthrough"
+        );
+        let document = Document::from_bundle(bundle.clone(), LIMITS).unwrap();
+        assert_eq!(
+            document.bundle(),
+            &bundle,
+            "fixture must need no stabilization/migration"
+        );
+        assert!(!document.dirty());
+        let project = document.project().clone();
+        let target = Id::parse_str("1b91f8a7-0bdb-514e-b1cd-955658e09927").unwrap();
+        assert_eq!(project.elements[&target].alias, OLD);
+        assert!(!project.identities().iter().any(|(_, alias)| *alias == NEW));
+        let mut expected_project = project.clone();
+        expected_project.elements.get_mut(&target).unwrap().alias = NEW.into();
+
+        // Independent literal source oracle, authored before running the rename.
+        // Do not replace the alias substring in filenames or the trace's alias.
+        let mut expected_bundle = bundle.clone();
+        let declarations = expected_bundle.files.get_mut(DECLARATIONS).unwrap();
+        assert_eq!(
+            declarations.matches("oa_activity oa_restore_work ").count(),
+            1
+        );
+        assert_eq!(declarations.matches("parent @oa_restore_work;").count(), 4);
+        *declarations = declarations
+            .replace(
+                "oa_activity oa_restore_work ",
+                "oa_activity oa_restore_pressure ",
+            )
+            .replace("parent @oa_restore_work;", "parent @oa_restore_pressure;");
+        let traces = expected_bundle.files.get_mut(ORIGIN).unwrap();
+        assert_eq!(traces.matches("oa @oa_restore_work;").count(), 1);
+        *traces = traces.replace("oa @oa_restore_work;", "oa @oa_restore_pressure;");
+        let source = &bundle.files[ORIGIN];
+        let start = source.rfind("@oa_restore_work;").unwrap() + 1;
+        let position = |offset| {
+            let prefix = &source[..offset];
+            text_editor::Position {
+                line: prefix.bytes().filter(|byte| *byte == b'\n').count(),
+                column: prefix
+                    .rsplit_once('\n')
+                    .map_or(prefix.len(), |(_, tail)| tail.len()),
+            }
+        };
+        let cursor = text_editor::Cursor {
+            position: position(start),
+            selection: Some(position(start + OLD.len())),
+        };
+        assert!(nav::exact_cursor(source, cursor));
+        println!(
+            "{}",
+            serde_json::json!({
+                "record": "fixture", "entry": entry, "reachable_files": bundle.files.len(),
+                "source_bytes": bundle.files.values().map(String::len).sum::<usize>(),
+                "identities": project.identities().len(), "active_file": ORIGIN,
+                "active_file_bytes": source.len(), "old": OLD, "new": NEW,
+                "warmups": 1, "measured_trials": 5, "debug_assertions": cfg!(debug_assertions),
+                "scope": "real worker helpers, guarded Document commit, App sync and Confirm update; no task polling or rendering"
+            })
+        );
+        Self {
+            bundle,
+            project,
+            expected_bundle,
+            expected_project,
+            target,
+            cursor,
+        }
+    }
+
+    fn app(&self) -> App {
+        let mut app = App::with_project(Project::empty());
+        app.document = Document::from_bundle(self.bundle.clone(), LIMITS).unwrap();
+        app.source_workspace = Workspace::new(app.document.bundle(), true);
+        app.source_workspace.active = ORIGIN.into();
+        app.selected = app.project().id;
+        app.page = Page::Text;
+        app.sync();
+        app.source_editor.move_to(self.cursor);
+        assert_eq!(app.project(), &self.project);
+        assert_eq!(app.document.bundle(), &self.bundle);
+        assert_eq!(app.document.revision(), 0);
+        assert!(!app.document.dirty() && !app.document.can_undo() && !app.document.can_redo());
+        assert!(app.rename_admission().is_ok());
+        app
+    }
+
+    fn check_candidate(&self, prepared: &PreparedAliasRename) {
+        assert!(prepared.changed());
+        assert_eq!(prepared.before().bundle, self.bundle);
+        assert_eq!(prepared.before().decoded.project, self.project);
+        assert_eq!(prepared.after().bundle, self.expected_bundle);
+        assert_eq!(prepared.after().decoded.project, self.expected_project);
+    }
+
+    fn check_adopted(&self, app: &mut App, candidate_address: *const CompiledSourceProject) {
+        assert!(
+            std::ptr::eq(app.document.compiled(), candidate_address),
+            "adopt exact candidate allocation"
+        );
+        assert_eq!(app.project(), &self.expected_project);
+        assert_eq!(app.document.bundle(), &self.expected_bundle);
+        assert_eq!(app.source_workspace.bundle(), self.expected_bundle);
+        assert_eq!(app.source_editor.text(), self.expected_bundle.files[ORIGIN]);
+        assert_eq!(app.document.revision(), 1);
+        assert!(app.document.dirty() && app.document.can_undo() && !app.document.can_redo());
+        assert!(app.document.undo());
+        assert_eq!(app.project(), &self.project);
+        assert_eq!(app.document.bundle(), &self.bundle);
+        assert!(
+            !app.document.dirty(),
+            "live known saved baseline remains authoritative"
+        );
+        assert!(
+            !app.document.can_undo(),
+            "exactly one preceding model transaction"
+        );
+        assert!(app.document.redo());
+        assert_eq!(app.project(), &self.expected_project);
+        assert_eq!(app.document.bundle(), &self.expected_bundle);
+        assert!(std::ptr::eq(app.document.compiled(), candidate_address));
+    }
+}
+
+#[derive(Default)]
+struct Samples(BTreeMap<&'static str, Vec<Duration>>);
+
+impl Samples {
+    fn time<T>(&mut self, phase: &'static str, trial: usize, action: impl FnOnce() -> T) -> T {
+        let started = Instant::now();
+        let result = action();
+        let elapsed = started.elapsed();
+        // Printing, assertions and dropping the returned value are outside this
+        // interval. Full Confirm still includes production's own local drops.
+        println!(
+            "{}",
+            serde_json::json!({
+                "record": "timing", "phase": phase, "trial": trial,
+                "warmup": trial == 0, "elapsed_ns": elapsed.as_nanos().to_string(),
+                "elapsed_ms": elapsed.as_secs_f64() * 1000.0
+            })
+        );
+        if trial != 0 {
+            self.0.entry(phase).or_default().push(elapsed);
+        }
+        result
+    }
+
+    fn report(mut self) {
+        for (phase, values) in &mut self.0 {
+            assert_eq!(values.len(), 5);
+            values.sort();
+            println!(
+                "{}",
+                serde_json::json!({
+                    "record": "summary", "phase": phase, "samples": values.len(),
+                    "min_ms": values[0].as_secs_f64() * 1000.0,
+                    "median_ms": values[2].as_secs_f64() * 1000.0,
+                    "max_ms": values[4].as_secs_f64() * 1000.0
+                })
+            );
+        }
+    }
+}
+
+fn resolve(app: &App, context: &Context) -> Target {
+    let snapshot = app
+        .with_source_input(|input| query::admit_owned(input, query::Limits::default()))
+        .unwrap()
+        .capture()
+        .unwrap();
+    let offset = nav::cursor_offset(app.source_workspace.text(), context.begin.cursor).unwrap();
+    resolve_target(&snapshot, context, offset).unwrap()
+}
+
+fn active_job(app: &App) -> Job {
+    let form = app.source_rename.form.as_ref().unwrap();
+    let id = form.pending.unwrap();
+    assert_eq!(app.source_rename.in_flight, Some(id));
+    Job {
+        id,
+        invocation: form.invocation,
+        generation: form.generation,
+        context: form.context.clone(),
+    }
+}
+
+fn separate_phases(fixture: &Fixture, samples: &mut Samples, trial: usize) {
+    let mut app = fixture.app();
+    let target = resolve(&app, &app.rename_context());
+    assert_eq!(target.id, fixture.target);
+    let request = samples
+        .time("document_request_mint", trial, || {
+            app.document.alias_rename_request(target.id, NEW.into())
+        })
+        .unwrap();
+    let prepared = samples
+        .time("worker_document_prepare", trial, || request.prepare())
+        .unwrap();
+    fixture.check_candidate(&prepared);
+    let approval = samples
+        .time("worker_preview_and_origin", trial, || {
+            prepare_approval(prepared, &target, ORIGIN)
+        })
+        .unwrap();
+    assert_eq!(approval.preview.files().len(), 2);
+    assert_eq!(approval.preview.changed_line_count(), 6);
+    let candidate_address = approval.prepared.after() as *const CompiledSourceProject;
+    // Same-destination save completion is a legitimate live update after Preview.
+    app.document.mark_saved(app.document.snapshot());
+    let changed = samples
+        .time("document_guarded_commit", trial, || {
+            app.document.commit_alias_rename(&approval.prepared)
+        })
+        .unwrap();
+    assert!(changed);
+    samples.time("app_sync", trial, || app.sync());
+    fixture.check_adopted(&mut app, candidate_address);
+}
+
+fn whole_confirm(fixture: &Fixture, samples: &mut Samples, trial: usize) {
+    let mut app = fixture.app();
+    let begin = app.source_rename_message();
+    // These Tasks are deliberately not polled: deterministic worker helpers
+    // supply the same results through the real readiness messages below.
+    drop(app.update(begin));
+    let target_job = active_job(&app);
+    let target = Arc::new(resolve(&app, &target_job.context));
+    assert_eq!(target.id, fixture.target);
+    drop(app.update(Message::SourceRenameReady(Completion {
+        job: target_job,
+        payload: Payload::Target(Ok(target.clone())),
+    })));
+    let invocation = app.source_rename.form.as_ref().unwrap().invocation;
+    drop(app.update(Message::SourceRename(Event::Input(invocation, NEW.into()))));
+    let generation = app.source_rename.form.as_ref().unwrap().generation;
+    drop(app.update(Message::SourceRename(Event::Preview(
+        invocation, generation,
+    ))));
+    let preview_job = active_job(&app);
+    let prepared = app
+        .document
+        .alias_rename_request(target.id, NEW.into())
+        .unwrap()
+        .prepare()
+        .unwrap();
+    fixture.check_candidate(&prepared);
+    let approval = Arc::new(prepare_approval(prepared, &target, ORIGIN).unwrap());
+    drop(target);
+    let candidate_address = approval.prepared.after() as *const CompiledSourceProject;
+    let expected_cursor = approval.cursor;
+    let approval_id = approval.id;
+    drop(app.update(Message::SourceRenameReady(Completion {
+        job: preview_job,
+        payload: Payload::Preview(Ok(approval)),
+    })));
+    assert_eq!(
+        app.source_rename
+            .form
+            .as_ref()
+            .unwrap()
+            .approval
+            .as_ref()
+            .unwrap()
+            .id,
+        approval_id
+    );
+    app.document.mark_saved(app.document.snapshot());
+    let confirm = Message::SourceRename(Event::Confirm(invocation, generation, approval_id));
+    let task = samples.time("app_confirm_update", trial, || app.update(confirm));
+    samples.time("confirm_returned_task_drop_without_polling", trial, || {
+        drop(task)
+    });
+    assert!(!app.source_rename.open());
+    assert!(app.source_rename.in_flight.is_none());
+    assert!(app.source_rename_undo_message().is_some());
+    assert_eq!(app.source_editor.cursor(), expected_cursor);
+    fixture.check_adopted(&mut app, candidate_address);
+}
+
+#[test]
+#[ignore = "manual Windows dev/debug rename latency trial; run alone with --ignored --nocapture --test-threads=1"]
+fn accepted_release1_prepare_commit_sync_and_confirm_timing() {
+    let fixture = Fixture::load();
+    let mut samples = Samples::default();
+    for trial in 0..=5 {
+        println!(
+            "{}",
+            serde_json::json!({ "record": "order", "trial": trial,
+            "warmup": trial == 0, "separate_phases_first": trial % 2 == 0 })
+        );
+        if trial % 2 == 0 {
+            separate_phases(&fixture, &mut samples, trial);
+            whole_confirm(&fixture, &mut samples, trial);
+        } else {
+            whole_confirm(&fixture, &mut samples, trial);
+            separate_phases(&fixture, &mut samples, trial);
+        }
+    }
+    samples.report();
+}

crates/oa-desktop/src/app/source_symbols.rs

@@ -0,0 +1,508 @@
+//! Current draft navigation, isolated from model application and disk discovery.
+use super::*;
+use crate::source_navigation::{self as nav, query};
+use std::sync::atomic::Ordering;
+
+fn admission_notice(error: query::AdmissionError) -> String {
+    use nav::symbols::{BuildError, InputProblem, Resource};
+    let (limit, resource) = match error {
+        query::AdmissionError::Index(BuildError::Limit { limit, resource, .. }) => (limit, resource),
+        query::AdmissionError::Outline { error, .. } => (error.limit, match error.resource {
+            language::OutlineResource::SourceBytes => Resource::SourceBytes,
+            language::OutlineResource::Tokens => Resource::Tokens,
+            language::OutlineResource::Declarations => Resource::Records,
+        }),
+        query::AdmissionError::Index(BuildError::Input { problem, .. }) => return match problem {
+            InputProblem::NonCanonicalPath | InputProblem::DuplicateOrCaseCollidingPath =>
+                "Navigation needs distinct relative source paths. Check file names and include paths.".into(),
+            _ => "Navigation could not verify the current source locations. Correct source errors and try again.".into(),
+        },
+    };
+    let unit = match resource {
+        Resource::Files => "loaded files",
+        Resource::SourceBytes => "source bytes",
+        Resource::PathBytes => "bytes in file paths",
+        Resource::Tokens => "source tokens",
+        Resource::Records => "declarations and references",
+    };
+    format!(
+        "Navigation reached its limit of {limit} {unit}. Reduce the loaded source size and try again."
+    )
+}
+
+impl App {
+    pub fn source_symbol_context(&self) -> nav::SymbolContext {
+        nav::SymbolContext {
+            session: self.source_workspace.session(),
+            path: self.source_workspace.active.clone(),
+        }
+    }
+
+    pub fn source_symbol_message(&self, event: nav::SymbolEvent) -> Message {
+        Message::SourceSymbols(self.source_symbol_context(), event)
+    }
+
+    pub fn source_find_close_message(&self) -> Message {
+        Message::SourceFindClose(self.source_symbol_context(), self.source_find_instance)
+    }
+    pub fn source_key(&self) -> query::SnapshotKey {
+        query::SnapshotKey {
+            workspace: self.source_workspace.session(),
+            revision: self.source_workspace.revision(),
+        }
+    }
+
+    pub(super) fn with_source_input<T>(&self, use_input: impl FnOnce(query::Input<'_>) -> T) -> T {
+        let files: Vec<_> = self
+            .source_workspace
+            .files
+            .iter()
+            .map(|(path, buffer)| query::DraftFile {
+                path,
+                text: &buffer.text,
+            })
+            .collect();
+        let accepted = self.document.bundle();
+        let validated: Vec<_> = accepted
+            .files
+            .iter()
+            .map(|(path, text)| query::DraftFile { path, text })
+            .collect();
+        use_input(query::Input {
+            key: self.source_key(),
+            entry: &self.source_workspace.entry,
+            files: &files,
+            applied: self.source_workspace.applied,
+            validation: self
+                .source_workspace
+                .applied
+                .then_some(query::ValidatedSources {
+                    entry: &accepted.entry,
+                    files: &validated,
+                }),
+        })
+    }
+
+    pub(super) fn source_snapshot_matches(&self, snapshot: &query::Snapshot) -> bool {
+        snapshot.key() == self.source_key()
+            && self.with_source_input(|input| snapshot.matches(input))
+    }
+
+    pub fn source_navigation_available(&self) -> bool {
+        self.page == Page::Text
+            && !self.source_rename.open()
+            && !self.busy
+            && self.pending.is_none()
+            && self.file_prompt.is_none()
+            && !self.delete_pending
+            && self.workflow.is_none()
+            && !self.hosted.visible
+            && self.model_menu.is_none()
+            && self.diagram_usages.is_none()
+            && !self.reference_input_active()
+            && self.architecture.is_none()
+            && !self.behavior.has_pending()
+    }
+
+    /// Mounted widget IDs change when another interaction supersedes a reveal.
+    /// A queued focus operation therefore cannot find a subsequently reused editor.
+    pub fn source_editor_id(&self) -> iced::widget::Id {
+        iced::widget::Id::from(format!(
+            "source-editor-{}-{}-{}",
+            self.source_workspace.session(),
+            self.source_workspace.active,
+            self.source_symbols.interaction
+        ))
+    }
+
+    pub fn source_reveal_ticket(&self) -> Option<Id> {
+        self.source_symbols
+            .reveal
+            .as_ref()
+            .map(|reveal| reveal.ticket)
+    }
+
+    pub(super) fn source_interaction(&mut self) {
+        self.source_symbols.interaction = Id::new_v4();
+        self.source_symbols.request = None;
+        self.source_symbols.reveal = None;
+        self.source_jump = None;
+    }
+
+    pub(super) fn queue_source_reveal(&mut self, cursor: text_editor::Cursor, select_line: bool) {
+        self.source_jump = Some(cursor);
+        self.source_select_line = select_line;
+        self.source_symbols.reveal = Some(nav::Reveal {
+            ticket: Id::new_v4(),
+            interaction: self.source_symbols.interaction,
+            raw_interaction: self.source_symbols.raw_interaction.load(Ordering::SeqCst),
+            snapshot: self.source_key(),
+            path: self.source_workspace.active.clone(),
+        });
+    }
+
+    pub(super) fn restore_source_editor_focus(&mut self) {
+        let cursor = self.source_editor.cursor();
+        if self.source_navigation_available()
+            && nav::exact_cursor(self.source_workspace.text(), cursor)
+        {
+            self.queue_source_reveal(cursor, false);
+        }
+    }
+
+    pub(super) fn source_viewport(&mut self, ticket: Option<Id>) -> Task<Message> {
+        let Some(reveal) = &self.source_symbols.reveal else {
+            return Task::none();
+        };
+        if Some(reveal.ticket) != ticket
+            || reveal.interaction != self.source_symbols.interaction
+            || !nav::interaction::is_current(
+                &self.source_symbols.raw_interaction,
+                reveal.raw_interaction,
+            )
+            || reveal.snapshot != self.source_key()
+            || reveal.path != self.source_workspace.active
+            || !self.source_navigation_available()
+        {
+            return Task::none();
+        }
+        let raw_interaction = reveal.raw_interaction;
+        self.source_symbols.reveal = None;
+        if let Some(cursor) = self.source_jump.take() {
+            if !nav::exact_cursor(self.source_workspace.text(), cursor) {
+                return Task::none();
+            }
+            self.source_editor.move_to(cursor);
+            if self.source_select_line && cursor.selection.is_none() {
+                self.source_editor.perform(text_editor::Action::SelectLine);
+            }
+            return nav::interaction::guarded_focus(
+                self.source_editor_id(),
+                self.source_symbols.raw_interaction.clone(),
+                raw_interaction,
+            );
+        }
+        Task::none()
+    }
+
+    pub(super) fn source_symbol_event(&mut self, event: nav::SymbolEvent) -> Task<Message> {
+        if !self.source_navigation_available() {
+            return Task::none();
+        }
+        match event {
+            nav::SymbolEvent::DiagramUsages => {
+                if self.source_dirty() || !self.source_workspace.applied {
+                    self.source_symbols.open = true;
+                    self.source_symbols.notice = Some("Apply source before finding diagram representations. Your current text is retained.".into());
+                    return Task::none();
+                }
+                let task = self.start_source_query(query::Action::Definition);
+                self.source_diagram_job = self
+                    .source_symbols
+                    .request
+                    .as_ref()
+                    .map(|request| request.job);
+                return task;
+            }
+            nav::SymbolEvent::Close => {
+                self.source_symbols.open = false;
+                self.source_symbols.results = None;
+                self.source_symbols.notice = None;
+            }
+            nav::SymbolEvent::Back => {
+                self.source_symbol_back();
+                // A successful Back needs no empty results panel. Retain an
+                // already open panel, or reveal an actionable return notice.
+                self.source_symbols.open |= self.source_symbols.notice.is_some();
+            }
+            nav::SymbolEvent::Choose {
+                stamp,
+                reference,
+                index,
+            } => {
+                let Some(results) = self.source_symbols.results.clone() else {
+                    return Task::none();
+                };
+                if results.stamp != stamp
+                    || stamp.snapshot != self.source_key()
+                    || self
+                        .source_symbols
+                        .cache
+                        .as_ref()
+                        .is_none_or(|cache| !self.source_snapshot_matches(cache))
+                {
+                    self.source_symbols.notice =
+                        Some("Source changed. Run navigation again for current locations.".into());
+                    return Task::none();
+                }
+                let destination = if reference {
+                    results
+                        .references
+                        .get(index)
+                        .map(|row| (&row.path, row.position, row.end_position))
+                } else {
+                    results
+                        .definitions
+                        .get(index)
+                        .map(|row| (&row.path, row.position, row.end_position))
+                };
+                if let Some((path, start, end)) = destination {
+                    self.source_symbol_jump(path, start, end);
+                }
+            }
+            nav::SymbolEvent::Query(action) => return self.start_source_query(action),
+        }
+        Task::none()
+    }
+
+    fn start_source_query(&mut self, action: query::Action) -> Task<Message> {
+        self.source_symbols.open = true;
+        if !nav::interaction::is_current(
+            &self.source_symbols.raw_interaction,
+            self.source_symbols.raw_interaction.load(Ordering::SeqCst),
+        ) {
+            self.source_symbols.notice = Some("Reopen this workspace to reset navigation.".into());
+            return Task::none();
+        }
+        if self.source_symbols.in_flight.is_some() {
+            self.source_symbols.notice = Some("Navigation is finishing. Try again shortly.".into());
+            return Task::none();
+        }
+        let cursor = self.source_editor.cursor();
+        let Some(offset) = nav::cursor_offset(self.source_workspace.text(), cursor) else {
+            self.source_symbols.notice =
+                Some("Place the cursor on an alias or its @ reference.".into());
+            return Task::none();
+        };
+        self.source_symbols.serial = match self.source_symbols.serial.checked_add(1) {
+            Some(serial) => serial,
+            None => {
+                self.source_workspace.reset_navigation_session();
+                self.source_symbols.back.clear();
+                self.source_symbols.cache = None;
+                0
+            }
+        };
+        let request = nav::Request {
+            job: Id::new_v4(),
+            interaction: self.source_symbols.interaction,
+            raw_interaction: self.source_symbols.raw_interaction.load(Ordering::SeqCst),
+            stamp: query::QueryStamp {
+                snapshot: self.source_key(),
+                serial: self.source_symbols.serial,
+            },
+            path: self.source_workspace.active.clone(),
+            offset,
+            cursor,
+            action,
+        };
+        let cache = self
+            .source_symbols
+            .cache
+            .as_ref()
+            .filter(|cache| self.source_snapshot_matches(cache))
+            .cloned();
+        let input = if cache.is_none() {
+            match self
+                .with_source_input(|input| query::admit_owned(input, query::Limits::default()))
+            {
+                Ok(input) => Some(input),
+                Err(error) => {
+                    self.source_symbols.notice = Some(admission_notice(error));
+                    return Task::none();
+                }
+            }
+        } else {
+            None
+        };
+        self.source_symbols.in_flight = Some(request.job);
+        self.source_symbols.request = Some(request.clone());
+        self.source_symbols.results = None;
+        self.source_symbols.notice = None;
+        Task::perform(
+            async move {
+                let worker_request = request.clone();
+                let result = tokio::task::spawn_blocking(move || {
+                    let snapshot = match cache {
+                        Some(cache) => cache,
+                        None => Arc::new(
+                            input
+                                .expect("admitted input for uncached request")
+                                .capture()
+                                .map_err(admission_notice)?,
+                        ),
+                    };
+                    let results = snapshot
+                        .query(query::Query {
+                            stamp: worker_request.stamp,
+                            path: &worker_request.path,
+                            byte_offset: worker_request.offset,
+                            action: worker_request.action,
+                        })
+                        .map_err(|error| match error {
+                            query::QueryError::ResultEnvelopeLimit => "These result details exceed the display limit. Try literal Find for this alias.".to_owned(),
+                            _ => "Navigation could not verify this location. Place the cursor on an alias and try again.".to_owned(),
+                        })?;
+                    Ok((snapshot, Arc::new(results)))
+                })
+                .await
+                .unwrap_or_else(|error| Err(format!("Navigation task failed: {error}")));
+                nav::Completion { request, result }
+            },
+            Message::SourceSymbolsReady,
+        )
+    }
+
+    pub(super) fn source_symbols_ready(&mut self, completion: nav::Completion) -> Task<Message> {
+        let request = completion.request;
+        if self.source_symbols.in_flight != Some(request.job) {
+            return Task::none();
+        }
+        self.source_symbols.in_flight = None;
+        let diagram_query = self.source_diagram_job == Some(request.job);
+        if diagram_query {
+            self.source_diagram_job = None;
+        }
+        let wanted = self
+            .source_symbols
+            .request
+            .take()
+            .is_some_and(|current| current.job == request.job)
+            && request.interaction == self.source_symbols.interaction
+            && request.stamp.snapshot == self.source_key()
+            && nav::interaction::is_current(
+                &self.source_symbols.raw_interaction,
+                request.raw_interaction,
+            )
+            && request.path == self.source_workspace.active
+            && request.cursor == self.source_editor.cursor()
+            && self.source_navigation_available();
+        if !wanted {
+            return Task::none();
+        }
+        match completion.result {
+            Ok((snapshot, results)) if self.source_snapshot_matches(&snapshot) => {
+                self.source_symbols.cache = Some(snapshot);
+                self.source_symbols.results = Some(results.clone());
+                if diagram_query {
+                    if results.disposition == query::Disposition::Direct
+                        && results.scope.validated
+                        && results.omitted_definitions == 0
+                        && let [row] = results.definitions.as_slice()
+                        && let query::Identity::Unique(identity) = row.declaration.identity
+                        && row.membership == query::Membership::Included
+                        && row.evidence == query::Evidence::Validated
+                        && self.project().contains(identity.id())
+                        && crate::diagram_usage::alias(self.project(), identity.id())
+                            == row.declaration.alias
+                    {
+                        self.source_symbols.open = false;
+                        return self.diagram_usage_event(crate::diagram_usage::Event::Open(
+                            crate::diagram_usage::Context {
+                                document: self.canvas_document,
+                                revision: self.document.revision(),
+                                subject: identity.id(),
+                            },
+                        ));
+                    }
+                    self.source_symbols.notice = Some("Place the caret on a uniquely resolved alias in applied source to find diagram representations.".into());
+                    return Task::none();
+                }
+                if results.disposition == query::Disposition::Direct
+                    && let Some(row) = results.definitions.first()
+                {
+                    self.source_symbol_jump(&row.path, row.position, row.end_position);
+                }
+            }
+            Ok(_) => {
+                self.source_symbols.notice = Some("Source changed. Run navigation again.".into())
+            }
+            Err(error) => self.source_symbols.notice = Some(error),
+        }
+        Task::none()
+    }
+
+    fn source_symbol_jump(&mut self, path: &str, start: query::Position, end: query::Position) {
+        let cursor = text_editor::Cursor {
+            position: text_editor::Position {
+                line: start.line,
+                column: start.byte_column,
+            },
+            selection: Some(text_editor::Position {
+                line: end.line,
+                column: end.byte_column,
+            }),
+        };
+        if self
+            .source_workspace
+            .files
+            .get(path)
+            .is_none_or(|buffer| !nav::exact_cursor(&buffer.text, cursor))
+        {
+            self.source_symbols.notice =
+                Some("That source location is no longer available. Run navigation again.".into());
+            return;
+        }
+        if let Some(buffer) = self
+            .source_workspace
+            .files
+            .get(&self.source_workspace.active)
+        {
+            let origin = nav::HistoryEntry {
+                session: self.source_workspace.session(),
+                path: self.source_workspace.active.clone(),
+                generation: buffer.generation(),
+                cursor: self.source_editor.cursor(),
+            };
+            self.source_symbols
+                .back
+                .retain(|entry| entry.session == origin.session);
+            if self.source_symbols.back.len() == 64 {
+                self.source_symbols.back.remove(0);
+            }
+            self.source_symbols.back.push(origin);
+        }
+        self.source_workspace
+            .switch(path, self.source_editor.cursor());
+        self.show_source_file(false);
+        self.queue_source_reveal(cursor, false);
+    }
+
+    fn source_symbol_back(&mut self) {
+        while let Some(origin) = self.source_symbols.back.pop() {
+            if origin.session != self.source_workspace.session() {
+                continue;
+            }
+            let Some(buffer) = self.source_workspace.files.get(&origin.path) else {
+                self.source_symbols.notice = Some("The previous file is no longer loaded.".into());
+                return;
+            };
+            let unchanged = origin.generation == buffer.generation();
+            let cursor = if unchanged {
+                origin.cursor
+            } else if origin.path == self.source_workspace.active {
+                self.source_editor.cursor()
+            } else {
+                buffer.cursor
+            };
+            if !nav::exact_cursor(&buffer.text, cursor) {
+                self.source_symbols.notice = Some(
+                    "The previous location changed. Open the file to choose a current position."
+                        .into(),
+                );
+                return;
+            }
+            self.source_workspace
+                .switch(&origin.path, self.source_editor.cursor());
+            self.show_source_file(false);
+            self.queue_source_reveal(cursor, false);
+            self.source_symbols.notice =
+                (!unchanged).then(|| "This draft changed; its current cursor was restored.".into());
+            return;
+        }
+        self.source_symbols.notice = Some("No previous source location in this workspace.".into());
+    }
+}
+
+#[cfg(test)]
+mod tests;

crates/oa-desktop/src/behavior/canvas_workspace.rs

@@ -0,0 +1,244 @@
+//! Shared presentation and input contract; contains no model commands.
+use crate::app::{App, Message};
+use iced::widget::{button, column, container, opaque, row, scrollable, stack, text, tooltip};
+use iced::{Element, Length::Fill, Point, Theme, Vector};
+use oa_core::Id;
+mod control;
+mod focus;
+mod viewport;
+pub use control::Control;
+pub use viewport::Viewport;
+
+pub fn keyboard_enabled(app: &crate::app::App) -> bool {
+    !app.busy
+        && !app.hosted.visible
+        && app.workflow.is_none()
+        && app.file_prompt.is_none()
+        && !app.delete_pending
+        && app.pending.is_none()
+        && app.model_menu.is_none()
+        && app.diagram_usages.is_none()
+        && !app.reference_input_active()
+}
+
+pub fn controls<'a>(
+    scope: Scope,
+    keyboard: bool,
+    scale: f32,
+    details: Message,
+    focus: Option<Message>,
+    zoom: impl Fn(Option<f32>) -> Message,
+    publish: impl Fn(Event) -> Message + Copy + 'a,
+) -> Element<'a, Message> {
+    let control = |name: &'static str, label: &'static str, message: Option<Message>| {
+        let message = message.map(|message| intent(scope, name, message));
+        Control::new(
+            button(text(label).size(12))
+                .padding(6)
+                .on_press_maybe(message.clone()),
+            scope,
+            name,
+            keyboard,
+            message,
+            publish,
+        )
+    };
+    row![
+        control("Details", "Details", Some(details)),
+        tooltip(control("Canvas", "Canvas", focus),
+            container(text("F6: enter/leave canvas controls · Tab: next · Enter/Space: activate · Esc: leave").size(12)).padding(7).style(crate::style::card),
+            tooltip::Position::Bottom),
+        control("Fit", "Fit", Some(zoom(None))),
+        control("ZoomOut", "−", Some(zoom(Some(scale / 1.25)))),
+        text(format!("{:.0}%", scale * 100.)).size(12),
+        control("ZoomIn", "+", Some(zoom(Some(scale * 1.25)))),
+        control("ActualSize", "100%", Some(zoom(Some(1.)))),
+    ].spacing(4).align_y(iced::Center).into()
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Scope {
+    pub document: Id,
+    pub owner: Id,
+    pub revision: u64,
+    pub epoch: u64,
+}
+impl Scope {
+    pub(crate) fn current(app: &App) -> Option<Self> {
+        if let Some(context) = app.scenario_context() {
+            Some(Self {
+                document: context.document,
+                owner: context.scenario,
+                revision: context.revision,
+                epoch: app.camera_epoch,
+            })
+        } else {
+            let context = app.topology_context()?;
+            Some(Self {
+                document: context.document,
+                owner: context.owner,
+                revision: context.revision,
+                epoch: app.camera_epoch,
+            })
+        }
+    }
+    pub(crate) fn input_owner(app: &App) -> Option<Self> {
+        if keyboard_enabled(app)
+            && !app.behavior.has_pending()
+            && !app.draft_dirty()
+            && !app.source_dirty()
+        {
+            Self::current(app)
+        } else {
+            None
+        }
+    }
+
+    pub fn control_id(self, name: &str) -> iced::advanced::widget::Id {
+        iced::advanced::widget::Id::from(format!(
+            "behavior-control:{}:{}:{}:{name}",
+            self.document, self.owner, self.revision
+        ))
+    }
+}
+/// Only a live presentation intent may carry a toolbar action across its own pan.
+#[derive(Debug, Clone)]
+pub struct Intent {
+    pub scope: Scope,
+    pub name: &'static str,
+    pub message: Box<Message>,
+}
+pub fn intent(scope: Scope, name: &'static str, message: Message) -> Message {
+    Message::BehaviorControl(Intent {
+        scope,
+        name,
+        message: Box::new(message),
+    })
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum Event {
+    CancelGesture,
+    Pan(Vector),
+    Zoom { factor: f32, at: Point, base: f32 },
+    Focus,
+    Traverse(bool),
+    ControlFocus(&'static str),
+    ToggleFocus,
+    Leave,
+}
+
+pub use focus::{focus_task, root as focus_root};
+/// Fold relative input in event order. The base scale is used only on leaving Fit.
+pub fn change(pan: &mut Vector, zoom: &mut Option<f32>, fit: &mut bool, event: Event) -> bool {
+    match event {
+        Event::Pan(delta) if delta.x.is_finite() && delta.y.is_finite() => {
+            let next = *pan + delta;
+            if next.x.is_finite() && next.y.is_finite() && next != *pan {
+                *pan = next;
+                true
+            } else {
+                false
+            }
+        }
+        Event::Zoom { factor, at, base }
+            if factor.is_finite()
+                && factor > 0.
+                && base.is_finite()
+                && base > 0.
+                && at.x.is_finite()
+                && at.y.is_finite() =>
+        {
+            let old = if *fit { base } else { zoom.unwrap_or(base) };
+            let next = (old * factor).clamp(0.05, 3.);
+            if old == next {
+                return false;
+            }
+            let anchor = Vector::new(at.x, at.y);
+            let next_pan = anchor - (anchor - *pan) * (next / old);
+            if !next_pan.x.is_finite() || !next_pan.y.is_finite() {
+                return false;
+            }
+            *pan = next_pan;
+            *zoom = Some(next);
+            *fit = false;
+            true
+        }
+        _ => false,
+    }
+}
+
+/// Constant-width labelled palette. Arming a tool never reallocates the canvas.
+pub fn palette<'a>(
+    scope: Scope,
+    keyboard: bool,
+    publish: impl Fn(Event) -> Message + Copy + 'a,
+    entries: impl IntoIterator<Item = (&'static str, &'static str, bool, Option<Message>)>,
+) -> Element<'a, Message> {
+    let mut tools = column![].spacing(3);
+    for (glyph, label, selected, message) in entries {
+        let message = message.map(|message| intent(scope, glyph, message));
+        tools = tools.push(tooltip(
+            container(Control::new(
+                button(text(glyph).size(12))
+                    .width(34)
+                    .height(30)
+                    .padding(3)
+                    .style(if selected {
+                        button::primary
+                    } else {
+                        crate::style::nav
+                    })
+                    .on_press_maybe(message.clone()),
+                scope,
+                glyph,
+                keyboard,
+                message,
+                publish,
+            ))
+            .id(format!("behavior-tool:{glyph}")),
+            container(text(label).size(12))
+                .padding(7)
+                .style(crate::style::card),
+            tooltip::Position::Left,
+        ));
+    }
+    container(scrollable(tools).id(scope.control_id("palette-scroll")))
+        .width(40)
+        .height(Fill)
+        .padding(3)
+        .style(crate::style::panel)
+        .into()
+}
+
+/// Header and palette are permanent. Details/editors overlay the same viewport.
+pub fn host<'a, Message: 'a, R: iced::advanced::text::Renderer + 'a>(
+    header: Element<'a, Message, Theme, R>,
+    palette: Element<'a, Message, Theme, R>,
+    canvas: Element<'a, Message, Theme, R>,
+    editor: Option<Element<'a, Message, Theme, R>>,
+) -> Element<'a, Message, Theme, R> {
+    let mut body = stack![canvas];
+    if let Some(editor) = editor {
+        body = body.push(
+            container(opaque(
+                container(editor)
+                    .width(300)
+                    .height(Fill)
+                    .style(crate::style::card),
+            ))
+            .align_right(Fill)
+            .height(Fill)
+            .padding(8),
+        );
+    }
+    column![header, row![body, palette].height(Fill)]
+        .spacing(6)
+        .padding(8)
+        .width(Fill)
+        .height(Fill)
+        .into()
+}
+
+#[cfg(test)]
+pub(crate) mod tests;

crates/oa-desktop/src/behavior/canvas_workspace/control.rs

@@ -0,0 +1,256 @@
+//! A real focusable keyboard target around the existing styled pointer button.
+use super::{Event as CameraEvent, Scope, focus::Member};
+use iced::advanced::{
+    Clipboard, Layout, Shell, Widget, layout, overlay, renderer,
+    widget::{Operation, Tree, operation, tree},
+};
+use iced::{Border, Element, Event, Length, Rectangle, Size, Theme, Vector, keyboard, mouse};
+
+#[derive(Default)]
+struct Input {
+    identity: Option<iced::advanced::widget::Id>,
+    focused: bool,
+}
+impl operation::Focusable for Input {
+    fn is_focused(&self) -> bool {
+        self.focused
+    }
+    fn focus(&mut self) {
+        self.focused = true;
+    }
+    fn unfocus(&mut self) {
+        self.focused = false;
+    }
+}
+pub struct Control<'a, Message, R = iced::Renderer>
+where
+    R: renderer::Renderer,
+{
+    content: Element<'a, Message, Theme, R>,
+    scope: Scope,
+    name: &'static str,
+    enabled: bool,
+    activate: Option<Message>,
+    publish: Box<dyn Fn(CameraEvent) -> Message + 'a>,
+}
+impl<'a, Message, R: renderer::Renderer> Control<'a, Message, R> {
+    pub fn new(
+        content: impl Into<Element<'a, Message, Theme, R>>,
+        scope: Scope,
+        name: &'static str,
+        enabled: bool,
+        activate: Option<Message>,
+        publish: impl Fn(CameraEvent) -> Message + 'a,
+    ) -> Self {
+        Self {
+            content: content.into(),
+            scope,
+            name,
+            enabled: enabled && activate.is_some(),
+            activate,
+            publish: Box::new(publish),
+        }
+    }
+}
+impl<Message: Clone, R: renderer::Renderer> Widget<Message, Theme, R> for Control<'_, Message, R> {
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<Input>()
+    }
+    fn state(&self) -> tree::State {
+        tree::State::new(Input {
+            identity: Some(self.scope.control_id(self.name)),
+            focused: false,
+        })
+    }
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(self.content.as_widget())]
+    }
+    fn diff(&self, tree: &mut Tree) {
+        let state = tree.state.downcast_mut::<Input>();
+        let identity = self.scope.control_id(self.name);
+        if state.identity.as_ref() != Some(&identity) || !self.enabled {
+            *state = Input {
+                identity: Some(identity),
+                focused: false,
+            };
+        }
+        tree.diff_children(std::slice::from_ref(&self.content));
+    }
+    fn size(&self) -> Size<Length> {
+        self.content.as_widget().size()
+    }
+    fn layout(&mut self, tree: &mut Tree, renderer: &R, limits: &layout::Limits) -> layout::Node {
+        self.content
+            .as_widget_mut()
+            .layout(&mut tree.children[0], renderer, limits)
+    }
+    fn operate(
+        &mut self,
+        tree: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &R,
+        operation: &mut dyn Operation,
+    ) {
+        let id = self.scope.control_id(self.name);
+        operation.container(Some(&id), layout.bounds());
+        if self.enabled {
+            operation.custom(Some(&id), layout.bounds(), &mut Member(self.scope));
+            operation.focusable(
+                Some(&id),
+                layout.bounds(),
+                tree.state.downcast_mut::<Input>(),
+            );
+        }
+        operation.traverse(&mut |operation| {
+            self.content.as_widget_mut().operate(
+                &mut tree.children[0],
+                layout,
+                renderer,
+                operation,
+            );
+        });
+    }
+    fn update(
+        &mut self,
+        tree: &mut Tree,
+        event: &Event,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        renderer: &R,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        viewport: &Rectangle,
+    ) {
+        if shell.is_event_captured() {
+            return;
+        }
+        let state = tree.state.downcast_mut::<Input>();
+        if self.enabled {
+            if let Event::Keyboard(keyboard::Event::KeyPressed {
+                key,
+                modifiers,
+                repeat,
+                ..
+            }) = event
+                && state.focused
+            {
+                use keyboard::{Key, key::Named};
+                let action = match key.as_ref() {
+                    Key::Named(Named::Tab) => {
+                        Some((self.publish)(CameraEvent::Traverse(modifiers.shift())))
+                    }
+                    Key::Named(Named::Escape) => Some((self.publish)(CameraEvent::Leave)),
+                    Key::Named(Named::F6) if modifiers.is_empty() && !repeat => {
+                        Some((self.publish)(CameraEvent::ToggleFocus))
+                    }
+                    Key::Named(Named::Enter | Named::Space) if modifiers.is_empty() && !repeat => {
+                        self.activate.clone()
+                    }
+                    _ => None,
+                };
+                if let Some(action) = action {
+                    shell.publish(action);
+                    shell.capture_event();
+                    shell.request_redraw();
+                    return;
+                }
+            }
+            if matches!(
+                event,
+                Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
+            ) && !layout
+                .bounds()
+                .intersection(viewport)
+                .is_some_and(|bounds| cursor.is_over(bounds))
+            {
+                state.focused = false;
+            }
+        }
+        if matches!(event, Event::Window(iced::window::Event::Unfocused)) {
+            state.focused = false;
+        }
+        self.content.as_widget_mut().update(
+            &mut tree.children[0],
+            event,
+            layout,
+            cursor,
+            renderer,
+            clipboard,
+            shell,
+            viewport,
+        );
+    }
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut R,
+        theme: &Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+    ) {
+        self.content.as_widget().draw(
+            &tree.children[0],
+            renderer,
+            theme,
+            style,
+            layout,
+            cursor,
+            viewport,
+        );
+        if self.enabled && tree.state.downcast_ref::<Input>().focused {
+            renderer.fill_quad(
+                renderer::Quad {
+                    bounds: layout.bounds(),
+                    border: Border {
+                        color: crate::style::INK,
+                        width: 2.,
+                        ..Default::default()
+                    },
+                    ..Default::default()
+                },
+                iced::Color::TRANSPARENT,
+            );
+        }
+    }
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+        renderer: &R,
+    ) -> mouse::Interaction {
+        self.content.as_widget().mouse_interaction(
+            &tree.children[0],
+            layout,
+            cursor,
+            viewport,
+            renderer,
+        )
+    }
+    fn overlay<'a>(
+        &'a mut self,
+        tree: &'a mut Tree,
+        layout: Layout<'a>,
+        renderer: &R,
+        viewport: &Rectangle,
+        translation: Vector,
+    ) -> Option<overlay::Element<'a, Message, Theme, R>> {
+        self.content.as_widget_mut().overlay(
+            &mut tree.children[0],
+            layout,
+            renderer,
+            viewport,
+            translation,
+        )
+    }
+}
+impl<'a, Message: Clone + 'a, R: renderer::Renderer + 'a> From<Control<'a, Message, R>>
+    for Element<'a, Message, Theme, R>
+{
+    fn from(control: Control<'a, Message, R>) -> Self {
+        Element::new(control)
+    }
+}

crates/oa-desktop/src/behavior/canvas_workspace/focus.rs

@@ -0,0 +1,293 @@
+//! Explicit canvas entry; ordinary initial Tab continues to belong to Inspector.
+use super::{Event, Scope};
+use iced::advanced::widget::{Id, Operation, Tree, operation};
+use iced::advanced::{Clipboard, Layout, Shell, Widget, layout, overlay, renderer};
+use iced::{Element, Event as InputEvent, Length, Rectangle, Size, Theme, Vector, mouse};
+
+pub(super) struct Member(pub Scope);
+
+pub fn focus_task<Message: Send + 'static>(scope: Scope, event: Event) -> iced::Task<Message> {
+    iced::advanced::widget::operate(Collect {
+        scope,
+        valid: false,
+        event,
+        members: vec![],
+        focused: None,
+        palette: None,
+    })
+}
+struct Collect {
+    scope: Scope,
+    valid: bool,
+    event: Event,
+    members: Vec<(Id, Rectangle)>,
+    focused: Option<usize>,
+    palette: Option<(Rectangle, Rectangle)>,
+}
+impl<T: Send + 'static> Operation<T> for Collect {
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn Operation<T>)) {
+        visit(self);
+    }
+    fn custom(&mut self, id: Option<&Id>, bounds: Rectangle, value: &mut dyn std::any::Any) {
+        if let Some(owner) = value.downcast_ref::<Owner>() {
+            self.valid = owner.0 == Some(self.scope);
+        }
+        if self.valid
+            && value
+                .downcast_ref::<Member>()
+                .is_some_and(|m| m.0 == self.scope)
+            && let Some(id) = id
+        {
+            self.members.push((id.clone(), bounds));
+        }
+    }
+    fn focusable(&mut self, id: Option<&Id>, _: Rectangle, value: &mut dyn operation::Focusable) {
+        if value.is_focused() {
+            self.focused = self
+                .members
+                .iter()
+                .position(|(member, _)| Some(member) == id)
+                .or(self.focused);
+        }
+    }
+    fn scrollable(
+        &mut self,
+        id: Option<&Id>,
+        bounds: Rectangle,
+        content: Rectangle,
+        _: Vector,
+        _: &mut dyn operation::Scrollable,
+    ) {
+        if id == Some(&self.scope.control_id("palette-scroll")) {
+            self.palette = Some((bounds, content));
+        }
+    }
+    fn finish(&self) -> operation::Outcome<T> {
+        let canvas = self.scope.control_id("viewport");
+        // An enabled viewport witnesses the live lifetime. Hidden/dirty/modal
+        // owners expose no members; a delayed request cannot clear their focus.
+        if !self.valid || !self.members.iter().any(|(id, _)| *id == canvas) {
+            return operation::Outcome::None;
+        }
+        let target = match self.event {
+            Event::Focus => Some(canvas),
+            Event::ControlFocus(name) => Some(self.scope.control_id(name)),
+            Event::ToggleFocus if self.focused.is_none() => Some(canvas),
+            Event::ToggleFocus | Event::Leave if self.focused.is_some() => None,
+            Event::Traverse(back) => {
+                let Some(current) = self.focused else {
+                    return operation::Outcome::None;
+                };
+                let next = if back {
+                    (current + self.members.len() - 1) % self.members.len()
+                } else {
+                    (current + 1) % self.members.len()
+                };
+                Some(self.members[next].0.clone())
+            }
+            _ => return operation::Outcome::None,
+        };
+        if target
+            .as_ref()
+            .is_some_and(|target| !self.members.iter().any(|(id, _)| id == target))
+        {
+            return operation::Outcome::None;
+        }
+        let reveal = target.as_ref().and_then(|target| {
+            let (_, field) = self.members.iter().find(|(id, _)| id == target)?;
+            let (bounds, content) = self.palette?;
+            // Only the palette has member controls inside this scrollable.
+            (field.x >= bounds.x && field.x < bounds.x + bounds.width).then(|| {
+                (field.center_y() - bounds.y - bounds.height / 2.)
+                    .clamp(0., (content.height - bounds.height).max(0.))
+            })
+        });
+        operation::Outcome::Chain(Box::new(Apply {
+            scope: self.scope,
+            valid: false,
+            target,
+            members: self.members.iter().map(|(id, _)| id.clone()).collect(),
+            palette: self.scope.control_id("palette-scroll"),
+            reveal,
+        }))
+    }
+}
+struct Apply {
+    scope: Scope,
+    valid: bool,
+    target: Option<Id>,
+    members: Vec<Id>,
+    palette: Id,
+    reveal: Option<f32>,
+}
+impl<T> Operation<T> for Apply {
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn Operation<T>)) {
+        visit(self);
+    }
+    fn custom(&mut self, _: Option<&Id>, _: Rectangle, value: &mut dyn std::any::Any) {
+        if let Some(owner) = value.downcast_ref::<Owner>() {
+            self.valid = owner.0 == Some(self.scope);
+        }
+    }
+    fn focusable(&mut self, id: Option<&Id>, _: Rectangle, state: &mut dyn operation::Focusable) {
+        if !self.valid {
+            return;
+        }
+        if self
+            .target
+            .as_ref()
+            .is_some_and(|target| Some(target) == id)
+        {
+            state.focus();
+        } else if self.target.is_some() || id.is_some_and(|id| self.members.contains(id)) {
+            state.unfocus();
+        }
+    }
+    fn scrollable(
+        &mut self,
+        id: Option<&Id>,
+        _: Rectangle,
+        _: Rectangle,
+        _: Vector,
+        state: &mut dyn operation::Scrollable,
+    ) {
+        if self.valid
+            && id == Some(&self.palette)
+            && let Some(y) = self.reveal
+        {
+            state.scroll_to(operation::scrollable::AbsoluteOffset {
+                x: None,
+                y: Some(y),
+            });
+        }
+    }
+}
+
+// Every Collect/Apply pass observes current ownership before touching any field.
+struct Owner(Option<Scope>);
+
+struct Root<'a, Message, R: renderer::Renderer> {
+    owner: Option<Scope>,
+    content: Element<'a, Message, Theme, R>,
+}
+
+pub fn root<'a, Message: 'a, R: renderer::Renderer + 'a>(
+    content: impl Into<Element<'a, Message, Theme, R>>,
+    owner: Option<Scope>,
+) -> Element<'a, Message, Theme, R> {
+    Element::new(Root {
+        owner,
+        content: content.into(),
+    })
+}
+
+impl<Message, R: renderer::Renderer> Widget<Message, Theme, R> for Root<'_, Message, R> {
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(self.content.as_widget())]
+    }
+
+    fn diff(&self, tree: &mut Tree) {
+        tree.diff_children(std::slice::from_ref(&self.content));
+    }
+
+    fn size(&self) -> Size<Length> {
+        self.content.as_widget().size()
+    }
+
+    fn layout(&mut self, tree: &mut Tree, renderer: &R, limits: &layout::Limits) -> layout::Node {
+        self.content
+            .as_widget_mut()
+            .layout(&mut tree.children[0], renderer, limits)
+    }
+
+    fn operate(
+        &mut self,
+        tree: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &R,
+        operation: &mut dyn Operation,
+    ) {
+        operation.custom(None, layout.bounds(), &mut Owner(self.owner));
+        self.content
+            .as_widget_mut()
+            .operate(&mut tree.children[0], layout, renderer, operation);
+    }
+
+    fn update(
+        &mut self,
+        tree: &mut Tree,
+        event: &InputEvent,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        renderer: &R,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        viewport: &Rectangle,
+    ) {
+        self.content.as_widget_mut().update(
+            &mut tree.children[0],
+            event,
+            layout,
+            cursor,
+            renderer,
+            clipboard,
+            shell,
+            viewport,
+        );
+    }
+
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut R,
+        theme: &Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+    ) {
+        self.content.as_widget().draw(
+            &tree.children[0],
+            renderer,
+            theme,
+            style,
+            layout,
+            cursor,
+            viewport,
+        );
+    }
+
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+        renderer: &R,
+    ) -> mouse::Interaction {
+        self.content.as_widget().mouse_interaction(
+            &tree.children[0],
+            layout,
+            cursor,
+            viewport,
+            renderer,
+        )
+    }
+
+    fn overlay<'b>(
+        &'b mut self,
+        tree: &'b mut Tree,
+        layout: Layout<'b>,
+        renderer: &R,
+        viewport: &Rectangle,
+        translation: Vector,
+    ) -> Option<overlay::Element<'b, Message, Theme, R>> {
+        self.content.as_widget_mut().overlay(
+            &mut tree.children[0],
+            layout,
+            renderer,
+            viewport,
+            translation,
+        )
+    }
+}

crates/oa-desktop/src/behavior/canvas_workspace/tests.rs

@@ -0,0 +1,757 @@
+use super::*;
+use crate::app::{App, Message};
+use iced::advanced::{Layout, Shell, layout, widget};
+use iced::futures::{
+    StreamExt,
+    stream::{BoxStream, SelectAll},
+};
+use iced::{Rectangle, Size, mouse};
+use iced_runtime::{
+    Action,
+    user_interface::{Cache, UserInterface},
+};
+use std::collections::HashMap;
+
+type Pending = SelectAll<BoxStream<'static, Action<Message>>>;
+
+// iced_winit drains messages while collecting immediately ready actions. A
+// pending Task stream survives until its widget operation sends its result.
+fn enqueue(task: iced::Task<Message>, ready: &mut Vec<Action<Message>>, pending: &mut Pending) {
+    if let Some(mut stream) = iced_runtime::task::into_stream(task) {
+        let waker = iced::futures::task::noop_waker();
+        let mut context = std::task::Context::from_waker(&waker);
+        loop {
+            match stream.poll_next_unpin(&mut context) {
+                std::task::Poll::Ready(Some(action)) => ready.push(action),
+                std::task::Poll::Ready(None) => break,
+                std::task::Poll::Pending => {
+                    pending.push(stream);
+                    break;
+                }
+            }
+        }
+    }
+}
+
+#[derive(Default)]
+pub(crate) struct Geometry {
+    pub containers: HashMap<widget::Id, Rectangle>,
+    pub focused: Vec<(Option<widget::Id>, Rectangle, bool)>,
+    pub text_inputs: Vec<Rectangle>,
+    pub scrolls: HashMap<widget::Id, (Rectangle, Vector)>,
+}
+impl widget::Operation for Geometry {
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn widget::Operation)) {
+        visit(self);
+    }
+    fn focusable(
+        &mut self,
+        id: Option<&widget::Id>,
+        bounds: Rectangle,
+        state: &mut dyn widget::operation::Focusable,
+    ) {
+        self.focused.push((id.cloned(), bounds, state.is_focused()));
+    }
+    fn text_input(
+        &mut self,
+        _: Option<&widget::Id>,
+        bounds: Rectangle,
+        _: &mut dyn widget::operation::TextInput,
+    ) {
+        self.text_inputs.push(bounds);
+    }
+    fn container(&mut self, id: Option<&widget::Id>, bounds: Rectangle) {
+        if let Some(id) = id {
+            self.containers.insert(id.clone(), bounds);
+        }
+    }
+    fn scrollable(
+        &mut self,
+        id: Option<&widget::Id>,
+        bounds: Rectangle,
+        _: Rectangle,
+        offset: Vector,
+        _: &mut dyn widget::operation::Scrollable,
+    ) {
+        if let Some(id) = id {
+            self.scrolls.insert(id.clone(), (bounds, offset));
+        }
+    }
+}
+impl Geometry {
+    pub fn bounds(&self, id: &str) -> Rectangle {
+        self.containers[&widget::Id::from(id.to_owned())]
+    }
+}
+
+/// Mount the actual App root, production widgets and renderer. Events are
+/// delivered in order with Iced's final-batch cursor, then fed through App::update.
+/// This deliberately does not seed any private canvas gesture state.
+pub(crate) struct Mounted {
+    pub renderer: iced::Renderer,
+    cache: Cache,
+    pub operations: usize,
+}
+impl Mounted {
+    pub async fn unshown() -> Self {
+        use iced::advanced::renderer::Headless;
+        let renderer = <iced::Renderer as Headless>::new(iced::Font::DEFAULT, 16.into(), None)
+            .await
+            .expect("production mounted tests require the supported WGPU headless renderer");
+        Self {
+            renderer,
+            cache: Cache::new(),
+            operations: 0,
+        }
+    }
+    pub async fn new(app: &mut App) -> Self {
+        let mut mounted = Self::unshown().await;
+        mounted.settle(app).await;
+        mounted
+    }
+    pub fn geometry(&mut self, app: &App) -> Geometry {
+        let mut geometry = Geometry::default();
+        self.operate(app, &mut geometry);
+        geometry
+    }
+    /// One operation pass, including every nested overlay, via installed Iced.
+    pub fn operate(&mut self, app: &App, operation: &mut dyn widget::Operation) {
+        let mut ui = UserInterface::build(
+            app.view(),
+            app.window_size,
+            std::mem::take(&mut self.cache),
+            &mut self.renderer,
+        );
+        ui.operate(&self.renderer, operation);
+        self.cache = ui.into_cache();
+    }
+    pub async fn settle(&mut self, app: &mut App) {
+        for _ in 0..3 {
+            self.batch(
+                app,
+                &[iced::Event::Window(iced::window::Event::RedrawRequested(
+                    std::time::Instant::now(),
+                ))],
+                mouse::Cursor::Unavailable,
+            )
+            .await;
+        }
+    }
+    pub async fn batch(
+        &mut self,
+        app: &mut App,
+        events: &[iced::Event],
+        cursor: mouse::Cursor,
+    ) -> Vec<Message> {
+        let messages = self.input(app, events, cursor);
+        let mut ready = vec![];
+        let mut pending = Pending::new();
+        for message in messages.iter().cloned() {
+            enqueue(app.update(message), &mut ready, &mut pending);
+        }
+        self.drain(app, ready, pending).await;
+        messages
+    }
+    pub fn input(
+        &mut self,
+        app: &App,
+        events: &[iced::Event],
+        cursor: mouse::Cursor,
+    ) -> Vec<Message> {
+        let mut messages = vec![];
+        let mut ui = UserInterface::build(
+            app.view(),
+            app.window_size,
+            std::mem::take(&mut self.cache),
+            &mut self.renderer,
+        );
+        let _ = ui.update(
+            events,
+            cursor,
+            &mut self.renderer,
+            &mut iced::advanced::clipboard::Null,
+            &mut messages,
+        );
+        self.cache = ui.into_cache();
+        messages
+    }
+    pub async fn perform(&mut self, app: &mut App, task: iced::Task<Message>) {
+        let mut ready = vec![];
+        let mut pending = Pending::new();
+        enqueue(task, &mut ready, &mut pending);
+        self.drain(app, ready, pending).await;
+    }
+    async fn drain(
+        &mut self,
+        app: &mut App,
+        mut ready: Vec<Action<Message>>,
+        mut pending: Pending,
+    ) {
+        loop {
+            let mut outputs = vec![];
+            if !ready.is_empty() {
+                // Build only after all App messages in this cycle have run.
+                let mut ui = UserInterface::build(
+                    app.view(),
+                    app.window_size,
+                    std::mem::take(&mut self.cache),
+                    &mut self.renderer,
+                );
+                for action in ready.drain(..) {
+                    match action {
+                        Action::Output(message) => outputs.push(message),
+                        Action::Widget(mut operation) => {
+                            self.operations += 1;
+                            loop {
+                                ui.operate(&self.renderer, &mut *operation);
+                                match operation.finish() {
+                                    widget::operation::Outcome::Chain(next) => operation = next,
+                                    widget::operation::Outcome::None
+                                    | widget::operation::Outcome::Some(()) => break,
+                                }
+                            }
+                        }
+                        action => {
+                            panic!("Unexpected native action in mounted App harness: {action:?}")
+                        }
+                    }
+                }
+                self.cache = ui.into_cache();
+            }
+            for message in outputs {
+                enqueue(app.update(message), &mut ready, &mut pending);
+            }
+            if !ready.is_empty() {
+                continue;
+            }
+            let Some(action) = pending.next().await else {
+                break;
+            };
+            ready.push(action);
+            let waker = iced::futures::task::noop_waker();
+            let mut context = std::task::Context::from_waker(&waker);
+            while let std::task::Poll::Ready(Some(action)) = pending.poll_next_unpin(&mut context) {
+                ready.push(action);
+            }
+        }
+    }
+    pub fn pixels(&mut self, app: &App) -> Vec<u8> {
+        use iced::advanced::renderer::Headless;
+        let mut ui = UserInterface::build(
+            app.view(),
+            app.window_size,
+            std::mem::take(&mut self.cache),
+            &mut self.renderer,
+        );
+        // update initializes the nested overlay layout used by draw.
+        let mut messages = vec![];
+        let _ = ui.update(
+            &[],
+            mouse::Cursor::Unavailable,
+            &mut self.renderer,
+            &mut iced::advanced::clipboard::Null,
+            &mut messages,
+        );
+        assert!(
+            messages.is_empty(),
+            "An empty draw preparation must not drop App messages"
+        );
+        ui.draw(
+            &mut self.renderer,
+            &crate::style::theme(),
+            &iced::advanced::renderer::Style {
+                text_color: crate::style::INK,
+            },
+            mouse::Cursor::Unavailable,
+        );
+        self.cache = ui.into_cache();
+        Headless::screenshot(
+            &mut self.renderer,
+            Size::new(app.window_size.width as u32, app.window_size.height as u32),
+            1.,
+            crate::style::BG,
+        )
+    }
+    pub async fn click(&mut self, app: &mut App, point: Point) -> Vec<Message> {
+        self.batch(
+            app,
+            &[
+                iced::Event::Mouse(mouse::Event::CursorMoved { position: point }),
+                iced::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)),
+                iced::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left)),
+            ],
+            mouse::Cursor::Available(point),
+        )
+        .await
+    }
+    pub async fn pan(&mut self, app: &mut App, start: Point, end: Point) -> Vec<Message> {
+        self.batch(
+            app,
+            &[
+                iced::Event::Mouse(mouse::Event::CursorMoved { position: start }),
+                iced::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Middle)),
+                iced::Event::Mouse(mouse::Event::CursorMoved { position: end }),
+                iced::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Middle)),
+            ],
+            mouse::Cursor::Available(end),
+        )
+        .await
+    }
+    pub fn scroll(&mut self, app: &App, id: &str, offset: f32) {
+        let mut operation = widget::operation::scrollable::scroll_to::<()>(
+            widget::Id::from(id.to_owned()),
+            widget::operation::scrollable::AbsoluteOffset {
+                x: None,
+                y: Some(offset),
+            },
+        );
+        self.operate(app, &mut operation);
+    }
+}
+
+pub(crate) fn key(named: iced::keyboard::key::Named) -> iced::Event {
+    use iced::keyboard::{self, Key};
+    iced::Event::Keyboard(keyboard::Event::KeyPressed {
+        key: Key::Named(named),
+        modified_key: Key::Named(named),
+        physical_key: keyboard::key::Physical::Unidentified(
+            keyboard::key::NativeCode::Unidentified,
+        ),
+        location: keyboard::Location::Standard,
+        modifiers: keyboard::Modifiers::empty(),
+        text: None,
+        repeat: false,
+    })
+}
+
+#[test]
+fn relative_camera_zoom_keeps_the_cursor_world_point_and_rejects_nonfinite_inputs() {
+    for scale in [0.05, 0.5, 1., 2.] {
+        let mut pan = Vector::new(-130., 75.);
+        let mut zoom = Some(scale);
+        let mut fit = false;
+        let at = Point::new(171., 93.);
+        let world = (at - Point::ORIGIN - pan) / scale;
+        change(
+            &mut pan,
+            &mut zoom,
+            &mut fit,
+            Event::Zoom {
+                factor: 1.25,
+                at,
+                base: scale,
+            },
+        );
+        let after = (at - Point::ORIGIN - pan) / zoom.unwrap();
+        assert!((after.x - world.x).abs() < 0.001 && (after.y - world.y).abs() < 0.001);
+        let before = (pan, zoom, fit);
+        for input in [
+            Event::Pan(Vector::new(f32::INFINITY, 0.)),
+            Event::Zoom {
+                factor: f32::NAN,
+                at,
+                base: scale,
+            },
+            Event::Zoom {
+                factor: 0.,
+                at,
+                base: scale,
+            },
+        ] {
+            assert!(!change(&mut pan, &mut zoom, &mut fit, input));
+            assert_eq!((pan, zoom, fit), before);
+        }
+    }
+}
+
+#[test]
+fn viewport_ordered_batch_uses_each_event_position_and_cancels_before_camera_motion() {
+    use iced::widget::Space;
+    let scope = Scope {
+        document: Id::new_v4(),
+        owner: Id::new_v4(),
+        revision: 2,
+        epoch: 0,
+    };
+    let mut view: Element<'_, Event, Theme, ()> = Viewport::new(
+        Space::new().width(Fill).height(Fill),
+        scope,
+        1.,
+        true,
+        |e| e,
+    )
+    .into();
+    let mut tree = widget::Tree::new(view.as_widget());
+    let node = view
+        .as_widget_mut()
+        .layout(
+            &mut tree,
+            &(),
+            &layout::Limits::new(Size::ZERO, Size::new(400., 300.)),
+        )
+        .move_to(Point::new(30., 80.));
+    let start = Point::new(90., 160.);
+    let middle = Point::new(125., 175.);
+    let end = Point::new(145., 185.);
+    let mut messages = vec![];
+    for event in [
+        mouse::Event::CursorMoved { position: start },
+        mouse::Event::ButtonPressed(mouse::Button::Middle),
+        mouse::Event::CursorMoved { position: middle },
+        mouse::Event::CursorMoved { position: end },
+        mouse::Event::ButtonReleased(mouse::Button::Middle),
+    ] {
+        view.as_widget_mut().update(
+            &mut tree,
+            &iced::Event::Mouse(event),
+            Layout::new(&node),
+            mouse::Cursor::Available(end),
+            &(),
+            &mut iced::advanced::clipboard::Null,
+            &mut Shell::new(&mut messages),
+            &Rectangle::with_size(Size::new(700., 600.)),
+        );
+    }
+    assert!(matches!(messages.first(), Some(Event::CancelGesture)));
+    let total = messages
+        .iter()
+        .fold(Vector::ZERO, |total, event| match event {
+            Event::Pan(delta) => total + *delta,
+            _ => total,
+        });
+    assert_eq!(total, end - start);
+}
+
+pub(crate) fn scope(app: &App) -> Scope {
+    if let Some(context) = app.scenario_context() {
+        Scope {
+            document: context.document,
+            owner: context.scenario,
+            revision: context.revision,
+            epoch: app.camera_epoch,
+        }
+    } else {
+        let context = app.topology_context().expect("mounted behavior owner");
+        Scope {
+            document: context.document,
+            owner: context.owner,
+            revision: context.revision,
+            epoch: app.camera_epoch,
+        }
+    }
+}
+pub(crate) fn focused(mounted: &mut Mounted, app: &App, name: &str) -> bool {
+    let id = scope(app).control_id(name);
+    mounted
+        .geometry(app)
+        .focused
+        .iter()
+        .any(|(member, _, focused)| member.as_ref() == Some(&id) && *focused)
+}
+pub(crate) async fn tab_to(mounted: &mut Mounted, app: &mut App, name: &str) {
+    for _ in 0..32 {
+        if focused(mounted, app, name) {
+            return;
+        }
+        mounted
+            .batch(
+                app,
+                &[key(iced::keyboard::key::Named::Tab)],
+                mouse::Cursor::Unavailable,
+            )
+            .await;
+    }
+    panic!("Keyboard traversal did not reach {name}");
+}
+pub(crate) fn camera_delta(messages: &[Message]) -> Message {
+    messages.iter().find(|m| matches!(m,
+        Message::ScenarioCanvas(crate::behavior::scenario::CanvasEvent::Camera(_, _, Event::Pan(delta)))
+        | Message::TopologyCanvas(crate::behavior::topology::CanvasEvent::Camera(_, _, Event::Pan(delta))) if *delta != Vector::ZERO
+    )).expect("actual nonzero camera delta from a mounted gesture").clone()
+}
+pub(crate) async fn press_middle(mounted: &mut Mounted, app: &mut App, point: Point) {
+    mounted
+        .batch(
+            app,
+            &[
+                iced::Event::Mouse(mouse::Event::CursorMoved { position: point }),
+                iced::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Middle)),
+            ],
+            mouse::Cursor::Available(point),
+        )
+        .await;
+}
+pub(crate) async fn release_middle(
+    mounted: &mut Mounted,
+    app: &mut App,
+    point: Point,
+) -> Vec<Message> {
+    mounted
+        .batch(
+            app,
+            &[
+                iced::Event::Mouse(mouse::Event::CursorMoved { position: point }),
+                iced::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Middle)),
+            ],
+            mouse::Cursor::Available(point),
+        )
+        .await
+}
+pub(crate) fn assert_drawn_focus(before: &[u8], after: &[u8], size: Size, bounds: Rectangle) {
+    let width = size.width as usize;
+    assert_eq!(before.len(), width * size.height as usize * 4);
+    assert_eq!(after.len(), before.len());
+    let mut changed = 0;
+    for y in bounds.y.ceil() as usize..(bounds.y + bounds.height).floor() as usize {
+        for x in bounds.x.ceil() as usize..(bounds.x + bounds.width).floor() as usize {
+            if x as f32 - bounds.x > 2.
+                && bounds.x + bounds.width - x as f32 > 2.
+                && y as f32 - bounds.y > 2.
+                && bounds.y + bounds.height - y as f32 > 2.
+            {
+                continue;
+            }
+            let start = (y * width + x) * 4;
+            if before[start..start + 3] != after[start..start + 3] {
+                changed += 1;
+            }
+        }
+    }
+    assert!(
+        changed >= bounds.width.min(bounds.height) as usize,
+        "Focus must change visible border pixels, changed={changed}, bounds={bounds:?}"
+    );
+}
+
+pub(crate) fn character(value: &str) -> iced::Event {
+    let mut event = key(iced::keyboard::key::Named::Space);
+    if let iced::Event::Keyboard(iced::keyboard::Event::KeyPressed {
+        key,
+        modified_key,
+        text,
+        ..
+    }) = &mut event
+    {
+        *key = iced::keyboard::Key::Character(value.into());
+        *modified_key = key.clone();
+        *text = Some(value.into());
+    }
+    event
+}
+
+/// Inspect the action without stripping the lifetime from retained packets.
+pub(crate) fn intent_action(message: &Message) -> &Message {
+    match message {
+        Message::BehaviorControl(intent) => &intent.message,
+        message => message,
+    }
+}
+
+/// Deliberately retain a returned Chain to test the stronger ownership invariant.
+/// Native Iced runs Chain passes synchronously; this is not a native interleaving.
+pub(crate) async fn retained_focus_apply(
+    mounted: &mut Mounted,
+    app: &mut App,
+) -> Box<dyn widget::Operation> {
+    let entry = mounted.input(
+        app,
+        &[key(iced::keyboard::key::Named::F6)],
+        mouse::Cursor::Unavailable,
+    );
+    assert_eq!(
+        entry.len(),
+        1,
+        "actual initial F6 must emit one canvas focus request"
+    );
+    let mut stream = iced_runtime::task::into_stream(app.update(entry[0].clone()))
+        .expect("F6 returns a widget Task");
+    let Some(Action::Widget(mut operation)) = stream.next().await else {
+        panic!("F6 first action must be Collect");
+    };
+    mounted.operate(app, &mut *operation);
+    match operation.finish() {
+        widget::operation::Outcome::Chain(apply) => apply,
+        _ => panic!("Live Collect must produce its guarded Apply pass"),
+    }
+}
+
+pub(crate) async fn overflow_last_tool(mounted: &mut Mounted, app: &mut App, last: &'static str) {
+    use iced::keyboard::key::Named;
+    let geometry = mounted.geometry(app);
+    let last_bounds = geometry.containers[&scope(app).control_id(last)];
+    let (rail, offset) = geometry.scrolls[&scope(app).control_id("palette-scroll")];
+    assert_eq!(offset.y, 0.);
+    assert!(
+        last_bounds.y >= rail.y + rail.height,
+        "last tool starts fully below the overflowing palette: tool={last_bounds:?}, rail={rail:?}"
+    );
+    mounted
+        .batch(app, &[key(Named::F6)], mouse::Cursor::Unavailable)
+        .await;
+    tab_to(mounted, app, last).await;
+    let geometry = mounted.geometry(app);
+    let mut visible = geometry.containers[&scope(app).control_id(last)];
+    let (rail, offset) = geometry.scrolls[&scope(app).control_id("palette-scroll")];
+    assert!(offset.y > 0., "keyboard traversal must scroll the palette");
+    visible.x -= offset.x;
+    visible.y -= offset.y;
+    assert!(
+        visible.y >= rail.y && visible.y + visible.height <= rail.y + rail.height + 0.5,
+        "the entire last tool is revealed: tool={visible:?}, rail={rail:?}"
+    );
+    let messages = mounted
+        .batch(app, &[key(Named::Enter)], mouse::Cursor::Unavailable)
+        .await;
+    assert!(
+        messages.iter().any(
+            |message| matches!(message, Message::BehaviorControl(intent) if intent.name == last)
+        ),
+        "the revealed last tool is keyboard activated"
+    );
+    assert!(focused(mounted, app, last));
+    let on = mounted.pixels(app);
+    mounted
+        .batch(app, &[key(Named::Escape)], mouse::Cursor::Unavailable)
+        .await;
+    let off = mounted.pixels(app);
+    assert_drawn_focus(&off, &on, app.window_size, visible);
+}
+
+pub(crate) async fn retained_toolbar_boundaries(
+    mounted: &mut Mounted,
+    app: &mut App,
+    tool: &'static str,
+) {
+    use iced::keyboard::key::Named;
+    for boundary in ["Chooser", "Dirty", "Picker"] {
+        let mut packets = vec![];
+        for name in ["Fit", tool, "Details", "Panels", "Canvas"] {
+            packets.push(capture_toolbar(mounted, app, name));
+        }
+        let lifetime = app.camera_epoch;
+        let epoch = app.canvas_epoch;
+        let process = app.behavior.topology.camera_boundary();
+        let scenario = app.behavior.scenario.camera_boundary();
+        match boundary {
+            "Chooser" => {
+                let draft = app.draft.as_ref().unwrap();
+                let id = crate::forms::reference_chooser::trigger::field_id(
+                    draft.reference_generation(),
+                    "/parent",
+                );
+                let bounds = mounted
+                    .geometry(app)
+                    .focused
+                    .iter()
+                    .find(|(field, _, _)| field.as_ref() == Some(&id))
+                    .expect("real Inspector parent reference trigger")
+                    .1;
+                let request = draft.reference_open(app.project(), "/parent", bounds);
+                let task = app.update(Message::FieldReferenceOpen(request));
+                mounted.perform(app, task).await;
+                assert!(app.reference_input_active());
+                mounted
+                    .batch(app, &[key(Named::Escape)], mouse::Cursor::Unavailable)
+                    .await;
+                assert!(!app.reference_input_active());
+            }
+            "Dirty" => {
+                let task = app.update(Message::Field(
+                    "/name".into(),
+                    "Unsaved camera boundary".into(),
+                ));
+                mounted.perform(app, task).await;
+                assert!(app.draft_dirty());
+                // Every retained packet is also rejected while the owner is dirty.
+                for packet in packets.iter().cloned() {
+                    let task = app.update(packet);
+                    mounted.perform(app, task).await;
+                }
+                assert!(app.draft_dirty());
+                let task = app.update(Message::RevertProperties);
+                mounted.perform(app, task).await;
+                assert!(!app.draft_dirty());
+            }
+            "Picker" => {
+                // Public transitions, with cancellation injected at the external
+                // picker boundary. Never poll the native dialog future here.
+                let picker = app.update(Message::Save(true));
+                if cfg!(target_os = "linux") {
+                    assert!(app.file_prompt.is_some());
+                    mounted.perform(app, picker).await;
+                    let task = app.update(Message::CancelFile);
+                    mounted.perform(app, task).await;
+                } else {
+                    assert!(app.busy, "Save As enters the real native-picker busy state");
+                    drop(picker);
+                    for packet in packets.iter().cloned() {
+                        let task = app.update(packet);
+                        mounted.perform(app, task).await;
+                    }
+                    let task = app.update(Message::SavePath(None));
+                    mounted.perform(app, task).await;
+                    assert!(!app.busy);
+                }
+            }
+            _ => unreachable!(),
+        }
+        assert_ne!(
+            app.camera_epoch, lifetime,
+            "{boundary} changes the presentation lifetime"
+        );
+        assert_eq!(
+            app.canvas_epoch, epoch,
+            "{boundary} cycle leaves semantic context unchanged"
+        );
+        let focus_before = mounted
+            .geometry(app)
+            .focused
+            .into_iter()
+            .filter(|(_, _, value)| *value)
+            .collect::<Vec<_>>();
+        let current_lifetime = app.camera_epoch;
+        for packet in packets {
+            let task = app.update(packet);
+            mounted.perform(app, task).await;
+        }
+        assert_eq!(
+            app.camera_epoch, current_lifetime,
+            "{boundary} retained intents cannot start a new lifetime"
+        );
+        assert!(
+            app.behavior.topology.camera_boundary() == process,
+            "{boundary} retained toolbar packet changed process presentation"
+        );
+        assert!(
+            app.behavior.scenario.camera_boundary() == scenario,
+            "{boundary} retained toolbar packet changed scenario presentation"
+        );
+        assert_eq!(
+            mounted
+                .geometry(app)
+                .focused
+                .into_iter()
+                .filter(|(_, _, value)| *value)
+                .collect::<Vec<_>>(),
+            focus_before,
+            "{boundary} retained toolbar packet stole field focus"
+        );
+    }
+}
+
+pub(crate) fn capture_toolbar(mounted: &mut Mounted, app: &App, name: &'static str) -> Message {
+    let point = mounted.geometry(app).containers[&scope(app).control_id(name)].center();
+    mounted
+        .input(
+            app,
+            &[
+                iced::Event::Mouse(mouse::Event::CursorMoved { position: point }),
+                iced::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)),
+                iced::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left)),
+            ],
+            mouse::Cursor::Available(point),
+        )
+        .into_iter()
+        .find(|message| matches!(message, Message::BehaviorControl(intent) if intent.name == name))
+        .expect("actual production toolbar packet")
+}

crates/oa-desktop/src/behavior/canvas_workspace/viewport.rs

@@ -0,0 +1,426 @@
+use super::{Event as CameraEvent, Scope};
+use iced::advanced::{
+    Clipboard, Layout, Shell, Widget, layout, overlay, renderer,
+    widget::{Operation, Tree, operation, tree},
+};
+use iced::{Border, Element, Event, Length, Point, Rectangle, Size, Theme, Vector};
+use iced::{keyboard, mouse};
+
+#[derive(Default)]
+struct Input {
+    scope: Option<Scope>,
+    focused: bool,
+    pointer: Option<Point>,
+    pan: Option<(mouse::Button, Point)>,
+    space: bool,
+    bounds: Option<Rectangle>,
+}
+impl operation::Focusable for Input {
+    fn is_focused(&self) -> bool {
+        self.focused
+    }
+    fn focus(&mut self) {
+        self.focused = true;
+    }
+    fn unfocus(&mut self) {
+        self.focused = false;
+        self.pan = None;
+        self.space = false;
+    }
+}
+pub struct Viewport<'a, Message, R = iced::Renderer>
+where
+    R: renderer::Renderer,
+{
+    content: Element<'a, Message, Theme, R>,
+    scope: Scope,
+    scale: f32,
+    keyboard: bool,
+    blank_pan: bool,
+    publish: Box<dyn Fn(CameraEvent) -> Message + 'a>,
+}
+impl<'a, Message, R: renderer::Renderer> Viewport<'a, Message, R> {
+    pub fn new(
+        content: impl Into<Element<'a, Message, Theme, R>>,
+        scope: Scope,
+        scale: f32,
+        keyboard: bool,
+        publish: impl Fn(CameraEvent) -> Message + 'a,
+    ) -> Self {
+        Self {
+            content: content.into(),
+            scope,
+            scale,
+            keyboard,
+            blank_pan: false,
+            publish: Box::new(publish),
+        }
+    }
+    pub fn pan_background(mut self, enabled: bool) -> Self {
+        self.blank_pan = enabled;
+        self
+    }
+}
+impl<Message, R: renderer::Renderer> Widget<Message, Theme, R> for Viewport<'_, Message, R> {
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<Input>()
+    }
+    fn state(&self) -> tree::State {
+        tree::State::new(Input {
+            scope: Some(self.scope),
+            ..Default::default()
+        })
+    }
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(self.content.as_widget())]
+    }
+    fn diff(&self, tree: &mut Tree) {
+        let state = tree.state.downcast_mut::<Input>();
+        if state.scope.is_none_or(|s| {
+            (s.document, s.owner, s.revision)
+                != (self.scope.document, self.scope.owner, self.scope.revision)
+        }) {
+            *state = Input::default();
+        }
+        if state
+            .scope
+            .is_some_and(|scope| scope.epoch != self.scope.epoch)
+            || !self.keyboard
+        {
+            state.pan = None;
+            state.space = false;
+        }
+        if !self.keyboard {
+            state.focused = false;
+        }
+        state.scope = Some(self.scope);
+        tree.diff_children(std::slice::from_ref(&self.content));
+    }
+    fn size(&self) -> Size<Length> {
+        Size::new(Length::Fill, Length::Fill)
+    }
+    fn layout(&mut self, tree: &mut Tree, renderer: &R, limits: &layout::Limits) -> layout::Node {
+        self.content
+            .as_widget_mut()
+            .layout(&mut tree.children[0], renderer, limits)
+    }
+    fn operate(
+        &mut self,
+        tree: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &R,
+        operation: &mut dyn Operation,
+    ) {
+        if self.keyboard {
+            let id = self.scope.control_id("viewport");
+            operation.custom(
+                Some(&id),
+                layout.bounds(),
+                &mut super::focus::Member(self.scope),
+            );
+            operation.focusable(
+                Some(&id),
+                layout.bounds(),
+                tree.state.downcast_mut::<Input>(),
+            );
+        }
+        self.content
+            .as_widget_mut()
+            .operate(&mut tree.children[0], layout, renderer, operation);
+    }
+    fn update(
+        &mut self,
+        tree: &mut Tree,
+        event: &Event,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        renderer: &R,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        viewport: &Rectangle,
+    ) {
+        if shell.is_event_captured() {
+            return;
+        }
+        let state = tree.state.downcast_mut::<Input>();
+        let changed_bounds = state.bounds.is_some_and(|bounds| bounds != layout.bounds());
+        state.bounds = Some(layout.bounds());
+        if changed_bounds || !self.keyboard {
+            state.pan = None;
+            state.space = false;
+        }
+        if !self.keyboard {
+            state.focused = false;
+        }
+        if let Event::Mouse(mouse::Event::CursorMoved { position }) = event {
+            state.pointer = Some(*position);
+        }
+        let pointer = match event {
+            Event::Mouse(
+                mouse::Event::ButtonPressed(_)
+                | mouse::Event::ButtonReleased(_)
+                | mouse::Event::WheelScrolled { .. },
+            ) => state.pointer.or_else(|| cursor.position()),
+            Event::Mouse(mouse::Event::CursorMoved { position }) => Some(*position),
+            _ => cursor.position().or(state.pointer),
+        };
+        let visible = layout.bounds().intersection(viewport);
+        let inside = pointer.is_some_and(|p| visible.is_some_and(|v| v.contains(p)))
+            && cursor.position().is_some();
+        if !self.keyboard {
+            state.space = false;
+        }
+        let mut cancel = changed_bounds;
+        let mut camera = None;
+        let mut capture = false;
+        match event {
+            Event::Window(iced::window::Event::Unfocused | iced::window::Event::Resized(_)) => {
+                state.pan = None;
+                state.space = false;
+                state.focused = false;
+            }
+            Event::Mouse(mouse::Event::CursorLeft) => {
+                state.pan = None;
+                state.pointer = None;
+            }
+            Event::Mouse(mouse::Event::ButtonPressed(button)) => {
+                if state.pan.is_some_and(|(held, _)| held != *button) || !inside {
+                    state.pan = None;
+                    state.space = false;
+                    cancel = true;
+                }
+                state.focused = inside && self.keyboard;
+                if inside
+                    && self.keyboard
+                    && (*button == mouse::Button::Middle
+                        || (*button == mouse::Button::Left && state.space))
+                {
+                    state.pan = pointer.map(|p| (*button, p));
+                    cancel = true;
+                    camera = Some(CameraEvent::CancelGesture);
+                    capture = true;
+                }
+            }
+            Event::Mouse(mouse::Event::CursorMoved { position }) => {
+                if let Some((button, previous)) = state.pan {
+                    state.pan = Some((button, *position));
+                    camera = Some(CameraEvent::Pan(*position - previous));
+                    capture = true;
+                }
+            }
+            Event::Mouse(mouse::Event::ButtonReleased(button)) => {
+                if let Some((held, previous)) = state.pan
+                    && held == *button
+                {
+                    state.pan = None;
+                    camera = pointer
+                        .filter(|_| inside)
+                        .map(|p| CameraEvent::Pan(p - previous));
+                    capture = true;
+                }
+            }
+            Event::Mouse(mouse::Event::WheelScrolled { delta }) if inside && state.focused => {
+                state.pan = None;
+                cancel = true;
+                let y = match delta {
+                    mouse::ScrollDelta::Lines { y, .. } => *y,
+                    mouse::ScrollDelta::Pixels { y, .. } => *y / 40.,
+                };
+                if y != 0. {
+                    let at = pointer.unwrap() - Vector::new(layout.bounds().x, layout.bounds().y);
+                    camera = Some(CameraEvent::Zoom {
+                        factor: 1.1_f32.powf(y.clamp(-8., 8.)),
+                        at,
+                        base: self.scale,
+                    });
+                    capture = true;
+                }
+            }
+            Event::Keyboard(keyboard::Event::KeyPressed {
+                key: keyboard::Key::Named(keyboard::key::Named::F6),
+                modifiers,
+                repeat: false,
+                ..
+            }) if self.keyboard && modifiers.is_empty() => {
+                camera = Some(CameraEvent::ToggleFocus);
+                capture = true;
+                cancel = true;
+            }
+            Event::Keyboard(keyboard::Event::KeyPressed { key, modifiers, .. })
+                if state.focused && self.keyboard =>
+            {
+                use keyboard::{Key, key::Named};
+                match key.as_ref() {
+                    Key::Named(Named::Space) => {
+                        state.space = true;
+                        cancel = true;
+                        camera = Some(CameraEvent::CancelGesture);
+                        capture = true;
+                    }
+                    Key::Named(Named::Tab) => {
+                        camera = Some(CameraEvent::Traverse(modifiers.shift()));
+                        capture = true;
+                    }
+                    Key::Named(Named::Escape) => {
+                        state.pan = None;
+                        state.space = false;
+                        camera = Some(CameraEvent::Leave);
+                        capture = true;
+                    }
+                    Key::Named(key) if modifiers.is_empty() => {
+                        let delta = match key {
+                            Named::ArrowLeft => Some(Vector::new(60., 0.)),
+                            Named::ArrowRight => Some(Vector::new(-60., 0.)),
+                            Named::ArrowUp => Some(Vector::new(0., 60.)),
+                            Named::ArrowDown => Some(Vector::new(0., -60.)),
+                            _ => None,
+                        };
+                        camera = delta.map(CameraEvent::Pan);
+                        capture = camera.is_some();
+                        cancel = capture;
+                    }
+                    _ => {}
+                }
+            }
+            Event::Keyboard(keyboard::Event::KeyReleased { key, .. })
+                if *key == keyboard::Key::Named(keyboard::key::Named::Space) =>
+            {
+                state.space = false;
+            }
+            _ => {}
+        }
+        if cancel {
+            self.content.as_widget_mut().update(
+                &mut tree.children[0],
+                &Event::Window(iced::window::Event::Unfocused),
+                layout,
+                cursor,
+                renderer,
+                clipboard,
+                shell,
+                viewport,
+            );
+        }
+        if let Some(event) = camera {
+            shell.publish((self.publish)(event));
+        }
+        if capture {
+            shell.capture_event();
+            shell.request_redraw();
+            return;
+        }
+        if matches!(event, Event::Keyboard(_)) && (!state.focused || !self.keyboard) {
+            return;
+        }
+        let child_cursor = if inside {
+            pointer.map_or(mouse::Cursor::Unavailable, mouse::Cursor::Available)
+        } else {
+            mouse::Cursor::Unavailable
+        };
+        self.content.as_widget_mut().update(
+            &mut tree.children[0],
+            event,
+            layout,
+            child_cursor,
+            renderer,
+            clipboard,
+            shell,
+            viewport,
+        );
+        // A semantic hit or armed creation tool gets first refusal. In Select,
+        // an otherwise unused blank press starts the same camera gesture.
+        if self.blank_pan
+            && self.keyboard
+            && inside
+            && !shell.is_event_captured()
+            && matches!(
+                event,
+                Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left))
+            )
+        {
+            state.pan = pointer.map(|p| (mouse::Button::Left, p));
+            shell.publish((self.publish)(CameraEvent::CancelGesture));
+            shell.capture_event();
+            shell.request_redraw();
+        }
+    }
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut R,
+        theme: &Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+    ) {
+        renderer.with_layer(layout.bounds(), |renderer| {
+            self.content.as_widget().draw(
+                &tree.children[0],
+                renderer,
+                theme,
+                style,
+                layout,
+                cursor,
+                viewport,
+            );
+        });
+        if tree.state.downcast_ref::<Input>().focused && self.keyboard {
+            renderer.fill_quad(
+                renderer::Quad {
+                    bounds: layout.bounds(),
+                    border: Border {
+                        color: crate::style::TEAL,
+                        width: 1.,
+                        ..Default::default()
+                    },
+                    ..Default::default()
+                },
+                iced::Color::TRANSPARENT,
+            );
+        }
+    }
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+        renderer: &R,
+    ) -> mouse::Interaction {
+        if tree.state.downcast_ref::<Input>().pan.is_some() {
+            mouse::Interaction::Grabbing
+        } else {
+            self.content.as_widget().mouse_interaction(
+                &tree.children[0],
+                layout,
+                cursor,
+                viewport,
+                renderer,
+            )
+        }
+    }
+    fn overlay<'a>(
+        &'a mut self,
+        tree: &'a mut Tree,
+        layout: Layout<'a>,
+        renderer: &R,
+        viewport: &Rectangle,
+        translation: Vector,
+    ) -> Option<overlay::Element<'a, Message, Theme, R>> {
+        self.content.as_widget_mut().overlay(
+            &mut tree.children[0],
+            layout,
+            renderer,
+            viewport,
+            translation,
+        )
+    }
+}
+impl<'a, Message: 'a, R: renderer::Renderer + 'a> From<Viewport<'a, Message, R>>
+    for Element<'a, Message, Theme, R>
+{
+    fn from(viewport: Viewport<'a, Message, R>) -> Self {
+        Element::new(viewport)
+    }
+}

crates/oa-desktop/src/behavior/creation.rs

@@ -75,6 +75,7 @@ impl Picker {
 }
 #[derive(Debug, Clone)]
 pub enum Event {
+    Source(super::source_draft::Event),
     Open(Layer),
     Choose(Family),
     Name(String),
@@ -97,6 +98,11 @@ struct Browser {
 #[derive(Clone, Serialize, Deserialize)]
 #[serde(deny_unknown_fields)]
 struct Draft {
+    #[serde(default)]
+    source: super::source_draft::State,
+    #[serde(default = "Id::new_v4")]
+    invocation: Id,
+
     version: u32,
     document: Id,
     layer: Layer,
@@ -125,6 +131,17 @@ pub struct Created {
 }
 
 impl State {
+    pub fn source_active(&self) -> bool {
+        self.draft.as_ref().is_some_and(|d| d.source.engaged())
+    }
+
+    pub fn source_open(&self) -> bool {
+        self.draft.as_ref().is_some_and(|d| d.source.is_open())
+    }
+    pub fn source_back(&mut self) -> bool {
+        self.draft.as_mut().is_some_and(|d| d.source.back())
+    }
+
     pub fn has_pending(&self) -> bool {
         self.draft.is_some()
     }
@@ -174,6 +191,49 @@ impl State {
             .command(p)
     }
     pub fn update(&mut self, p: &Project, event: Event) -> Result<Option<Command>, String> {
+        if let Event::Source(event) = event {
+            if self
+                .draft
+                .as_mut()
+                .ok_or("Start the consumer form first.")?
+                .source
+                .dismiss(&event)?
+            {
+                return Ok(None);
+            }
+            let d = self
+                .draft
+                .as_ref()
+                .ok_or("Start the consumer form first.")?;
+            if d.family != Some(Family::Machine) {
+                return Err("This reference does not support staged source creation.".into());
+            }
+            if d.document != p.id {
+                return Err("This behavior draft belongs to another document.".into());
+            }
+            let mut next = d.clone();
+            if let Some(id) = next.source.update(
+                p,
+                super::source_draft::Scope::Machine { layer: d.layer },
+                d.invocation,
+                event,
+            )? {
+                next.owner = Some(id);
+                let preview = next
+                    .source
+                    .preview(p, next.owner)?
+                    .ok_or("New owner preview is missing.")?;
+                if !eligible(&preview, next.layer, Picker::Owner, id) {
+                    return Err("This participant cannot own the machine.".into());
+                }
+            }
+            self.draft = Some(next);
+            return Ok(None);
+        }
+        if self.source_open() && !matches!(&event, Event::Cancel) {
+            return Err("Use the new source or go Back before editing the parent form.".into());
+        }
+
         match event {
             Event::Cancel => {
                 self.draft = None;
@@ -184,6 +244,8 @@ impl State {
                     return Err("Create or cancel the pending behavior first.".into());
                 }
                 self.draft = Some(Draft {
+                    source: Default::default(),
+                    invocation: Id::new_v4(),
                     version: 1,
                     document: p.id,
                     layer,
@@ -332,7 +394,7 @@ fn reference_context(p: &Project, e: &Element) -> String {
     };
     format!("{} · {} · {location}", e.kind(), e.alias)
 }
-fn reference_label(p: &Project, id: Id) -> String {
+pub(super) fn reference_label(p: &Project, id: Id) -> String {
     p.elements
         .get(&id)
         .map(|e| format!("{} · {}", e.name, reference_context(p, e)))
@@ -340,6 +402,15 @@ fn reference_label(p: &Project, id: Id) -> String {
 }
 impl Draft {
     fn command(&self, p: &Project) -> Result<Command, String> {
+        self.source.check_scope(
+            super::source_draft::Scope::Machine { layer: self.layer },
+            self.owner,
+        )?;
+        let preview = self.source.preview(p, self.owner)?;
+        let command = self.consumer_command(preview.as_ref().unwrap_or(p))?;
+        self.source.combine(p, self.owner, command)
+    }
+    fn consumer_command(&self, p: &Project) -> Result<Command, String> {
         if self.document != p.id {
             return Err("This draft belongs to another document.".into());
         }
@@ -475,6 +546,21 @@ impl State {
         p: &'a Project,
     ) -> Option<UiElement<'a, Event, iced::Theme, R>> {
         let d = self.draft.as_ref()?;
+        if let Some(view) = d.source.view(p) {
+            return Some(
+                column![
+                    text(format!(
+                        "State machine name: {}",
+                        crate::views::short(&d.name, 60)
+                    ))
+                    .size(12),
+                    view.map(Event::Source)
+                ]
+                .spacing(6)
+                .height(Fill)
+                .into(),
+            );
+        }
         let mut fields = column![].spacing(10);
         let title = if let Some(family) = d.family {
             fields = fields.push(
@@ -488,7 +574,7 @@ impl State {
                 Family::Sequence => {
                     fields = fields.push(
                         text(format!(
-                            "Owned by the {} layer root. Involve existing work after creation.",
+                            "Owned by the {} layer root. Add work and exchange contributions after creation.",
                             d.layer
                         ))
                         .size(12),
@@ -531,7 +617,17 @@ impl State {
                     }
                 }
                 Family::Machine => {
+                    if let Some(label) = d.source.label(d.owner) {
+                        fields = fields.push(text(label).size(13)).push(text("Create and open commits the new owner and machine together, including the first view only when selected.").size(12));
+                    }
                     fields = fields.push(picker_view(p, d, Picker::Owner));
+                    fields = fields.push(
+                        button("Create new owner…")
+                            .on_press(Event::Source(super::source_draft::Event::Open(
+                                d.invocation,
+                            )))
+                            .padding(7),
+                    );
                     fields = fields.push(
                         checkbox(d.first_view)
                             .label("Create the first state view")
@@ -544,9 +640,9 @@ impl State {
         } else {
             for family in [Family::Sequence, Family::Scenario, Family::Machine] {
                 let purpose = match family {
-                    Family::Sequence => "A path through existing work and exchanges",
+                    Family::Sequence => "A path through work and exchanges",
                     Family::Scenario => "Ordered interactions from an explicit viewpoint",
-                    Family::Machine => "States and modes of an existing participant",
+                    Family::Machine => "States and modes of an explicitly chosen participant",
                 };
                 fields = fields.push(
                     button(
@@ -598,7 +694,9 @@ fn picker_view<'a, R: iced::advanced::text::Renderer + 'a>(
         Picker::Owner => d.owner,
         Picker::Context => d.context,
     };
+    let staged_owner = picker == Picker::Owner && d.source.label(selected).is_some();
     let title = match picker {
+        Picker::Owner if staged_owner => "Or choose an existing participant",
         Picker::Owner => "Owned by participant",
         Picker::Context => "Scenario context · optional",
     };
@@ -609,14 +707,17 @@ fn picker_view<'a, R: iced::advanced::text::Renderer + 'a>(
             .padding(6)
     ]
     .spacing(5);
-    if let Some(id) = selected {
+    if let Some(id) = selected
+        && !staged_owner
+    {
         out = out.push(text(format!("Selected: {}", reference_label(p, id))).size(12));
     } else if picker == Picker::Context {
         out = out.push(text("No context selected").size(12));
     }
     if options.is_empty() {
         out = out.push(text(match picker {
-            Picker::Owner => "No matching participant. Refine the search, or cancel and create a participant in Architecture first.",
+            Picker::Owner if staged_owner => "No existing participants match this search. The new owner above remains selected.",
+            Picker::Owner => "No matching participant. Refine the search or choose Create new owner.",
             Picker::Context => "No matching context. Refine the search, or leave this optional reference empty.",
         }).size(12));
     }

crates/oa-desktop/src/behavior/form_session.rs

@@ -0,0 +1,148 @@
+//! Keep behavior field state within one editing session and reset it on replacement.
+use iced::advanced::widget::{Operation, Tree, tree};
+use iced::advanced::{Clipboard, Layout, Shell, Widget, layout, overlay, renderer};
+use iced::{Element, Event, Length, Rectangle, Size, Theme, Vector, mouse};
+use oa_core::Id;
+
+struct Identity(Id);
+
+struct Session<'a, Message, R: renderer::Renderer> {
+    identity: Id,
+    content: Element<'a, Message, Theme, R>,
+}
+
+pub(super) fn reset_on_change<'a, Message: 'a, R: renderer::Renderer + 'a>(
+    identity: Id,
+    content: impl Into<Element<'a, Message, Theme, R>>,
+) -> Element<'a, Message, Theme, R> {
+    Element::new(Session {
+        identity,
+        content: content.into(),
+    })
+}
+
+impl<Message, R: renderer::Renderer> Widget<Message, Theme, R> for Session<'_, Message, R> {
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<Identity>()
+    }
+
+    fn state(&self) -> tree::State {
+        tree::State::new(Identity(self.identity))
+    }
+
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(self.content.as_widget())]
+    }
+
+    fn diff(&self, tree: &mut Tree) {
+        let retained = tree.state.downcast_mut::<Identity>();
+        if retained.0 != self.identity {
+            retained.0 = self.identity;
+            // Iced's keyed column preserves same-length child replacements.
+            // An editing-session replacement must instead get fresh field state.
+            tree.children = self.children();
+        } else {
+            tree.diff_children(std::slice::from_ref(&self.content));
+        }
+    }
+
+    fn size(&self) -> Size<Length> {
+        self.content.as_widget().size()
+    }
+
+    fn layout(&mut self, tree: &mut Tree, renderer: &R, limits: &layout::Limits) -> layout::Node {
+        self.content
+            .as_widget_mut()
+            .layout(&mut tree.children[0], renderer, limits)
+    }
+
+    fn operate(
+        &mut self,
+        tree: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &R,
+        operation: &mut dyn Operation,
+    ) {
+        self.content
+            .as_widget_mut()
+            .operate(&mut tree.children[0], layout, renderer, operation);
+    }
+
+    fn update(
+        &mut self,
+        tree: &mut Tree,
+        event: &Event,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        renderer: &R,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        viewport: &Rectangle,
+    ) {
+        self.content.as_widget_mut().update(
+            &mut tree.children[0],
+            event,
+            layout,
+            cursor,
+            renderer,
+            clipboard,
+            shell,
+            viewport,
+        );
+    }
+
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut R,
+        theme: &Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+    ) {
+        self.content.as_widget().draw(
+            &tree.children[0],
+            renderer,
+            theme,
+            style,
+            layout,
+            cursor,
+            viewport,
+        );
+    }
+
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+        renderer: &R,
+    ) -> mouse::Interaction {
+        self.content.as_widget().mouse_interaction(
+            &tree.children[0],
+            layout,
+            cursor,
+            viewport,
+            renderer,
+        )
+    }
+
+    fn overlay<'b>(
+        &'b mut self,
+        tree: &'b mut Tree,
+        layout: Layout<'b>,
+        renderer: &R,
+        viewport: &Rectangle,
+        translation: Vector,
+    ) -> Option<overlay::Element<'b, Message, Theme, R>> {
+        self.content.as_widget_mut().overlay(
+            &mut tree.children[0],
+            layout,
+            renderer,
+            viewport,
+            translation,
+        )
+    }
+}

crates/oa-desktop/src/behavior/scenario.rs

@@ -4,7 +4,10 @@ use super::topology::{occurrence, unique_batch};
 use super::*;
 use iced::widget::{Column, column, text_input};
 use std::{cell::RefCell, collections::BTreeSet};
+pub(crate) mod focus;
+mod usage;
 mod workspace;
+pub(crate) use workspace::NAME_INPUT;
 pub use workspace::{Shelf, view};
 
 #[cfg(test)]
@@ -97,7 +100,9 @@ pub enum CanvasEvent {
     Scrolled(Context, ScrollArea, iced::Vector),
     Restored(Context, Id, ScrollArea, iced::Vector),
     Viewport(Context, Size),
+    FormShown(Context, Id),
     Zoom(Context, Option<f32>),
+    Camera(Context, u64, super::canvas_workspace::Event),
     Focus(Context),
     Shelf(Context, Shelf),
     OpenUse(Context, Id),
@@ -125,8 +130,7 @@ pub enum CanvasEvent {
 }
 #[derive(Debug, Clone, Copy)]
 pub enum ScrollArea {
-    Canvas,
-    // Retained navigation channel, now the independent Selection/outline shelf.
+    // The independent Details/outline scroller; viewport motion uses Camera.
     Page,
 }
 impl CanvasEvent {
@@ -135,7 +139,9 @@ impl CanvasEvent {
             Self::Scrolled(context, _, _)
             | Self::Restored(context, ..)
             | Self::Viewport(context, _)
+            | Self::FormShown(context, _)
             | Self::Zoom(context, _)
+            | Self::Camera(context, ..)
             | Self::Focus(context)
             | Self::Shelf(context, _)
             | Self::OpenUse(context, _)
@@ -162,6 +168,7 @@ impl std::fmt::Display for Operator {
 }
 #[derive(Debug, Clone)]
 pub enum Event {
+    Source(super::source_draft::Event),
     Start(Id, Tool),
     Cancel,
     Submit,
@@ -197,11 +204,14 @@ const VALUE_PAGE_SIZE: usize = 24;
 #[derive(Default)]
 pub struct State {
     draft: Option<Draft>,
+    form_session: Id,
+    form_mount: Id,
+    form_focus_pending: bool,
     canvas_tool: Option<(Id, CanvasTool)>,
     call_choices: RefCell<Option<(CallChoiceContext, Vec<Choice>)>>,
-    scroll_offsets: [iced::Vector; 2],
+    details_offset: iced::Vector,
     return_to: Vec<Caller>,
-    restore: Option<ViewportRestore>,
+    restore: Option<DetailsRestore>,
     presentation: workspace::Presentation,
 }
 const CALLER_LIMIT: usize = 32;
@@ -211,15 +221,14 @@ pub(crate) struct Caller {
     pub occurrence: Id,
     target: Id,
     tool: CanvasTool,
-    offsets: [iced::Vector; 2],
+    details_offset: iced::Vector,
     presentation: workspace::Presentation,
 }
-struct ViewportRestore {
+struct DetailsRestore {
     document: Id,
     owner: Id,
     token: Id,
-    offsets: [iced::Vector; 2],
-    pending: [bool; 2],
+    offset: iced::Vector,
 }
 #[derive(Clone, Copy)]
 pub(super) struct ScrollRestore {
@@ -240,6 +249,13 @@ struct CallChoiceContext {
 #[derive(Clone, serde::Serialize, serde::Deserialize)]
 #[serde(deny_unknown_fields)]
 struct Draft {
+    #[serde(default)]
+    source: super::source_draft::State,
+    #[serde(default = "Id::new_v4")]
+    invocation: Id,
+    #[serde(default)]
+    source_origin: Option<(Id, oa_core::Element)>,
+
     owner: Id,
     parent: Id,
     before: Option<Id>,
@@ -272,6 +288,44 @@ struct Draft {
     choice_page: usize,
 }
 impl State {
+    pub(crate) fn camera_boundary(&self) -> impl PartialEq + use<> {
+        (
+            self.canvas_tool,
+            self.presentation.focused,
+            self.presentation.shelf,
+            self.presentation.viewport,
+            self.presentation.pan,
+            self.presentation.zoom,
+            self.presentation.fit,
+        )
+    }
+
+    pub(super) fn pending_name(&self) -> Option<&str> {
+        self.draft.as_ref().map(|d| d.name.as_str())
+    }
+    pub(super) fn source_view<'a>(&'a self, p: &'a Project) -> Option<iced::Element<'a, Event>> {
+        self.draft
+            .as_ref()?
+            .source
+            .view(p)
+            .map(|v| v.map(Event::Source))
+    }
+
+    pub fn source_active(&self) -> bool {
+        self.draft.as_ref().is_some_and(|d| d.source.engaged())
+    }
+
+    pub fn source_open(&self) -> bool {
+        self.draft.as_ref().is_some_and(|d| d.source.is_open())
+    }
+    pub fn source_back(&mut self) -> bool {
+        let returned = self.draft.as_mut().is_some_and(|d| d.source.back());
+        if returned {
+            self.remount_form();
+        }
+        returned
+    }
+
     pub(crate) fn enter(&mut self, document: Id, owner: Id) {
         if self.presentation.identity != Some((document, owner)) {
             self.presentation = workspace::Presentation {
@@ -279,16 +333,38 @@ impl State {
                 focused: self.presentation.focused,
                 ..Default::default()
             };
-            self.scroll_offsets = [iced::Vector::ZERO; 2];
+            self.details_offset = iced::Vector::ZERO;
             self.restore = None;
         }
     }
     pub(crate) fn viewport(&mut self, size: Size) -> bool {
         self.presentation.viewport(size)
     }
+    pub(crate) fn camera(&mut self, event: super::canvas_workspace::Event) -> bool {
+        let p = &mut self.presentation;
+        super::canvas_workspace::change(&mut p.pan, &mut p.zoom, &mut p.fit, event)
+    }
     pub(crate) fn zoom(&mut self, scale: Option<f32>) -> bool {
         self.presentation.zoom(scale)
     }
+    pub(crate) fn camera_zoom(&mut self, p: &Project, owner: Id, zoom: Option<f32>) -> bool {
+        let size = Scene::sequence(p, owner, owner).size;
+        let old = self.presentation.scale(size);
+        if let Some(next) = zoom {
+            let viewport = self.presentation.viewport.unwrap_or(Size::new(500., 300.));
+            self.camera(super::canvas_workspace::Event::Zoom {
+                factor: next / old,
+                at: Point::new(viewport.width / 2., viewport.height / 2.),
+                base: old,
+            })
+        } else {
+            self.zoom(None);
+            let fitted = self.presentation.scale(size);
+            self.zoom(Some(fitted));
+            self.presentation.pan = iced::Vector::ZERO;
+            true
+        }
+    }
     pub(crate) fn focused(&self) -> bool {
         self.presentation.focused
     }
@@ -317,11 +393,11 @@ impl State {
             occurrence,
             target,
             tool: self.canvas_tool(context.scenario),
-            offsets: self.scroll_offsets,
+            details_offset: self.details_offset,
             presentation: self.presentation.clone(),
         });
         self.canvas_tool = Some((target, CanvasTool::Select));
-        self.scroll_offsets = [iced::Vector::ZERO; 2];
+        self.details_offset = iced::Vector::ZERO;
         self.restore = None;
         Ok(target)
     }
@@ -348,34 +424,30 @@ impl State {
             return;
         }
         self.canvas_tool = Some((frame.owner, frame.tool));
-        self.scroll_offsets = frame.offsets;
+        self.details_offset = frame.details_offset;
         self.presentation = frame.presentation;
         self.presentation.identity = Some((context.document, context.scenario));
-        self.restore = Some(ViewportRestore {
+        self.restore = Some(DetailsRestore {
             document: context.document,
             owner: frame.owner,
             token: Id::new_v4(),
-            offsets: frame.offsets,
-            pending: [true; 2],
+            offset: frame.details_offset,
         });
     }
     pub(super) fn scroll_restore(
         &self,
         context: Context,
-        area: ScrollArea,
+        ScrollArea::Page: ScrollArea,
     ) -> Option<ScrollRestore> {
-        let index = match area {
-            ScrollArea::Canvas => 0,
-            ScrollArea::Page => 1,
-        };
-        let restore = self.restore.as_ref().filter(|r| {
-            r.document == context.document && r.owner == context.scenario && r.pending[index]
-        })?;
+        let restore = self
+            .restore
+            .as_ref()
+            .filter(|r| r.document == context.document && r.owner == context.scenario)?;
         Some(ScrollRestore {
             document: restore.document,
             owner: restore.owner,
             token: restore.token,
-            offset: restore.offsets[index],
+            offset: restore.offset,
         })
     }
     pub(crate) fn restored(
@@ -385,22 +457,12 @@ impl State {
         area: ScrollArea,
         offset: iced::Vector,
     ) -> bool {
-        let index = match area {
-            ScrollArea::Canvas => 0,
-            ScrollArea::Page => 1,
-        };
-        let Some(restore) = self.restore.as_mut().filter(|r| {
-            r.document == context.document
-                && r.owner == context.scenario
-                && r.token == token
-                && r.pending[index]
-        }) else {
+        if !self.restore.as_ref().is_some_and(|r| {
+            r.document == context.document && r.owner == context.scenario && r.token == token
+        }) {
             return false;
-        };
-        restore.pending[index] = false;
-        if !restore.pending.contains(&true) {
-            self.restore = None;
         }
+        self.restore = None;
         self.scrolled(area, offset)
     }
     pub(super) fn recovery_snapshot(&self) -> Result<Option<serde_json::Value>, String> {
@@ -413,28 +475,57 @@ impl State {
 
     pub(super) fn from_recovery(value: serde_json::Value) -> Result<Self, String> {
         let draft = serde_json::from_value(value).map_err(|e| e.to_string())?;
+        let session = Id::new_v4();
         Ok(Self {
             draft: Some(draft),
+            form_session: session,
+            form_mount: session,
+            form_focus_pending: true,
             ..Default::default()
         })
     }
 
-    pub(crate) fn scrolled(&mut self, area: ScrollArea, offset: iced::Vector) -> bool {
+    pub(crate) fn form_session(&self) -> Option<Id> {
+        self.draft.as_ref().map(|_| self.form_session)
+    }
+
+    pub(crate) fn form_mount(&self) -> Option<Id> {
+        self.draft
+            .as_ref()
+            .filter(|d| !d.source.is_open())
+            .map(|_| self.form_mount)
+    }
+
+    pub(crate) fn focus_stamp(&self, context: Context) -> Option<focus::Stamp> {
+        (self.draft.as_ref()?.owner == context.scenario).then_some(focus::Stamp::new(
+            context,
+            self.form_session,
+            self.form_mount()?,
+        ))
+    }
+
+    fn remount_form(&mut self) {
+        self.form_mount = Id::new_v4();
+        self.form_focus_pending = true;
+    }
+
+    pub(crate) fn take_form_focus(&mut self, mount: Id) -> bool {
+        if self.form_mount() == Some(mount) && self.form_focus_pending {
+            self.form_focus_pending = false;
+            true
+        } else {
+            false
+        }
+    }
+
+    pub(crate) fn scrolled(&mut self, ScrollArea::Page: ScrollArea, offset: iced::Vector) -> bool {
         if !offset.x.is_finite() || !offset.y.is_finite() || offset.x < 0. || offset.y < 0. {
             return false;
         }
-        let index = match area {
-            ScrollArea::Canvas => 0,
-            ScrollArea::Page => 1,
-        };
-        let changed = self.scroll_offsets[index] != offset;
-        self.scroll_offsets[index] = offset;
+        let changed = self.details_offset != offset;
+        self.details_offset = offset;
         changed
     }
-    fn scroll_offset(&self) -> iced::Vector {
-        // The former page scroll now belongs to a sibling outline shelf.
-        self.scroll_offsets[0]
-    }
     fn call_choices(&self, p: &Project, context: Context, draft: &Draft) -> Vec<Choice> {
         let key = CallChoiceContext {
             document: context.document,
@@ -452,8 +543,16 @@ impl State {
         }
         cached.as_ref().unwrap().1.clone()
     }
-    pub(crate) fn created_selection(&self, command: &Command) -> Option<Id> {
+    pub(crate) fn created_selection(&self, p: &Project, command: &Command) -> Option<Id> {
         let draft = self.draft.as_ref()?;
+        if self
+            .draft
+            .as_ref()
+            .is_some_and(|d| d.source.label(d.target).is_some())
+            && self.prepare_pending(p).ok().as_ref() != Some(command)
+        {
+            return None;
+        }
         fn created(command: &Command, parent: Id) -> Option<Id> {
             match command {
                 Command::CreateElement(element) if element.parent == Some(parent) => {
@@ -568,6 +667,66 @@ impl State {
     }
 
     pub fn update(&mut self, p: &Project, event: Event) -> Result<Option<Command>, String> {
+        if let Event::Source(event) = event {
+            if self
+                .draft
+                .as_mut()
+                .ok_or("Start the consumer form first.")?
+                .source
+                .dismiss(&event)?
+            {
+                self.remount_form();
+                return Ok(None);
+            }
+            let d = self
+                .draft
+                .as_ref()
+                .ok_or("Start the consumer form first.")?;
+            if d.tool != Tool::Lifeline {
+                return Err("This reference does not support staged source creation.".into());
+            }
+            if d.source_origin.as_ref().is_some_and(|(document, owner)| {
+                *document != p.id || p.elements.get(&d.owner) != Some(owner)
+            }) {
+                return Err("The original consumer changed. Cancel and reopen its form; the current draft is retained.".into());
+            }
+            if d.source_origin.is_none() && d.source.engaged() {
+                return Err("The recovered source draft has no original document binding. Go Back or cancel it.".into());
+            }
+            let mut next = d.clone();
+            if next.source_origin.is_none() && matches!(&event, super::source_draft::Event::Open(_))
+            {
+                next.source_origin = Some((
+                    p.id,
+                    p.elements
+                        .get(&d.owner)
+                        .ok_or("The consumer owner no longer exists.")?
+                        .clone(),
+                ));
+            }
+            if let Some(id) = next.source.update(
+                p,
+                super::source_draft::Scope::Lifeline {
+                    owner: d.owner,
+                    viewpoint: viewpoint(p, d.owner),
+                },
+                d.invocation,
+                event,
+            )? {
+                next.target = Some(id);
+                next.command(p)?;
+            }
+            let returned = d.source.is_open() && !next.source.is_open();
+            self.draft = Some(next);
+            if returned {
+                self.remount_form();
+            }
+            return Ok(None);
+        }
+        if self.source_open() && !matches!(&event, Event::Cancel) {
+            return Err("Use the new source or go Back before editing the parent form.".into());
+        }
+
         if self.draft.is_some() && matches!(&event, Event::Start(..)) {
             return Err(PENDING_DRAFT.into());
         }
@@ -576,7 +735,13 @@ impl State {
                 if p.elements.get(&owner).map(oa_core::Element::kind) != Some(Kind::Scenario) {
                     return Err("Choose a scenario.".into());
                 }
+                self.form_session = Id::new_v4();
+                self.form_mount = self.form_session;
+                self.form_focus_pending = true;
                 self.draft = Some(Draft {
+                    source: Default::default(),
+                    invocation: Id::new_v4(),
+                    source_origin: Some((p.id, p.elements[&owner].clone())),
                     owner,
                     parent: owner,
                     before: None,
@@ -940,7 +1105,14 @@ fn valid_body_choice(p: &Project, owner: Id, body: OccurrenceBody) -> bool {
     execute_batch(p, &[Command::CreateElement(e)]).is_ok()
 }
 fn sources(p: &Project, d: &Draft) -> Vec<Choice> {
-    let layer = p.elements[&d.owner].layer();
+    let Some(owner) = p
+        .elements
+        .get(&d.owner)
+        .filter(|e| e.kind() == Kind::Scenario)
+    else {
+        return vec![];
+    };
+    let layer = owner.layer();
     let mut values: Vec<_> = p
         .elements
         .values()
@@ -1256,6 +1428,28 @@ impl Draft {
         e
     }
     fn command(&self, p: &Project) -> Result<Command, String> {
+        if self.source.engaged()
+            && self.source_origin.as_ref().is_none_or(|(document, owner)| {
+                *document != p.id || p.elements.get(&self.owner) != Some(owner)
+            })
+        {
+            return Err("The original consumer document or owner changed. Cancel and reopen its form; your draft is retained.".into());
+        }
+        self.source.check_scope(
+            super::source_draft::Scope::Lifeline {
+                owner: self.owner,
+                viewpoint: viewpoint(p, self.owner),
+            },
+            self.target,
+        )?;
+        let preview = self.source.preview(p, self.target)?;
+        let command = self.consumer_command(preview.as_ref().unwrap_or(p))?;
+        self.source.combine(p, self.target, command)
+    }
+    fn consumer_command(&self, p: &Project) -> Result<Command, String> {
+        if p.elements.get(&self.owner).map(oa_core::Element::kind) != Some(Kind::Scenario) {
+            return Err("The scenario no longer exists. Cancel or restore its owner.".into());
+        }
         if !parents(p, self.owner).iter().any(|c| c.id == self.parent) {
             return Err("Choose this scenario or one of its operands as destination.".into());
         }
@@ -1266,6 +1460,8 @@ impl Draft {
             .unwrap_or(self.tool.label());
         let name = if self.name.trim().is_empty() {
             default
+        } else if self.source.label(self.target).is_some() {
+            self.name.as_str()
         } else {
             self.name.trim()
         };
@@ -1857,20 +2053,31 @@ pub(crate) mod direct_tests {
             navigation_event(&mut app, |ctx| {
                 CanvasEvent::Choose(ctx, CanvasTool::Add(Tool::Reuse))
             });
+            navigation_event(&mut app, |ctx| CanvasEvent::Zoom(ctx, None));
+            let camera_epoch = app.camera_epoch;
             navigation_event(&mut app, |ctx| {
-                CanvasEvent::Scrolled(ctx, ScrollArea::Canvas, iced::Vector::new(25., 170.))
+                CanvasEvent::Camera(
+                    ctx,
+                    camera_epoch,
+                    super::super::canvas_workspace::Event::Pan(iced::Vector::new(25., 170.)),
+                )
             });
             navigation_event(&mut app, |ctx| {
                 CanvasEvent::Scrolled(ctx, ScrollArea::Page, iced::Vector::new(0., 80.))
             });
             navigation_event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, caller));
             assert_eq!(app.selected, b);
-            assert_eq!(app.behavior.scenario.scroll_offset(), iced::Vector::ZERO);
+            assert_eq!(app.behavior.scenario.presentation.pan, iced::Vector::ZERO);
             navigation_event(&mut app, |ctx| {
                 CanvasEvent::Choose(ctx, CanvasTool::Message(MessageStyle::Timer))
             });
+            let camera_epoch = app.camera_epoch;
             navigation_event(&mut app, |ctx| {
-                CanvasEvent::Scrolled(ctx, ScrollArea::Canvas, iced::Vector::new(0., 115.))
+                CanvasEvent::Camera(
+                    ctx,
+                    camera_epoch,
+                    super::super::canvas_workspace::Event::Pan(iced::Vector::new(0., 115.)),
+                )
             });
             navigation_event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, nested));
             assert_eq!(app.selected, c);
@@ -1881,7 +2088,7 @@ pub(crate) mod direct_tests {
                 CanvasTool::Message(MessageStyle::Timer)
             );
             assert_eq!(
-                app.behavior.scenario.scroll_offset(),
+                app.behavior.scenario.presentation.pan,
                 iced::Vector::new(0., 115.)
             );
             navigation_event(&mut app, CanvasEvent::Back);
@@ -1892,11 +2099,11 @@ pub(crate) mod direct_tests {
                 CanvasTool::Add(Tool::Reuse)
             );
             assert_eq!(
-                app.behavior.scenario.scroll_offset(),
+                app.behavior.scenario.presentation.pan,
                 iced::Vector::new(25., 170.)
             );
             assert_eq!(
-                app.behavior.scenario.scroll_offsets[1],
+                app.behavior.scenario.details_offset,
                 iced::Vector::new(0., 80.),
                 "The caller's independent outline scroll is restored separately"
             );
@@ -2074,22 +2281,24 @@ pub(crate) mod direct_tests {
                     let before = app.document.bundle().clone();
                     let mut scene = Scene::sequence(app.project(), f.owner, f.call);
                     scene.interaction = Some((context, CanvasTool::Add(tool), true));
-                    scene.scroll_offset = iced::Vector::new(23., 80.);
-                    let bounds = Rectangle::new(Point::new(20., 40.), scene.size);
+                    scene.camera_pan = iced::Vector::new(23., 80.);
+                    let bounds = Rectangle::new(
+                        Point::new(20., 40.),
+                        Size::new(scene.size.width + 46., scene.size.height + 160.),
+                    );
                     let y = scene.slots.iter().find(|s| s.slot == slot).unwrap().y;
                     let x = if on_lifeline {
                         scene.lanes[&f.sender]
                     } else {
                         scene.size.width - 35.
                     };
-                    let point = Point::new(bounds.x + x, bounds.y + y);
+                    let point = Point::new(bounds.x + x, bounds.y + y) + scene.camera_pan;
+                    assert!(bounds.contains(point));
                     let mut input = SequenceInput::default();
                     canvas_mouse(
                         &scene,
                         &mut input,
-                        mouse::Event::CursorMoved {
-                            position: point - scene.scroll_offset,
-                        },
+                        mouse::Event::CursorMoved { position: point },
                         point,
                         bounds,
                     );
@@ -2265,10 +2474,10 @@ pub(crate) mod direct_tests {
             assert!(!app.behavior.has_pending());
         }
         let old_context = app.scenario_context().unwrap();
-        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Scrolled(
+        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Camera(
             old_context,
-            ScrollArea::Canvas,
-            iced::Vector::new(0., 100.),
+            app.camera_epoch,
+            super::super::canvas_workspace::Event::Pan(iced::Vector::new(0., 100.)),
         )));
         let _ = app.update(Message::ScenarioCanvas(event(old_context)));
         assert!(!app.behavior.has_pending());
@@ -2459,26 +2668,29 @@ pub(crate) mod direct_tests {
         );
     }
     #[test]
-    fn direct_busy_save_keeps_observed_scroll_current_for_the_next_pointer_gesture() {
+    fn direct_busy_save_keeps_details_current_and_camera_for_the_next_pointer_gesture() {
         let f = fixture();
         let mut app = App::with_project(f.project.clone());
         let _ = app.update(Message::Select(f.owner));
         let _ = app.update(Message::Page(crate::app::Page::Behavior));
         let context = app.scenario_context().unwrap();
+        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Camera(
+            context,
+            app.camera_epoch,
+            super::super::canvas_workspace::Event::Pan(iced::Vector::new(-25., -100.)),
+        )));
+        let context = app.scenario_context().unwrap();
         let original = app.document.snapshot();
         app.busy = true;
-        for (area, offset) in [
-            (ScrollArea::Canvas, iced::Vector::new(25., 100.)),
-            (ScrollArea::Page, iced::Vector::new(0., 40.)),
-        ] {
-            let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Scrolled(
-                context, area, offset,
-            )));
-        }
+        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Scrolled(
+            context,
+            ScrollArea::Page,
+            iced::Vector::new(0., 40.),
+        )));
         assert!(app.busy);
         assert_eq!(
-            app.behavior.scenario.scroll_offset(),
-            iced::Vector::new(25., 100.)
+            app.behavior.scenario.details_offset,
+            iced::Vector::new(0., 40.)
         );
         assert_ne!(
             app.scenario_context(),
@@ -2489,14 +2701,14 @@ pub(crate) mod direct_tests {
         stale.document = Id::new_v4();
         let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Scrolled(
             stale,
-            ScrollArea::Canvas,
+            ScrollArea::Page,
             iced::Vector::new(0., 900.),
         )));
         assert_eq!(
-            app.behavior.scenario.scroll_offset(),
-            iced::Vector::new(25., 100.)
+            app.behavior.scenario.details_offset,
+            iced::Vector::new(0., 40.)
         );
-        let root = std::path::PathBuf::from("scenario-scroll-save-fixture");
+        let root = std::path::PathBuf::from("scenario-details-save-fixture");
         let receipt = crate::app::FileSnapshot {
             document: context.document,
             revision: context.revision,
@@ -2517,12 +2729,17 @@ pub(crate) mod direct_tests {
         let context = app.scenario_context().unwrap();
         let mut scene = Scene::sequence(app.project(), f.owner, f.call);
         scene.interaction = Some((context, CanvasTool::Message(MessageStyle::CallReply), true));
-        scene.scroll_offset = app.behavior.scenario.scroll_offset();
+        assert_eq!(
+            app.behavior.scenario.presentation.pan,
+            iced::Vector::new(-25., -100.)
+        );
+        scene.camera_pan = app.behavior.scenario.presentation.pan;
         let slot = scene.slots.last().unwrap().slot;
         let bounds = Rectangle::new(Point::new(20., 250.), scene.size);
         let y = bounds.y + scene.slots.last().unwrap().y;
-        let a = Point::new(bounds.x + scene.lanes[&f.sender], y) - scene.scroll_offset;
-        let b = Point::new(bounds.x + scene.lanes[&f.receiver], y) - scene.scroll_offset;
+        let a = Point::new(bounds.x + scene.lanes[&f.sender], y) + scene.camera_pan;
+        let b = Point::new(bounds.x + scene.lanes[&f.receiver], y) + scene.camera_pan;
+        assert!(bounds.contains(a) && bounds.contains(b));
         let mut input = super::super::SequenceInput::default();
         let mut published = vec![];
         for event in [
@@ -2536,7 +2753,7 @@ pub(crate) mod direct_tests {
                 &mut input,
                 &canvas::Event::Mouse(event),
                 bounds,
-                mouse::Cursor::Available(b + scene.scroll_offset),
+                mouse::Cursor::Available(b),
             )
             .and_then(|action| action.into_inner().0)
             {

crates/oa-desktop/src/behavior/scenario/focus.rs

@@ -0,0 +1,334 @@
+//! A delayed focus request must still own the live parent tree when executed.
+//! Collect first: a missing target must not unfocus unrelated fields.
+use super::Context;
+use iced::advanced::widget::{Id, Operation, Tree, operation};
+use iced::advanced::{Clipboard, Layout, Shell, Widget, layout, overlay, renderer};
+use iced::{Element, Event, Length, Rectangle, Size, Task, Theme, Vector, mouse};
+use oa_core::Id as ModelId;
+use std::collections::BTreeMap;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct Stamp {
+    document: ModelId,
+    owner: ModelId,
+    revision: u64,
+    session: ModelId,
+    mount: ModelId,
+}
+impl Stamp {
+    pub(crate) fn new(context: Context, session: ModelId, mount: ModelId) -> Self {
+        Self {
+            document: context.document,
+            owner: context.scenario,
+            revision: context.revision,
+            session,
+            mount,
+        }
+    }
+}
+pub(crate) fn name_id(stamp: Stamp) -> Id {
+    Id::from(format!(
+        "{}:{}:{}:{}:{}:{}",
+        super::NAME_INPUT,
+        stamp.document,
+        stamp.owner,
+        stamp.revision,
+        stamp.session,
+        stamp.mount
+    ))
+}
+struct Owner(Option<Stamp>);
+struct Root<'a, Message, R: renderer::Renderer> {
+    content: Element<'a, Message, Theme, R>,
+    owner: Option<Stamp>,
+}
+pub(crate) fn root<'a, Message: 'a, R: renderer::Renderer + 'a>(
+    content: impl Into<Element<'a, Message, Theme, R>>,
+    owner: Option<Stamp>,
+) -> Element<'a, Message, Theme, R> {
+    Element::new(Root {
+        content: content.into(),
+        owner,
+    })
+}
+impl<Message, R: renderer::Renderer> Widget<Message, Theme, R> for Root<'_, Message, R> {
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(self.content.as_widget())]
+    }
+    fn diff(&self, tree: &mut Tree) {
+        tree.diff_children(std::slice::from_ref(&self.content));
+    }
+    fn size(&self) -> Size<Length> {
+        self.content.as_widget().size()
+    }
+    fn layout(&mut self, tree: &mut Tree, renderer: &R, limits: &layout::Limits) -> layout::Node {
+        self.content
+            .as_widget_mut()
+            .layout(&mut tree.children[0], renderer, limits)
+    }
+    fn operate(
+        &mut self,
+        tree: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &R,
+        op: &mut dyn Operation,
+    ) {
+        // This is computed from the current App view, never retained widget state.
+        op.custom(None, layout.bounds(), &mut Owner(self.owner));
+        self.content
+            .as_widget_mut()
+            .operate(&mut tree.children[0], layout, renderer, op);
+    }
+    fn update(
+        &mut self,
+        tree: &mut Tree,
+        event: &Event,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        renderer: &R,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        viewport: &Rectangle,
+    ) {
+        self.content.as_widget_mut().update(
+            &mut tree.children[0],
+            event,
+            layout,
+            cursor,
+            renderer,
+            clipboard,
+            shell,
+            viewport,
+        );
+    }
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut R,
+        theme: &Theme,
+        style: &renderer::Style,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+    ) {
+        self.content.as_widget().draw(
+            &tree.children[0],
+            renderer,
+            theme,
+            style,
+            layout,
+            cursor,
+            viewport,
+        );
+    }
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+        renderer: &R,
+    ) -> mouse::Interaction {
+        self.content.as_widget().mouse_interaction(
+            &tree.children[0],
+            layout,
+            cursor,
+            viewport,
+            renderer,
+        )
+    }
+    fn overlay<'b>(
+        &'b mut self,
+        tree: &'b mut Tree,
+        layout: Layout<'b>,
+        renderer: &R,
+        viewport: &Rectangle,
+        translation: Vector,
+    ) -> Option<overlay::Element<'b, Message, Theme, R>> {
+        self.content.as_widget_mut().overlay(
+            &mut tree.children[0],
+            layout,
+            renderer,
+            viewport,
+            translation,
+        )
+    }
+}
+
+#[derive(Clone)]
+struct Scroll {
+    index: usize,
+    bounds: Rectangle,
+    capacity: Vector,
+    offset: Vector,
+}
+struct Collect {
+    stamp: Stamp,
+    valid: bool,
+    translation: Vector,
+    scrolls: Vec<Scroll>,
+    pending: Option<Scroll>,
+    index: usize,
+    target: Option<(Rectangle, Vec<Scroll>)>,
+}
+pub(crate) fn task<Message: Send + 'static>(stamp: Stamp) -> Task<Message> {
+    iced::advanced::widget::operate(Collect {
+        stamp,
+        valid: false,
+        translation: Vector::ZERO,
+        scrolls: vec![],
+        pending: None,
+        index: 0,
+        target: None,
+    })
+    .discard()
+}
+impl Operation for Collect {
+    fn custom(&mut self, _: Option<&Id>, _: Rectangle, state: &mut dyn std::any::Any) {
+        if let Some(owner) = state.downcast_ref::<Owner>() {
+            self.valid = owner.0 == Some(self.stamp);
+        }
+    }
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn Operation)) {
+        let previous = (self.translation, self.scrolls.len());
+        if let Some(scroll) = self.pending.take() {
+            self.translation += scroll.offset;
+            self.scrolls.push(scroll);
+        }
+        visit(self);
+        self.translation = previous.0;
+        self.scrolls.truncate(previous.1);
+    }
+    fn scrollable(
+        &mut self,
+        _: Option<&Id>,
+        bounds: Rectangle,
+        content: Rectangle,
+        offset: Vector,
+        _: &mut dyn operation::Scrollable,
+    ) {
+        self.pending = Some(Scroll {
+            index: self.index,
+            bounds: translated(bounds, self.translation),
+            capacity: Vector::new(
+                (content.width - bounds.width).max(0.),
+                (content.height - bounds.height).max(0.),
+            ),
+            offset,
+        });
+        self.index += 1;
+    }
+    fn focusable(&mut self, id: Option<&Id>, bounds: Rectangle, _: &mut dyn operation::Focusable) {
+        if id == Some(&name_id(self.stamp)) {
+            self.target = Some((translated(bounds, self.translation), self.scrolls.clone()));
+        }
+    }
+    fn finish(&self) -> operation::Outcome<()> {
+        if !self.valid {
+            return operation::Outcome::None;
+        }
+        let Some((mut bounds, ancestors)) = self.target.clone() else {
+            return operation::Outcome::None;
+        };
+        let mut shifts = BTreeMap::new();
+        for ancestor in ancestors.iter().rev() {
+            let dx = reveal(
+                bounds.x,
+                bounds.width,
+                ancestor.bounds.x,
+                ancestor.bounds.width,
+            );
+            let dy = reveal(
+                bounds.y,
+                bounds.height,
+                ancestor.bounds.y,
+                ancestor.bounds.height,
+            );
+            // Drawing offsets are rounded; an already-visible axis must not
+            // acquire a scroll delta from a fractional capacity alone.
+            let delta = Vector::new(
+                if dx == 0. {
+                    0.
+                } else {
+                    (ancestor.offset.x + dx).clamp(0., ancestor.capacity.x) - ancestor.offset.x
+                },
+                if dy == 0. {
+                    0.
+                } else {
+                    (ancestor.offset.y + dy).clamp(0., ancestor.capacity.y) - ancestor.offset.y
+                },
+            );
+            if delta != Vector::ZERO {
+                shifts.insert(ancestor.index, delta);
+            }
+            bounds = translated(bounds, delta);
+        }
+        operation::Outcome::Chain(Box::new(Apply {
+            stamp: self.stamp,
+            valid: false,
+            shifts,
+            index: 0,
+        }))
+    }
+}
+fn translated(bounds: Rectangle, delta: Vector) -> Rectangle {
+    Rectangle {
+        x: bounds.x - delta.x,
+        y: bounds.y - delta.y,
+        ..bounds
+    }
+}
+fn reveal(start: f32, length: f32, viewport: f32, size: f32) -> f32 {
+    if start < viewport || length > size {
+        start - viewport
+    } else {
+        (start + length - viewport - size).max(0.)
+    }
+}
+struct Apply {
+    stamp: Stamp,
+    valid: bool,
+    shifts: BTreeMap<usize, Vector>,
+    index: usize,
+}
+impl Operation for Apply {
+    fn custom(&mut self, _: Option<&Id>, _: Rectangle, state: &mut dyn std::any::Any) {
+        if let Some(owner) = state.downcast_ref::<Owner>() {
+            self.valid = owner.0 == Some(self.stamp);
+        }
+    }
+    fn traverse(&mut self, visit: &mut dyn FnMut(&mut dyn Operation)) {
+        visit(self);
+    }
+    fn focusable(&mut self, id: Option<&Id>, _: Rectangle, state: &mut dyn operation::Focusable) {
+        if self.valid {
+            if id == Some(&name_id(self.stamp)) {
+                state.focus();
+            } else {
+                state.unfocus();
+            }
+        }
+    }
+    fn scrollable(
+        &mut self,
+        _: Option<&Id>,
+        bounds: Rectangle,
+        content: Rectangle,
+        _: Vector,
+        state: &mut dyn operation::Scrollable,
+    ) {
+        if self.valid
+            && let Some(delta) = self.shifts.get(&self.index)
+        {
+            state.scroll_by(
+                operation::scrollable::AbsoluteOffset {
+                    x: delta.x,
+                    y: delta.y,
+                },
+                bounds,
+                content,
+            );
+        }
+        self.index += 1;
+    }
+}

crates/oa-desktop/src/behavior/scenario/usage.rs

@@ -0,0 +1,207 @@
+//! Navigation is derived from the same opaque-reference scene that is painted.
+use super::*;
+use crate::diagram_usage::{Surface, Target, Usage};
+
+/// The renderer collapses whitespace before shortening. Require at least one
+/// actual character of this field, rather than an ellipsis at its start.
+fn label_field_visible(full: &str, prefix: &str, value: &str) -> bool {
+    if value.trim().is_empty() {
+        return false;
+    }
+    let normalized = full.split_whitespace().collect::<Vec<_>>().join(" ");
+    let normalized_prefix = prefix.split_whitespace().collect::<Vec<_>>().join(" ");
+    let start = normalized_prefix.len()
+        + usize::from(prefix.ends_with(char::is_whitespace) && !normalized_prefix.is_empty());
+    let painted = crate::views::short(full, 32);
+    let retained = normalized
+        .chars()
+        .zip(painted.chars())
+        .take_while(|(a, b)| a == b)
+        .map(|(c, _)| c.len_utf8())
+        .sum::<usize>();
+    start < retained
+}
+
+fn usages(p: &Project, owner: Id, subject: Id, scene: &Scene) -> Vec<Usage> {
+    let mut result = Vec::new();
+    let mut add = |id, bounds, role: &str| {
+        // Activation bars share the occurrence identity with a labelled message;
+        // they must not inflate its target count.
+        if !result
+            .iter()
+            .any(|u: &Usage| u.target == Target::ScenarioObject(id))
+        {
+            result.push(Usage {
+                subject,
+                surface: Surface::Scenario(owner),
+                target: Target::ScenarioObject(id),
+                role: role.into(),
+                bounds,
+            });
+        }
+    };
+    for item in scene.boxes.iter().filter(|item| !item.title.is_empty()) {
+        let Some(element) = p.elements.get(&item.id) else {
+            continue;
+        };
+        if subject == item.id {
+            // A fragment's selectable header is useful even when its frame is
+            // much larger than the viewport.
+            let mut bounds = item.rect;
+            if item.marker == Some(Kind::Occurrence) {
+                bounds.height = bounds.height.min(38.);
+            }
+            add(item.id, bounds, "scenario object");
+        }
+        let represented = match element.shared() {
+            Some(SharedBody::Lifeline { represented }) => represented.map(|id| (id, "lifeline")),
+            Some(SharedBody::Occurrence { body, .. }) => match body {
+                OccurrenceBody::Action { action, .. } => action.map(|id| (id, "action occurrence")),
+                OccurrenceBody::State { state, .. } => state.map(|id| (id, "state observation")),
+                OccurrenceBody::SequenceReference { sequence } => {
+                    sequence.map(|id| (id, "process reference"))
+                }
+                OccurrenceBody::ScenarioUse { scenario, .. } => {
+                    scenario.map(|id| (id, "scenario reference"))
+                }
+                // An incomplete message fallback box only paints the occurrence
+                // name and a repair hint, not its exchange or operation.
+                _ => None,
+            },
+            _ => None,
+        };
+        if let Some((id, role)) = represented.filter(|(id, _)| *id == subject) {
+            let _ = id;
+            add(item.id, item.rect, role);
+        }
+    }
+    for line in scene.lines.iter().filter(|line| !line.label.is_empty()) {
+        let Some(element) = p.elements.get(&line.id) else {
+            continue;
+        };
+        let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange { exchange, .. },
+            ..
+        }) = element.shared()
+        else {
+            continue;
+        };
+        let bounds = line.label_bounds();
+        if subject == line.id || *exchange == Some(subject) {
+            add(line.id, bounds, "message occurrence");
+        }
+        // Replies derive their operation from the exact call, matching the
+        // operation label formatter rather than scanning raw reference fields.
+        if let Ok(operations::OperationResolution::Selected(operation)) =
+            operations::resolve(p, line.id)
+            && let Some(label) = crate::data_values::operation_label(p, element)
+            && let Some(prefix) = line.label.strip_suffix(&label)
+        {
+            let allocation = &p.relations[&operation.allocation];
+            let operation_prefix = if matches!(
+                element.shared(),
+                Some(SharedBody::Occurrence {
+                    body: OccurrenceBody::Exchange {
+                        message_kind: MessageKind::Reply,
+                        ..
+                    },
+                    ..
+                })
+            ) {
+                "Reply operation from Call: "
+            } else {
+                "Operation: "
+            };
+            let fields = [
+                (allocation.source(), format!("{prefix}{operation_prefix}")),
+                (
+                    allocation.target(),
+                    format!(
+                        "{prefix}{operation_prefix}{} / ",
+                        p.named(allocation.source())
+                    ),
+                ),
+                (
+                    allocation.id,
+                    format!(
+                        "{prefix}{operation_prefix}{} / {} · ",
+                        p.named(allocation.source()),
+                        p.named(allocation.target())
+                    ),
+                ),
+            ];
+            for (id, prefix) in fields {
+                if id == subject && label_field_visible(&line.label, &prefix, p.named(id)) {
+                    add(line.id, bounds, "operation label");
+                }
+            }
+        }
+    }
+    if subject == owner {
+        result.insert(
+            0,
+            Usage {
+                subject,
+                surface: Surface::Scenario(owner),
+                target: Target::Whole,
+                role: "scenario".into(),
+                bounds: Rectangle::new(Point::ORIGIN, scene.size),
+            },
+        );
+    }
+    result
+}
+
+impl State {
+    pub(crate) fn diagram_usages(&self, p: &Project, owner: Id, subject: Id) -> Vec<Usage> {
+        if !p
+            .elements
+            .get(&owner)
+            .is_some_and(|e| e.kind() == Kind::Scenario)
+        {
+            return vec![];
+        }
+        usages(p, owner, subject, &Scene::sequence(p, owner, subject))
+    }
+
+    pub(crate) fn reveal_usage(
+        &mut self,
+        p: &Project,
+        document: Id,
+        owner: Id,
+        target: &Target,
+    ) -> bool {
+        if self.draft.is_some()
+            || !p
+                .elements
+                .get(&owner)
+                .is_some_and(|e| e.kind() == Kind::Scenario)
+        {
+            return false;
+        }
+        let id = match target {
+            Target::Whole => owner,
+            Target::ScenarioObject(id) => *id,
+            _ => return false,
+        };
+        let Some(usage) = self
+            .diagram_usages(p, owner, id)
+            .into_iter()
+            .find(|u| &u.target == target)
+        else {
+            return false;
+        };
+        // Preserve an existing mounted viewport across enter's owner reset.
+        let viewport = self.presentation.viewport.unwrap_or(Size::new(500., 300.));
+        self.enter(document, owner);
+        self.presentation.viewport = Some(viewport);
+        self.canvas_tool = Some((owner, CanvasTool::Select));
+        let (zoom, pan) = crate::diagram_usage::camera_for(target, usage.bounds, viewport);
+        self.presentation.zoom(Some(zoom));
+        self.presentation.pan = pan;
+        true
+    }
+}
+
+#[cfg(test)]
+mod tests;

crates/oa-desktop/src/behavior/scenario/usage/tests.rs

@@ -0,0 +1,276 @@
+use super::*;
+
+fn add_occurrence(p: &mut Project, owner: Id, name: &str, body: OccurrenceBody) -> Id {
+    let layer = p.elements[&owner].layer();
+    let id = p
+        .add_element(Kind::Occurrence, layer, name, Some(owner))
+        .unwrap();
+    *p.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Occurrence {
+        body,
+        precondition: String::new(),
+        postcondition: String::new(),
+    };
+    if let Some(steps) = p.elements.get_mut(&owner).unwrap().steps_mut() {
+        if !steps.contains(&id) {
+            steps.push(id);
+        }
+    }
+    id
+}
+
+fn targets(state: &State, p: &Project, owner: Id, subject: Id) -> BTreeSet<Id> {
+    state
+        .diagram_usages(p, owner, subject)
+        .into_iter()
+        .filter_map(|u| match u.target {
+            Target::ScenarioObject(id) => Some(id),
+            _ => None,
+        })
+        .collect()
+}
+
+#[test]
+fn scenario_usage_counts_nested_occurrences_and_lifelines_but_keeps_reuse_opaque() {
+    for (layer, work_kind, participant_kind) in [
+        (Layer::Oa, Kind::Activity, Kind::Entity),
+        (Layer::Sa, Kind::Function, Kind::SystemActor),
+    ] {
+        let mut p = Project::empty();
+        let owner = p
+            .add_element(Kind::Scenario, layer, "Caller", None)
+            .unwrap();
+        let other = p
+            .add_element(Kind::Scenario, layer, "Definition", None)
+            .unwrap();
+        let work = p.add_element(work_kind, layer, "Respond", None).unwrap();
+        let unused = p.add_element(work_kind, layer, "Respond", None).unwrap();
+        let participant = p
+            .add_element(participant_kind, layer, "Operator", None)
+            .unwrap();
+        let lanes = ["First role", "Second role"].map(|name| {
+            let id = p
+                .add_element(Kind::Lifeline, layer, name, Some(owner))
+                .unwrap();
+            *p.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Lifeline {
+                represented: Some(participant),
+            };
+            id
+        });
+        let first = add_occurrence(
+            &mut p,
+            owner,
+            "First action",
+            OccurrenceBody::Action {
+                action: Some(work),
+                lifeline: Some(lanes[0]),
+            },
+        );
+        let fragment = add_occurrence(
+            &mut p,
+            owner,
+            "Decision",
+            OccurrenceBody::Fragment {
+                operator: FragmentOperator::Alternative,
+                branches: vec![],
+            },
+        );
+        let branch = add_occurrence(
+            &mut p,
+            fragment,
+            "When ready",
+            OccurrenceBody::Branch {
+                guard: "ready".into(),
+                occurrences: vec![],
+            },
+        );
+        if let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Fragment { branches, .. },
+            ..
+        }) = p.elements.get_mut(&fragment).unwrap().shared_mut()
+        {
+            branches.push(branch);
+        }
+        let nested = add_occurrence(
+            &mut p,
+            branch,
+            "Again",
+            OccurrenceBody::Action {
+                action: Some(work),
+                lifeline: Some(lanes[1]),
+            },
+        );
+        let inside = add_occurrence(
+            &mut p,
+            other,
+            "Hidden inside definition",
+            OccurrenceBody::Action {
+                action: Some(unused),
+                lifeline: None,
+            },
+        );
+        let use_a = add_occurrence(
+            &mut p,
+            owner,
+            "Use A",
+            OccurrenceBody::ScenarioUse {
+                scenario: Some(other),
+                bindings: vec![],
+            },
+        );
+        let use_b = add_occurrence(
+            &mut p,
+            owner,
+            "Use B",
+            OccurrenceBody::ScenarioUse {
+                scenario: Some(other),
+                bindings: vec![],
+            },
+        );
+        let before = p.clone();
+        let state = State::default();
+        assert_eq!(
+            targets(&state, &p, owner, work),
+            BTreeSet::from([first, nested])
+        );
+        assert_eq!(
+            targets(&state, &p, owner, participant),
+            BTreeSet::from(lanes)
+        );
+        assert_eq!(
+            targets(&state, &p, owner, other),
+            BTreeSet::from([use_a, use_b])
+        );
+        assert!(targets(&state, &p, owner, unused).is_empty());
+        assert!(targets(&state, &p, owner, inside).is_empty());
+        assert_eq!(targets(&state, &p, owner, branch), BTreeSet::from([branch]));
+        assert_eq!(
+            state.diagram_usages(&p, owner, owner)[0].target,
+            Target::Whole
+        );
+        assert_eq!(p, before);
+    }
+}
+
+#[test]
+fn scenario_usage_keeps_repeated_messages_and_reveal_is_read_only_and_revalidated() {
+    let f = super::super::direct_tests::fixture();
+    let mut p = f.project;
+    let mut state = State::default();
+    assert_eq!(
+        targets(&state, &p, f.owner, f.exchange),
+        BTreeSet::from([f.call, f.reply])
+    );
+    let before = p.clone();
+    let target = Target::ScenarioObject(f.reply);
+    state.viewport(Size::new(900., 500.));
+    assert!(state.reveal_usage(&p, Id::new_v4(), f.owner, &target));
+    let usage = state
+        .diagram_usages(&p, f.owner, f.reply)
+        .into_iter()
+        .find(|u| u.target == target)
+        .unwrap();
+    let zoom = state
+        .presentation
+        .scale(Scene::sequence(&p, f.owner, f.reply).size);
+    let centered = Point::new(
+        usage.bounds.center_x() * zoom,
+        usage.bounds.center_y() * zoom,
+    ) + state.presentation.pan;
+    assert!((centered.x - 450.).abs() < 0.01 && (centered.y - 250.).abs() < 0.01);
+    assert!(zoom >= 0.5);
+    assert_eq!(p, before);
+    // Keeping an orphan semantic occurrence does not keep its painted target.
+    p.elements
+        .get_mut(&f.owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap()
+        .retain(|id| *id != f.reply);
+    let camera = state.camera_boundary();
+    assert!(!state.reveal_usage(&p, Id::new_v4(), f.owner, &target));
+    assert!(camera == state.camera_boundary());
+    assert!(!state.reveal_usage(&p, Id::new_v4(), f.owner, &Target::Edge(f.exchange)));
+    // A message whose endpoints are incomplete paints only its repair box.
+    if let Some(SharedBody::Occurrence {
+        body: OccurrenceBody::Exchange { receiver, .. },
+        ..
+    }) = p.elements.get_mut(&f.call).unwrap().shared_mut()
+    {
+        *receiver = None;
+    }
+    assert!(targets(&state, &p, f.owner, f.exchange).is_empty());
+    assert_eq!(
+        targets(&state, &p, f.owner, f.call),
+        BTreeSet::from([f.call])
+    );
+}
+
+#[test]
+fn scenario_operation_label_membership_excludes_ellipsis_only_and_normalizes_whitespace() {
+    assert!(label_field_visible(
+        "1. call · X · Operation: I / O",
+        "1. call · X · Operation: ",
+        "I"
+    ));
+    assert!(!label_field_visible(
+        "1234567890123456789012345678901Ixyz",
+        "1234567890123456789012345678901",
+        "Ixyz"
+    ));
+    assert!(!label_field_visible(
+        "A very long occurrence label · Operation: I",
+        "A very long occurrence label · Operation: ",
+        "I"
+    ));
+    assert!(label_field_visible(
+        "call\n\t· Operation: 界",
+        "call\n\t· Operation: ",
+        "界"
+    ));
+    assert!(!label_field_visible("Operation: ", "Operation: ", ""));
+}
+
+#[test]
+fn scenario_usage_only_reports_the_resolved_operation_fields_actually_in_the_label() {
+    let mut p = persistence::decode(include_bytes!(concat!(
+        env!("CARGO_MANIFEST_DIR"),
+        "/../../harness/fixtures/interface-operation-probe/output/boundary-only.json"
+    )))
+    .unwrap();
+    let id = |n| Id::parse_str(&format!("52060906-0000-4000-8000-{n:012x}")).unwrap();
+    let (owner, call, exchange, allocation) = (id(40), id(43), id(34), id(30));
+    let (interface, item) = (
+        p.relations[&allocation].source(),
+        p.relations[&allocation].target(),
+    );
+    for (id, name) in [(call, "x"), (interface, "I"), (item, "O")] {
+        p.elements.get_mut(&id).unwrap().name = name.into();
+    }
+    p.relations.get_mut(&exchange).unwrap().name = "x".into();
+    p.relations.get_mut(&allocation).unwrap().name = "A".into();
+    if let Some(SharedBody::Occurrence {
+        body: OccurrenceBody::Exchange { operation, .. },
+        ..
+    }) = p.elements.get_mut(&call).unwrap().shared_mut()
+    {
+        *operation = Some(OperationUse {
+            allocation: Some(allocation),
+        });
+    }
+    assert!(matches!(
+        operations::resolve(&p, call),
+        Ok(operations::OperationResolution::Selected(_))
+    ));
+    let state = State::default();
+    let before = p.clone();
+    assert_eq!(
+        targets(&state, &p, owner, interface),
+        BTreeSet::from([call])
+    );
+    assert_eq!(targets(&state, &p, owner, item), BTreeSet::from([call]));
+    assert!(targets(&state, &p, owner, allocation).is_empty());
+    assert_eq!(p, before);
+    p.elements.get_mut(&call).unwrap().name = "This occurrence has a deliberately long name".into();
+    assert!(targets(&state, &p, owner, interface).is_empty());
+    assert!(targets(&state, &p, owner, item).is_empty());
+}

crates/oa-desktop/src/behavior/scenario_label.rs

@@ -0,0 +1,430 @@
+//! Unwired single-line scenario label experiment. No renderer or schema is changed.
+//!
+//! Iced 0.14.0 WGPU `geometry::Frame::fill_text` shapes positive uniform-scale
+//! canvas text at `size * zoom`; its `text::prepare` uses graphics text::Cache.
+//! This adapter uses that same allocator/font system/attributes, not a character
+//! width estimate. Canvas Text::max_width is wrapping, so it stays infinite.
+//! Experimental parity requires settled fonts and a fresh renderer/cache after
+//! font loading. Iced's WGPU text cache key omits FontSystem::Version, so merely
+//! remeasuring here cannot repair its cached glyph buffers after dynamic loading.
+//! A RenderSession is caller attestation of that lifecycle, not its enforcement.
+//! No fonts may be loaded between measurement, guarded access and actual draw.
+//!
+//! Integration seam: after lifecycle/activation endpoint alignment, a caller
+//! supplies a usable text width in world units and retains one cache per live
+//! labelled occurrence across Scene rebuilds. Paint, hit testing, navigation and extents
+//! consume the returned Label. Position/color do not invalidate measurement.
+//! This does NOT choose a self-call, reversed-arrow or obstacle corridor policy.
+//! It measures layout advances, not raster ink; overhang/clip/activation-border
+//! acceptance still requires the real WGPU evaluator. The old 32-grapheme/225px
+//! renderer is deliberately untouched for a later baseline comparison.
+use iced::advanced::{
+    graphics::text as graphics_text,
+    text::{Alignment, LineHeight, Shaping},
+};
+use iced::{Color, Font, Pixels, Point, Rectangle, Size, widget::canvas::Text};
+use std::{collections::VecDeque, ops::Range, sync::Arc};
+use unicode_segmentation::UnicodeSegmentation;
+
+const MAX_SOURCE_BYTES: usize = 64 * 1024;
+const MAX_GRAPHEMES: usize = 4096;
+const MAX_ENTRIES: usize = 2;
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub(super) struct Style {
+    pub font: Font,
+    pub size: Pixels,
+    pub line_height: LineHeight,
+    pub shaping: Shaping,
+}
+
+impl Default for Style {
+    fn default() -> Self {
+        let text = Text::default();
+        Self {
+            font: text.font,
+            size: Pixels(12.),
+            line_height: text.line_height,
+            shaping: text.shaping,
+        }
+    }
+}
+
+impl Style {
+    fn scaled(self, zoom: f32) -> (f32, f32) {
+        let size = Pixels(self.size.0 * zoom);
+        let line_height = match self.line_height {
+            LineHeight::Absolute(value) => LineHeight::Absolute(Pixels(value.0 * zoom)),
+            LineHeight::Relative(value) => LineHeight::Relative(value),
+        };
+        (size.0, line_height.to_absolute(size).0)
+    }
+}
+
+/// Explicit experimental contract: the caller finishes loading fonts and starts
+/// a fresh renderer/cache BEFORE capturing this session, then keeps fonts fixed.
+/// This module cannot inspect or reset the actual renderer's text cache.
+#[derive(Clone, Debug)]
+pub(super) struct RenderSession {
+    version: graphics_text::Version,
+    identity: Arc<()>,
+}
+
+impl RenderSession {
+    pub fn after_fonts_settled_and_renderer_reset() -> Result<Self, Error> {
+        let fonts = graphics_text::font_system()
+            .read()
+            .map_err(|_| Error::FontSystemUnavailable)?;
+        Ok(Self {
+            version: fonts.version(),
+            identity: Arc::new(()),
+        })
+    }
+}
+
+#[derive(Clone, Debug)]
+pub(super) struct Label {
+    source: String,
+    displayed: String,
+    /// Original-label bytes represented before any added ellipsis. Includes
+    /// collapsed whitespace, but `retains_any` never counts whitespace as text.
+    retained_source: Range<usize>,
+    /// World-space layout advances, at origin; not glyph-ink containment.
+    bounds: Rectangle,
+    style: Style,
+    measured_session: RenderSession,
+    measured_zoom: f32,
+}
+
+impl Label {
+    fn check(&self, session: &RenderSession, zoom: f32) -> Result<(), Error> {
+        if !Arc::ptr_eq(&self.measured_session.identity, &session.identity) {
+            return Err(Error::StaleRenderSession);
+        }
+        if !zoom.is_finite() || zoom != self.measured_zoom {
+            return Err(Error::StaleZoom);
+        }
+        let fonts = graphics_text::font_system()
+            .read()
+            .map_err(|_| Error::FontSystemUnavailable)?;
+        if fonts.version() != self.measured_session.version || fonts.version() != session.version {
+            return Err(Error::FontSetChanged);
+        }
+        Ok(())
+    }
+
+    pub fn displayed(&self, session: &RenderSession, zoom: f32) -> Result<&str, Error> {
+        self.check(session, zoom)?;
+        Ok(&self.displayed)
+    }
+
+    pub fn retained_source(
+        &self,
+        session: &RenderSession,
+        zoom: f32,
+    ) -> Result<Range<usize>, Error> {
+        self.check(session, zoom)?;
+        Ok(self.retained_source.clone())
+    }
+
+    pub fn retains_any(
+        &self,
+        session: &RenderSession,
+        zoom: f32,
+        field: Range<usize>,
+    ) -> Result<bool, Error> {
+        self.check(session, zoom)?;
+        if field.start > field.end || self.source.get(field.clone()).is_none() {
+            return Ok(false);
+        }
+        let end = field.end.min(self.retained_source.end);
+        Ok(field.start < end
+            && self
+                .source
+                .get(field.start..end)
+                .is_some_and(|text| text.chars().any(|c| !c.is_whitespace())))
+    }
+
+    /// Validate finite world position and rectangle endpoints only. Camera
+    /// transforms and raster bounds remain a separate integration contract.
+    pub fn bounds_at(
+        &self,
+        session: &RenderSession,
+        zoom: f32,
+        position: Point,
+    ) -> Result<Rectangle, Error> {
+        self.check(session, zoom)?;
+        translated_bounds(position, self.bounds.size())
+    }
+
+    /// Paint under the same positive uniform zoom used for `Cache::resolve`.
+    /// No per-label wrapping or implicit text maximum is introduced.
+    /// The returned Text must be consumed immediately in this session/zoom;
+    /// retaining raw Text past another font load/zoom change bypasses the guard.
+    pub fn canvas_text(
+        &self,
+        session: &RenderSession,
+        zoom: f32,
+        position: Point,
+        color: Color,
+    ) -> Result<Text, Error> {
+        self.bounds_at(session, zoom, position)?;
+        Ok(Text {
+            content: self.displayed.clone(),
+            position,
+            color,
+            size: self.style.size,
+            line_height: self.style.line_height,
+            font: self.style.font,
+            shaping: self.style.shaping,
+            max_width: f32::INFINITY,
+            ..Text::default()
+        })
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(super) enum Error {
+    InvalidMetrics,
+    SourceBudget,
+    GraphemeBudget,
+    FontSystemUnavailable,
+    InvalidMeasurement,
+    InvalidPosition,
+    StaleZoom,
+    StaleRenderSession,
+    FontSetChanged,
+}
+
+struct Entry {
+    source: String,
+    style: Style,
+    zoom: f32,
+    width: f32,
+    label: Arc<Label>,
+}
+
+#[derive(Default)]
+/// Two recent resolutions for ONE live labelled occurrence. A global small LRU
+/// would thrash when a larger Scene is rebuilt in order. The integration owner
+/// must retain these by occurrence identity and prune on removal/document change.
+pub(super) struct Cache {
+    version: Option<graphics_text::Version>,
+    session: Option<Arc<()>>,
+    entries: VecDeque<Entry>,
+    #[cfg(test)]
+    allocations: usize,
+}
+
+impl Cache {
+    /// `width` excludes any caller-chosen backplate padding. Zero is valid.
+    /// Cache ownership must survive redraws; constructing one per Scene defeats
+    /// reuse. Changed fonts invalidate the SESSION: the caller must establish
+    /// a fresh renderer and a new settled session, not just remeasure this cache.
+    /// Error handling/fallback for these explicit experiment budgets is an
+    /// integration decision; never silently paint the old truncated contract.
+    pub fn resolve(
+        &mut self,
+        session: &RenderSession,
+        source: &str,
+        width: f32,
+        zoom: f32,
+        style: Style,
+    ) -> Result<Arc<Label>, Error> {
+        let (size, line_height) = style.scaled(zoom);
+        if !width.is_finite()
+            || width < 0.
+            || !zoom.is_finite()
+            || zoom <= 0.
+            || !size.is_finite()
+            || size <= 0.
+            || !line_height.is_finite()
+            || line_height <= 0.
+            || !(width * zoom).is_finite()
+            || !(size / zoom).is_finite()
+            || !(line_height / zoom).is_finite()
+        {
+            return Err(Error::InvalidMetrics);
+        }
+        if source.len() > MAX_SOURCE_BYTES {
+            return Err(Error::SourceBudget);
+        }
+        let mut fonts = graphics_text::font_system()
+            .write()
+            .map_err(|_| Error::FontSystemUnavailable)?;
+        if session.version != fonts.version() {
+            return Err(Error::FontSetChanged);
+        }
+        if self.version != Some(fonts.version())
+            || self
+                .session
+                .as_ref()
+                .is_none_or(|identity| !Arc::ptr_eq(identity, &session.identity))
+        {
+            self.entries.clear();
+            self.version = Some(fonts.version());
+            self.session = Some(session.identity.clone());
+        }
+        if let Some(index) = self.entries.iter().position(|entry| {
+            entry.source == source
+                && entry.style == style
+                && entry.zoom == zoom
+                && entry.width == width
+        }) {
+            let entry = self.entries.remove(index).unwrap();
+            let label = entry.label.clone();
+            self.entries.push_back(entry);
+            return Ok(label);
+        }
+        let normalized = Normalized::new(source);
+        let cuts: Vec<usize> = normalized
+            .text
+            .grapheme_indices(true)
+            .map(|(i, _)| i)
+            .chain(std::iter::once(normalized.text.len()))
+            .collect();
+        if cuts.len().saturating_sub(1) > MAX_GRAPHEMES {
+            return Err(Error::GraphemeBudget);
+        }
+        // Candidate buffers are temporary. Only the resolved strings/metrics
+        // survive, bounded by MAX_ENTRIES; renderer caching remains independent.
+        let mut shapes = graphics_text::Cache::new();
+        let mut measure = |content: &str| -> Result<Size, Error> {
+            if content.is_empty() {
+                return Ok(Size::ZERO);
+            }
+            #[cfg(test)]
+            {
+                self.allocations += 1;
+            }
+            let (_, entry) = shapes.allocate(
+                fonts.raw(),
+                graphics_text::cache::Key {
+                    content,
+                    size,
+                    line_height,
+                    font: style.font,
+                    bounds: Size::INFINITE,
+                    shaping: style.shaping,
+                    align_x: Alignment::Default,
+                },
+            );
+            if entry.buffer.layout_runs().count() != 1
+                || !entry.min_bounds.width.is_finite()
+                || !entry.min_bounds.height.is_finite()
+            {
+                return Err(Error::InvalidMeasurement);
+            }
+            world_size(entry.min_bounds, zoom)
+        };
+        let full = measure(&normalized.text)?;
+        let (displayed, retained, measured) = if full.width <= width {
+            (normalized.text.clone(), normalized.text.len(), full)
+        } else {
+            let ellipsis = measure("…")?;
+            if ellipsis.width > width {
+                (String::new(), 0, Size::ZERO)
+            } else {
+                // Every accepted candidate is actually shaped and fits. Search
+                // is bounded/logarithmic; contextual shaping is not universally
+                // monotone, so this does NOT promise the globally longest prefix.
+                // Full content is always checked first and never needlessly cut.
+                let mut best = ("…".to_owned(), 0, ellipsis);
+                let (mut low, mut high) = (1, cuts.len().saturating_sub(1));
+                while low < high {
+                    let middle = low + (high - low) / 2;
+                    let candidate = format!("{}…", &normalized.text[..cuts[middle]]);
+                    let measured = measure(&candidate)?;
+                    if measured.width <= width {
+                        best = (candidate, cuts[middle], measured);
+                        low = middle + 1;
+                    } else {
+                        high = middle;
+                    }
+                }
+                best
+            }
+        };
+        let label = Arc::new(Label {
+            source: source.into(),
+            displayed,
+            retained_source: 0..normalized.source_end(retained),
+            bounds: Rectangle::with_size(measured),
+            style,
+            measured_session: session.clone(),
+            measured_zoom: zoom,
+        });
+        if self.entries.len() == MAX_ENTRIES {
+            self.entries.pop_front();
+        }
+        self.entries.push_back(Entry {
+            source: source.into(),
+            style,
+            zoom,
+            width,
+            label: label.clone(),
+        });
+        Ok(label)
+    }
+}
+
+fn world_size(scaled: Size, zoom: f32) -> Result<Size, Error> {
+    let world = Size::new(scaled.width / zoom, scaled.height / zoom);
+    if !world.width.is_finite()
+        || !world.height.is_finite()
+        || world.width < 0.
+        || world.height < 0.
+    {
+        return Err(Error::InvalidMeasurement);
+    }
+    Ok(world)
+}
+
+fn translated_bounds(position: Point, size: Size) -> Result<Rectangle, Error> {
+    if !position.x.is_finite()
+        || !position.y.is_finite()
+        || !(position.x + size.width).is_finite()
+        || !(position.y + size.height).is_finite()
+    {
+        return Err(Error::InvalidPosition);
+    }
+    Ok(Rectangle::new(position, size))
+}
+
+struct Normalized {
+    text: String,
+    ends: Vec<(usize, usize)>,
+}
+impl Normalized {
+    fn new(source: &str) -> Self {
+        let mut result = Self {
+            text: String::new(),
+            ends: vec![(0, 0)],
+        };
+        let mut separator = false;
+        for (start, c) in source.char_indices() {
+            if c.is_whitespace() {
+                separator = !result.text.is_empty();
+                continue;
+            }
+            if separator {
+                result.text.push(' ');
+                result.ends.push((result.text.len(), start));
+                separator = false;
+            }
+            result.text.push(c);
+            result.ends.push((result.text.len(), start + c.len_utf8()));
+        }
+        result
+    }
+    fn source_end(&self, normalized_end: usize) -> usize {
+        self.ends
+            .binary_search_by_key(&normalized_end, |(end, _)| *end)
+            .map(|index| self.ends[index].1)
+            .expect("grapheme cuts are character boundaries")
+    }
+}
+
+#[cfg(test)]
+#[path = "scenario_label/tests.rs"]
+mod tests;

crates/oa-desktop/src/behavior/scenario_label/corridor.rs

@@ -0,0 +1,231 @@
+//! Unwired corridor-policy candidate for the measured scenario-label experiment.
+//!
+//! The caller supplies a finite structural label band AFTER endpoint/activation
+//! alignment, with padding already removed from its edges. Blockers include
+//! padded activation/card/header bounds over the complete text band, including
+//! stroke/ink clearance. This function does not infer a self-message corridor,
+//! alter scene extents, change zoom, or establish raster-ink containment.
+use iced::Rectangle;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(super) struct InvalidGeometry;
+
+fn edges(rect: Rectangle) -> Result<(f32, f32, f32, f32), InvalidGeometry> {
+    let right = rect.x + rect.width;
+    let bottom = rect.y + rect.height;
+    if [rect.x, rect.y, rect.width, rect.height, right, bottom]
+        .into_iter()
+        .any(|value| !value.is_finite())
+        || rect.width < 0.
+        || rect.height < 0.
+    {
+        return Err(InvalidGeometry);
+    }
+    Ok((rect.x, right, rect.y, bottom))
+}
+
+/// Select one connected clear interval; never assemble text across blockers.
+/// Prefer greater width, then proximity to the previous label anchor, then the
+/// leftmost interval. Input order has no influence. A zero-area band has no
+/// corridor. Touching the padded vertical band is conservatively obstructing;
+/// a zero-area blocker has no area and must receive stroke padding upstream.
+pub(super) fn widest_clear(
+    band: Rectangle,
+    blockers: &[Rectangle],
+    preferred_anchor: f32,
+) -> Result<Option<Rectangle>, InvalidGeometry> {
+    let (left, right, top, bottom) = edges(band)?;
+    if !preferred_anchor.is_finite() {
+        return Err(InvalidGeometry);
+    }
+    let mut blocked = Vec::new();
+    for &blocker in blockers {
+        let (x0, x1, y0, y1) = edges(blocker)?;
+        if blocker.width > 0. && blocker.height > 0. && y1 >= top && y0 <= bottom {
+            let interval = (x0.max(left), x1.min(right));
+            if interval.0 < interval.1 {
+                blocked.push(interval);
+            }
+        }
+    }
+    if band.width == 0. || band.height == 0. {
+        return Ok(None);
+    }
+    blocked.sort_by(|a, b| a.0.total_cmp(&b.0).then(a.1.total_cmp(&b.1)));
+    let mut best: Option<Rectangle> = None;
+    let mut consider = |start: f32, end: f32| {
+        if start >= end {
+            return;
+        }
+        let candidate = Rectangle {
+            x: start,
+            width: contained_width(start, end),
+            ..band
+        };
+        // Use f64 only for comparison distance: subtracting two admitted f32
+        // world coordinates can overflow even though each rectangle is finite.
+        let distance = |x: f32| (f64::from(x) - f64::from(preferred_anchor)).abs();
+        if best.is_none_or(|old| {
+            candidate.width > old.width
+                || (candidate.width == old.width
+                    && (distance(candidate.x) < distance(old.x)
+                        || (distance(candidate.x) == distance(old.x) && candidate.x < old.x)))
+        }) {
+            best = Some(candidate);
+        }
+    };
+    let mut cursor = left;
+    for (start, end) in blocked {
+        consider(cursor, start);
+        cursor = cursor.max(end);
+    }
+    consider(cursor, right);
+    Ok(best)
+}
+
+/// Finite f32 endpoints can subtract to infinity or round across a blocker.
+/// Compute in f64, cap to finite f32, and round inward if nearest rounding
+/// overshot the admitted interval's end.
+fn contained_width(start: f32, end: f32) -> f32 {
+    let exact = f64::from(end) - f64::from(start);
+    let mut width = exact.min(f64::from(f32::MAX)) as f32;
+    if f64::from(start) + f64::from(width) > f64::from(end) {
+        width = width.next_down();
+    }
+    width
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn rect(x: f32, y: f32, width: f32, height: f32) -> Rectangle {
+        Rectangle {
+            x,
+            y,
+            width,
+            height,
+        }
+    }
+
+    #[test]
+    fn long_message_does_not_cross_an_intermediate_execution() {
+        let band = rect(20., 100., 700., 22.);
+        let blockers = [rect(250., 80., 16., 80.), rect(490., 90., 28., 140.)];
+        let result = widest_clear(band, &blockers, band.x).unwrap().unwrap();
+        assert_eq!(result, rect(20., 100., 230., 22.));
+        for blocker in blockers {
+            assert!(result.x + result.width <= blocker.x || result.x >= blocker.x + blocker.width);
+        }
+        assert_eq!(widest_clear(band, &[], band.x).unwrap(), Some(band));
+    }
+
+    #[test]
+    fn overlapping_unsorted_blockers_merge_and_widest_gap_wins() {
+        let band = rect(-100., 10., 600., 20.);
+        let blockers = [
+            rect(50., 0., 80., 60.),
+            rect(0., 5., 70., 30.),
+            rect(450., 0., 100., 60.),
+        ];
+        let expected = Some(rect(130., 10., 320., 20.));
+        assert_eq!(widest_clear(band, &blockers, -100.).unwrap(), expected);
+        let mut reversed = blockers;
+        reversed.reverse();
+        assert_eq!(widest_clear(band, &reversed, -100.).unwrap(), expected);
+    }
+
+    #[test]
+    fn complete_padded_band_and_touching_boundaries_are_obstructed() {
+        let band = rect(0., 100., 200., 20.);
+        // The first blocker ends at the band top: checking only a baseline
+        // would miss it. The second starts at the band bottom.
+        let blockers = [rect(0., 70., 60., 30.), rect(150., 120., 50., 30.)];
+        assert_eq!(
+            widest_clear(band, &blockers, 0.).unwrap(),
+            Some(rect(60., 100., 90., 20.))
+        );
+        let outside = [rect(0., 70., 200., 29.), rect(0., 121., 200., 30.)];
+        assert_eq!(widest_clear(band, &outside, 0.).unwrap(), Some(band));
+    }
+
+    #[test]
+    fn ties_keep_the_nearest_anchor_then_choose_leftmost() {
+        let band = rect(0., 0., 300., 20.);
+        let blockers = [rect(100., 0., 100., 20.)];
+        assert_eq!(
+            widest_clear(band, &blockers, 190.).unwrap(),
+            Some(rect(200., 0., 100., 20.))
+        );
+        assert_eq!(
+            widest_clear(band, &blockers, 100.).unwrap(),
+            Some(rect(0., 0., 100., 20.))
+        );
+    }
+
+    #[test]
+    fn caller_defined_self_and_reversed_corridors_keep_their_geometry() {
+        // Direction and self-loop policy are explicit caller inputs. Neither
+        // a zero endpoint gap nor screen width can silently supply a corridor.
+        for band in [rect(420., 40., 180., 22.), rect(-400., 90., 350., 22.)] {
+            assert_eq!(widest_clear(band, &[], band.x).unwrap(), Some(band));
+        }
+        assert_eq!(
+            widest_clear(rect(420., 40., 0., 22.), &[], 420.).unwrap(),
+            None
+        );
+        assert_eq!(
+            widest_clear(rect(420., 40., 180., 0.), &[], 420.).unwrap(),
+            None
+        );
+        assert_eq!(
+            widest_clear(rect(0., 0., 100., 20.), &[rect(-10., -10., 200., 50.)], 0.).unwrap(),
+            None
+        );
+    }
+
+    #[test]
+    fn invalid_or_overflowing_geometry_never_enters_a_corridor() {
+        let band = rect(0., 0., 100., 20.);
+        for invalid in [
+            rect(f32::NAN, 0., 10., 20.),
+            rect(0., 0., -1., 20.),
+            rect(f32::MAX, 0., f32::MAX, 20.),
+            rect(0., f32::MAX, 10., f32::MAX),
+        ] {
+            assert_eq!(widest_clear(invalid, &[], 0.), Err(InvalidGeometry));
+            assert_eq!(widest_clear(band, &[invalid], 0.), Err(InvalidGeometry));
+        }
+        assert_eq!(widest_clear(band, &[], f32::INFINITY), Err(InvalidGeometry));
+    }
+
+    #[test]
+    fn finite_band_cannot_reconstruct_an_infinite_width() {
+        let band = rect(f32::from_bits(0xfe79636e), 0., f32::MAX, 20.);
+        let right = band.x + band.width;
+        assert!(right.is_finite());
+        assert!(
+            (right - band.x).is_infinite(),
+            "counterexample must exercise f32 subtraction overflow"
+        );
+        let result = widest_clear(band, &[], 0.).unwrap().unwrap();
+        assert!(result.width.is_finite() && result.width > 0.);
+        assert!(result.x + result.width <= right);
+        assert!(f64::from(result.x) + f64::from(result.width) <= f64::from(right));
+    }
+
+    #[test]
+    fn reconstructed_width_rounds_inward_at_a_blocker() {
+        let band = rect(-999_948.562_5, 0., 1_000_000., 20.);
+        let blocker = rect(2.1, 0., 10., 20.);
+        assert!(
+            band.x + (blocker.x - band.x) > blocker.x,
+            "counterexample must cross the blocker under naive reconstruction"
+        );
+        let result = widest_clear(band, &[blocker], 0.).unwrap().unwrap();
+        assert_eq!(result.x, band.x);
+        assert!(result.width > 999_000.);
+        assert!(result.x + result.width <= blocker.x);
+        assert!(f64::from(result.x) + f64::from(result.width) <= f64::from(blocker.x));
+    }
+}

crates/oa-desktop/src/behavior/scenario_label/tests.rs

@@ -0,0 +1,487 @@
+//! Unexecuted evaluator candidates; the module is intentionally not wired yet.
+use super::*;
+use iced::advanced::{
+    graphics::text::Paragraph,
+    text::{Paragraph as _, Text as ParagraphText, Wrapping},
+};
+
+// Independent paragraph construction: no candidate cache, normalization, search,
+// or character-width estimate is used by this measurement oracle.
+fn paragraph_size(content: &str, zoom: f32, style: Style) -> Size {
+    let size = Pixels(style.size.0 * zoom);
+    let line_height = match style.line_height {
+        LineHeight::Relative(factor) => LineHeight::Relative(factor),
+        LineHeight::Absolute(pixels) => LineHeight::Absolute(Pixels(pixels.0 * zoom)),
+    };
+    let paragraph = Paragraph::with_text(ParagraphText {
+        content,
+        bounds: Size::INFINITE,
+        size,
+        line_height,
+        font: style.font,
+        align_x: Alignment::Default,
+        align_y: iced::alignment::Vertical::Top,
+        shaping: style.shaping,
+        wrapping: Wrapping::default(),
+    });
+    assert_eq!(paragraph.buffer().layout_runs().count(), 1);
+    Size::new(paragraph.min_width() / zoom, paragraph.min_height() / zoom)
+}
+
+#[test]
+fn adequate_corridor_reveals_full_realistic_names_and_distinguishing_suffixes() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let style = Style::default();
+    for text in [
+        "1. call · Request valve repair · Technician service conversation",
+        "2. reply · Return pressure after repair · Technician service conversation",
+        "1. call · Request redundant hydraulic pressure calibration channel A",
+        "1. call · Request redundant hydraulic pressure calibration channel B",
+    ] {
+        let wide = cache.resolve(&session, text, 1600., 1., style).unwrap();
+        assert_eq!(wide.displayed(&session, 1.).unwrap(), text);
+        assert_eq!(wide.retained_source(&session, 1.).unwrap(), 0..text.len());
+        assert_eq!(wide.bounds.size(), paragraph_size(text, 1., style));
+        let narrow = cache.resolve(&session, text, 80., 1., style).unwrap();
+        assert_ne!(narrow.displayed, text);
+        assert!(narrow.bounds.width <= 80.);
+        assert_eq!(
+            narrow.bounds.size(),
+            paragraph_size(&narrow.displayed, 1., style)
+        );
+    }
+}
+
+#[test]
+fn normalized_visible_prefix_maps_to_original_bytes_without_claiming_hidden_operation() {
+    let raw = " \t1.  call · Pump\r\n  · Operation: Need\u{301}le  ";
+    let expected = "1. call · Pump · Operation: Need\u{301}le";
+    let n = Normalized::new(raw);
+    assert_eq!(n.text, expected);
+    let prefix = "1. call · Pump ";
+    assert_eq!(n.source_end(prefix.len()), raw.find("· Operation").unwrap());
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let wide = cache
+        .resolve(&session, raw, 1600., 1., Style::default())
+        .unwrap();
+    assert_eq!(wide.displayed, expected);
+    assert_eq!(wide.retained_source.end, raw.trim_end().len());
+    let field = raw.find("Need").unwrap()..raw.trim_end().len();
+    assert!(wide.retains_any(&session, 1., field.clone()).unwrap());
+    assert!(
+        !wide.retains_any(&session, 1., 0..2).unwrap(),
+        "normalized whitespace is not a visible field"
+    );
+    let small = cache
+        .resolve(&session, raw, 70., 1., Style::default())
+        .unwrap();
+    assert!(!small.retains_any(&session, 1., field).unwrap());
+    assert!(small.retained_source.end < raw.find("Operation").unwrap());
+}
+
+#[test]
+fn grapheme_prefixes_and_zoom_match_actual_paragraph_layout() {
+    let text = "call · 戻り値 圧力 e\u{301} 👩‍🔬 safety valve verification";
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    for zoom in [0.66, 1., 1.75] {
+        let label = cache
+            .resolve(&session, text, 105., zoom, Style::default())
+            .unwrap();
+        assert!(label.bounds.width <= 105.);
+        assert_eq!(
+            label.bounds.size(),
+            paragraph_size(&label.displayed, zoom, Style::default())
+        );
+        assert!(
+            text.grapheme_indices(true)
+                .any(|(i, _)| i == label.retained_source.end)
+                || label.retained_source.end == text.len()
+        );
+        let painted = label
+            .canvas_text(&session, zoom, Point::new(400., 90.), Color::BLACK)
+            .unwrap();
+        assert_eq!(painted.content, label.displayed);
+        assert!(painted.max_width.is_infinite());
+        assert_eq!(
+            label
+                .bounds_at(&session, zoom, painted.position)
+                .unwrap()
+                .size(),
+            label.bounds.size()
+        );
+    }
+}
+
+#[test]
+fn empty_and_too_narrow_labels_never_claim_source_visibility() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    for text in ["", " \t\n", "Operation: Pump"] {
+        let label = cache
+            .resolve(&session, text, 0., 1., Style::default())
+            .unwrap();
+        assert_eq!(label.displayed, "");
+        assert_eq!(label.retained_source, 0..0);
+        assert_eq!(label.bounds.size(), Size::ZERO);
+        assert!(!label.retains_any(&session, 1., 0..text.len()).unwrap());
+    }
+}
+
+#[test]
+fn redraws_reuse_resolution_but_width_zoom_and_style_are_dependencies() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let text = "call · Pressure verification with a descriptive operation label";
+    let style = Style::default();
+    let a = cache.resolve(&session, text, 100., 1., style).unwrap();
+    let measured = cache.allocations;
+    let b = cache.resolve(&session, text, 100., 1., style).unwrap();
+    assert!(Arc::ptr_eq(&a, &b));
+    assert_eq!(cache.allocations, measured);
+    for (width, zoom, style) in [
+        (120., 1., style),
+        (100., 0.66, style),
+        (
+            100.,
+            1.,
+            Style {
+                size: Pixels(14.),
+                ..style
+            },
+        ),
+    ] {
+        let other = cache.resolve(&session, text, width, zoom, style).unwrap();
+        assert!(!Arc::ptr_eq(&a, &other));
+    }
+}
+
+#[test]
+fn resident_entry_is_remeasured_for_a_fresh_settled_render_session() {
+    let mut cache = Cache::default();
+    let old_session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let text = "call · Pressure verification";
+    let a = cache
+        .resolve(&old_session, text, 100., 1., Style::default())
+        .unwrap();
+    assert_eq!(cache.entries.len(), 1);
+    assert!(Arc::ptr_eq(&cache.entries.front().unwrap().label, &a));
+    let measured = cache.allocations;
+    assert!(measured > 0);
+    assert!(Arc::ptr_eq(
+        &a,
+        &cache
+            .resolve(&old_session, text, 100., 1., Style::default())
+            .unwrap()
+    ));
+    assert_eq!(cache.allocations, measured);
+    // A fresh renderer session invalidates a still-resident entry. This does
+    // not mutate global fonts or purport to test dynamic WGPU font loading.
+    let new_session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let refreshed = cache
+        .resolve(&new_session, text, 100., 1., Style::default())
+        .unwrap();
+    assert!(!Arc::ptr_eq(&a, &refreshed));
+    assert!(cache.allocations > measured);
+    assert_eq!(cache.entries.len(), 1);
+    assert!(Arc::ptr_eq(
+        &cache.entries.front().unwrap().label,
+        &refreshed
+    ));
+}
+
+#[test]
+fn resident_entry_remeasures_after_local_font_epoch_invalidation() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let text = "call · Resident pressure label";
+    let a = cache
+        .resolve(&session, text, 100., 1., Style::default())
+        .unwrap();
+    assert_eq!(cache.entries.len(), 1);
+    assert!(Arc::ptr_eq(&cache.entries.front().unwrap().label, &a));
+    let measured = cache.allocations;
+    assert!(measured > 0);
+    // Exercise the local memo epoch branch while a is still resident. No
+    // intervening width/zoom/style resolution can cause incidental eviction.
+    // This is not an actual font-load or renderer-cache acceptance test.
+    cache.version = None;
+    let refreshed = cache
+        .resolve(&session, text, 100., 1., Style::default())
+        .unwrap();
+    assert!(!Arc::ptr_eq(&a, &refreshed));
+    assert!(cache.allocations > measured);
+    assert_eq!(cache.entries.len(), 1);
+    assert!(Arc::ptr_eq(
+        &cache.entries.front().unwrap().label,
+        &refreshed
+    ));
+}
+
+#[test]
+fn retained_artifact_rejects_other_zoom_and_render_session_for_every_consumer() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let label = cache
+        .resolve(&session, "Operation: Pressure", 200., 1., Style::default())
+        .unwrap();
+    let other = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    for (context, zoom, expected) in [
+        (&session, 0.66, Error::StaleZoom),
+        (&other, 1., Error::StaleRenderSession),
+    ] {
+        assert_eq!(label.displayed(context, zoom).unwrap_err(), expected);
+        assert_eq!(label.retained_source(context, zoom).unwrap_err(), expected);
+        assert_eq!(
+            label.retains_any(context, zoom, 0..9).unwrap_err(),
+            expected
+        );
+        assert_eq!(
+            label.bounds_at(context, zoom, Point::ORIGIN).unwrap_err(),
+            expected
+        );
+        assert_eq!(
+            label
+                .canvas_text(context, zoom, Point::ORIGIN, Color::BLACK)
+                .unwrap_err(),
+            expected
+        );
+    }
+    assert!(
+        label
+            .canvas_text(&session, 1., Point::ORIGIN, Color::BLACK)
+            .is_ok()
+    );
+}
+
+#[test]
+fn finite_scaled_metrics_cannot_escape_as_infinite_world_dimensions() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let style = Style {
+        size: Pixels(2.),
+        line_height: LineHeight::Relative(f32::MAX),
+        ..Style::default()
+    };
+    // At zoom 0.5 the scaled size=1 and line height=MAX are finite. The
+    // required world line height is not; reject before passing it to shaping.
+    let scaled = style.scaled(0.5);
+    assert!(scaled.0.is_finite() && scaled.1.is_finite());
+    assert_eq!(
+        cache
+            .resolve(&session, "call", 100., 0.5, style)
+            .unwrap_err(),
+        Error::InvalidMetrics
+    );
+    assert_eq!(cache.allocations, 0);
+    assert!(cache.entries.is_empty());
+    // Independently exercise validation after division for actual measured
+    // dimensions: finite scaled width/height do not imply finite world values.
+    assert_eq!(
+        world_size(Size::new(f32::MAX, 1.), 0.5),
+        Err(Error::InvalidMeasurement)
+    );
+    assert_eq!(
+        world_size(Size::new(1., f32::MAX), 0.5),
+        Err(Error::InvalidMeasurement)
+    );
+    assert_eq!(
+        world_size(Size::new(20., 8.), 0.5).unwrap(),
+        Size::new(40., 16.)
+    );
+}
+
+#[test]
+fn malformed_metrics_and_explicit_experiment_budgets_fail_without_a_cached_candidate() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    for (width, zoom) in [(f32::NAN, 1.), (-1., 1.), (100., 0.), (100., f32::INFINITY)] {
+        assert_eq!(
+            cache
+                .resolve(&session, "call", width, zoom, Style::default())
+                .unwrap_err(),
+            Error::InvalidMetrics
+        );
+    }
+    assert_eq!(
+        cache
+            .resolve(
+                &session,
+                &"x".repeat(MAX_SOURCE_BYTES + 1),
+                100.,
+                1.,
+                Style::default()
+            )
+            .unwrap_err(),
+        Error::SourceBudget
+    );
+    assert_eq!(
+        cache
+            .resolve(
+                &session,
+                &"x".repeat(MAX_GRAPHEMES + 1),
+                100.,
+                1.,
+                Style::default()
+            )
+            .unwrap_err(),
+        Error::GraphemeBudget
+    );
+    assert!(cache.entries.is_empty());
+}
+
+#[test]
+fn bounds_translation_rejects_nonfinite_world_positions_and_endpoints() {
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let label = cache
+        .resolve(&session, "call", 100., 1., Style::default())
+        .unwrap();
+    for position in [Point::new(f32::NAN, 0.), Point::new(0., f32::INFINITY)] {
+        assert_eq!(
+            label.bounds_at(&session, 1., position).unwrap_err(),
+            Error::InvalidPosition
+        );
+        assert_eq!(
+            label
+                .canvas_text(&session, 1., position, Color::BLACK)
+                .unwrap_err(),
+            Error::InvalidPosition
+        );
+    }
+    assert_eq!(
+        translated_bounds(Point::new(f32::MAX, 0.), Size::new(f32::MAX, 1.)),
+        Err(Error::InvalidPosition)
+    );
+    assert_eq!(
+        translated_bounds(Point::new(0., f32::MAX), Size::new(1., f32::MAX)),
+        Err(Error::InvalidPosition)
+    );
+    assert_eq!(
+        label
+            .bounds_at(&session, 1., Point::new(-20., -10.))
+            .unwrap()
+            .position(),
+        Point::new(-20., -10.)
+    );
+}
+
+/// Must run as the ONLY selected test in a dedicated, fresh test process.
+/// The ignored marker keeps this global-font mutation out of normal parallel
+/// desktop tests. See the evidence directory's exact executable runner.
+#[test]
+#[ignore = "mutates the global font database; run only this exact test in a fresh process"]
+fn actual_font_load_rejects_retained_label_and_old_session() {
+    use graphics_text::cosmic_text::fontdb;
+    use std::borrow::Cow;
+
+    let mut cache = Cache::default();
+    let session = RenderSession::after_fonts_settled_and_renderer_reset().unwrap();
+    let source = "Operation: Pressure";
+    let label = cache
+        .resolve(&session, source, 200., 1., Style::default())
+        .unwrap();
+    assert_eq!(label.displayed(&session, 1.).unwrap(), source);
+    assert!(
+        label
+            .canvas_text(&session, 1., Point::ORIGIN, Color::BLACK)
+            .is_ok()
+    );
+    let measured = cache.allocations;
+    assert!(measured > 0);
+    assert!(Arc::ptr_eq(&cache.entries.front().unwrap().label, &label));
+
+    let (version_before, version_after, faces_before, faces_after) = {
+        let mut fonts = graphics_text::font_system().write().unwrap();
+        let face = fonts
+            .raw()
+            .db()
+            .faces()
+            .find(|face| {
+                face.families
+                    .iter()
+                    .any(|(family, _)| family == "Iced-Icons")
+            })
+            .expect("Iced 0.14 embeds and loads its known Iced-Icons.ttf face")
+            .id;
+        let bytes = fonts
+            .raw()
+            .db()
+            .with_face_data(face, |data, _| data.to_vec())
+            .expect("the built-in binary font has accessible bytes");
+        assert!(!bytes.is_empty());
+        // load_font increments Version even for invalid bytes. Independently
+        // establish actual face admission so this cannot pass with invalid data.
+        let mut probe = fontdb::Database::new();
+        probe.load_font_data(bytes.clone());
+        let admitted = probe
+            .faces()
+            .filter(|face| {
+                face.families
+                    .iter()
+                    .any(|(family, _)| family == "Iced-Icons")
+            })
+            .count();
+        assert!(
+            admitted > 0,
+            "the extracted bytes parse as the expected real font"
+        );
+        let before = fonts.version();
+        assert_eq!(before, session.version);
+        let count = fonts.raw().db().faces().count();
+        // Owned bytes intentionally bypass Borrowed-address deduplication.
+        // This is an actual valid duplicate-face load, not a claim the chosen
+        // face or rendered metrics change; the stale-epoch rule is the oracle.
+        fonts.load_font(Cow::Owned(bytes));
+        (
+            before,
+            fonts.version(),
+            count,
+            fonts.raw().db().faces().count(),
+        )
+    };
+    assert_ne!(version_before, version_after);
+    assert!(
+        faces_after > faces_before,
+        "actual font admission must accompany the version increment"
+    );
+    assert_eq!(
+        label.displayed(&session, 1.).unwrap_err(),
+        Error::FontSetChanged
+    );
+    assert_eq!(
+        label.retained_source(&session, 1.).unwrap_err(),
+        Error::FontSetChanged
+    );
+    assert_eq!(
+        label.retains_any(&session, 1., 0..9).unwrap_err(),
+        Error::FontSetChanged
+    );
+    assert_eq!(
+        label.bounds_at(&session, 1., Point::ORIGIN).unwrap_err(),
+        Error::FontSetChanged
+    );
+    assert_eq!(
+        label
+            .canvas_text(&session, 1., Point::ORIGIN, Color::BLACK)
+            .unwrap_err(),
+        Error::FontSetChanged
+    );
+    assert_eq!(
+        cache
+            .resolve(&session, source, 200., 1., Style::default())
+            .unwrap_err(),
+        Error::FontSetChanged
+    );
+    assert_eq!(
+        cache.allocations, measured,
+        "an invalid session must not remeasure and imply renderer repair"
+    );
+    println!(
+        "Valid Iced-Icons load: faces {faces_before}->{faces_after}, font Version {version_before:?}->{version_after:?}; old label and session rejected"
+    );
+    // Do not create a fresh session or claim dynamic WGPU cache recovery here.
+    // Process exit is the isolation boundary; no other test may run afterward.
+}

crates/oa-desktop/src/behavior/scenario_lifecycle.rs

@@ -0,0 +1,285 @@
+//! Read-only lifecycle geometry. Operand screen order is never execution order.
+use oa_core::{FragmentOperator, Id, Kind, MessageKind, OccurrenceBody, Project, SharedBody};
+use std::collections::{BTreeMap, BTreeSet};
+
+pub(super) mod render;
+
+/// Maps already recorded by the sequence renderer. Rows carry their owning sequence.
+pub(crate) struct Geometry<'a> {
+    pub rows: &'a BTreeMap<Id, (Id, f32)>,
+    pub scopes: &'a BTreeMap<Id, (f32, f32)>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub(crate) struct Span {
+    pub start: f32,
+    pub end: f32,
+}
+impl Span {
+    fn valid(self) -> bool {
+        self.start.is_finite() && self.end.is_finite() && self.start <= self.end
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum Life {
+    Alive,
+    Absent,
+    Unresolved,
+}
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub(crate) struct Interval {
+    pub scope: Id,
+    pub span: Span,
+    pub life: Life,
+}
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum MarkerKind {
+    Birth,
+    Death,
+}
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub(crate) struct Marker {
+    pub occurrence: Id,
+    pub scope: Id,
+    pub y: f32,
+    pub kind: MarkerKind,
+}
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum UncertaintyReason {
+    Conditional,
+    Repeated,
+    Parallel,
+    MissingGeometry,
+}
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct Uncertainty {
+    pub scope: Id,
+    pub reason: UncertaintyReason,
+}
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) struct LaneLifetime {
+    pub lifeline: Id,
+    pub intervals: Vec<Interval>,
+    pub markers: Vec<Marker>,
+    pub uncertainties: Vec<Uncertainty>,
+}
+
+/// Stable lane-ID order; source/model/history and caller-owned geometry are untouched.
+/// An opaque ScenarioUse is a local use, not a caller birth/death contract.
+pub(crate) fn project_lifetimes(
+    project: &Project,
+    scenario: Id,
+    geometry: &Geometry<'_>,
+) -> Vec<LaneLifetime> {
+    if project
+        .elements
+        .get(&scenario)
+        .is_none_or(|e| e.kind() != Kind::Scenario)
+    {
+        return vec![];
+    }
+    project
+        .elements
+        .values()
+        .filter(|e| e.kind() == Kind::Lifeline && e.parent == Some(scenario))
+        .map(|e| {
+            let mut projection = Projection {
+                project,
+                geometry,
+                lane: e.id,
+                visiting: BTreeSet::new(),
+                result: LaneLifetime {
+                    lifeline: e.id,
+                    intervals: vec![],
+                    markers: vec![],
+                    uncertainties: vec![],
+                },
+            };
+            let initial = if projection.contains(scenario, Some(MarkerKind::Birth)) {
+                Life::Unresolved
+            } else {
+                Life::Alive
+            };
+            projection.sequence(scenario, initial);
+            projection.result
+        })
+        .collect()
+}
+
+struct Projection<'a, 'g> {
+    project: &'a Project,
+    geometry: &'a Geometry<'g>,
+    lane: Id,
+    visiting: BTreeSet<Id>,
+    result: LaneLifetime,
+}
+impl Projection<'_, '_> {
+    fn body(&self, id: Id) -> Option<&OccurrenceBody> {
+        match self.project.elements.get(&id)?.shared()? {
+            SharedBody::Occurrence { body, .. } => Some(body),
+            _ => None,
+        }
+    }
+    fn event(&self, id: Id) -> Option<MarkerKind> {
+        match self.body(id)? {
+            OccurrenceBody::Exchange {
+                receiver: Some(line),
+                message_kind,
+                ..
+            } if *line == self.lane => match message_kind {
+                MessageKind::Create => Some(MarkerKind::Birth),
+                MessageKind::Delete => Some(MarkerKind::Death),
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+    fn contains(&self, scope: Id, kind: Option<MarkerKind>) -> bool {
+        // Local structural walk only: no guards, iteration simulation or reuse expansion.
+        let mut pending = vec![scope];
+        let mut seen = BTreeSet::new();
+        while let Some(id) = pending.pop() {
+            if !seen.insert(id) {
+                continue;
+            }
+            if self
+                .event(id)
+                .is_some_and(|event| kind.is_none_or(|k| event == k))
+            {
+                return true;
+            }
+            if let Some(steps) = self.project.elements.get(&id).and_then(|e| e.steps()) {
+                pending.extend(steps);
+            }
+            if let Some(OccurrenceBody::Fragment { branches, .. }) = self.body(id) {
+                pending.extend(branches);
+            }
+        }
+        false
+    }
+    fn span(&self, scope: Id) -> Option<Span> {
+        let &(start, end) = self.geometry.scopes.get(&scope)?;
+        let span = Span { start, end };
+        span.valid().then_some(span)
+    }
+    fn uncertain(&mut self, scope: Id, reason: UncertaintyReason) {
+        let value = Uncertainty { scope, reason };
+        if !self.result.uncertainties.contains(&value) {
+            self.result.uncertainties.push(value);
+        }
+    }
+    fn interval(&mut self, scope: Id, start: f32, end: f32, life: Life) {
+        if start < end && start.is_finite() && end.is_finite() {
+            self.result.intervals.push(Interval {
+                scope,
+                span: Span { start, end },
+                life,
+            });
+        }
+    }
+    fn sequence(&mut self, scope: Id, entry: Life) -> Life {
+        let Some(span) = self.span(scope) else {
+            self.uncertain(scope, UncertaintyReason::MissingGeometry);
+            return Life::Unresolved;
+        };
+        if !self.visiting.insert(scope) {
+            self.uncertain(scope, UncertaintyReason::MissingGeometry);
+            return Life::Unresolved;
+        }
+        let steps = self
+            .project
+            .elements
+            .get(&scope)
+            .and_then(|e| e.steps())
+            .cloned()
+            .unwrap_or_default();
+        // A creation directly in this sequence fixes its local birth boundary.
+        // A creation only in a nested operand cannot fix its ancestor's entry.
+        let mut life = if steps
+            .iter()
+            .any(|&id| self.event(id) == Some(MarkerKind::Birth))
+        {
+            Life::Absent
+        } else {
+            entry
+        };
+        let mut cursor = span.start;
+        for id in steps {
+            let event = self.event(id);
+            let fragment = match self.body(id) {
+                Some(OccurrenceBody::Fragment { operator, branches }) => {
+                    Some((*operator, branches.clone()))
+                }
+                _ => None,
+            };
+            if event.is_none() && fragment.is_none() {
+                continue;
+            }
+            let y = self
+                .geometry
+                .rows
+                .get(&id)
+                .filter(|(owner, y)| {
+                    *owner == scope && y.is_finite() && *y >= cursor && *y <= span.end
+                })
+                .map(|(_, y)| *y);
+            let Some(y) = y else {
+                self.uncertain(id, UncertaintyReason::MissingGeometry);
+                life = Life::Unresolved;
+                continue;
+            };
+            self.interval(scope, cursor, y, life);
+            cursor = y;
+            if let Some(kind) = event {
+                self.result.markers.push(Marker {
+                    occurrence: id,
+                    scope,
+                    y,
+                    kind,
+                });
+                life = match kind {
+                    MarkerKind::Birth => Life::Alive,
+                    MarkerKind::Death => Life::Absent,
+                };
+            }
+            if let Some((operator, branches)) = fragment {
+                let entry = life;
+                let mut missing = false;
+                for branch in branches {
+                    let bounds = self
+                        .span(branch)
+                        .filter(|s| s.start >= cursor && s.end <= span.end);
+                    if let Some(bounds) = bounds {
+                        // Every sibling inherits the same entry, never its displayed predecessor's exit.
+                        self.sequence(branch, entry);
+                        cursor = bounds.end;
+                    } else {
+                        self.uncertain(branch, UncertaintyReason::MissingGeometry);
+                        missing = true;
+                    }
+                }
+                if self.contains(id, None) {
+                    let reason = match operator {
+                        FragmentOperator::Alternative | FragmentOperator::Optional => {
+                            UncertaintyReason::Conditional
+                        }
+                        FragmentOperator::Loop => UncertaintyReason::Repeated,
+                        FragmentOperator::Parallel => UncertaintyReason::Parallel,
+                    };
+                    self.uncertain(id, reason);
+                    life = Life::Unresolved;
+                } else if missing {
+                    life = Life::Unresolved;
+                }
+            }
+        }
+        self.interval(scope, cursor, span.end, life);
+        self.visiting.remove(&scope);
+        life
+    }
+}
+
+#[cfg(test)]
+#[path = "scenario_lifecycle/tests.rs"]
+mod tests;

crates/oa-desktop/src/behavior/scenario_lifecycle/render.rs

@@ -0,0 +1,392 @@
+//! Scene bridge for local lifetime geometry; no authoring or model mutations.
+use super::{Geometry, LaneLifetime, Life, Marker, MarkerKind, Span, project_lifetimes};
+use crate::{behavior::Line, style, views::short};
+use iced::{
+    Color, Point, Rectangle, Size,
+    widget::canvas::{self, Frame, Path, Stroke, Text},
+};
+use oa_core::{Id, OccurrenceBody, Project, SharedBody};
+use std::collections::BTreeMap;
+
+#[derive(Debug, Clone, PartialEq)]
+struct EventMarker {
+    event: Marker,
+    lifeline: Id,
+    center: Point,
+    capsule: Rectangle,
+    name: String,
+    sender_x: Option<f32>,
+}
+
+#[derive(Debug, Default, Clone, PartialEq)]
+pub(in crate::behavior) struct Rendering {
+    // Complete rendering positions, including warning-admitted unassigned lanes.
+    // Scene.lanes independently retains the existing authoring eligibility rule.
+    lanes: BTreeMap<Id, f32>,
+    span: Option<Span>,
+    lifetimes: Vec<LaneLifetime>,
+    markers: Vec<EventMarker>,
+}
+
+impl Rendering {
+    pub(in crate::behavior) fn new(
+        project: &Project,
+        owner: Id,
+        lanes: &BTreeMap<Id, f32>,
+        rows: &BTreeMap<Id, (Id, f32)>,
+        insertion_scopes: &BTreeMap<Id, (f32, f32)>,
+        height: f32,
+    ) -> Self {
+        let span = Span {
+            start: 85.,
+            end: height - 20.,
+        };
+        if !span.valid() {
+            return Self::default();
+        }
+        // Insertion scopes deliberately start later and end earlier. Empty and
+        // Create-only scenarios still have the full visible lifetime extent.
+        let mut scopes = insertion_scopes.clone();
+        for (scope, (start, end)) in &mut scopes {
+            if *scope != owner && *start == *end && start.is_finite() {
+                // An empty operand has 42 px between its insertion axis and
+                // frame end. Match the existing 26 px open-activation allowance.
+                *end = *start + 26.;
+            }
+        }
+        scopes.insert(owner, (span.start, span.end));
+        let lifetimes = project_lifetimes(
+            project,
+            owner,
+            &Geometry {
+                rows,
+                scopes: &scopes,
+            },
+        );
+        let lanes: BTreeMap<_, _> = lanes
+            .iter()
+            .filter(|(_, x)| x.is_finite())
+            .map(|(id, x)| (*id, *x))
+            .collect();
+        let mut markers = Vec::new();
+        for lane in &lifetimes {
+            let Some(&x) = lanes.get(&lane.lifeline) else {
+                continue;
+            };
+            for event in &lane.markers {
+                let sender_x = project
+                    .elements
+                    .get(&event.occurrence)
+                    .and_then(|e| e.shared())
+                    .and_then(|body| match body {
+                        SharedBody::Occurrence {
+                            body:
+                                OccurrenceBody::Exchange {
+                                    sender: Some(sender),
+                                    ..
+                                },
+                            ..
+                        } => lanes.get(sender).copied(),
+                        _ => None,
+                    });
+                markers.push(EventMarker {
+                    event: *event,
+                    lifeline: lane.lifeline,
+                    center: Point::new(x, event.y),
+                    capsule: Rectangle::new(
+                        Point::new(x - 70., event.y - 14.),
+                        Size::new(140., 28.),
+                    ),
+                    name: project.named(lane.lifeline).to_owned(),
+                    sender_x,
+                });
+            }
+        }
+        Self {
+            lanes,
+            span: Some(span),
+            lifetimes,
+            markers,
+        }
+    }
+
+    pub(in crate::behavior) fn align_messages(&self, lines: &mut [Line]) {
+        for marker in &self.markers {
+            let Some(sender) = marker.sender_x else {
+                continue;
+            };
+            let Some(line) = lines
+                .iter_mut()
+                .find(|line| line.id == marker.event.occurrence)
+            else {
+                continue;
+            };
+            let x = marker.center.x;
+            let y = marker.center.y;
+            let self_message = sender == x;
+            let end_x = match marker.event.kind {
+                MarkerKind::Birth if sender < x => marker.capsule.x,
+                MarkerKind::Birth => marker.capsule.x + marker.capsule.width,
+                MarkerKind::Death => x,
+            };
+            line.points = if self_message {
+                // The receiver is on the recorded occurrence row, including self
+                // lifecycle events. The elbow stays outside the birth capsule.
+                let elbow = x + 112.;
+                line.label_at = Point::new(x + 12., y - 52.);
+                vec![
+                    Point::new(x, y - 24.),
+                    Point::new(elbow, y - 24.),
+                    Point::new(elbow, y),
+                    Point::new(end_x, y),
+                ]
+            } else {
+                if marker.event.kind == MarkerKind::Birth {
+                    // Keep the label above the capsule, including right-to-left
+                    // messages whose existing label starts beside the receiver.
+                    line.label_at.y = y - 40.;
+                }
+                vec![Point::new(sender, y), Point::new(end_x, y)]
+            };
+        }
+    }
+
+    pub(in crate::behavior) fn alive_spans(
+        &self,
+        lifeline: Id,
+        scope: Id,
+        top: f32,
+        bottom: f32,
+    ) -> Vec<Span> {
+        if !top.is_finite() || !bottom.is_finite() || bottom <= top {
+            return vec![];
+        }
+        self.lifetimes
+            .iter()
+            .find(|lane| lane.lifeline == lifeline)
+            .into_iter()
+            .flat_map(|lane| &lane.intervals)
+            .filter(|interval| interval.scope == scope && interval.life == Life::Alive)
+            .filter_map(|interval| {
+                let start = top.max(interval.span.start);
+                let end = bottom.min(interval.span.end);
+                (start < end).then_some(Span { start, end })
+            })
+            .collect()
+    }
+
+    pub(in crate::behavior) fn marker_at(&self, point: Point) -> Option<Id> {
+        self.markers
+            .iter()
+            .rev()
+            .find(|marker| match marker.event.kind {
+                MarkerKind::Birth => marker.capsule.contains(point),
+                MarkerKind::Death => marker_distance(marker, point) <= 1.25,
+            })
+            .map(|marker| marker.event.occurrence)
+    }
+
+    pub(in crate::behavior) fn nearest_marker(&self, point: Point) -> Option<(Id, f32)> {
+        if !point.x.is_finite() || !point.y.is_finite() {
+            return None;
+        }
+        // Exact visible shapes are tested first by Scene. A low-zoom tolerance
+        // must not outrank another marker's actual capsule, a header, or a label.
+        self.markers
+            .iter()
+            .map(|marker| (marker.event.occurrence, marker_distance(marker, point)))
+            .min_by(|a, b| a.1.total_cmp(&b.1).then_with(|| a.0.cmp(&b.0)))
+    }
+
+    pub(in crate::behavior) fn lane_at(&self, point: Point, scale: f32) -> Option<Id> {
+        let span = self.span?;
+        if !scale.is_finite() || scale <= 0. || point.y < span.start || point.y > span.end {
+            return None;
+        }
+        self.lanes
+            .iter()
+            .filter(|(_, x)| (**x - point.x).abs() < 12. / scale)
+            .min_by(|a, b| (a.1 - point.x).abs().total_cmp(&(b.1 - point.x).abs()))
+            .map(|(id, _)| *id)
+    }
+
+    pub(in crate::behavior) fn draw_lanes(&self, frame: &mut Frame, selected: Id) {
+        let Some(span) = self.span else {
+            return;
+        };
+        for (&id, &x) in &self.lanes {
+            frame.stroke(
+                &Path::line(Point::new(x, span.start), Point::new(x, span.end)),
+                Stroke {
+                    line_dash: canvas::LineDash {
+                        segments: &[2., 5.],
+                        offset: 0,
+                    },
+                    ..Stroke::default()
+                        .with_width(1.)
+                        .with_color(if id == selected {
+                            Color::from_rgb8(148, 190, 187)
+                        } else {
+                            Color::from_rgb8(214, 222, 222)
+                        })
+                },
+            );
+        }
+        for lifetime in &self.lifetimes {
+            let Some(&x) = self.lanes.get(&lifetime.lifeline) else {
+                continue;
+            };
+            for interval in &lifetime.intervals {
+                match interval.life {
+                    Life::Alive => frame.stroke(
+                        &Path::line(
+                            Point::new(x, interval.span.start),
+                            Point::new(x, interval.span.end),
+                        ),
+                        Stroke::default().with_width(2.).with_color(
+                            if lifetime.lifeline == selected {
+                                style::TEAL
+                            } else {
+                                Color::from_rgb8(91, 113, 113)
+                            },
+                        ),
+                    ),
+                    Life::Unresolved if interval.span.end - interval.span.start >= 16. => {
+                        frame.fill_text(Text {
+                            content: "?".into(),
+                            position: Point::new(x + 9., interval.span.start + 2.),
+                            size: 11.into(),
+                            color: style::MUTED,
+                            ..Default::default()
+                        });
+                    }
+                    _ => {}
+                }
+            }
+        }
+        if !self.lanes.is_empty() {
+            frame.fill_text(Text {
+                content:
+                    "Dotted: editing guide · Solid: local lifetime · ?: lifetime depends on path"
+                        .into(),
+                position: Point::new(28., span.end + 4.),
+                size: 10.into(),
+                color: style::MUTED,
+                ..Default::default()
+            });
+        }
+    }
+
+    pub(in crate::behavior) fn draw_markers(
+        &self,
+        frame: &mut Frame,
+        selected: Id,
+        scale: f32,
+        pan: iced::Vector,
+    ) {
+        for marker in &self.markers {
+            let color = if selected == marker.event.occurrence || selected == marker.lifeline {
+                style::TEAL
+            } else {
+                style::INK
+            };
+            match marker.event.kind {
+                MarkerKind::Birth => {
+                    let path = Path::rounded_rectangle(
+                        marker.capsule.position(),
+                        marker.capsule.size(),
+                        6.into(),
+                    );
+                    frame.fill(&path, Color::from_rgb8(243, 248, 248));
+                    frame.stroke(
+                        &path,
+                        Stroke::default().with_color(color).with_width(
+                            if selected == marker.event.occurrence {
+                                2.5
+                            } else {
+                                1.5
+                            },
+                        ),
+                    );
+                    if let Some(clip) = birth_label_clip(pan, marker.capsule, scale, frame.size()) {
+                        // WGPU clipped frames start with an identity transform;
+                        // neither the parent's pan/scale nor its clip is inherited.
+                        frame.with_clip(clip, |label| {
+                            label.translate(pan);
+                            label.scale(scale);
+                            label.fill_text(Text {
+                                content: short(&marker.name, 18),
+                                position: marker.capsule.position() + iced::Vector::new(8., 6.),
+                                size: 12.into(),
+                                color,
+                                ..Default::default()
+                            });
+                        });
+                    }
+                }
+                MarkerKind::Death => {
+                    for (a, b) in death_strokes(marker.center) {
+                        frame.stroke(
+                            &Path::line(a, b),
+                            Stroke::default().with_color(color).with_width(2.5),
+                        );
+                    }
+                }
+            }
+        }
+    }
+}
+
+fn birth_label_clip(
+    pan: iced::Vector,
+    capsule: Rectangle,
+    scale: f32,
+    viewport: Size,
+) -> Option<Rectangle> {
+    if !pan.x.is_finite() || !pan.y.is_finite() || !scale.is_finite() || scale <= 0. {
+        return None;
+    }
+    Rectangle::new(
+        Point::new(
+            pan.x + (capsule.x + 8.) * scale,
+            pan.y + (capsule.y + 4.) * scale,
+        ),
+        Size::new((capsule.width - 16.) * scale, (capsule.height - 8.) * scale),
+    )
+    .intersection(&Rectangle::new(Point::ORIGIN, viewport))
+}
+
+fn marker_distance(marker: &EventMarker, point: Point) -> f32 {
+    match marker.event.kind {
+        MarkerKind::Birth => {
+            let dx = (marker.capsule.x - point.x)
+                .max(point.x - marker.capsule.x - marker.capsule.width)
+                .max(0.);
+            let dy = (marker.capsule.y - point.y)
+                .max(point.y - marker.capsule.y - marker.capsule.height)
+                .max(0.);
+            dx.hypot(dy)
+        }
+        MarkerKind::Death => death_strokes(marker.center)
+            .iter()
+            .map(|(a, b)| crate::diagram::distance_to_segment(point, *a, *b))
+            .fold(f32::INFINITY, f32::min),
+    }
+}
+
+fn death_strokes(center: Point) -> [(Point, Point); 2] {
+    [
+        (
+            center + iced::Vector::new(-7., -7.),
+            center + iced::Vector::new(7., 7.),
+        ),
+        (
+            center + iced::Vector::new(-7., 7.),
+            center + iced::Vector::new(7., -7.),
+        ),
+    ]
+}
+
+#[cfg(test)]
+#[path = "render_tests.rs"]
+mod tests;

crates/oa-desktop/src/behavior/scenario_lifecycle/render_tests.rs

@@ -0,0 +1,973 @@
+use super::*;
+use crate::{behavior::Scene, document::Document};
+use iced::Size;
+use oa_core::*;
+
+struct Fixture {
+    project: Project,
+    owner: Id,
+    sender: Id,
+    receiver: Id,
+    work: Id,
+    exchange: Id,
+}
+impl Fixture {
+    fn new(layer: Layer) -> Self {
+        let mut project = Project::empty();
+        let kind = if layer == Layer::Oa {
+            Kind::Activity
+        } else {
+            Kind::Function
+        };
+        let a = project.add_element(kind, layer, "Request", None).unwrap();
+        let work = project.add_element(kind, layer, "Provide", None).unwrap();
+        let exchange = project.relate(
+            if layer == Layer::Oa {
+                RelationKind::Interaction
+            } else {
+                RelationKind::FunctionalExchange
+            },
+            "Service",
+            a,
+            work,
+        );
+        let owner = project
+            .add_element(Kind::Scenario, layer, "Lifecycle", None)
+            .unwrap();
+        let mut lane = |name, represented| {
+            let id = project
+                .add_element(Kind::Lifeline, layer, name, Some(owner))
+                .unwrap();
+            *project.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Lifeline {
+                represented: Some(represented),
+            };
+            id
+        };
+        let sender = lane("Requester", a);
+        let receiver = lane("Provider", work);
+        Self {
+            project,
+            owner,
+            sender,
+            receiver,
+            work,
+            exchange,
+        }
+    }
+    fn occurrence(&mut self, parent: Id, name: &str, body: OccurrenceBody) -> Id {
+        let mut element = self
+            .project
+            .make_element(
+                Kind::Occurrence,
+                self.project.elements[&parent].layer(),
+                name,
+                Some(parent),
+            )
+            .unwrap();
+        let id = element.id;
+        *element.shared_mut().unwrap() = SharedBody::Occurrence {
+            body,
+            precondition: String::new(),
+            postcondition: String::new(),
+        };
+        self.project.elements.insert(id, element);
+        let parent = self.project.elements.get_mut(&parent).unwrap();
+        if let Some(steps) = parent.steps_mut() {
+            steps.push(id);
+        } else if let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Fragment { branches, .. },
+            ..
+        }) = parent.shared_mut()
+        {
+            branches.push(id);
+        } else {
+            panic!("fixture parent must own ordered occurrences or operands");
+        }
+        id
+    }
+    fn message(&mut self, parent: Id, kind: MessageKind) -> Id {
+        self.occurrence(
+            parent,
+            "Message",
+            OccurrenceBody::Exchange {
+                exchange: Some(self.exchange),
+                sender: Some(self.sender),
+                receiver: Some(self.receiver),
+                message_kind: kind,
+                operation: None,
+                reply_to: None,
+                values: vec![],
+            },
+        )
+    }
+    fn fragment(&mut self, parent: Id, operator: FragmentOperator) -> Id {
+        self.occurrence(
+            parent,
+            "Paths",
+            OccurrenceBody::Fragment {
+                operator,
+                branches: vec![],
+            },
+        )
+    }
+    fn branch(&mut self, fragment: Id) -> Id {
+        self.occurrence(
+            fragment,
+            "Operand",
+            OccurrenceBody::Branch {
+                guard: "condition".into(),
+                occurrences: vec![],
+            },
+        )
+    }
+    fn document(&self) -> Document {
+        validate_candidate(&self.project).expect("ordinary core admission must succeed");
+        let mut bundle = source_project::format_bundle(&self.project);
+        for text in bundle.files.values_mut() {
+            *text = format!(
+                "// Retain exact authored CRLF and Unicode Ω\r\n{}",
+                text.replace('\n', "\r\n")
+            );
+        }
+        let document =
+            Document::from_bundle(bundle.clone(), source_project::ProjectLimits::default())
+                .unwrap();
+        assert_eq!(document.project(), &self.project);
+        assert_eq!(document.bundle(), &bundle);
+        document
+    }
+    fn scene(&self) -> Scene {
+        let document = self.document();
+        let before = document.snapshot();
+        let scene = Scene::sequence(document.project(), self.owner, self.owner);
+        assert_eq!(document.project(), &before.decoded.project);
+        assert_eq!(document.bundle(), &before.bundle);
+        assert_eq!(document.revision(), 0);
+        assert!(!document.can_undo() && !document.can_redo() && !document.dirty());
+        assert_eq!(
+            scene.lifecycle,
+            Scene::sequence(document.project(), self.owner, self.owner).lifecycle
+        );
+        assert!(
+            scene
+                .lines
+                .iter()
+                .flat_map(|line| &line.points)
+                .all(|p| p.x.is_finite() && p.y.is_finite())
+        );
+        scene
+    }
+}
+
+fn intervals(scene: &Scene, lifeline: Id, scope: Id) -> Vec<(f32, f32, Life)> {
+    scene
+        .lifecycle
+        .lifetimes
+        .iter()
+        .find(|lane| lane.lifeline == lifeline)
+        .unwrap()
+        .intervals
+        .iter()
+        .filter(|i| i.scope == scope)
+        .map(|i| (i.span.start, i.span.end, i.life))
+        .collect()
+}
+
+#[test]
+fn real_scene_long_header_title_and_detail_keep_names_and_have_bounded_clips() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        for name in [
+            "W".repeat(18),
+            "界".repeat(24),
+            "e\u{301}".repeat(24),
+            "👩\u{200d}🔧".repeat(12),
+        ] {
+            let mut f = Fixture::new(layer);
+            f.project.elements.get_mut(&f.receiver).unwrap().name = name.clone();
+            f.project.elements.get_mut(&f.work).unwrap().name = name.clone();
+            let scene = f.scene();
+            let header = scene.boxes.iter().find(|b| b.id == f.receiver).unwrap();
+            assert_eq!(header.title, format!("Lane · {name}"));
+            assert_eq!(header.detail, name);
+            assert_eq!(header.rect.size(), Size::new(204., 70.));
+            assert_eq!(scene.hit(header.rect.center()), Some(f.receiver));
+            // Scroll offset is handled by the existing outer canvas/scrollable;
+            // these are the local drawing frame's coordinates, not screen input.
+            for scale in [0.05, 0.5, 0.512, 0.64, 0.8, 1., 1.953125, 2.] {
+                let clip = crate::behavior::box_text_clip(
+                    iced::Vector::ZERO,
+                    header.rect,
+                    scale,
+                    Size::new(2000., 2000.),
+                )
+                .unwrap();
+                let world = Rectangle::new(
+                    Point::new(clip.x / scale, clip.y / scale),
+                    Size::new(clip.width / scale, clip.height / scale),
+                );
+                assert!((world.x - header.rect.x - 10.).abs() < 0.001);
+                assert!((world.y - header.rect.y - 8.).abs() < 0.001);
+                assert!((world.width - 184.).abs() < 0.001);
+                assert!((world.height - 54.).abs() < 0.001);
+                assert!(header.rect.contains(world.position()));
+                assert!(
+                    header
+                        .rect
+                        .contains(Point::new(world.x + world.width, world.y + world.height,))
+                );
+            }
+        }
+    }
+}
+
+#[test]
+fn box_text_clip_intersects_parent_viewport_and_rejects_empty_interiors() {
+    use crate::behavior::box_text_clip;
+    let card = Rectangle::new(Point::new(100., 200.), Size::new(204., 70.));
+    assert_eq!(
+        box_text_clip(iced::Vector::ZERO, card, 2., Size::new(300., 500.)),
+        Some(Rectangle::new(Point::new(220., 416.), Size::new(80., 84.)))
+    );
+    assert_eq!(
+        box_text_clip(
+            iced::Vector::ZERO,
+            Rectangle::new(Point::new(-20., -10.), card.size()),
+            2.,
+            Size::new(300., 500.),
+        ),
+        Some(Rectangle::new(Point::ORIGIN, Size::new(300., 104.)))
+    );
+    for viewport in [Size::new(200., 500.), Size::new(300., 400.), Size::ZERO] {
+        assert_eq!(box_text_clip(iced::Vector::ZERO, card, 2., viewport), None);
+    }
+    for scale in [0., -1., f32::NAN, f32::INFINITY] {
+        assert_eq!(
+            box_text_clip(iced::Vector::ZERO, card, scale, Size::new(1000., 1000.)),
+            None
+        );
+    }
+    for size in [Size::new(20., 70.), Size::new(204., 16.), Size::ZERO] {
+        assert_eq!(
+            box_text_clip(
+                iced::Vector::ZERO,
+                Rectangle::new(Point::ORIGIN, size),
+                1.,
+                card.size()
+            ),
+            None
+        );
+    }
+}
+
+#[test]
+fn real_scene_wide_latin_header_exceeds_old_character_budget() {
+    use iced::advanced::text::{self, Paragraph as _};
+    let mut f = Fixture::new(Layer::Oa);
+    f.project.elements.get_mut(&f.receiver).unwrap().name = "W".repeat(18);
+    f.project.elements.get_mut(&f.work).unwrap().name = "W".repeat(24);
+    let scene = f.scene();
+    let header = scene.boxes.iter().find(|b| b.id == f.receiver).unwrap();
+    for (content, size, divisor) in [(&header.title, 13., 7.), (&header.detail, 11., 6.)] {
+        let label = iced::widget::canvas::Text {
+            content: crate::views::short(content, ((header.rect.width - 25.) / divisor) as usize),
+            size: size.into(),
+            ..Default::default()
+        };
+        // Use the same real paragraph/font/shaping defaults as canvas Text.
+        // The native defect survives short(): glyph width, not scalar count,
+        // is what exceeds the card. This is a font witness, not a pixel gate.
+        let paragraph = <iced::Renderer as text::Renderer>::Paragraph::with_text(text::Text {
+            content: label.content.as_str(),
+            bounds: Size::INFINITE,
+            size: label.size,
+            line_height: label.line_height,
+            font: label.font,
+            align_x: label.align_x,
+            align_y: label.align_y,
+            shaping: label.shaping,
+            wrapping: text::Wrapping::default(),
+        });
+        let old_available = header.rect.width - 12.;
+        assert!(
+            paragraph.min_width() > old_available,
+            "wide glyph fixture must overflow the old unbounded card: {} <= {old_available}",
+            paragraph.min_width()
+        );
+    }
+}
+
+#[test]
+fn birth_label_clip_keeps_padded_world_bounds_at_each_scene_scale() {
+    let capsule = Rectangle::new(Point::new(100., 200.), Size::new(140., 28.));
+    for (scale, expected) in [
+        (
+            0.05,
+            Rectangle::new(Point::new(5.4, 10.2), Size::new(6.2, 1.)),
+        ),
+        (
+            0.5,
+            Rectangle::new(Point::new(54., 102.), Size::new(62., 10.)),
+        ),
+        (
+            1.,
+            Rectangle::new(Point::new(108., 204.), Size::new(124., 20.)),
+        ),
+        (
+            2.,
+            Rectangle::new(Point::new(216., 408.), Size::new(248., 40.)),
+        ),
+    ] {
+        let clip =
+            birth_label_clip(iced::Vector::ZERO, capsule, scale, Size::new(1000., 1000.)).unwrap();
+        for (actual, expected) in [
+            (clip.x, expected.x),
+            (clip.y, expected.y),
+            (clip.width, expected.width),
+            (clip.height, expected.height),
+        ] {
+            assert!((actual - expected).abs() < 0.0001);
+        }
+        assert!(capsule.contains(Point::new(clip.x / scale, clip.y / scale)));
+        assert!(capsule.contains(Point::new(
+            (clip.x + clip.width) / scale,
+            (clip.y + clip.height) / scale,
+        )));
+    }
+}
+
+#[test]
+fn birth_label_clip_preserves_parent_viewport_bounds() {
+    let capsule = Rectangle::new(Point::new(100., 200.), Size::new(140., 28.));
+    assert_eq!(
+        birth_label_clip(iced::Vector::ZERO, capsule, 2., Size::new(300., 420.)),
+        Some(Rectangle::new(Point::new(216., 408.), Size::new(84., 12.)))
+    );
+    let crossing_origin = Rectangle::new(Point::new(-20., -10.), Size::new(140., 28.));
+    assert_eq!(
+        birth_label_clip(
+            iced::Vector::ZERO,
+            crossing_origin,
+            2.,
+            Size::new(300., 420.)
+        ),
+        Some(Rectangle::new(Point::ORIGIN, Size::new(224., 28.)))
+    );
+    for viewport in [Size::new(200., 420.), Size::new(300., 400.), Size::ZERO] {
+        assert_eq!(
+            birth_label_clip(iced::Vector::ZERO, capsule, 2., viewport),
+            None
+        );
+    }
+    for scale in [0., -1., f32::NAN, f32::INFINITY] {
+        assert_eq!(
+            birth_label_clip(iced::Vector::ZERO, capsule, scale, Size::new(1000., 1000.)),
+            None
+        );
+    }
+}
+
+#[test]
+fn real_scene_empty_and_create_only_use_visible_root_extents_not_insertion_bounds() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = Fixture::new(layer);
+        let empty = f.scene();
+        assert_eq!(empty.sequence_bounds[&f.owner], (106., 106.));
+        assert_eq!(
+            intervals(&empty, f.receiver, f.owner),
+            vec![(85., empty.size.height - 20., Life::Alive)]
+        );
+        assert!(empty.lines.is_empty(), "lane guides are not message lines");
+        let create = f.message(f.owner, MessageKind::Create);
+        let scene = f.scene();
+        let birth = scene.rows[&create].1;
+        assert_eq!(birth, 148.);
+        assert_eq!(scene.sequence_bounds[&f.owner], (106., 198.));
+        assert_eq!(
+            intervals(&scene, f.receiver, f.owner),
+            vec![
+                (85., birth, Life::Absent),
+                (birth, scene.size.height - 20., Life::Alive),
+            ]
+        );
+        assert_eq!(
+            intervals(&scene, f.sender, f.owner),
+            vec![(85., scene.size.height - 20., Life::Alive)]
+        );
+        assert_eq!(scene.slots[0].y, 106.);
+        assert_eq!(
+            scene.lane_at(Point::new(scene.lanes[&f.receiver], 90.)),
+            Some(f.receiver)
+        );
+    }
+}
+
+#[test]
+fn real_scene_birth_death_markers_align_endpoints_and_win_selection_without_mutating_source() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = Fixture::new(layer);
+        let create = f.message(f.owner, MessageKind::Create);
+        f.occurrence(
+            f.owner,
+            "Work",
+            OccurrenceBody::Action {
+                action: Some(f.work),
+                lifeline: Some(f.receiver),
+            },
+        );
+        let delete = f.message(f.owner, MessageKind::Delete);
+        let mut scene = f.scene();
+        let birth = scene.rows[&create].1;
+        let death = scene.rows[&delete].1;
+        assert_eq!(
+            intervals(&scene, f.receiver, f.owner),
+            vec![
+                (85., birth, Life::Absent),
+                (birth, death, Life::Alive),
+                (death, scene.size.height - 20., Life::Absent),
+            ]
+        );
+        let capsule = scene
+            .lifecycle
+            .markers
+            .iter()
+            .find(|m| m.event.occurrence == create)
+            .unwrap()
+            .capsule;
+        let line = scene.lines.iter().find(|l| l.id == create).unwrap();
+        let expected_x = if scene.lanes[&f.sender] < scene.lanes[&f.receiver] {
+            capsule.x
+        } else {
+            capsule.x + capsule.width
+        };
+        assert_eq!(line.points.last(), Some(&Point::new(expected_x, birth)));
+        assert!(
+            line.label_at.y + 22. < capsule.y,
+            "message caption clears birth capsule"
+        );
+        let line = scene.lines.iter().find(|l| l.id == delete).unwrap();
+        assert_eq!(
+            line.points.last(),
+            Some(&Point::new(scene.lanes[&f.receiver], death))
+        );
+        for scale in [0.5, 1., 2.] {
+            scene.scale = scale;
+            assert_eq!(
+                scene.hit(Point::new(scene.lanes[&f.receiver], birth)),
+                Some(create)
+            );
+            assert_eq!(
+                scene.hit(Point::new(scene.lanes[&f.receiver], death)),
+                Some(delete)
+            );
+            assert_eq!(
+                scene.hit(Point::new(
+                    scene.lanes[&f.receiver],
+                    scene.size.height - 25.
+                )),
+                Some(f.receiver)
+            );
+            assert_eq!(
+                scene.hit(Point::new(scene.lanes[&f.receiver], 40.)),
+                Some(f.receiver)
+            );
+        }
+    }
+}
+
+#[test]
+fn real_scene_branch_delete_clips_only_its_activation_and_keeps_unanswered_call_visible() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = Fixture::new(layer);
+        let call = f.message(f.owner, MessageKind::Call);
+        let fragment = f.fragment(f.owner, FragmentOperator::Alternative);
+        let left = f.branch(fragment);
+        let delete = f.message(left, MessageKind::Delete);
+        let right = f.branch(fragment);
+        let scene = f.scene();
+        let death = scene.rows[&delete].1;
+        let (left_start, left_end) = scene.sequence_bounds[&left];
+        let (right_start, _) = scene.sequence_bounds[&right];
+        let bars: Vec<_> = scene
+            .boxes
+            .iter()
+            .filter(|b| b.id == call && b.rect.width == 8.)
+            .map(|b| b.rect)
+            .collect();
+        assert!(
+            bars.iter()
+                .any(|r| r.y == left_start && r.y + r.height == death)
+        );
+        assert!(
+            !bars
+                .iter()
+                .any(|r| r.y < left_end && r.y + r.height > death && r.y >= left_start)
+        );
+        assert!(
+            bars.iter().any(|r| r.y == right_start && r.height == 26.),
+            "empty exclusive sibling retains its own open activation"
+        );
+        assert_eq!(
+            intervals(&scene, f.receiver, right),
+            vec![(right_start, right_start + 26., Life::Alive)]
+        );
+        let frame_end = scene.boxes.iter().find(|b| b.id == fragment).unwrap().rect;
+        assert!(
+            !bars.iter().any(|r| r.y >= frame_end.y + frame_end.height),
+            "uncertain post-fragment lifetime cannot carry a definite activation bar"
+        );
+        assert!(
+            scene
+                .open_calls
+                .iter()
+                .any(|p| p.y < death && p.y > left_start)
+        );
+        assert!(scene.open_calls.iter().any(|p| p.y > right_start));
+        assert_eq!(
+            intervals(&scene, f.receiver, left),
+            vec![
+                (left_start, death, Life::Alive),
+                (death, left_end, Life::Absent)
+            ]
+        );
+        assert_eq!(
+            intervals(&scene, f.receiver, f.owner).last().unwrap().2,
+            Life::Unresolved
+        );
+        assert!(!f.project.elements.values().any(|e| matches!(
+            e.shared(),
+            Some(SharedBody::Occurrence {
+                body: OccurrenceBody::Exchange {
+                    message_kind: MessageKind::Reply,
+                    ..
+                },
+                ..
+            })
+        )));
+    }
+}
+
+#[test]
+fn real_scene_unassigned_lanes_and_explicit_incomplete_receiver_keep_real_marker_identity() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = Fixture::new(layer);
+        *f.project
+            .elements
+            .get_mut(&f.receiver)
+            .unwrap()
+            .shared_mut()
+            .unwrap() = SharedBody::Lifeline { represented: None };
+        let create = f.message(f.owner, MessageKind::Create);
+        if let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange { exchange, .. },
+            ..
+        }) = f.project.elements.get_mut(&create).unwrap().shared_mut()
+        {
+            *exchange = None;
+        }
+        let scene = f.scene();
+        assert!(
+            !scene.lanes.contains_key(&f.receiver),
+            "authoring eligibility remains separate"
+        );
+        let x = scene.lifecycle.lanes[&f.receiver];
+        assert_eq!(scene.lifecycle.markers[0].lifeline, f.receiver);
+        assert_eq!(
+            scene.hit(Point::new(x, scene.rows[&create].1)),
+            Some(create)
+        );
+        assert_eq!(scene.hit(Point::new(x, 40.)), Some(f.receiver));
+        assert_eq!(
+            scene.hit(Point::new(x, scene.size.height - 25.)),
+            Some(f.receiver)
+        );
+        assert_eq!(scene.lane_at(Point::new(x, 90.)), None);
+        if let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange {
+                receiver, exchange, ..
+            },
+            ..
+        }) = f.project.elements.get_mut(&create).unwrap().shared_mut()
+        {
+            *receiver = None;
+            *exchange = Some(f.exchange);
+        }
+        let missing = f.scene();
+        assert!(
+            missing.lifecycle.markers.is_empty(),
+            "do not infer receiver from global exchange"
+        );
+    }
+}
+
+#[test]
+fn real_scene_minimum_zoom_marker_halos_do_not_steal_adjacent_capsule_or_header_hits() {
+    let mut f = Fixture::new(Layer::Sa);
+    *f.project
+        .elements
+        .get_mut(&f.receiver)
+        .unwrap()
+        .shared_mut()
+        .unwrap() = SharedBody::Lifeline { represented: None };
+    let create = f.message(f.owner, MessageKind::Create);
+    let delete = f.message(f.owner, MessageKind::Delete);
+    for event in [create, delete] {
+        if let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange { exchange, .. },
+            ..
+        }) = f.project.elements.get_mut(&event).unwrap().shared_mut()
+        {
+            *exchange = None;
+        }
+    }
+    let mut scene = f.scene();
+    let x = scene.lifecycle.lanes[&f.receiver];
+    assert_eq!(scene.rows[&delete].1 - scene.rows[&create].1, 92.);
+    for scale in [0.05, 0.1, 0.5, 1., 2.] {
+        scene.scale = scale;
+        assert_eq!(
+            scene.hit(Point::new(x, scene.rows[&create].1)),
+            Some(create)
+        );
+        assert_eq!(
+            scene.hit(Point::new(x, scene.rows[&delete].1)),
+            Some(delete)
+        );
+        assert_eq!(scene.hit(Point::new(x, 40.)), Some(f.receiver));
+        if scale <= 0.1 {
+            for offset in [-25., -15., 15., 25.] {
+                assert_eq!(
+                    scene.hit(Point::new(x, scene.rows[&delete].1 + offset)),
+                    Some(delete),
+                    "a nearby death halo must beat an earlier message's wider tolerance"
+                );
+            }
+        }
+    }
+}
+
+#[test]
+fn real_scene_minimum_zoom_near_ordinary_message_wins_over_lifecycle_halos() {
+    let mut f = Fixture::new(Layer::Sa);
+    f.message(f.owner, MessageKind::Create);
+    let ordinary = f.message(f.owner, MessageKind::Asynchronous);
+    f.message(f.owner, MessageKind::Delete);
+    let mut scene = f.scene();
+    let x = (scene.lanes[&f.sender] + scene.lanes[&f.receiver]) / 2.;
+    for scale in [0.05, 0.1] {
+        scene.scale = scale;
+        assert_eq!(
+            scene.hit(Point::new(x, scene.rows[&ordinary].1 + 2.)),
+            Some(ordinary)
+        );
+    }
+}
+
+#[test]
+fn real_scene_self_lifecycle_elbows_end_on_recorded_marker_rows() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        for kind in [MessageKind::Create, MessageKind::Delete] {
+            let mut f = Fixture::new(layer);
+            let event = f.message(f.owner, kind);
+            if let Some(SharedBody::Occurrence {
+                body:
+                    OccurrenceBody::Exchange {
+                        exchange, sender, ..
+                    },
+                ..
+            }) = f.project.elements.get_mut(&event).unwrap().shared_mut()
+            {
+                *exchange = None;
+                *sender = Some(f.receiver);
+            }
+            let scene = f.scene();
+            let marker = &scene.lifecycle.markers[0];
+            let line = scene.lines.iter().find(|l| l.id == event).unwrap();
+            assert_eq!(line.points.len(), 4);
+            assert_eq!(line.points[0].y, marker.center.y - 24.);
+            assert_eq!(line.points[3].y, marker.center.y);
+            assert_eq!(
+                line.points[3].x,
+                if marker.event.kind == MarkerKind::Birth {
+                    marker.capsule.x + marker.capsule.width
+                } else {
+                    marker.center.x
+                }
+            );
+            assert!(line.points[1].x > marker.capsule.x + marker.capsule.width);
+            assert_eq!(scene.hit(marker.center), Some(event));
+        }
+    }
+}
+
+#[test]
+fn real_scene_self_delete_caption_clears_the_preceding_action_box() {
+    let mut f = Fixture::new(Layer::Sa);
+    let action = f.occurrence(
+        f.owner,
+        "Finish work",
+        OccurrenceBody::Action {
+            action: Some(f.work),
+            lifeline: Some(f.receiver),
+        },
+    );
+    let delete = f.message(f.owner, MessageKind::Delete);
+    if let Some(SharedBody::Occurrence {
+        body: OccurrenceBody::Exchange {
+            exchange, sender, ..
+        },
+        ..
+    }) = f.project.elements.get_mut(&delete).unwrap().shared_mut()
+    {
+        *exchange = None;
+        *sender = Some(f.receiver);
+    }
+    let scene = f.scene();
+    let action = scene.boxes.iter().find(|b| b.id == action).unwrap();
+    let line = scene.lines.iter().find(|l| l.id == delete).unwrap();
+    assert!(line.label_at.y > action.rect.y + action.rect.height);
+    assert!(line.label_at.y + 22. < line.points[0].y);
+    assert_eq!(line.points[3].y, scene.rows[&delete].1);
+    assert_eq!(
+        scene
+            .slots
+            .iter()
+            .find(|s| s.slot.before == Some(delete))
+            .unwrap()
+            .y,
+        scene.rows[&delete].1 - 42.
+    );
+}
+
+#[test]
+fn real_scene_conditional_repeated_and_parallel_scopes_do_not_claim_definite_continuation() {
+    for operator in [
+        FragmentOperator::Alternative,
+        FragmentOperator::Optional,
+        FragmentOperator::Loop,
+        FragmentOperator::Parallel,
+    ] {
+        let mut f = Fixture::new(Layer::Sa);
+        let fragment = f.fragment(f.owner, operator);
+        let first = f.branch(fragment);
+        let create = f.message(first, MessageKind::Create);
+        let scene = f.scene();
+        assert_eq!(scene.lifecycle.markers[0].event.occurrence, create);
+        assert_eq!(
+            intervals(&scene, f.receiver, f.owner).first().unwrap().2,
+            Life::Unresolved
+        );
+        assert_eq!(
+            intervals(&scene, f.receiver, f.owner).last().unwrap().2,
+            Life::Unresolved
+        );
+        assert!(
+            scene
+                .lifecycle
+                .lifetimes
+                .iter()
+                .find(|l| l.lifeline == f.sender)
+                .unwrap()
+                .intervals
+                .iter()
+                .all(|i| i.life == Life::Alive)
+        );
+    }
+}
+
+#[test]
+fn real_scene_lifecycle_edit_undo_redo_restores_exact_source_and_changed_geometry() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = Fixture::new(layer);
+        let create = f.message(f.owner, MessageKind::Create);
+        let mut document = f.document();
+        let before = document.snapshot();
+        let geometry = Scene::sequence(document.project(), f.owner, create).lifecycle;
+        let mut edited = document.project().elements[&create].clone();
+        if let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange { message_kind, .. },
+            ..
+        }) = edited.shared_mut()
+        {
+            *message_kind = MessageKind::Asynchronous;
+        }
+        document
+            .execute(Command::EditElement(create, edited))
+            .unwrap();
+        let after = document.snapshot();
+        let changed = Scene::sequence(document.project(), f.owner, create).lifecycle;
+        assert_ne!(geometry, changed);
+        assert!(changed.markers.is_empty());
+        assert_ne!(before.bundle, after.bundle);
+        assert!(document.undo());
+        assert_eq!(document.project(), &before.decoded.project);
+        assert_eq!(document.bundle(), &before.bundle);
+        assert_eq!(
+            Scene::sequence(document.project(), f.owner, create).lifecycle,
+            geometry
+        );
+        assert!(!document.can_undo() && document.can_redo());
+        assert!(document.redo());
+        assert_eq!(document.project(), &after.decoded.project);
+        assert_eq!(document.bundle(), &after.bundle);
+        assert_eq!(
+            Scene::sequence(document.project(), f.owner, create).lifecycle,
+            changed
+        );
+        assert!(!document.can_redo());
+    }
+}
+
+#[test]
+fn panned_header_and_create_clips_use_screen_translation_and_actual_viewport() {
+    use crate::behavior::box_text_clip;
+    use iced::Vector;
+    let header = Rectangle::new(Point::new(100., 200.), Size::new(204., 70.));
+    let capsule = Rectangle::new(header.position(), Size::new(140., 28.));
+    let rect = |x, y, w, h| Rectangle::new(Point::new(x, y), Size::new(w, h));
+    for (pan, scale, viewport, header_expected, birth_expected) in [
+        (
+            Vector::new(37., -41.),
+            0.5,
+            Size::new(300., 400.),
+            rect(92., 63., 92., 27.),
+            rect(91., 61., 62., 10.),
+        ),
+        (
+            Vector::new(37., -41.),
+            1.,
+            Size::new(300., 400.),
+            rect(147., 167., 153., 54.),
+            rect(145., 163., 124., 20.),
+        ),
+        (
+            Vector::new(37., -41.),
+            2.,
+            Size::new(300., 400.),
+            rect(257., 375., 43., 25.),
+            rect(253., 367., 47., 33.),
+        ),
+        (
+            Vector::new(-200., -400.),
+            2.,
+            Size::new(300., 100.),
+            rect(20., 16., 280., 84.),
+            rect(16., 8., 248., 40.),
+        ),
+        (
+            Vector::new(-237., -411.),
+            2.,
+            Size::new(300., 100.),
+            rect(0., 5., 300., 95.),
+            rect(0., 0., 227., 37.),
+        ),
+    ] {
+        assert_eq!(
+            box_text_clip(pan, header, scale, viewport),
+            Some(header_expected)
+        );
+        assert_eq!(
+            birth_label_clip(pan, capsule, scale, viewport),
+            Some(birth_expected)
+        );
+    }
+    for pan in [
+        Vector::new(1000., 1000.),
+        Vector::new(-1000., -1000.),
+        Vector::new(f32::NAN, 0.),
+        Vector::new(0., f32::INFINITY),
+    ] {
+        assert_eq!(box_text_clip(pan, header, 2., Size::new(300., 100.)), None);
+        assert_eq!(
+            birth_label_clip(pan, capsule, 2., Size::new(300., 100.)),
+            None
+        );
+    }
+}
+
+#[test]
+fn real_scene_panned_zoomed_program_keeps_header_birth_and_death_hit_identity() {
+    use crate::{
+        app::Message,
+        behavior::{
+            SequenceInput,
+            scenario::{CanvasEvent, CanvasTool},
+        },
+    };
+    use iced::{Vector, mouse, widget::canvas};
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = Fixture::new(layer);
+        f.project.elements.get_mut(&f.receiver).unwrap().name = "界".repeat(24);
+        let create = f.message(f.owner, MessageKind::Create);
+        let delete = f.message(f.owner, MessageKind::Delete);
+        let document = f.document();
+        let before = document.snapshot();
+        for scale in [0.5, 1., 2.] {
+            for pan in [Vector::new(35., 40.), Vector::new(-35., -5.)] {
+                let mut scene = f.scene();
+                scene.scale = scale;
+                scene.camera_pan = pan;
+                let context = crate::behavior::scenario::direct_tests::context(f.owner);
+                scene.interaction = Some((context, CanvasTool::Select, true));
+                let header = scene.boxes.iter().find(|b| b.id == f.sender).unwrap();
+                let targets = [
+                    (f.sender, header.rect.center()),
+                    (
+                        create,
+                        scene
+                            .lifecycle
+                            .markers
+                            .iter()
+                            .find(|m| m.event.occurrence == create)
+                            .unwrap()
+                            .center,
+                    ),
+                    (
+                        delete,
+                        scene
+                            .lifecycle
+                            .markers
+                            .iter()
+                            .find(|m| m.event.occurrence == delete)
+                            .unwrap()
+                            .center,
+                    ),
+                ];
+                // Absolute widget origin models the outer layout/scroll translation;
+                // camera pan remains local screen units and must be subtracted once.
+                let bounds = Rectangle::new(Point::new(73., 119.), Size::new(2000., 1200.));
+                for (expected, world) in targets {
+                    let screen =
+                        bounds.position() + pan + Vector::new(world.x * scale, world.y * scale);
+                    assert!(bounds.contains(screen));
+                    let mut state = SequenceInput::default();
+                    let mut published = Vec::new();
+                    for event in [
+                        mouse::Event::CursorMoved { position: screen },
+                        mouse::Event::ButtonPressed(mouse::Button::Left),
+                        mouse::Event::ButtonReleased(mouse::Button::Left),
+                    ] {
+                        if let Some(message) = canvas::Program::update(
+                            &scene,
+                            &mut state,
+                            &canvas::Event::Mouse(event),
+                            bounds,
+                            mouse::Cursor::Available(screen),
+                        )
+                        .and_then(|a| a.into_inner().0)
+                        {
+                            published.push(message);
+                        }
+                    }
+                    assert!(
+                        matches!(published.as_slice(), [Message::ScenarioCanvas(CanvasEvent::Select(actual_context, actual))] if *actual_context == context && *actual == expected),
+                        "Pan/zoom must retain the typed hit identity"
+                    );
+                }
+                assert_eq!(scene.lifecycle, f.scene().lifecycle);
+            }
+        }
+        assert_eq!(document.project(), &before.decoded.project);
+        assert_eq!(document.bundle(), &before.bundle);
+        assert!(!document.can_undo() && !document.dirty());
+    }
+}

crates/oa-desktop/src/behavior/scenario_lifecycle/tests.rs

@@ -0,0 +1,470 @@
+use super::*;
+use oa_core::*;
+
+struct Fixture {
+    p: Project,
+    owner: Id,
+    a: Id,
+    b: Id,
+    exchange: Id,
+    rows: BTreeMap<Id, (Id, f32)>,
+    scopes: BTreeMap<Id, (f32, f32)>,
+}
+impl Fixture {
+    fn new(layer: Layer) -> Self {
+        let mut p = Project::empty();
+        let kind = if layer == Layer::Oa {
+            Kind::Activity
+        } else {
+            Kind::Function
+        };
+        let a = p.add_element(kind, layer, "Request", None).unwrap();
+        let b = p.add_element(kind, layer, "Provide", None).unwrap();
+        let owner = p
+            .add_element(Kind::Scenario, layer, "Lifecycle", None)
+            .unwrap();
+        let exchange = p.relate(
+            if layer == Layer::Oa {
+                RelationKind::Interaction
+            } else {
+                RelationKind::FunctionalExchange
+            },
+            "Service",
+            a,
+            b,
+        );
+        let line = |p: &mut Project, represented| {
+            let id = p
+                .add_element(Kind::Lifeline, layer, "Participant", Some(owner))
+                .unwrap();
+            *p.elements.get_mut(&id).unwrap().shared_mut().unwrap() = SharedBody::Lifeline {
+                represented: Some(represented),
+            };
+            id
+        };
+        let a = line(&mut p, a);
+        let b = line(&mut p, b);
+        Self {
+            p,
+            owner,
+            a,
+            b,
+            exchange,
+            rows: BTreeMap::new(),
+            scopes: [(owner, (0., 600.))].into(),
+        }
+    }
+    fn occurrence(&mut self, owner: Id, y: f32, body: OccurrenceBody) -> Id {
+        let mut e = self
+            .p
+            .make_element(
+                Kind::Occurrence,
+                self.p.elements[&owner].layer(),
+                "Occurrence",
+                Some(owner),
+            )
+            .unwrap();
+        let id = e.id;
+        *e.shared_mut().unwrap() = SharedBody::Occurrence {
+            body,
+            precondition: String::new(),
+            postcondition: String::new(),
+        };
+        self.p.elements.insert(id, e);
+        if let Some(steps) = self.p.elements.get_mut(&owner).unwrap().steps_mut() {
+            steps.push(id);
+        } else if let Some(SharedBody::Occurrence {
+            body: OccurrenceBody::Fragment { branches, .. },
+            ..
+        }) = self.p.elements.get_mut(&owner).unwrap().shared_mut()
+        {
+            branches.push(id);
+        }
+        self.rows.insert(id, (owner, y));
+        id
+    }
+    fn message(&mut self, owner: Id, y: f32, kind: MessageKind) -> Id {
+        self.occurrence(
+            owner,
+            y,
+            OccurrenceBody::Exchange {
+                exchange: Some(self.exchange),
+                sender: Some(self.a),
+                receiver: Some(self.b),
+                message_kind: kind,
+                operation: None,
+                reply_to: None,
+                values: vec![],
+            },
+        )
+    }
+    fn fragment(&mut self, owner: Id, y: f32, operator: FragmentOperator) -> Id {
+        self.occurrence(
+            owner,
+            y,
+            OccurrenceBody::Fragment {
+                operator,
+                branches: vec![],
+            },
+        )
+    }
+    fn branch(&mut self, fragment: Id, start: f32, end: f32) -> Id {
+        let id = self.occurrence(
+            fragment,
+            start,
+            OccurrenceBody::Branch {
+                guard: "condition".into(),
+                occurrences: vec![],
+            },
+        );
+        self.scopes.insert(id, (start, end));
+        id
+    }
+    fn project(&self) -> Vec<LaneLifetime> {
+        let errors: Vec<_> = validation::validate(&self.p)
+            .into_iter()
+            .filter(|i| i.severity == validation::Severity::Error)
+            .collect();
+        assert!(
+            errors.is_empty(),
+            "fixture must be ordinarily admitted: {errors:?}"
+        );
+        let before = self.p.clone();
+        let source = source_project::format_bundle(&self.p);
+        let geometry = Geometry {
+            rows: &self.rows,
+            scopes: &self.scopes,
+        };
+        let result = project_lifetimes(&self.p, self.owner, &geometry);
+        assert_eq!(result, project_lifetimes(&self.p, self.owner, &geometry));
+        assert_eq!(self.p, before);
+        assert_eq!(source_project::format_bundle(&self.p), source);
+        assert!(
+            result
+                .windows(2)
+                .all(|pair| pair[0].lifeline < pair[1].lifeline)
+        );
+        result
+    }
+    fn lane(&self) -> LaneLifetime {
+        self.project()
+            .into_iter()
+            .find(|lane| lane.lifeline == self.b)
+            .unwrap()
+    }
+}
+fn intervals(lane: &LaneLifetime, scope: Id) -> Vec<(f32, f32, Life)> {
+    lane.intervals
+        .iter()
+        .filter(|i| i.scope == scope)
+        .map(|i| (i.span.start, i.span.end, i.life))
+        .collect()
+}
+
+#[test]
+fn root_lifetime_has_exact_birth_death_boundaries_without_source_mutation() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let mut f = Fixture::new(layer);
+        let create = f.message(f.owner, 100., MessageKind::Create);
+        f.message(f.owner, 200., MessageKind::Asynchronous);
+        let delete = f.message(f.owner, 300., MessageKind::Delete);
+        let lane = f.lane();
+        assert_eq!(
+            intervals(&lane, f.owner),
+            vec![
+                (0., 100., Life::Absent),
+                (100., 300., Life::Alive),
+                (300., 600., Life::Absent)
+            ]
+        );
+        assert_eq!(
+            lane.markers,
+            vec![
+                Marker {
+                    occurrence: create,
+                    scope: f.owner,
+                    y: 100.,
+                    kind: MarkerKind::Birth
+                },
+                Marker {
+                    occurrence: delete,
+                    scope: f.owner,
+                    y: 300.,
+                    kind: MarkerKind::Death
+                },
+            ]
+        );
+        let sender = f
+            .project()
+            .into_iter()
+            .find(|lane| lane.lifeline == f.a)
+            .unwrap();
+        assert_eq!(intervals(&sender, f.owner), vec![(0., 600., Life::Alive)]);
+    }
+}
+
+#[test]
+fn alternative_death_does_not_kill_its_displayed_sibling() {
+    let mut f = Fixture::new(Layer::Sa);
+    let fragment = f.fragment(f.owner, 100., FragmentOperator::Alternative);
+    let left = f.branch(fragment, 120., 250.);
+    let right = f.branch(fragment, 300., 450.);
+    f.message(left, 200., MessageKind::Delete);
+    f.message(right, 350., MessageKind::Asynchronous);
+    let lane = f.lane();
+    assert_eq!(
+        intervals(&lane, left),
+        vec![(120., 200., Life::Alive), (200., 250., Life::Absent)]
+    );
+    assert_eq!(intervals(&lane, right), vec![(300., 450., Life::Alive)]);
+    assert_eq!(
+        intervals(&lane, f.owner),
+        vec![(0., 100., Life::Alive), (450., 600., Life::Unresolved)]
+    );
+    assert_eq!(
+        lane.uncertainties,
+        vec![Uncertainty {
+            scope: fragment,
+            reason: UncertaintyReason::Conditional
+        }]
+    );
+}
+
+#[test]
+fn conditional_birth_does_not_infer_absence_in_siblings_or_ancestors() {
+    for operator in [FragmentOperator::Alternative, FragmentOperator::Optional] {
+        let mut f = Fixture::new(Layer::Oa);
+        let fragment = f.fragment(f.owner, 100., operator);
+        let left = f.branch(fragment, 120., 250.);
+        let right = f.branch(fragment, 300., 450.);
+        f.message(left, 200., MessageKind::Create);
+        let lane = f.lane();
+        assert_eq!(
+            intervals(&lane, left),
+            vec![(120., 200., Life::Absent), (200., 250., Life::Alive)]
+        );
+        assert_eq!(
+            intervals(&lane, right),
+            vec![(300., 450., Life::Unresolved)]
+        );
+        assert_eq!(
+            intervals(&lane, f.owner),
+            vec![(0., 100., Life::Unresolved), (450., 600., Life::Unresolved)]
+        );
+    }
+}
+
+#[test]
+fn loop_lifetime_is_local_and_warning_bearing_loops_remain_drawable() {
+    for balanced in [true, false] {
+        let mut f = Fixture::new(Layer::Sa);
+        let fragment = f.fragment(f.owner, 100., FragmentOperator::Loop);
+        let iteration = f.branch(fragment, 120., 450.);
+        let create = f.message(iteration, 160., MessageKind::Create);
+        f.message(iteration, 250., MessageKind::Asynchronous);
+        if balanced {
+            f.message(iteration, 350., MessageKind::Delete);
+        }
+        let lane = f.lane();
+        assert_eq!(lane.markers.len(), if balanced { 2 } else { 1 });
+        assert_eq!(lane.markers[0].occurrence, create);
+        assert!(lane.uncertainties.contains(&Uncertainty {
+            scope: fragment,
+            reason: UncertaintyReason::Repeated
+        }));
+        assert_eq!(
+            intervals(&lane, f.owner).last().unwrap().2,
+            Life::Unresolved
+        );
+        assert_eq!(
+            validation::validate(&f.p)
+                .iter()
+                .any(|i| i.code == "lifeline_repetition"),
+            !balanced
+        );
+    }
+}
+
+#[test]
+fn optional_cleanup_inside_loop_does_not_claim_balanced_or_definite_exit() {
+    let mut f = Fixture::new(Layer::Sa);
+    let repeated = f.fragment(f.owner, 100., FragmentOperator::Loop);
+    let iteration = f.branch(repeated, 120., 500.);
+    f.message(iteration, 160., MessageKind::Create);
+    let optional = f.fragment(iteration, 280., FragmentOperator::Optional);
+    let cleanup = f.branch(optional, 320., 400.);
+    f.message(cleanup, 350., MessageKind::Delete);
+    let lane = f.lane();
+    assert_eq!(
+        intervals(&lane, cleanup),
+        vec![(320., 350., Life::Alive), (350., 400., Life::Absent)]
+    );
+    assert_eq!(
+        intervals(&lane, iteration),
+        vec![
+            (120., 160., Life::Absent),
+            (160., 280., Life::Alive),
+            (400., 500., Life::Unresolved)
+        ]
+    );
+    assert!(
+        validation::validate(&f.p)
+            .iter()
+            .any(|i| i.code == "lifeline_repetition")
+    );
+    assert!(lane.uncertainties.contains(&Uncertainty {
+        scope: optional,
+        reason: UncertaintyReason::Conditional
+    }));
+    assert!(lane.uncertainties.contains(&Uncertainty {
+        scope: repeated,
+        reason: UncertaintyReason::Repeated
+    }));
+}
+
+#[test]
+fn lifecycle_free_fragments_do_not_poison_other_lanes() {
+    let mut f = Fixture::new(Layer::Oa);
+    let fragment = f.fragment(f.owner, 100., FragmentOperator::Parallel);
+    let left = f.branch(fragment, 120., 250.);
+    let right = f.branch(fragment, 300., 450.);
+    f.message(left, 200., MessageKind::Delete);
+    let result = f.project();
+    let sender = result.iter().find(|lane| lane.lifeline == f.a).unwrap();
+    assert!(sender.intervals.iter().all(|i| i.life == Life::Alive));
+    assert!(sender.uncertainties.is_empty());
+    let target = result.iter().find(|lane| lane.lifeline == f.b).unwrap();
+    assert!(target.uncertainties.contains(&Uncertainty {
+        scope: fragment,
+        reason: UncertaintyReason::Parallel
+    }));
+    assert_eq!(intervals(target, right), vec![(300., 450., Life::Alive)]);
+}
+
+#[test]
+fn explicit_receiver_is_authoritative_even_with_missing_exchange() {
+    let mut f = Fixture::new(Layer::Oa);
+    let create = f.message(f.owner, 100., MessageKind::Create);
+    if let Some(SharedBody::Occurrence {
+        body: OccurrenceBody::Exchange { exchange, .. },
+        ..
+    }) = f.p.elements.get_mut(&create).unwrap().shared_mut()
+    {
+        *exchange = None;
+    }
+    assert_eq!(f.lane().markers[0].occurrence, create);
+    if let Some(SharedBody::Occurrence {
+        body: OccurrenceBody::Exchange {
+            receiver, exchange, ..
+        },
+        ..
+    }) = f.p.elements.get_mut(&create).unwrap().shared_mut()
+    {
+        *receiver = None;
+        *exchange = Some(f.exchange);
+    }
+    assert!(
+        f.lane().markers.is_empty(),
+        "exchange endpoints never invent a receiver"
+    );
+}
+
+#[test]
+fn missing_geometry_is_reported_without_nonfinite_or_guessed_markers() {
+    let mut f = Fixture::new(Layer::Oa);
+    let create = f.message(f.owner, 100., MessageKind::Create);
+    f.rows.insert(create, (f.owner, f32::NAN));
+    let lane = f.lane();
+    assert!(lane.markers.is_empty());
+    assert_eq!(
+        lane.uncertainties,
+        vec![Uncertainty {
+            scope: create,
+            reason: UncertaintyReason::MissingGeometry
+        }]
+    );
+    assert_eq!(
+        intervals(&lane, f.owner),
+        vec![(0., 600., Life::Unresolved)]
+    );
+    f.scopes.remove(&f.owner);
+    let lane = f.lane();
+    assert!(lane.intervals.is_empty());
+    assert_eq!(lane.uncertainties[0].scope, f.owner);
+}
+
+#[test]
+fn scenario_use_is_opaque_and_never_imports_callee_lifecycle_events() {
+    let mut f = Fixture::new(Layer::Oa);
+    let callee =
+        f.p.add_element(Kind::Scenario, Layer::Oa, "Callee", None)
+            .unwrap();
+    let remote_a =
+        f.p.add_element(Kind::Lifeline, Layer::Oa, "Remote A", Some(callee))
+            .unwrap();
+    let remote_b =
+        f.p.add_element(Kind::Lifeline, Layer::Oa, "Remote B", Some(callee))
+            .unwrap();
+    for (remote, local) in [(remote_a, f.a), (remote_b, f.b)] {
+        let body = f.p.elements[&local].shared().unwrap().clone();
+        *f.p.elements.get_mut(&remote).unwrap().shared_mut().unwrap() = body;
+    }
+    f.occurrence(
+        callee,
+        200.,
+        OccurrenceBody::Exchange {
+            exchange: Some(f.exchange),
+            sender: Some(remote_a),
+            receiver: Some(remote_b),
+            message_kind: MessageKind::Create,
+            operation: None,
+            reply_to: None,
+            values: vec![],
+        },
+    );
+    f.occurrence(
+        f.owner,
+        100.,
+        OccurrenceBody::ScenarioUse {
+            scenario: Some(callee),
+            bindings: vec![
+                LifelineBinding {
+                    referenced: remote_a,
+                    local: f.a,
+                },
+                LifelineBinding {
+                    referenced: remote_b,
+                    local: f.b,
+                },
+            ],
+        },
+    );
+    let lane = f.lane();
+    assert_eq!(intervals(&lane, f.owner), vec![(0., 600., Life::Alive)]);
+    assert!(lane.markers.is_empty());
+    assert!(lane.uncertainties.is_empty());
+}
+
+#[test]
+fn projection_retains_exact_authored_source_and_does_not_enter_history() {
+    use crate::document::Document;
+    let mut f = Fixture::new(Layer::Oa);
+    f.message(f.owner, 100., MessageKind::Create);
+    f.message(f.owner, 300., MessageKind::Delete);
+    let mut source = source_project::format_bundle(&f.p);
+    let text = source.files.get_mut(&source.entry).unwrap();
+    *text = format!("// Retained author note — 雨\r\n{text}\n");
+    let document =
+        Document::from_bundle(source.clone(), source_project::ProjectLimits::default()).unwrap();
+    let accepted = document.project().clone();
+    let geometry = Geometry {
+        rows: &f.rows,
+        scopes: &f.scopes,
+    };
+    let result = project_lifetimes(document.project(), f.owner, &geometry);
+    assert_eq!(result, f.project());
+    assert_eq!(document.bundle(), &source);
+    assert_eq!(document.project(), &accepted);
+    assert!(!document.can_undo());
+    assert!(!document.can_redo());
+}

crates/oa-desktop/src/behavior/state_canvas.rs

@@ -27,6 +27,8 @@ pub struct StateCanvas<'a> {
     pub diagram: Id,
     pub context: Context,
     pub selected: Id,
+    /// Presentation-only navigation marker; never an authoring placement.
+    pub navigation_focus: Option<Rectangle>,
     pub tool: Tool,
     pub zoom: f32,
     pub pan: Vector,
@@ -415,6 +417,171 @@ fn state_action_label(project: &Project, relation: &Relation) -> String {
     format!("{phase} / {}", project.named(target))
 }
 
+/// Match a typed label field by its structural offset, never by a display-name
+/// substring (names may duplicate or also occur in free-form guards).
+fn retained_label_field(full: &str, painted: &str, start: usize) -> bool {
+    start
+        < full
+            .chars()
+            .zip(painted.chars())
+            .take_while(|(a, b)| a == b)
+            .map(|(c, _)| c.len_utf8())
+            .sum::<usize>()
+}
+
+fn transition_label_role(
+    project: &Project,
+    relation: &Relation,
+    subject: Id,
+    width: f32,
+) -> Option<&'static str> {
+    let full = routing::state_transition_summary(project, relation);
+    transition_label_role_in_text(project, relation, subject, &short(&full, width, 10.))
+}
+
+fn transition_label_role_in_text(
+    project: &Project,
+    relation: &Relation,
+    subject: Id,
+    painted: &str,
+) -> Option<&'static str> {
+    let RelationBody::StateTransition {
+        transition_kind,
+        triggers,
+        effects,
+        effect,
+        ..
+    } = &relation.body
+    else {
+        return None;
+    };
+    if project.named(subject).trim().is_empty() {
+        return None;
+    }
+    let full = routing::state_transition_summary(project, relation);
+    let mut offset = format!("{transition_kind:?} · ").len();
+    for id in triggers {
+        if *id == subject && retained_label_field(&full, painted, offset) {
+            return Some("transition trigger");
+        }
+        offset += project.named(*id).len() + " OR ".len();
+    }
+    if !effects.is_empty() {
+        // The canonical routing summary appends typed effects before optional
+        // authored effect prose. Derive its offset from that exact suffix.
+        let mut suffix = format!(
+            " / {}",
+            effects
+                .iter()
+                .map(|id| project.named(*id))
+                .collect::<Vec<_>>()
+                .join(", ")
+        );
+        if !effect.is_empty() {
+            suffix.push_str(&format!(" / {effect}"));
+        }
+        if let Some(prefix) = full.strip_suffix(&suffix) {
+            offset = prefix.len() + " / ".len();
+            for id in effects {
+                if *id == subject && retained_label_field(&full, painted, offset) {
+                    return Some("transition effect");
+                }
+                offset += project.named(*id).len() + ", ".len();
+            }
+        }
+    }
+    None
+}
+
+/// Actual state compartments and painted transition-reference labels. Generic
+/// projected node/edge identities are handled by the shared saved-view query.
+pub(crate) fn diagram_usages(
+    project: &Project,
+    diagram: &Diagram,
+    view: &ProjectedView,
+    subject: Id,
+) -> Vec<crate::diagram_usage::Usage> {
+    use crate::diagram_usage::{Surface, Target, Usage};
+    if diagram.projection.state_machine().is_none() {
+        return vec![];
+    }
+    let mut result = Vec::new();
+    for node in &view.nodes {
+        for (relation, bounds) in state_action_rows(project, node) {
+            let label = state_action_label(project, relation);
+            let painted = short(&label, bounds.width - 12., 11.);
+            let role = if relation.id == subject {
+                Some("state action")
+            } else if relation.target() == subject
+                && retained_label_field(
+                    &label,
+                    &painted,
+                    label.len() - project.named(subject).len(),
+                )
+            {
+                Some("state action work")
+            } else {
+                None
+            };
+            if let Some(role) = role {
+                result.push(Usage {
+                    subject,
+                    surface: Surface::Saved(diagram.id),
+                    target: Target::StateRow {
+                        placement: node.id,
+                        relation: relation.id,
+                    },
+                    role: role.into(),
+                    bounds,
+                });
+            }
+        }
+        for (relation, bounds) in internal_rows(project, node) {
+            let role = if relation.id == subject {
+                Some("internal transition")
+            } else {
+                transition_label_role(project, relation, subject, bounds.width - 12.)
+            };
+            if let Some(role) = role {
+                result.push(Usage {
+                    subject,
+                    surface: Surface::Saved(diagram.id),
+                    target: Target::StateRow {
+                        placement: node.id,
+                        relation: relation.id,
+                    },
+                    role: role.into(),
+                    bounds,
+                });
+            }
+        }
+    }
+    for edge in routing::route_diagram(project, diagram, view)
+        .edges
+        .values()
+    {
+        let Some(relation) = project.relations.get(&edge.id) else {
+            continue;
+        };
+        if edge.id == subject || edge.label.text.is_empty() {
+            continue;
+        }
+        // Routing already shortens external summaries before the canvas applies
+        // its width limit. Compare against precisely that doubly shortened text.
+        let painted = short(&edge.label.text, edge.label.bounds.size.width - 10., 10.);
+        if let Some(role) = transition_label_role_in_text(project, relation, subject, &painted) {
+            result.push(Usage {
+                subject,
+                surface: Surface::Saved(diagram.id),
+                target: Target::Edge(edge.id),
+                role: role.into(),
+                bounds: crate::diagram_usage::edge_focus_bounds(edge),
+            });
+        }
+    }
+    result
+}
+
 impl StateCanvas<'_> {
     fn scale(&self) -> f32 {
         if self.zoom.is_finite() {
@@ -1148,6 +1315,14 @@ impl canvas::Program<Event> for StateCanvas<'_> {
         overlay.with_clip(content, |frame| {
             frame.translate(self.offset());
             frame.scale(self.scale());
+            if let Some(bounds) = self.navigation_focus {
+                frame.stroke(
+                    &Path::rectangle(bounds.position(), bounds.size()),
+                    Stroke::default()
+                        .with_color(style::TEAL)
+                        .with_width(2.5 / self.scale()),
+                );
+            }
             if let Some(at) = world
                 && self.editable
             {
@@ -1537,6 +1712,7 @@ mod tests {
                 layer: Layer::Sa,
                 projection: ProjectionKind::StateMachine { machine },
                 nodes: BTreeMap::new(),
+                layout: None,
                 routes: vec![],
                 view_options: Default::default(),
             },
@@ -1575,6 +1751,189 @@ mod tests {
         }
     }
 
+    #[test]
+    fn diagram_usage_state_rows_and_label_references_follow_actual_projection() {
+        use crate::diagram_usage::Target;
+        let mut f = fixture();
+        let work = f
+            .project
+            .add_element(Kind::Function, Layer::Sa, "Act", None)
+            .unwrap();
+        let event = f
+            .project
+            .add_element(Kind::Event, Layer::Sa, "E", None)
+            .unwrap();
+        let unused = f
+            .project
+            .add_element(Kind::Event, Layer::Sa, "E", None)
+            .unwrap();
+        let action = f
+            .project
+            .relate(RelationKind::StateAction, "Entry", f.a, work);
+        let internal = f
+            .project
+            .relate(RelationKind::StateTransition, "Internal", f.a, f.a);
+        let external = f
+            .project
+            .relate(RelationKind::StateTransition, "External", f.a, f.b);
+        for (id, kind) in [
+            (internal, TransitionKind::Internal),
+            (external, TransitionKind::External),
+        ] {
+            if let RelationBody::StateTransition {
+                transition_kind,
+                triggers,
+                effects,
+                ..
+            } = &mut f.project.relations.get_mut(&id).unwrap().body
+            {
+                *transition_kind = kind;
+                *triggers = vec![event];
+                *effects = vec![work];
+            }
+        }
+        let before = f.project.clone();
+        let diagram = &f.project.diagrams[&f.diagram];
+        let view = projection::project_diagram(&f.project, diagram);
+        let placement = view.nodes.iter().find(|n| n.element == f.a).unwrap().id;
+        let action_target = Target::StateRow {
+            placement,
+            relation: action,
+        };
+        let internal_target = Target::StateRow {
+            placement,
+            relation: internal,
+        };
+        assert_eq!(
+            diagram_usages(&f.project, diagram, &view, action)[0].target,
+            action_target
+        );
+        assert_eq!(
+            diagram_usages(&f.project, diagram, &view, internal)[0].target,
+            internal_target
+        );
+        let events = diagram_usages(&f.project, diagram, &view, event);
+        assert_eq!(events.len(), 2);
+        assert!(events.iter().any(|u| u.target == internal_target));
+        assert!(events.iter().any(|u| u.target == Target::Edge(external)));
+        assert!(diagram_usages(&f.project, diagram, &view, unused).is_empty());
+        // External edge identity belongs to the shared saved-view adapter.
+        assert!(diagram_usages(&f.project, diagram, &view, external).is_empty());
+        let work_usages = diagram_usages(&f.project, diagram, &view, work);
+        assert!(work_usages.iter().any(|u| u.target == action_target));
+        assert!(work_usages.iter().any(|u| u.target == internal_target));
+        let row = work_usages
+            .iter()
+            .find(|u| u.target == action_target)
+            .unwrap();
+        let canvas = canvas(&f, Tool::Select, 1.);
+        let scene = canvas.scene(&State::default()).unwrap();
+        assert_eq!(
+            canvas.hit(&scene, row.bounds.center()),
+            Some(Hit::StateAction(action))
+        );
+        assert_eq!(f.project, before);
+        f.project
+            .diagrams
+            .get_mut(&f.diagram)
+            .unwrap()
+            .nodes
+            .get_mut(&placement)
+            .unwrap()
+            .collapsed = true;
+        let diagram = &f.project.diagrams[&f.diagram];
+        let folded = projection::project_diagram(&f.project, diagram);
+        assert!(diagram_usages(&f.project, diagram, &folded, action).is_empty());
+        assert!(diagram_usages(&f.project, diagram, &folded, internal).is_empty());
+    }
+
+    #[test]
+    fn diagram_usage_transition_labels_do_not_match_prose_or_fields_beyond_cutoff() {
+        let mut f = fixture();
+        let early = f
+            .project
+            .add_element(Kind::Event, Layer::Sa, "A", None)
+            .unwrap();
+        let late = f
+            .project
+            .add_element(Kind::Event, Layer::Sa, "B", None)
+            .unwrap();
+        let relation = f
+            .project
+            .relate(RelationKind::StateTransition, "Transition", f.a, f.b);
+        if let RelationBody::StateTransition {
+            triggers, guard, ..
+        } = &mut f.project.relations.get_mut(&relation).unwrap().body
+        {
+            *triggers = vec![early, late];
+            *guard = "B".into();
+        }
+        let relation = &f.project.relations[&relation];
+        assert_eq!(
+            transition_label_role(&f.project, relation, early, 84.),
+            Some("transition trigger")
+        );
+        assert_eq!(transition_label_role(&f.project, relation, late, 84.), None);
+        assert_eq!(
+            transition_label_role(&f.project, relation, late, 800.),
+            Some("transition trigger")
+        );
+        assert!(!retained_label_field("1234A678", "1234…", 4));
+    }
+
+    #[test]
+    fn diagram_usage_external_labels_obey_routing_cutoff_while_internal_rows_retain_full_summary() {
+        use crate::diagram_usage::Target;
+        let mut f = fixture();
+        let first = f
+            .project
+            .add_element(Kind::Event, Layer::Sa, &"A".repeat(35), None)
+            .unwrap();
+        let second = f
+            .project
+            .add_element(Kind::Event, Layer::Sa, "Second", None)
+            .unwrap();
+        let external = f
+            .project
+            .relate(RelationKind::StateTransition, "External", f.a, f.b);
+        let internal = f
+            .project
+            .relate(RelationKind::StateTransition, "Internal", f.a, f.a);
+        for (id, kind) in [
+            (external, TransitionKind::External),
+            (internal, TransitionKind::Internal),
+        ] {
+            if let RelationBody::StateTransition {
+                transition_kind,
+                triggers,
+                ..
+            } = &mut f.project.relations.get_mut(&id).unwrap().body
+            {
+                *transition_kind = kind;
+                *triggers = vec![first, second];
+            }
+        }
+        let diagram = &f.project.diagrams[&f.diagram];
+        let view = projection::project_diagram(&f.project, diagram);
+        let routed = routing::route_diagram(&f.project, diagram, &view);
+        let edge = &routed.edges[&external];
+        let painted = short(&edge.label.text, edge.label.bounds.size.width - 10., 10.);
+        // Independent painted-text oracle: 11 prefix characters + 35 As, then
+        // only the space before OR survives the routing limit.
+        assert_eq!(edge.label.text, format!("External · {} …", "A".repeat(35)));
+        assert!(!painted.contains("Second"));
+        let usages = diagram_usages(&f.project, diagram, &view, second);
+        assert!(!usages.iter().any(|u| u.target == Target::Edge(external)));
+        assert!(usages.iter().any(
+            |u| matches!(u.target, Target::StateRow { relation, .. } if relation == internal)
+        ));
+        assert!(
+            diagram_usages(&f.project, diagram, &view, first)
+                .iter()
+                .any(|u| u.target == Target::Edge(external))
+        );
+    }
+
     fn canvas(f: &Fixture, tool: Tool, zoom: f32) -> StateCanvas<'_> {
         StateCanvas {
             project: &f.project,
@@ -1586,6 +1945,7 @@ mod tests {
                 epoch: 3,
             },
             selected: f.machine,
+            navigation_focus: None,
             tool,
             zoom,
             pan: Vector::new(20., 30.),

crates/oa-desktop/src/behavior/state_edit.rs

@@ -292,6 +292,7 @@ pub fn create_view(project: &Project, machine: Id) -> Result<Plan, ModelError> {
             layer: owner.layer(),
             projection: ProjectionKind::StateMachine { machine },
             nodes: BTreeMap::new(),
+            layout: None,
             routes: vec![],
             view_options: Default::default(),
         },

crates/oa-desktop/src/behavior/state_view.rs

@@ -165,6 +165,9 @@ pub fn view<'a>(app: &'a App, machine: Id, mut out: Column<'a, Message>) -> Elem
         diagram: id,
         context,
         selected: app.selected,
+        navigation_focus: app
+            .diagram_focus(crate::diagram_usage::Surface::Saved(id))
+            .map(|usage| usage.bounds),
         tool: state.tool,
         zoom: state.zoom,
         pan: state.pan,

crates/oa-desktop/src/behavior/topology.rs

@@ -5,6 +5,7 @@ use iced::widget::{Column, text_input};
 use std::collections::BTreeSet;
 pub(crate) mod contextual;
 mod direct;
+mod usages;
 mod view;
 use direct::Input;
 pub(crate) use direct::{
@@ -38,6 +39,7 @@ impl Tool {
 }
 #[derive(Debug, Clone)]
 pub enum Event {
+    Source(super::source_draft::Event),
     Start(Id, Tool, Option<Id>),
     Cancel,
     Submit,
@@ -58,7 +60,6 @@ pub enum Event {
 }
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Shelf {
-    Tools,
     Selection,
 }
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -79,10 +80,11 @@ pub struct State {
     identity: Option<(Id, Id)>,
     tool: CanvasTool,
     expanded: BTreeSet<Id>,
-    scroll_offsets: [iced::Vector; 2],
-    return_to: Vec<(Id, Id, Option<oa_core::topology_context::ContextAddress>)>,
+    details_offset: iced::Vector,
+    return_to: Vec<direct::ReturnFrame>,
     draft: Option<Draft>,
     viewport: Option<Size>,
+    pan: iced::Vector,
     zoom: Option<f32>,
     fit: bool,
     pub(crate) focused: bool,
@@ -90,15 +92,22 @@ pub struct State {
     selected_context: Option<oa_core::topology_context::ContextAddress>,
     shelf: Option<Shelf>,
 }
-#[derive(Default, serde::Serialize, serde::Deserialize)]
+#[derive(Clone, Default, serde::Serialize, serde::Deserialize)]
 #[serde(deny_unknown_fields)]
 struct Browser {
     search: String,
     page: usize,
 }
-#[derive(serde::Serialize, serde::Deserialize)]
+#[derive(Clone, serde::Serialize, serde::Deserialize)]
 #[serde(deny_unknown_fields)]
 struct Draft {
+    #[serde(default)]
+    source: super::source_draft::State,
+    #[serde(default = "Id::new_v4")]
+    invocation: Id,
+    #[serde(default)]
+    source_origin: Option<(Id, oa_core::Element)>,
+
     #[serde(with = "recovery_insertion")]
     insertion: Insertion,
     fixed: bool,
@@ -117,6 +126,40 @@ struct Draft {
     contextual: Option<contextual::Draft>,
 }
 impl State {
+    pub(crate) fn camera_boundary(&self) -> impl PartialEq + use<> {
+        (
+            self.tool,
+            self.focused,
+            self.shelf,
+            self.viewport,
+            self.pan,
+            self.zoom,
+            self.fit,
+        )
+    }
+
+    pub(super) fn pending_name(&self) -> Option<&str> {
+        self.draft.as_ref().map(|d| d.name.as_str())
+    }
+    pub(super) fn source_view<'a>(&'a self, p: &'a Project) -> Option<iced::Element<'a, Event>> {
+        self.draft
+            .as_ref()?
+            .source
+            .view(p)
+            .map(|v| v.map(Event::Source))
+    }
+
+    pub fn source_active(&self) -> bool {
+        self.draft.as_ref().is_some_and(|d| d.source.engaged())
+    }
+
+    pub fn source_open(&self) -> bool {
+        self.draft.as_ref().is_some_and(|d| d.source.is_open())
+    }
+    pub fn source_back(&mut self) -> bool {
+        self.draft.as_mut().is_some_and(|d| d.source.back())
+    }
+
     pub(super) fn recovery_snapshot(&self) -> Result<Option<serde_json::Value>, String> {
         self.draft
             .as_ref()
@@ -152,6 +195,58 @@ impl State {
     }
 
     pub fn update(&mut self, p: &Project, event: Event) -> Result<Option<Command>, String> {
+        if let Event::Source(event) = event {
+            if self
+                .draft
+                .as_mut()
+                .ok_or("Start the consumer form first.")?
+                .source
+                .dismiss(&event)?
+            {
+                return Ok(None);
+            }
+            let d = self
+                .draft
+                .as_ref()
+                .ok_or("Start the consumer form first.")?;
+            if d.tool != Tool::Work {
+                return Err("This reference does not support staged source creation.".into());
+            }
+            if d.source_origin.as_ref().is_some_and(|(document, owner)| {
+                *document != p.id || p.elements.get(&d.owner) != Some(owner)
+            }) {
+                return Err("The original consumer changed. Cancel and reopen its form; the current draft is retained.".into());
+            }
+            if d.source_origin.is_none() && d.source.engaged() {
+                return Err("The recovered source draft has no original document binding. Go Back or cancel it.".into());
+            }
+            let mut next = d.clone();
+            if next.source_origin.is_none() && matches!(&event, super::source_draft::Event::Open(_))
+            {
+                next.source_origin = Some((
+                    p.id,
+                    p.elements
+                        .get(&d.owner)
+                        .ok_or("The consumer owner no longer exists.")?
+                        .clone(),
+                ));
+            }
+            if let Some(id) = next.source.update(
+                p,
+                super::source_draft::Scope::Work { owner: d.owner },
+                d.invocation,
+                event,
+            )? {
+                next.target = Some(id);
+                next.command(p)?;
+            }
+            self.draft = Some(next);
+            return Ok(None);
+        }
+        if self.source_open() && !matches!(&event, Event::Cancel) {
+            return Err("Use the new source or go Back before editing the parent form.".into());
+        }
+
         if self.draft.is_some() && matches!(&event, Event::Start(..)) {
             return Err(PENDING_DRAFT.into());
         }
@@ -184,6 +279,9 @@ impl State {
                     }
                 });
                 self.draft = Some(Draft {
+                    source: Default::default(),
+                    invocation: Id::new_v4(),
+                    source_origin: Some((p.id, p.elements[&owner].clone())),
                     insertion: Insertion::default(),
                     fixed: false,
                     browsers: Default::default(),
@@ -253,8 +351,8 @@ impl State {
     }
 
     fn fit_area(&self, fallback_width: f32) -> Size {
-        // The sensor measures the inner scroller, independent of graph content.
-        // Leave a small gutter for scrollbars; before first layout use a compact
+        // The sensor measures the viewport, independent of graph content.
+        // Leave a small content gutter; before first layout use a compact
         // provisional viewport and recompute when the sensor reports actual size.
         let viewport = self.viewport.unwrap_or(Size::new(fallback_width, 180.));
         Size::new(
@@ -263,10 +361,7 @@ impl State {
         )
     }
 
-    fn canvas_offset(&self) -> iced::Vector {
-        self.scroll_offsets[0]
-    }
-
+    #[cfg(test)]
     fn fit_limited(&self, graph: Size, fallback_width: f32) -> bool {
         let available = self.fit_area(fallback_width);
         self.fit && (graph.width * 0.05 > available.width || graph.height * 0.05 > available.height)
@@ -508,6 +603,22 @@ fn link(p: &Project, source: Id, target: Id, guard: &str) -> Command {
 }
 impl Draft {
     fn command(&self, p: &Project) -> Result<Command, String> {
+        if self.source.engaged()
+            && self.source_origin.as_ref().is_none_or(|(document, owner)| {
+                *document != p.id || p.elements.get(&self.owner) != Some(owner)
+            })
+        {
+            return Err("The original consumer document or owner changed. Cancel and reopen its form; your draft is retained.".into());
+        }
+        self.source.check_scope(
+            super::source_draft::Scope::Work { owner: self.owner },
+            self.target,
+        )?;
+        let preview = self.source.preview(p, self.target)?;
+        let command = self.consumer_command(preview.as_ref().unwrap_or(p))?;
+        self.source.combine(p, self.target, command)
+    }
+    fn consumer_command(&self, p: &Project) -> Result<Command, String> {
         let owner = p
             .elements
             .get(&self.owner)
@@ -615,6 +726,8 @@ impl Draft {
         });
         let name = if self.name.trim().is_empty() {
             default_name
+        } else if self.source.label(self.target).is_some() {
+            self.name.as_str()
         } else {
             self.name.trim()
         };
@@ -798,6 +911,13 @@ fn sequence_links(p: &Project, owner: Id) -> Vec<&Relation> {
         })
         .collect()
 }
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct PreviewLink {
+    relation: Id,
+    source: OccurrenceEndpoint,
+    target: OccurrenceEndpoint,
+}
+
 struct GraphNode {
     id: Id,
     rect: Rectangle,
@@ -806,26 +926,98 @@ struct GraphNode {
     control: Option<ControlKind>,
     source: Option<Id>,
     preview: Vec<(OccurrenceEndpoint, String)>,
-    preview_links: Vec<(OccurrenceEndpoint, OccurrenceEndpoint)>,
+    preview_links: Vec<PreviewLink>,
     preview_total: usize,
 }
 impl GraphNode {
+    fn preview_link_points(&self, link: &PreviewLink) -> Option<[Point; 2]> {
+        if ![&link.source, &link.target]
+            .into_iter()
+            .all(|endpoint| self.preview.iter().any(|(shown, _)| shown == endpoint))
+        {
+            return None;
+        }
+        let a = self.endpoint_rect(&link.source);
+        let b = self.endpoint_rect(&link.target);
+        Some([
+            Point::new(a.x + a.width, a.center_y()),
+            Point::new(b.x, b.center_y()),
+        ])
+    }
+
+    fn preview_link_visible_segment(&self, link: &PreviewLink) -> Option<[Point; 2]> {
+        visible_preview_segment(
+            self.preview_link_points(link)?,
+            (0..self.preview.len()).map(|index| self.preview_rect(index)),
+        )
+    }
+
+    fn preview_rect(&self, index: usize) -> Rectangle {
+        Rectangle::new(
+            Point::new(
+                self.rect.x + 12. + (index % 2) as f32 * 125.,
+                self.rect.y + 118. + (index / 2) as f32 * 44.,
+            ),
+            Size::new(113., 32.),
+        )
+    }
+
     fn endpoint_rect(&self, endpoint: &OccurrenceEndpoint) -> Rectangle {
         self.preview
             .iter()
             .position(|(candidate, _)| candidate == endpoint)
-            .map(|i| {
-                Rectangle::new(
-                    Point::new(
-                        self.rect.x + 12. + (i % 2) as f32 * 125.,
-                        self.rect.y + 118. + (i / 2) as f32 * 44.,
-                    ),
-                    Size::new(113., 32.),
-                )
-            })
+            .map(|index| self.preview_rect(index))
             .unwrap_or(self.rect)
     }
 }
+
+/// Preview tiles are painted after their arrows. Focus only a remaining line
+/// segment, excluding opaque tile interiors and their one-pixel borders.
+fn visible_preview_segment(
+    [a, b]: [Point; 2],
+    tiles: impl Iterator<Item = Rectangle>,
+) -> Option<[Point; 2]> {
+    let delta = b - a;
+    let length = (delta.x * delta.x + delta.y * delta.y).sqrt();
+    if !length.is_finite() || length <= 0.5 {
+        return None;
+    }
+    let mut hidden = Vec::new();
+    for tile in tiles {
+        let mut low = 0_f32;
+        let mut high = 1_f32;
+        for (origin, step, min, max) in [
+            (a.x, delta.x, tile.x - 1., tile.x + tile.width + 1.),
+            (a.y, delta.y, tile.y - 1., tile.y + tile.height + 1.),
+        ] {
+            if step.abs() <= f32::EPSILON {
+                if origin < min || origin > max {
+                    high = -1.;
+                    break;
+                }
+            } else {
+                let first = (min - origin) / step;
+                let last = (max - origin) / step;
+                low = low.max(first.min(last));
+                high = high.min(first.max(last));
+            }
+        }
+        if high > low {
+            hidden.push((low, high));
+        }
+    }
+    hidden.sort_by(|a, b| a.0.total_cmp(&b.0));
+    let mut cursor = 0_f32;
+    let mut best = (0_f32, 0_f32);
+    for (low, high) in hidden.into_iter().chain([(1., 1.)]) {
+        if low - cursor > best.1 - best.0 {
+            best = (cursor, low);
+        }
+        cursor = cursor.max(high);
+    }
+    ((best.1 - best.0) * length > 0.5).then(|| [a + delta * best.0, a + delta * best.1])
+}
+
 struct GraphEdge {
     id: Id,
     source: Id,
@@ -866,13 +1058,16 @@ mod contextual_routing;
 struct Graph<'a> {
     project: &'a Project,
     interaction: Option<(Context, CanvasTool, bool)>,
-    scroll_offset: iced::Vector,
+    camera_pan: iced::Vector,
+    pending_insertion: Option<Insertion>,
     nodes: Vec<GraphNode>,
     edges: Vec<GraphEdge>,
     ordered_paths: Vec<OrderedPath>,
     ordered: bool,
     size: Size,
     selected: Id,
+    selected_preview: Option<OccurrenceEndpoint>,
+    selected_preview_link: Option<PreviewLink>,
     scale: f32,
 }
 impl<'a> Graph<'a> {
@@ -1021,17 +1216,16 @@ impl<'a> Graph<'a> {
                                         occurrence: r.target(),
                                     })
                                 })
-                                .map(|r| {
-                                    (
-                                        OccurrenceEndpoint {
-                                            references: vec![e.id],
-                                            occurrence: r.source(),
-                                        },
-                                        OccurrenceEndpoint {
-                                            references: vec![e.id],
-                                            occurrence: r.target(),
-                                        },
-                                    )
+                                .map(|r| PreviewLink {
+                                    relation: r.id,
+                                    source: OccurrenceEndpoint {
+                                        references: vec![e.id],
+                                        occurrence: r.source(),
+                                    },
+                                    target: OccurrenceEndpoint {
+                                        references: vec![e.id],
+                                        occurrence: r.target(),
+                                    },
                                 })
                                 .collect();
                         }
@@ -1198,13 +1392,16 @@ impl<'a> Graph<'a> {
         Self {
             project: p,
             interaction: None,
-            scroll_offset: iced::Vector::ZERO,
+            camera_pan: iced::Vector::ZERO,
+            pending_insertion: None,
             nodes,
             edges,
             ordered_paths,
             ordered: !order.is_empty(),
             size,
             selected,
+            selected_preview: None,
+            selected_preview_link: None,
             scale: 1.,
         }
     }
@@ -1298,6 +1495,7 @@ impl canvas::Program<Message> for Graph<'_> {
     ) -> Vec<canvas::Geometry> {
         let mut f = Frame::new(renderer, bounds.size());
         f.fill_rectangle(Point::ORIGIN, bounds.size(), Color::WHITE);
+        f.translate(self.camera_pan);
         f.scale(self.scale);
         for pass in PAINT_PASSES {
             match pass {
@@ -1433,39 +1631,41 @@ impl canvas::Program<Message> for Graph<'_> {
                             let mini: BTreeMap<_, _> = n
                                 .preview
                                 .iter()
-                                .enumerate()
-                                .map(|(i, (id, _))| {
-                                    (
-                                        id.clone(),
-                                        Rectangle::new(
-                                            Point::new(
-                                                n.rect.x + 12. + (i % 2) as f32 * 125.,
-                                                n.rect.y + 118. + (i / 2) as f32 * 44.,
-                                            ),
-                                            Size::new(113., 32.),
-                                        ),
-                                    )
-                                })
+                                .map(|(id, _)| (id.clone(), n.endpoint_rect(id)))
                                 .collect();
-                            for (a, b) in &n.preview_links {
-                                let a = mini[a];
-                                let b = mini[b];
+                            for link in &n.preview_links {
+                                let Some(points) = n.preview_link_points(link) else {
+                                    continue;
+                                };
+                                let selected = self.selected_preview_link.as_ref() == Some(link);
                                 draw_arrow(
                                     &mut f,
-                                    &[
-                                        Point::new(a.x + a.width, a.center_y()),
-                                        Point::new(b.x, b.center_y()),
-                                    ],
-                                    style::MUTED,
-                                    1.,
+                                    &points,
+                                    if selected { style::TEAL } else { style::MUTED },
+                                    if selected { 3. } else { 1. },
                                 );
                             }
                             for (id, name) in &n.preview {
                                 let r = mini[id];
-                                f.fill_rectangle(r.position(), r.size(), Color::WHITE);
+                                let selected = self.selected_preview.as_ref() == Some(id);
+                                f.fill_rectangle(
+                                    r.position(),
+                                    r.size(),
+                                    if selected {
+                                        Color::from_rgb8(224, 247, 242)
+                                    } else {
+                                        Color::WHITE
+                                    },
+                                );
                                 f.stroke(
                                     &Path::rectangle(r.position(), r.size()),
-                                    Stroke::default().with_color(style::LINE),
+                                    Stroke::default()
+                                        .with_color(if selected {
+                                            style::TEAL
+                                        } else {
+                                            style::LINE
+                                        })
+                                        .with_width(if selected { 2.5 } else { 1. }),
                                 );
                                 draw_text(
                                     &mut f,
@@ -1513,7 +1713,10 @@ impl canvas::Program<Message> for Graph<'_> {
         cursor: mouse::Cursor,
     ) -> mouse::Interaction {
         if cursor.position_in(bounds).is_some_and(|p| {
-            let p = Point::new(p.x / self.scale, p.y / self.scale);
+            let p = Point::new(
+                (p.x - self.camera_pan.x) / self.scale,
+                (p.y - self.camera_pan.y) / self.scale,
+            );
             self.nodes.iter().any(|n| n.rect.contains(p))
                 || self.ordered_paths.iter().any(|path| {
                     path.points.windows(2).any(|pair| {
@@ -1587,6 +1790,9 @@ mod tests {
     }
     fn branch(owner: Id, a: Id, b: Id, before: Id, after: Id) -> Draft {
         Draft {
+            source: Default::default(),
+            invocation: Id::new_v4(),
+            source_origin: None,
             insertion: Insertion::default(),
             fixed: false,
             browsers: Default::default(),
@@ -2043,7 +2249,6 @@ mod tests {
         let accepted = app.document.snapshot();
         assert!(app.behavior.prepare_pending(app.project()).is_err());
         for (shelf, expected) in [
-            (Shelf::Tools, Some(Shelf::Tools)),
             (Shelf::Selection, Some(Shelf::Selection)),
             (Shelf::Selection, None),
         ] {
@@ -2060,10 +2265,12 @@ mod tests {
     }
 
     #[test]
-    fn process_fit_canvas_selection_ignores_retained_ordered_page_scroll() {
+    fn process_camera_selection_ignores_independent_details_scroll() {
         let (p, owner, _, _, _, _) = fixture();
         let mut state = State::default();
-        state.scrolled(scenario::ScrollArea::Canvas, iced::Vector::new(11., 19.));
+        state.camera(crate::behavior::canvas_workspace::Event::Pan(
+            iced::Vector::new(11., 19.),
+        ));
         state.scrolled(scenario::ScrollArea::Page, iced::Vector::new(0., 370.));
         let context = Context {
             document: p.id,
@@ -2074,16 +2281,17 @@ mod tests {
         for scale in [0.45, 1.] {
             let mut graph = Graph::new(&p, owner, owner);
             graph.scale = scale;
-            graph.scroll_offset = state.canvas_offset();
+            graph.camera_pan = state.pan;
             graph.interaction = Some((context, CanvasTool::Select, true));
             let node = &graph.nodes[0];
             let id = node.id;
             let point = node.rect.center();
             let bounds = Rectangle::new(Point::new(40., 100.), Size::new(800., 300.));
             let screen = Point::new(
-                bounds.x + point.x * scale - 11.,
-                bounds.y + point.y * scale - 19.,
+                bounds.x + point.x * scale + 11.,
+                bounds.y + point.y * scale + 19.,
             );
+            assert!(bounds.contains(screen));
             let message = graph
                 .input(
                     &mut Input::default(),

crates/oa-desktop/src/behavior/topology/contextual.rs

@@ -33,7 +33,7 @@ pub enum Event {
     Search(String),
     Page(usize),
 }
-#[derive(Default, serde::Serialize, serde::Deserialize)]
+#[derive(Clone, Default, serde::Serialize, serde::Deserialize)]
 #[serde(deny_unknown_fields)]
 pub(super) struct Draft {
     edit: Option<Id>,
@@ -608,7 +608,11 @@ mod tests {
             "Authored endpoint is retained for explicit repair"
         );
         assert!(state.prepare_pending(&deleted).is_err());
-        state.remember(owner, reference);
+        state.remember(
+            owner,
+            reference,
+            super::super::direct::referenced(&p, owner, reference).unwrap(),
+        );
         assert_eq!(state.back(&deleted), Some((owner, reference)));
         assert!(state.selected_context.is_none());
         state.draft = None;

crates/oa-desktop/src/behavior/topology/direct.rs

@@ -60,6 +60,7 @@ pub enum CanvasEvent {
     Open(Context, Id),
     Back(Context),
     Zoom(Context, Option<f32>),
+    Camera(Context, u64, super::super::canvas_workspace::Event),
     Focus(Context),
     Viewport(Context, Size),
 }
@@ -77,6 +78,7 @@ impl CanvasEvent {
             | Self::Back(c)
             | Self::AppendExchange(c)
             | Self::Zoom(c, ..)
+            | Self::Camera(c, ..)
             | Self::Focus(c)
             | Self::Viewport(c, ..) => *c,
             Self::Begin { context, .. }
@@ -86,6 +88,19 @@ impl CanvasEvent {
         }
     }
 }
+pub(super) struct ReturnFrame {
+    identity: Option<(Id, Id)>,
+    owner: Id,
+    occurrence: Id,
+    target: Id,
+    address: Option<oa_core::topology_context::ContextAddress>,
+    pan: iced::Vector,
+    zoom: Option<f32>,
+    fit: bool,
+    viewport: Option<Size>,
+    expanded: BTreeSet<Id>,
+    contextual_expanded: BTreeSet<OccurrenceEndpoint>,
+}
 impl State {
     pub(crate) fn select_context(&mut self, address: oa_core::topology_context::ContextAddress) {
         self.selected_context = Some(address);
@@ -138,35 +153,49 @@ impl State {
         if self.identity != Some((document, owner)) {
             self.identity = Some((document, owner));
             self.tool = CanvasTool::Select;
+            self.pan = iced::Vector::ZERO;
             self.zoom = Some(1.);
             self.fit = false;
             self.viewport = None;
             self.expanded.clear();
-            self.scroll_offsets = [iced::Vector::ZERO; 2];
+            self.details_offset = iced::Vector::ZERO;
         }
     }
     #[cfg(test)]
-    pub(crate) fn scroll_offset(&self) -> iced::Vector {
-        self.scroll_offsets[0] + self.scroll_offsets[1]
+    pub(crate) fn details_offset(&self) -> iced::Vector {
+        self.details_offset
     }
-    pub(crate) fn scrolled(&mut self, area: scenario::ScrollArea, offset: iced::Vector) -> bool {
-        let index = match area {
-            scenario::ScrollArea::Canvas => 0,
-            scenario::ScrollArea::Page => 1,
-        };
-        let changed = self.scroll_offsets[index] != offset;
-        self.scroll_offsets[index] = offset;
+    pub(crate) fn scrolled(
+        &mut self,
+        scenario::ScrollArea::Page: scenario::ScrollArea,
+        offset: iced::Vector,
+    ) -> bool {
+        if !offset.x.is_finite() || !offset.y.is_finite() || offset.x < 0. || offset.y < 0. {
+            return false;
+        }
+        let changed = self.details_offset != offset;
+        self.details_offset = offset;
         changed
     }
     pub(crate) fn choose(&mut self, tool: CanvasTool) {
         // Choosing how to edit must retain the user's current view.
         self.tool = tool;
     }
+    pub(crate) fn camera(&mut self, event: super::super::canvas_workspace::Event) -> bool {
+        super::super::canvas_workspace::change(&mut self.pan, &mut self.zoom, &mut self.fit, event)
+    }
     pub(crate) fn zoom(&mut self, value: Option<f32>) {
         self.fit = value.is_none();
-        self.zoom = value.map(|v| v.clamp(0.5, 2.));
+        self.zoom = value.map(|v| v.clamp(0.05, 3.));
     }
     pub(crate) fn viewport(&mut self, size: Size) -> bool {
+        if !size.width.is_finite()
+            || !size.height.is_finite()
+            || size.width <= 0.
+            || size.height <= 0.
+        {
+            return false;
+        }
         let changed = self.viewport != Some(size);
         self.viewport = Some(size);
         changed
@@ -188,26 +217,83 @@ impl State {
         }
         true
     }
-    pub(crate) fn remember(&mut self, owner: Id, occurrence: Id) {
-        self.return_to
-            .push((owner, occurrence, self.selected_context.clone()));
+    pub(crate) fn remember(&mut self, owner: Id, occurrence: Id, target: Id) {
+        if self.return_to.len() == 32 {
+            self.return_to.remove(0);
+        }
+        self.return_to.push(ReturnFrame {
+            identity: self.identity,
+            owner,
+            occurrence,
+            target,
+            address: self.selected_context.clone(),
+            pan: self.pan,
+            zoom: self.zoom,
+            fit: self.fit,
+            viewport: self.viewport,
+            expanded: self.expanded.clone(),
+            contextual_expanded: self.contextual_expanded.clone(),
+        });
     }
     pub(crate) fn back(&mut self, p: &Project) -> Option<(Id, Id)> {
-        while let Some((owner, occurrence, address)) = self.return_to.pop() {
-            if is_contribution(p, owner, occurrence) {
-                self.selected_context = address.filter(|address| {
-                    address.owner == owner
-                        && oa_core::topology_context::TopologyIndex::new(p)
-                            .resolve(owner, &address.endpoint)
-                            .is_ok()
+        while let Some(frame) = self.return_to.pop() {
+            if frame.identity.map(|i| i.0) != self.identity.map(|i| i.0) {
+                continue;
+            }
+            let valid = referenced(p, frame.owner, frame.occurrence) == Some(frame.target)
+                || if let Some(address) = &frame.address {
+                    oa_core::topology_context::TopologyIndex::new(p)
+                        .resolve(frame.owner, &address.endpoint)
+                        .is_ok_and(|r| r.defining_sequence == frame.target)
+                } else {
+                    false
+                };
+            if valid && is_contribution(p, frame.owner, frame.occurrence) {
+                self.identity = frame.identity;
+                self.selected_context = frame.address.filter(|a| {
+                    oa_core::topology_context::TopologyIndex::new(p)
+                        .resolve(frame.owner, &a.endpoint)
+                        .is_ok()
                 });
-                return Some((owner, occurrence));
+                self.pan = frame.pan;
+                self.zoom = frame.zoom;
+                self.fit = frame.fit;
+                self.viewport = frame.viewport;
+                self.expanded = frame.expanded;
+                self.contextual_expanded = frame.contextual_expanded;
+                return Some((frame.owner, frame.occurrence));
             }
         }
         None
     }
-    pub(crate) fn created_selection(&self, command: &Command) -> Option<Id> {
+    pub(crate) fn camera_zoom(&mut self, p: &Project, owner: Id, zoom: Option<f32>) {
+        let graph =
+            Graph::expanded_qualified(p, owner, owner, &self.expanded, &self.contextual_expanded);
+        let old = self.scale(graph.size, 500.);
+        if let Some(next) = zoom {
+            let size = self.viewport.unwrap_or(Size::new(500., 300.));
+            self.camera(super::super::canvas_workspace::Event::Zoom {
+                factor: next / old,
+                at: Point::new(size.width / 2., size.height / 2.),
+                base: old,
+            });
+        } else {
+            self.zoom(None);
+            let fitted = self.scale(graph.size, 500.);
+            self.zoom(Some(fitted));
+            self.pan = iced::Vector::ZERO;
+        }
+    }
+    pub(crate) fn created_selection(&self, p: &Project, command: &Command) -> Option<Id> {
         let owner = self.pending_owner()?;
+        if self
+            .draft
+            .as_ref()
+            .is_some_and(|d| d.source.label(d.target).is_some())
+            && self.prepare_pending(p).ok().as_ref() != Some(command)
+        {
+            return None;
+        }
         if let Command::CreateRelation(r) | Command::EditRelation(_, r) = command
             && matches!(&r.body, RelationBody::ContextualLink { owner: caller, .. } if *caller == owner)
         {
@@ -539,7 +625,7 @@ impl Graph<'_> {
                 {
                     *moved |= position.distance(*start) >= 3.;
                 }
-                mouse::Cursor::Available(*position + self.scroll_offset)
+                mouse::Cursor::Available(*position)
             }
             canvas::Event::Mouse(mouse::Event::WheelScrolled { .. } | mouse::Event::CursorLeft)
             | canvas::Event::Window(
@@ -558,18 +644,19 @@ impl Graph<'_> {
             }
             canvas::Event::Mouse(
                 mouse::Event::ButtonPressed(_) | mouse::Event::ButtonReleased(_),
-            ) => state
-                .pointer
-                .map_or(cursor, |p| mouse::Cursor::Available(p + self.scroll_offset)),
+            ) => state.pointer.map_or(cursor, mouse::Cursor::Available),
             canvas::Event::Window(iced::window::Event::RedrawRequested(_)) => {
-                state.pointer = cursor.position().map(|p| p - self.scroll_offset);
+                state.pointer = cursor.position();
                 cursor
             }
             _ => cursor,
         };
-        let world = cursor
-            .position_in(bounds)
-            .map(|p| Point::new(p.x / self.scale, p.y / self.scale));
+        let world = cursor.position_in(bounds).map(|p| {
+            Point::new(
+                (p.x - self.camera_pan.x) / self.scale,
+                (p.y - self.camera_pan.y) / self.scale,
+            )
+        });
         let publish = |event| Some(Action::publish(Message::TopologyCanvas(event)).and_capture());
         match event {
             canvas::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)) if visible => {
@@ -583,7 +670,7 @@ impl Graph<'_> {
                 if !editable {
                     return None;
                 }
-                let start = cursor.position()? - self.scroll_offset;
+                let start = cursor.position()?;
                 match tool {
                     CanvasTool::Add(..) => {
                         state.press = Some(Press::Add {
@@ -722,15 +809,35 @@ impl Graph<'_> {
         let Some((context, tool, editable)) = self.interaction else {
             return;
         };
+        if let Some(insertion) = self.pending_insertion {
+            if let Some(edge) = insertion
+                .link
+                .and_then(|id| self.edges.iter().find(|e| e.id == id))
+            {
+                draw_arrow(f, &edge.points, style::TEAL, 3.);
+            } else if let Some(node) = insertion
+                .before
+                .and_then(|id| self.nodes.iter().find(|n| n.id == id))
+            {
+                f.stroke(
+                    &Path::rounded_rectangle(node.rect.position(), node.rect.size(), 10.into()),
+                    Stroke::default().with_color(style::TEAL).with_width(3.),
+                );
+            }
+        }
         if !editable {
             return;
         }
         let point = state
             .pointer
-            .map(|p| p + self.scroll_offset)
             .or_else(|| cursor.position())
             .filter(|p| bounds.contains(*p))
-            .map(|p| Point::new((p.x - bounds.x) / self.scale, (p.y - bounds.y) / self.scale));
+            .map(|p| {
+                Point::new(
+                    (p.x - bounds.x - self.camera_pan.x) / self.scale,
+                    (p.y - bounds.y - self.camera_pan.y) / self.scale,
+                )
+            });
         let live =
             state.context == Some(context) && state.tool == tool && state.bounds == Some(bounds);
         if live && let Some(source) = state.source {
@@ -845,12 +952,7 @@ impl Graph<'_> {
 }
 
 impl State {
-    pub(crate) fn selection_offset(
-        &self,
-        p: &Project,
-        owner: Id,
-        id: Id,
-    ) -> Option<scrollable::AbsoluteOffset> {
+    pub(crate) fn reveal_selection(&mut self, p: &Project, owner: Id, id: Id) -> bool {
         let graph =
             Graph::expanded_qualified(p, owner, id, &self.expanded, &self.contextual_expanded);
         let scale = self.scale(graph.size, 500.);
@@ -862,10 +964,25 @@ impl State {
                 self.qualified_selection(p, owner)
                     .map_or(n.rect, |a| n.endpoint_rect(&a.endpoint))
             })
-            .or_else(|| graph.edges.iter().find(|e| e.id == id).map(|e| e.label))?;
-        Some(scrollable::AbsoluteOffset {
-            x: (rect.x * scale - 12.).max(0.),
-            y: (rect.y * scale - 12.).max(0.),
-        })
+            .or_else(|| graph.edges.iter().find(|e| e.id == id).map(|e| e.label));
+        let Some(rect) = rect else {
+            return false;
+        };
+        let viewport = self.viewport.unwrap_or(Size::new(500., 300.));
+        let x = rect.x * scale + self.pan.x;
+        let y = rect.y * scale + self.pan.y;
+        let delta = iced::Vector::new(
+            if x < 12. || x + rect.width * scale > viewport.width - 12. {
+                12. - x
+            } else {
+                0.
+            },
+            if y < 12. || y + rect.height * scale > viewport.height - 12. {
+                12. - y
+            } else {
+                0.
+            },
+        );
+        self.camera(super::super::canvas_workspace::Event::Pan(delta))
     }
 }

crates/oa-desktop/src/behavior/topology/direct_tests.rs

@@ -540,7 +540,7 @@ fn send(
         input,
         &canvas::Event::Mouse(event),
         bounds,
-        mouse::Cursor::Available(point + graph.scroll_offset),
+        mouse::Cursor::Available(point),
     )
     .and_then(|a| a.into_inner().0)
 }
@@ -554,16 +554,20 @@ fn position(graph: &Graph<'_>, id: Id) -> Point {
         .center()
 }
 #[test]
-fn direct_process_production_click_click_drag_insert_and_scroll_coordinates() {
+fn direct_process_production_click_click_drag_insert_and_camera_coordinates() {
     let f = fixture(Layer::Oa);
     for drag in [false, true] {
         let mut graph = graph(&f, CanvasTool::Connect);
-        graph.scroll_offset = iced::Vector::new(35., 90.);
-        let bounds = Rectangle::new(Point::new(10., 20.), graph.size);
+        graph.camera_pan = iced::Vector::new(35., 90.);
+        let bounds = Rectangle::new(
+            Point::new(10., 20.),
+            Size::new(graph.size.width + 70., graph.size.height + 180.),
+        );
         let screen =
-            |id| position(&graph, id) + iced::Vector::new(bounds.x, bounds.y) - graph.scroll_offset;
+            |id| position(&graph, id) + iced::Vector::new(bounds.x, bounds.y) + graph.camera_pan;
         let a = screen(f.nodes[0]);
         let b = screen(f.nodes[2]);
+        assert!(bounds.contains(a) && bounds.contains(b));
         let mut input = Input::default();
         send(
             &graph,
@@ -732,7 +736,7 @@ fn direct_process_readable_default_fit_expansion_and_bounded_choices() {
     state.zoom(None);
     assert!(state.scale(Size::new(3262., 220.), 500.) < 0.2);
     state.zoom(Some(0.1));
-    assert_eq!(state.scale(Size::new(3262., 220.), 500.), 0.5);
+    assert_eq!(state.scale(Size::new(3262., 220.), 500.), 0.1);
     state.enter(Id::new_v4(), f.owner);
     assert_eq!(state.scale(Size::new(3262., 220.), 500.), 1.);
     let mut all = Vec::new();
@@ -1331,7 +1335,9 @@ fn direct_process_palette_preserves_fit_and_manual_camera() {
         let document = Id::new_v4();
         state.enter(document, f.owner);
         state.viewport(Size::new(500., 300.));
-        state.scrolled(scenario::ScrollArea::Canvas, iced::Vector::new(35., 90.));
+        state.camera(super::super::canvas_workspace::Event::Pan(
+            iced::Vector::new(35., 90.),
+        ));
         state.scrolled(scenario::ScrollArea::Page, iced::Vector::new(0., 120.));
         for camera in [None, Some(0.75), Some(1.5)] {
             state.zoom(camera);
@@ -1353,90 +1359,16 @@ fn direct_process_palette_preserves_fit_and_manual_camera() {
                     "{layer:?} {camera:?} {tool:?}"
                 );
                 assert_eq!(state.fit, camera.is_none());
-                assert_eq!(state.scroll_offset(), iced::Vector::new(35., 210.));
+                assert_eq!(state.pan, iced::Vector::new(35., 90.));
+                assert_eq!(state.details_offset(), iced::Vector::new(0., 120.));
                 state.enter(document, f.owner);
                 assert_eq!(state.scale(size, 500.), before);
             }
         }
         state.enter(Id::new_v4(), f.owner);
         assert_eq!(state.scale(Size::new(690., 250.), 500.), 1.);
-        assert_eq!(state.scroll_offset(), iced::Vector::ZERO);
-    }
-}
-
-#[test]
-fn direct_process_pending_form_diff_retains_the_canvas_scroll_state() {
-    use iced::advanced::widget::{Tree, tree};
-    use std::rc::Rc;
-    fn path_to(tree: &Tree, tag: tree::Tag) -> Option<Vec<usize>> {
-        if tree.tag == tag {
-            return Some(Vec::new());
-        }
-        tree.children.iter().enumerate().find_map(|(index, child)| {
-            let mut path = path_to(child, tag)?;
-            path.insert(0, index);
-            Some(path)
-        })
-    }
-    fn at<'a>(mut tree: &'a mut Tree, path: &[usize]) -> &'a mut Tree {
-        for &index in path {
-            tree = &mut tree.children[index];
-        }
-        tree
-    }
-    for layer in [Layer::Oa, Layer::Sa] {
-        for size in [Size::new(1440., 900.), Size::new(1100., 700.)] {
-            for tool in [Tool::Control, Tool::Branch, Tool::Connect] {
-                let f = fixture(layer);
-                let mut app = App::with_project(f.p.clone());
-                let _ = app.update(Message::Select(f.nodes[1]));
-                let _ = app.update(Message::Page(crate::app::Page::Behavior));
-                app.window_size = size;
-                let original = app.document.snapshot();
-                let graph: Element<'_, Message> =
-                    canvas::Canvas::new(Graph::new(app.project(), f.owner, f.nodes[1])).into();
-                let canvas_tag = Tree::new(graph.as_widget()).tag;
-                drop(graph);
-                let scroll: Element<'_, Message> = scrollable(text("")).into();
-                let scroll_tag = Tree::new(scroll.as_widget()).tag;
-                let mut tree = Tree::new(view::view(&app, f.owner, Column::new()).as_widget());
-                let mut scroll_path = path_to(&tree, canvas_tag).unwrap();
-                scroll_path.pop();
-                assert_eq!(at(&mut tree, &scroll_path).tag, scroll_tag);
-                // Scrollable::diff treats its local state as opaque. A retained marker
-                // proves the real Iced diff preserves the state that owns the offsets.
-                // No layout or input operation runs on this test-only marker state.
-                let marker = Rc::new(());
-                at(&mut tree, &scroll_path).state = tree::State::new(Rc::clone(&marker));
-                let _ = app.update(Message::Behavior(super::super::Event::Topology(
-                    Event::Start(f.owner, tool, Some(f.nodes[1])),
-                )));
-                assert!(app.behavior.has_pending());
-                tree.diff(view::view(&app, f.owner, Column::new()).as_widget());
-                assert_eq!(
-                    Rc::strong_count(&marker),
-                    2,
-                    "form open: {layer:?} {size:?} {tool:?}"
-                );
-                let mut current_path = path_to(&tree, canvas_tag).unwrap();
-                current_path.pop();
-                assert_eq!(current_path, scroll_path);
-                assert!(Rc::ptr_eq(
-                    at(&mut tree, &scroll_path).state.downcast_ref::<Rc<()>>(),
-                    &marker,
-                ));
-                let _ = app.update(Message::Behavior(super::super::Event::Topology(
-                    Event::Cancel,
-                )));
-                tree.diff(view::view(&app, f.owner, Column::new()).as_widget());
-                assert_eq!(
-                    Rc::strong_count(&marker),
-                    2,
-                    "form cancel: {layer:?} {size:?} {tool:?}"
-                );
-                assert!(std::sync::Arc::ptr_eq(&app.document.snapshot(), &original));
-            }
-        }
+        assert_eq!(state.pan, iced::Vector::ZERO);
+        assert_eq!(state.details_offset(), iced::Vector::ZERO);
     }
 }
 
@@ -1447,15 +1379,18 @@ fn direct_process_scaled_control_and_link_gestures_use_visible_positions() {
         for scale in [0.15, 0.6898551, 1.5] {
             let mut graph = graph(&f, CanvasTool::Add(Tool::Control, ControlKind::Choice));
             graph.scale = scale;
-            graph.scroll_offset = iced::Vector::new(11., 19.);
+            graph.camera_pan = iced::Vector::new(11., 19.);
             let bounds = Rectangle::new(
                 Point::new(40., 70.),
-                Size::new(graph.size.width * scale, graph.size.height * scale),
+                Size::new(
+                    graph.size.width * scale + 22.,
+                    graph.size.height * scale + 38.,
+                ),
             );
             let screen = |world: Point| {
                 Point::new(
-                    world.x * scale + bounds.x - 11.,
-                    world.y * scale + bounds.y - 19.,
+                    world.x * scale + bounds.x + 11.,
+                    world.y * scale + bounds.y + 19.,
                 )
             };
             let edge = &graph.edges[0];
@@ -1463,6 +1398,7 @@ fn direct_process_scaled_control_and_link_gestures_use_visible_positions() {
                 (edge.points[0].x + edge.points[1].x) / 2.,
                 edge.points[0].y,
             ));
+            assert!(bounds.contains(point));
             let mut input = Input::default();
             send(
                 &graph,
@@ -1493,6 +1429,7 @@ fn direct_process_scaled_control_and_link_gestures_use_visible_positions() {
                 let mut input = Input::default();
                 let a = screen(position(&graph, f.nodes[0]));
                 let b = screen(position(&graph, f.nodes[2]));
+                assert!(bounds.contains(a) && bounds.contains(b));
                 send(
                     &graph,
                     &mut input,

crates/oa-desktop/src/behavior/topology/usages.rs

@@ -0,0 +1,274 @@
+//! Read-only usages of the actual process graph, including bounded reuse tiles.
+use super::*;
+use crate::diagram_usage::{Surface, Target, Usage};
+
+/// The only presentation inputs needed by a background usage query. Drafts,
+/// focus, camera, history and widget state never cross the worker boundary.
+#[derive(Clone)]
+pub(crate) struct UsageSnapshot {
+    identity: Option<(Id, Id)>,
+    expanded: BTreeSet<Id>,
+    contextual_expanded: BTreeSet<OccurrenceEndpoint>,
+}
+
+impl UsageSnapshot {
+    pub(crate) fn into_query_state(self) -> State {
+        State {
+            identity: self.identity,
+            expanded: self.expanded,
+            contextual_expanded: self.contextual_expanded,
+            ..State::default()
+        }
+    }
+}
+
+impl State {
+    pub(crate) fn usage_snapshot(&self) -> UsageSnapshot {
+        UsageSnapshot {
+            identity: self.identity,
+            expanded: self.expanded.clone(),
+            contextual_expanded: self.contextual_expanded.clone(),
+        }
+    }
+}
+
+fn owner_exists(p: &Project, owner: Id) -> bool {
+    p.elements
+        .get(&owner)
+        .is_some_and(|e| matches!(e.kind(), Kind::Process | Kind::FunctionalChain))
+}
+
+fn occurrence_role(p: &Project, occurrence: Id, subject: Id) -> Option<&'static str> {
+    let e = p.elements.get(&occurrence)?;
+    if occurrence == subject {
+        return Some("contribution");
+    }
+    match e.shared()? {
+        SharedBody::Occurrence {
+            body: OccurrenceBody::Action {
+                action: Some(id), ..
+            },
+            ..
+        } if *id == subject => Some("action occurrence"),
+        SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange {
+                exchange: Some(id), ..
+            },
+            ..
+        } if *id == subject => Some("exchange occurrence"),
+        SharedBody::Occurrence {
+            body: OccurrenceBody::SequenceReference { sequence: Some(id) },
+            ..
+        } if *id == subject => Some("reused process / chain"),
+        _ => None,
+    }
+}
+
+impl Graph<'_> {
+    fn usage_bounds(&self, target: &Target) -> Option<Rectangle> {
+        match target {
+            Target::Whole => Some(Rectangle::new(Point::ORIGIN, self.size)),
+            Target::ProcessOccurrence(endpoint) => {
+                let root = endpoint
+                    .references
+                    .first()
+                    .copied()
+                    .unwrap_or(endpoint.occurrence);
+                let node = self.nodes.iter().find(|node| node.id == root)?;
+                if endpoint.references.is_empty() {
+                    Some(node.rect)
+                } else {
+                    // endpoint_rect intentionally has a proxy fallback for other callers;
+                    // a usage promises an actual tile and must never take that fallback.
+                    node.preview
+                        .iter()
+                        .any(|(shown, _)| shown == endpoint)
+                        .then(|| node.endpoint_rect(endpoint))
+                }
+            }
+            Target::ProcessLink(id) => {
+                let edge = self.edges.iter().find(|edge| edge.id == *id)?;
+                if !edge.guard.is_empty() {
+                    Some(edge.label)
+                } else {
+                    let segment = edge
+                        .points
+                        .windows(2)
+                        .nth(edge.points.len().saturating_sub(1) / 2)?;
+                    let center = Point::new(
+                        (segment[0].x + segment[1].x) / 2.,
+                        (segment[0].y + segment[1].y) / 2.,
+                    );
+                    Some(Rectangle::new(
+                        center - iced::Vector::new(16., 16.),
+                        Size::new(32., 32.),
+                    ))
+                }
+            }
+            Target::ProcessPreviewLink {
+                relation,
+                source,
+                target,
+            } => {
+                let node = self
+                    .nodes
+                    .iter()
+                    .find(|node| source.references.first() == Some(&node.id))?;
+                let link = node.preview_links.iter().find(|link| {
+                    link.relation == *relation && link.source == *source && link.target == *target
+                })?;
+                let [a, b] = node.preview_link_visible_segment(link)?;
+                Some(Rectangle::new(
+                    Point::new((a.x + b.x) / 2. - 16., (a.y + b.y) / 2. - 16.),
+                    Size::new(32., 32.),
+                ))
+            }
+            _ => None,
+        }
+    }
+}
+
+impl State {
+    /// Inactive owners use the same default preview policy as entering their canvas.
+    fn usage_graph<'a>(&self, p: &'a Project, owner: Id) -> Graph<'a> {
+        if self.identity.is_some_and(|(_, current)| current == owner) {
+            Graph::expanded_qualified(p, owner, owner, &self.expanded, &self.contextual_expanded)
+        } else {
+            Graph::new(p, owner, owner)
+        }
+    }
+
+    pub(crate) fn diagram_usages(&self, p: &Project, owner: Id, subject: Id) -> Vec<Usage> {
+        if !owner_exists(p, owner)
+            || !(p.elements.contains_key(&subject) || p.relations.contains_key(&subject))
+        {
+            return vec![];
+        }
+        let graph = self.usage_graph(p, owner);
+        let mut usages = vec![];
+        let mut add = |target: Target, role: &str| {
+            if let Some(bounds) = graph.usage_bounds(&target) {
+                usages.push(Usage {
+                    subject,
+                    surface: Surface::Process(owner),
+                    target,
+                    role: role.into(),
+                    bounds,
+                });
+            }
+        };
+        if subject == owner {
+            add(Target::Whole, "process / chain canvas");
+        }
+        for node in &graph.nodes {
+            if let Some(role) = occurrence_role(p, node.id, subject) {
+                add(
+                    Target::ProcessOccurrence(OccurrenceEndpoint {
+                        references: vec![],
+                        occurrence: node.id,
+                    }),
+                    role,
+                );
+            }
+            for (endpoint, _) in &node.preview {
+                if let Some(role) = occurrence_role(p, endpoint.occurrence, subject) {
+                    add(
+                        Target::ProcessOccurrence(endpoint.clone()),
+                        &format!("reused {role}"),
+                    );
+                }
+            }
+            for link in &node.preview_links {
+                if link.relation == subject {
+                    add(
+                        Target::ProcessPreviewLink {
+                            relation: link.relation,
+                            source: link.source.clone(),
+                            target: link.target.clone(),
+                        },
+                        "reused sequence link",
+                    );
+                }
+            }
+        }
+        for edge in &graph.edges {
+            let role = if edge.id == subject {
+                Some("process link")
+            } else {
+                match p.relations.get(&edge.id).map(|r| &r.body) {
+                    Some(RelationBody::ContextualLink {
+                        purpose: ContextualLinkPurpose::Exchange { exchange },
+                        ..
+                    }) if *exchange == subject => Some("assembly exchange"),
+                    Some(RelationBody::ContextualLink {
+                        purpose: ContextualLinkPurpose::CommonWork { work },
+                        ..
+                    }) if *work == subject => Some("common work"),
+                    _ => None,
+                }
+            };
+            if let Some(role) = role {
+                add(Target::ProcessLink(edge.id), role);
+            }
+        }
+        usages
+    }
+
+    /// Returns success, not whether the camera changed. App must separately guard
+    /// its other drafts and revalidate the queried subject's current usage.
+    pub(crate) fn reveal_usage(
+        &mut self,
+        p: &Project,
+        document: Id,
+        owner: Id,
+        target: &Target,
+    ) -> bool {
+        if !owner_exists(p, owner) || self.draft.is_some() {
+            return false;
+        }
+        let same = self.identity == Some((document, owner));
+        let graph = if same {
+            self.usage_graph(p, owner)
+        } else {
+            Graph::new(p, owner, owner)
+        };
+        let Some(bounds) = graph.usage_bounds(target) else {
+            return false;
+        };
+        let address = if let Target::ProcessOccurrence(endpoint) = target {
+            let Ok(resolved) =
+                oa_core::topology_context::TopologyIndex::new(p).resolve(owner, endpoint)
+            else {
+                return false;
+            };
+            (!endpoint.references.is_empty()).then_some(resolved.address)
+        } else {
+            None
+        };
+        let viewport = self.viewport.unwrap_or(Size::new(500., 300.));
+        self.enter(document, owner);
+        if !same {
+            self.contextual_expanded.clear();
+        }
+        self.selected_context = address;
+        self.tool = CanvasTool::Select;
+        self.viewport = Some(viewport);
+        let fit = ((viewport.width - 48.).max(1.) / bounds.width.max(1.))
+            .min((viewport.height - 48.).max(1.) / bounds.height.max(1.));
+        let scale = if matches!(target, Target::Whole) {
+            fit.clamp(0.0001, 1.)
+        } else {
+            fit.clamp(0.6, 1.25)
+        };
+        self.zoom = Some(scale);
+        self.fit = false;
+        self.pan = iced::Vector::new(
+            viewport.width / 2. - bounds.center_x() * scale,
+            viewport.height / 2. - bounds.center_y() * scale,
+        );
+        true
+    }
+}
+
+#[cfg(test)]
+mod tests;

crates/oa-desktop/src/behavior/topology/usages/tests.rs

@@ -0,0 +1,439 @@
+use super::*;
+
+fn add(p: &mut Project, owner: Id, name: &str, body: OccurrenceBody) -> Id {
+    let e = occurrence(p, owner, name, body);
+    let id = e.id;
+    *p = execute_batch(p, &[Command::CreateElement(e)]).unwrap();
+    id
+}
+
+fn reused_fixture() -> (Project, Id, Id, Id, [Id; 2], Vec<Id>) {
+    let f = super::super::direct_tests::fixture(Layer::Oa);
+    let mut p = f.p;
+    let sequence = p
+        .make_element(Kind::Process, Layer::Oa, "Reviewed checks", None)
+        .unwrap();
+    let sequence_id = sequence.id;
+    p = execute_batch(&p, &[Command::CreateElement(sequence)]).unwrap();
+    let mut leaves = vec![];
+    for name in [
+        "Check one",
+        "Check two",
+        "Check three",
+        "Check four",
+        "Check five",
+    ] {
+        leaves.push(add(
+            &mut p,
+            sequence_id,
+            name,
+            OccurrenceBody::Action {
+                action: Some(f.work[0]),
+                lifeline: None,
+            },
+        ));
+    }
+    let first = add(
+        &mut p,
+        f.owner,
+        "First invocation",
+        OccurrenceBody::SequenceReference {
+            sequence: Some(sequence_id),
+        },
+    );
+    let second = add(
+        &mut p,
+        f.owner,
+        "Second invocation",
+        OccurrenceBody::SequenceReference {
+            sequence: Some(sequence_id),
+        },
+    );
+    (p, f.owner, sequence_id, f.work[0], [first, second], leaves)
+}
+
+#[test]
+fn process_usages_exclude_endpoint_coincidence_and_keep_actual_occurrences_and_links() {
+    for layer in [Layer::Oa, Layer::Sa] {
+        let f = super::super::direct_tests::fixture(layer);
+        let mut p = f.p;
+        let state = State::default();
+        // Both exchange endpoints have Action contributions, but there is no
+        // Exchange occurrence and no exchange arrow in this process.
+        assert!(state.diagram_usages(&p, f.owner, f.exchange).is_empty());
+        let direct = state.diagram_usages(&p, f.owner, f.work[0]);
+        assert_eq!(direct.len(), 1);
+        assert_eq!(
+            direct[0].target,
+            Target::ProcessOccurrence(OccurrenceEndpoint {
+                references: vec![],
+                occurrence: f.nodes[0]
+            })
+        );
+        let link = state.diagram_usages(&p, f.owner, f.link);
+        assert_eq!(link.len(), 1);
+        assert_eq!(link[0].target, Target::ProcessLink(f.link));
+        let first = add(
+            &mut p,
+            f.owner,
+            "First exchange",
+            OccurrenceBody::Exchange {
+                exchange: Some(f.exchange),
+                sender: None,
+                receiver: None,
+                message_kind: MessageKind::Asynchronous,
+                reply_to: None,
+                values: vec![],
+                operation: None,
+            },
+        );
+        let second = add(
+            &mut p,
+            f.owner,
+            "Second exchange",
+            OccurrenceBody::Exchange {
+                exchange: Some(f.exchange),
+                sender: None,
+                receiver: None,
+                message_kind: MessageKind::Asynchronous,
+                reply_to: None,
+                values: vec![],
+                operation: None,
+            },
+        );
+        let usages = state.diagram_usages(&p, f.owner, f.exchange);
+        assert_eq!(usages.len(), 2);
+        assert_eq!(
+            usages
+                .iter()
+                .map(|usage| usage.target.clone())
+                .collect::<Vec<_>>(),
+            vec![
+                Target::ProcessOccurrence(OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence: first
+                }),
+                Target::ProcessOccurrence(OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence: second
+                }),
+            ]
+        );
+    }
+}
+
+#[test]
+fn process_usages_keep_caller_paths_and_exclude_unshown_fifth_preview() {
+    let (p, owner, sequence, work, calls, leaves) = reused_fixture();
+    let before = p.clone();
+    let mut state = State::default();
+    let leaf = state.diagram_usages(&p, owner, leaves[0]);
+    assert_eq!(leaf.len(), 2);
+    for (usage, call) in leaf.iter().zip(calls) {
+        assert_eq!(
+            usage.target,
+            Target::ProcessOccurrence(OccurrenceEndpoint {
+                references: vec![call],
+                occurrence: leaves[0]
+            })
+        );
+    }
+    assert_ne!(leaf[0].bounds, leaf[1].bounds);
+    assert!(state.diagram_usages(&p, owner, leaves[4]).is_empty());
+    assert_eq!(state.diagram_usages(&p, owner, sequence).len(), 2);
+    // One local action and four tiles in each of two caller boxes.
+    assert_eq!(state.diagram_usages(&p, owner, work).len(), 9);
+    state.enter(Id::new_v4(), owner);
+    assert!(state.expand(&p, owner, calls[0]));
+    let fifth = state.diagram_usages(&p, owner, leaves[4]);
+    assert_eq!(fifth.len(), 1);
+    assert_eq!(
+        fifth[0].target,
+        Target::ProcessOccurrence(OccurrenceEndpoint {
+            references: vec![calls[0]],
+            occurrence: leaves[4]
+        })
+    );
+    // Another active owner must not leak its expansion to this queried canvas.
+    state.enter(Id::new_v4(), sequence);
+    assert!(state.diagram_usages(&p, owner, leaves[4]).is_empty());
+    assert_eq!(p, before);
+}
+
+#[test]
+fn process_usage_reveal_validates_before_state_changes_and_centers_the_exact_tile() {
+    let (p, owner, _, _, calls, leaves) = reused_fixture();
+    let before = p.clone();
+    let document = Id::new_v4();
+    let mut state = State::default();
+    state.enter(document, owner);
+    state.viewport(Size::new(880., 460.));
+    state.pan = iced::Vector::new(-3000., -900.);
+    let hidden = Target::ProcessOccurrence(OccurrenceEndpoint {
+        references: vec![calls[0]],
+        occurrence: leaves[4],
+    });
+    let prior = (
+        state.identity,
+        state.pan,
+        state.zoom,
+        state.fit,
+        state.selected_context.clone(),
+    );
+    assert!(!state.reveal_usage(&p, document, owner, &hidden));
+    assert_eq!(
+        (
+            state.identity,
+            state.pan,
+            state.zoom,
+            state.fit,
+            state.selected_context.clone()
+        ),
+        prior
+    );
+    assert!(!state.reveal_usage(&p, document, Id::new_v4(), &Target::Whole));
+    assert_eq!(
+        (
+            state.identity,
+            state.pan,
+            state.zoom,
+            state.fit,
+            state.selected_context.clone()
+        ),
+        prior
+    );
+    let endpoint = OccurrenceEndpoint {
+        references: vec![calls[1]],
+        occurrence: leaves[0],
+    };
+    let target = Target::ProcessOccurrence(endpoint.clone());
+    assert!(state.reveal_usage(&p, document, owner, &target));
+    assert_eq!(state.selected_context.as_ref().unwrap().endpoint, endpoint);
+    let bounds = state
+        .diagram_usages(&p, owner, leaves[0])
+        .into_iter()
+        .find(|usage| usage.target == target)
+        .unwrap()
+        .bounds;
+    let scale = state.zoom.unwrap();
+    assert!(scale >= 0.6);
+    assert!((bounds.center_x() * scale + state.pan.x - 440.).abs() < 0.01);
+    assert!((bounds.center_y() * scale + state.pan.y - 230.).abs() < 0.01);
+    assert!(state.reveal_usage(&p, document, owner, &Target::Whole));
+    assert!(state.selected_context.is_none());
+    state
+        .update(&p, Event::Start(owner, Tool::Work, None))
+        .unwrap();
+    let draft = state.recovery_snapshot().unwrap();
+    let camera = (state.pan, state.zoom, state.fit);
+    assert!(!state.reveal_usage(&p, document, owner, &target));
+    assert_eq!(state.recovery_snapshot().unwrap(), draft);
+    assert_eq!((state.pan, state.zoom, state.fit), camera);
+    assert_eq!(p, before);
+}
+
+#[test]
+fn process_contextual_purpose_and_painted_preview_links_keep_distinct_identities() {
+    let (mut p, owner, sequence, work, calls, leaves) = reused_fixture();
+    let source = OccurrenceEndpoint {
+        references: vec![calls[0]],
+        occurrence: leaves[0],
+    };
+    let target = OccurrenceEndpoint {
+        references: vec![calls[1]],
+        occurrence: leaves[0],
+    };
+    let relation = Relation {
+        id: Id::new_v4(),
+        alias: "same_check".into(),
+        name: "One common check".into(),
+        description: String::new(),
+        body: RelationBody::ContextualLink {
+            owner,
+            source,
+            target,
+            purpose: ContextualLinkPurpose::CommonWork { work },
+        },
+    };
+    let contextual = relation.id;
+    p = execute_batch(&p, &[Command::CreateRelation(relation)]).unwrap();
+    let Command::CreateRelation(relation) = link(&p, leaves[0], leaves[1], "next") else {
+        unreachable!()
+    };
+    let local_link = relation.id;
+    p = execute_batch(&p, &[Command::CreateRelation(relation)]).unwrap();
+    let state = State::default();
+    assert!(
+        state
+            .diagram_usages(&p, owner, work)
+            .iter()
+            .any(|usage| usage.target == Target::ProcessLink(contextual)
+                && usage.role == "common work")
+    );
+    assert_eq!(state.diagram_usages(&p, owner, contextual).len(), 1);
+    let previews = state.diagram_usages(&p, owner, local_link);
+    assert_eq!(previews.len(), 2);
+    for (usage, call) in previews.iter().zip(calls) {
+        assert_eq!(
+            usage.target,
+            Target::ProcessPreviewLink {
+                relation: local_link,
+                source: OccurrenceEndpoint {
+                    references: vec![call],
+                    occurrence: leaves[0]
+                },
+                target: OccurrenceEndpoint {
+                    references: vec![call],
+                    occurrence: leaves[1]
+                },
+            }
+        );
+    }
+    assert_eq!(state.diagram_usages(&p, sequence, local_link).len(), 1);
+}
+
+#[test]
+fn preview_arrow_focus_is_in_the_painted_gap_and_hidden_endpoints_never_fallback() {
+    let (mut p, owner, _, _, calls, leaves) = reused_fixture();
+    let Command::CreateRelation(shown) = link(&p, leaves[0], leaves[1], "next") else {
+        unreachable!()
+    };
+    let shown_id = shown.id;
+    p = execute_batch(&p, &[Command::CreateRelation(shown)]).unwrap();
+    let Command::CreateRelation(hidden) = link(&p, leaves[0], leaves[4], "later") else {
+        unreachable!()
+    };
+    let hidden_id = hidden.id;
+    p = execute_batch(&p, &[Command::CreateRelation(hidden)]).unwrap();
+    let before = p.clone();
+    let document = Id::new_v4();
+    let mut state = State::default();
+    state.enter(document, owner);
+    state.viewport(Size::new(800., 460.));
+    let rows = state.diagram_usages(&p, owner, shown_id);
+    assert_eq!(rows.len(), 2);
+    let graph = Graph::new(&p, owner, owner);
+    for (row, call) in rows.iter().zip(calls) {
+        let node = graph.nodes.iter().find(|n| n.id == call).unwrap();
+        // The painter places 113px tiles 125px apart, beginning 12px in.
+        // The 12px gap is centered 131px into the caller, 134px below its top.
+        assert_eq!(
+            row.bounds.center(),
+            Point::new(node.rect.x + 131., node.rect.y + 134.)
+        );
+        assert!(
+            node.preview
+                .iter()
+                .all(|(e, _)| !node.endpoint_rect(e).contains(row.bounds.center()))
+        );
+    }
+    assert_ne!(rows[0].bounds, rows[1].bounds);
+    assert!(state.diagram_usages(&p, owner, hidden_id).is_empty());
+    assert!(state.reveal_usage(&p, document, owner, &rows[1].target));
+    assert!(
+        state.selected_context.is_none(),
+        "an arrow is not an occurrence authoring context"
+    );
+    let zoom = state.zoom.unwrap();
+    assert!((rows[1].bounds.center_x() * zoom + state.pan.x - 400.).abs() < 0.01);
+    assert!((rows[1].bounds.center_y() * zoom + state.pan.y - 230.).abs() < 0.01);
+    assert!(state.expand(&p, owner, calls[0]));
+    let expanded = state.diagram_usages(&p, owner, hidden_id);
+    assert_eq!(expanded.len(), 1);
+    assert!(
+        matches!(&expanded[0].target, Target::ProcessPreviewLink { source, .. }
+        if source.references == vec![calls[0]])
+    );
+    let mut stale = rows[1].target.clone();
+    if let Target::ProcessPreviewLink { source, .. } = &mut stale {
+        source.references = vec![Id::new_v4()];
+    }
+    let prior = (state.pan, state.zoom, state.fit);
+    assert!(!state.reveal_usage(&p, document, owner, &stale));
+    assert_eq!((state.pan, state.zoom, state.fit), prior);
+    assert_eq!(p, before);
+}
+
+#[test]
+fn visible_preview_segment_excludes_all_opaque_tiles_for_reverse_and_cross_row_arrows() {
+    let tiles = [
+        Rectangle::new(Point::new(12., 118.), Size::new(113., 32.)),
+        Rectangle::new(Point::new(137., 118.), Size::new(113., 32.)),
+        Rectangle::new(Point::new(12., 162.), Size::new(113., 32.)),
+        Rectangle::new(Point::new(137., 162.), Size::new(113., 32.)),
+    ];
+    for points in [
+        [Point::new(250., 134.), Point::new(12., 134.)],
+        [Point::new(125., 134.), Point::new(137., 178.)],
+        [Point::new(250., 178.), Point::new(12., 134.)],
+    ] {
+        let [a, b] = visible_preview_segment(points, tiles.into_iter()).unwrap();
+        for fraction in [0.1, 0.5, 0.9] {
+            let point = a + (b - a) * fraction;
+            assert!(tiles.iter().all(|tile| !tile.contains(point)));
+        }
+    }
+    assert!(
+        visible_preview_segment(
+            [Point::new(30., 134.), Point::new(100., 134.)],
+            tiles.into_iter()
+        )
+        .is_none()
+    );
+    assert!(
+        visible_preview_segment([Point::new(1., 1.), Point::new(1., 1.)], tiles.into_iter())
+            .is_none()
+    );
+}
+
+#[test]
+fn expanded_nested_tiles_do_not_invent_links_the_preview_painter_does_not_emit() {
+    let (mut p, owner, sequence, work, calls, _) = reused_fixture();
+    let nested = p
+        .make_element(Kind::Process, Layer::Oa, "Nested checks", None)
+        .unwrap();
+    let nested_id = nested.id;
+    p = execute_batch(&p, &[Command::CreateElement(nested)]).unwrap();
+    let leaves: Vec<_> = ["Nested one", "Nested two"]
+        .into_iter()
+        .map(|name| {
+            add(
+                &mut p,
+                nested_id,
+                name,
+                OccurrenceBody::Action {
+                    action: Some(work),
+                    lifeline: None,
+                },
+            )
+        })
+        .collect();
+    let Command::CreateRelation(relation) = link(&p, leaves[0], leaves[1], "next") else {
+        unreachable!()
+    };
+    let relation_id = relation.id;
+    p = execute_batch(&p, &[Command::CreateRelation(relation)]).unwrap();
+    let reference = add(
+        &mut p,
+        sequence,
+        "Nested invocation",
+        OccurrenceBody::SequenceReference {
+            sequence: Some(nested_id),
+        },
+    );
+    let mut state = State::default();
+    state.enter(Id::new_v4(), owner);
+    state.expanded.insert(calls[0]);
+    state.contextual_expanded.insert(OccurrenceEndpoint {
+        references: vec![calls[0]],
+        occurrence: reference,
+    });
+    let shown = state.diagram_usages(&p, owner, leaves[0]);
+    assert_eq!(shown.len(), 1);
+    assert!(
+        matches!(&shown[0].target, Target::ProcessOccurrence(endpoint)
+        if endpoint.references == vec![calls[0], reference])
+    );
+    assert!(state.diagram_usages(&p, owner, relation_id).is_empty());
+    assert_eq!(state.diagram_usages(&p, nested_id, relation_id).len(), 1);
+}

crates/oa-desktop/src/behavior/topology/view.rs

@@ -66,107 +66,7 @@ pub(super) fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Ele
     let pending = state.draft.is_some();
     let ordered = !legacy_order(p, owner).is_empty();
     let selected = is_contribution(p, owner, app.selected).then_some(app.selected);
-    let choose = |tool| Message::TopologyCanvas(CanvasEvent::Choose(context, tool));
-    let mut controls = Column::new().spacing(6);
-    if !pending {
-        controls = controls
-            .push(
-                row![
-                    button("Select / reorder")
-                        .style(if state.tool == CanvasTool::Select {
-                            button::primary
-                        } else {
-                            style::nav
-                        })
-                        .on_press(choose(CanvasTool::Select)),
-                    button("Work")
-                        .style(
-                            if state.tool == CanvasTool::Add(Tool::Work, ControlKind::Choice) {
-                                button::primary
-                            } else {
-                                style::nav
-                            }
-                        )
-                        .on_press(choose(CanvasTool::Add(Tool::Work, ControlKind::Choice))),
-                    button("Exchange")
-                        .style(
-                            if state.tool == CanvasTool::Add(Tool::Exchange, ControlKind::Choice) {
-                                button::primary
-                            } else {
-                                style::nav
-                            }
-                        )
-                        .on_press(choose(CanvasTool::Add(Tool::Exchange, ControlKind::Choice))),
-                    button("Reuse")
-                        .style(
-                            if state.tool == CanvasTool::Add(Tool::Reuse, ControlKind::Choice) {
-                                button::primary
-                            } else {
-                                style::nav
-                            }
-                        )
-                        .on_press(choose(CanvasTool::Add(Tool::Reuse, ControlKind::Choice)))
-                ]
-                .spacing(6),
-            )
-            .push(
-                row![
-                    pick_list(
-                        vec![
-                            ControlKind::Choice,
-                            ControlKind::Merge,
-                            ControlKind::Fork,
-                            ControlKind::Join,
-                            ControlKind::Loop
-                        ]
-                        .into_iter()
-                        .map(ControlChoice)
-                        .collect::<Vec<_>>(),
-                        if let CanvasTool::Add(Tool::Control, kind) = state.tool {
-                            Some(ControlChoice(kind))
-                        } else {
-                            None
-                        },
-                        move |c| Message::TopologyCanvas(CanvasEvent::Choose(
-                            context,
-                            CanvasTool::Add(Tool::Control, c.0)
-                        ))
-                    )
-                    .placeholder("Draw control…")
-                    .text_size(12)
-                    .padding(8),
-                    button("Sequence link")
-                        .style(if state.tool == CanvasTool::Connect {
-                            button::primary
-                        } else {
-                            style::nav
-                        })
-                        .on_press(choose(CanvasTool::Connect)),
-                    button("Two paths…").on_press(event(Event::Start(
-                        owner,
-                        Tool::Branch,
-                        selected
-                    )))
-                ]
-                .spacing(6),
-            );
-    }
-    controls=controls.push(label(if pending{"Pending contribution · apply or cancel below"}else if ordered{"Ordered exchange path · click a path to insert or empty canvas to continue; the edit preserves its order"}else{match state.tool{
-        CanvasTool::Select=>"Select local contributions and paths · drag path endpoints to reconnect · ↕ reorders within a column",
-        CanvasTool::Connect=>"Sequence link · click or drag from preceding to following contribution · Escape cancels",
-        CanvasTool::Add(..)=>"Choose a highlighted path or contribution position · existing work stays shared · Escape cancels"}}));
-    if !pending && ordered {
-        controls = controls.push(button("Append exchange…").on_press(Message::TopologyCanvas(
-            CanvasEvent::AppendExchange(context),
-        )));
-        let commands = preserved_order(p, owner, None);
-        if !commands.is_empty() {
-            controls = controls.push(
-                button("Edit path links and guards")
-                    .on_press(Message::Command(unique_batch(p, commands))),
-            );
-        }
-    }
+    let clean = !app.behavior.has_pending() && !app.draft_dirty() && !app.source_dirty();
     // A fixed sibling keeps Iced's canvas scroll state through selection/form changes.
     let mut navigation = column![].spacing(6);
     if let Some(Relation {
@@ -211,11 +111,6 @@ pub(super) fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Ele
             );
         }
     }
-    if !pending {
-        controls = controls.push(button("Qualified link / assembly…").on_press(event(
-            Event::Start(owner, Tool::Contextual, Some(app.selected)),
-        )));
-    }
     if let Some(id) = selected {
         let mut actions =
             row![button("Contribution properties").on_press(Message::EditProperties(id))]
@@ -256,27 +151,105 @@ pub(super) fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Ele
             button("Back to caller").on_press(Message::TopologyCanvas(CanvasEvent::Back(context))),
         );
     }
-    let diagram = {
-        let mut graph = Graph::expanded_qualified(
-            p,
-            owner,
-            app.selected,
-            &state.expanded,
-            &state.contextual_expanded,
+    navigation = navigation
+        .push(
+            button("Two paths...").on_press_maybe(clean.then_some(event(Event::Start(
+                owner,
+                Tool::Branch,
+                selected,
+            )))),
+        )
+        .push(
+            button("Qualified link / assembly...").on_press_maybe(clean.then_some(event(
+                Event::Start(owner, Tool::Contextual, Some(app.selected)),
+            ))),
         );
-        graph.scale = state.scale(graph.size, (app.window_size.width - 600.).max(200.));
-        graph.interaction = Some((
-            context,
-            state.tool,
-            !app.behavior.has_pending() && !app.draft_dirty() && !app.source_dirty(),
-        ));
-        // Explicit graphs no longer have a scrolling page ancestor. A retained
-        // offset from an ordered view must not distort their pointer coordinates.
-        graph.scroll_offset = state.canvas_offset();
-        let scale = graph.scale;
-        let mut header = column![
-            row![
-                out.width(Fill),
+    if ordered {
+        navigation = navigation.push(button("Append exchange...").on_press_maybe(clean.then_some(
+            Message::TopologyCanvas(CanvasEvent::AppendExchange(context)),
+        )));
+        let commands = preserved_order(p, owner, None);
+        if !commands.is_empty() {
+            navigation = navigation.push(
+                button("Edit path links and guards")
+                    .on_press_maybe(clean.then_some(Message::Command(unique_batch(p, commands)))),
+            );
+        }
+    }
+    let mut graph = Graph::expanded_qualified(
+        p,
+        owner,
+        app.selected,
+        &state.expanded,
+        &state.contextual_expanded,
+    );
+    graph.selected_preview = state
+        .qualified_selection(p, owner)
+        .filter(|address| {
+            address
+                .endpoint
+                .references
+                .first()
+                .copied()
+                .unwrap_or(address.endpoint.occurrence)
+                == app.selected
+        })
+        .map(|address| address.endpoint.clone());
+    graph.selected_preview_link = app
+        .diagram_focus(crate::diagram_usage::Surface::Process(owner))
+        .and_then(|usage| match &usage.target {
+            crate::diagram_usage::Target::ProcessPreviewLink {
+                relation,
+                source,
+                target,
+            } => Some(PreviewLink {
+                relation: *relation,
+                source: source.clone(),
+                target: target.clone(),
+            }),
+            _ => None,
+        });
+    graph.scale = state.scale(graph.size, (app.window_size.width - 600.).max(200.));
+    graph.camera_pan = state.pan;
+    graph.pending_insertion = state
+        .draft
+        .as_ref()
+        .filter(|d| d.owner == owner && d.fixed)
+        .map(|d| d.insertion);
+    graph.interaction = Some((context, state.tool, clean));
+    let scale = graph.scale;
+    let scope = super::super::canvas_workspace::Scope {
+        document: context.document,
+        owner,
+        revision: context.revision,
+        epoch: app.camera_epoch,
+    };
+    let keyboard = clean && super::super::canvas_workspace::keyboard_enabled(app);
+    let camera = move |e| Message::TopologyCanvas(CanvasEvent::Camera(context, scope.epoch, e));
+    let canvas = container(
+        iced::widget::sensor(
+            super::super::canvas_workspace::Viewport::new(
+                canvas::Canvas::new(graph).width(Fill).height(Fill),
+                scope,
+                scale,
+                keyboard,
+                camera,
+            )
+            .pan_background(state.tool == CanvasTool::Select),
+        )
+        .key((context.document, owner))
+        .on_show(move |size| Message::TopologyCanvas(CanvasEvent::Viewport(context, size)))
+        .on_resize(move |size| Message::TopologyCanvas(CanvasEvent::Viewport(context, size))),
+    )
+    .id("process-viewport")
+    .width(Fill)
+    .height(Fill)
+    .style(style::card)
+    .into();
+    let header = column![
+        row![
+            out.width(Fill),
+            super::super::canvas_workspace::Control::new(
                 button(
                     text(if state.focused {
                         "Restore panels"
@@ -285,368 +258,352 @@ pub(super) fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Ele
                     })
                     .size(12)
                 )
-                .on_press(Message::TopologyCanvas(CanvasEvent::Focus(context)))
                 .padding(6)
-            ]
-            .spacing(6)
-            .align_y(iced::Center),
-            row![
-                button(text("Tools").size(12))
-                    .padding(6)
-                    .style(if state.shelf == Some(Shelf::Tools) {
-                        button::primary
-                    } else {
-                        style::nav
-                    })
-                    .on_press(event(Event::Shelf(Shelf::Tools))),
-                button(text("Selection details").size(12))
-                    .padding(6)
-                    .style(if state.shelf == Some(Shelf::Selection) {
-                        button::primary
-                    } else {
-                        style::nav
-                    })
-                    .on_press(event(Event::Shelf(Shelf::Selection))),
-                button(text("Fit overview").size(12))
-                    .padding(6)
-                    .on_press(Message::TopologyCanvas(CanvasEvent::Zoom(context, None))),
-                button(text("−").size(12))
-                    .padding(6)
-                    .on_press(Message::TopologyCanvas(CanvasEvent::Zoom(
-                        context,
-                        Some(scale / 1.25)
-                    ))),
-                label(format!("{:.0}%", scale * 100.)),
-                button(text("+").size(12))
-                    .padding(6)
-                    .on_press(Message::TopologyCanvas(CanvasEvent::Zoom(
-                        context,
-                        Some(scale * 1.25)
-                    ))),
-                button(text("100%").size(12))
-                    .padding(6)
-                    .on_press(Message::TopologyCanvas(CanvasEvent::Zoom(
-                        context,
-                        Some(1.)
-                    )))
-            ]
-            .spacing(6)
-            .wrap(),
+                .on_press(super::super::canvas_workspace::intent(
+                    scope,
+                    "Panels",
+                    Message::TopologyCanvas(CanvasEvent::Focus(context))
+                )),
+                scope,
+                "Panels",
+                keyboard,
+                Some(super::super::canvas_workspace::intent(
+                    scope,
+                    "Panels",
+                    Message::TopologyCanvas(CanvasEvent::Focus(context))
+                )),
+                camera
+            )
         ]
-        .spacing(6);
-        if state.fit_limited(graph.size, (app.window_size.width - 600.).max(200.)) {
-            header = header
-                .push(text("Minimum zoom reached · scroll to see the remaining graph.").size(11));
-        }
-        if graph.nodes.is_empty() {
-            controls = controls.push(label(
-                "Choose Work, Exchange, Reuse or a control, then click the canvas to start.",
-            ));
-        }
-        let size = Size::new(graph.size.width * scale, graph.size.height * scale);
-        let canvas = scrollable(
-            canvas::Canvas::new(graph)
-                .width(size.width)
-                .height(size.height),
-        )
-        .id("process-canvas")
-        .direction(scrollable::Direction::Both {
-            vertical: scrollable::Scrollbar::default(),
-            horizontal: scrollable::Scrollbar::default(),
-        })
-        .width(Fill)
-        .height(Fill);
-        let canvas = container(
-            iced::widget::sensor(super::super::scenario_scroll::observe_topology(
+        .spacing(6),
+        super::super::canvas_workspace::controls(
+            scope,
+            keyboard,
+            scale,
+            event(Event::Shelf(Shelf::Selection)),
+            clean.then_some(Message::TopologyCanvas(CanvasEvent::Camera(
                 context,
-                scenario::ScrollArea::Canvas,
-                canvas,
-            ))
-            .on_show(move |size| Message::TopologyCanvas(CanvasEvent::Viewport(context, size)))
-            .on_resize(move |size| Message::TopologyCanvas(CanvasEvent::Viewport(context, size))),
+                scope.epoch,
+                super::super::canvas_workspace::Event::Focus
+            ))),
+            move |zoom| Message::TopologyCanvas(CanvasEvent::Zoom(context, zoom)),
+            camera
         )
-        .padding(8)
-        .width(Fill)
-        .height(Fill)
-        .style(style::card);
-        let details: Element<'_, Message> = match state.shelf {
-            Some(Shelf::Tools) => controls.into(),
-            _ => navigation.push(text("Full qualified identities and definition actions appear here for the selected contribution or link.").size(11)).into(),
-        };
-        explicit_pane(
-            header.into(),
-            details,
-            canvas.into(),
-            state.shelf.is_some(),
-            pending,
-        )
-    };
+    ]
+    .spacing(4);
+    let entries = [
+        ("S", "Select contributions or paths", CanvasTool::Select),
+        (
+            "W",
+            "Work: click a path or empty space",
+            CanvasTool::Add(Tool::Work, ControlKind::Choice),
+        ),
+        (
+            "E",
+            "Exchange: click a path or empty space",
+            CanvasTool::Add(Tool::Exchange, ControlKind::Choice),
+        ),
+        (
+            "ref",
+            "Reuse process / chain",
+            CanvasTool::Add(Tool::Reuse, ControlKind::Choice),
+        ),
+        (
+            "OR",
+            "Choice",
+            CanvasTool::Add(Tool::Control, ControlKind::Choice),
+        ),
+        (
+            "M",
+            "Merge",
+            CanvasTool::Add(Tool::Control, ControlKind::Merge),
+        ),
+        (
+            "AND",
+            "Fork",
+            CanvasTool::Add(Tool::Control, ControlKind::Fork),
+        ),
+        (
+            "J",
+            "Join",
+            CanvasTool::Add(Tool::Control, ControlKind::Join),
+        ),
+        (
+            "IT",
+            "Loop",
+            CanvasTool::Add(Tool::Control, ControlKind::Loop),
+        ),
+        (
+            "->",
+            "Sequence link: click or drag between contributions",
+            CanvasTool::Connect,
+        ),
+    ];
+    let palette = super::super::canvas_workspace::palette(
+        scope,
+        keyboard,
+        camera,
+        entries.into_iter().map(|(glyph, label, choice)| {
+            (
+                glyph,
+                label,
+                choice == state.tool,
+                clean.then_some(Message::TopologyCanvas(CanvasEvent::Choose(
+                    context, choice,
+                ))),
+            )
+        }),
+    );
+    let details = scrollable(navigation.push(text("Layout is derived. The reorder handle changes display order within its column; it does not author a position.").size(11)))
+        .id("process-details").width(Fill).height(Fill).into();
     let mut form_panel: Element<'_, Message> = iced::widget::Space::new().height(0).into();
     if let Some(d) = state.draft.as_ref().filter(|d| d.owner == owner) {
-        let mut form = column![text(d.tool.title()).size(16)].spacing(8);
-        if let Some(contextual) = &d.contextual {
-            form = form
-                .push(
-                    text_input("Link name (retain current when blank)", &d.name)
-                        .on_input(|v| event(Event::Name(v)))
-                        .padding(8)
-                        .size(12),
-                )
-                .push(super::contextual::view(p, owner, contextual));
+        if let Some(child) = d.source.view(p) {
+            form_panel = column![
+                text(format!(
+                    "Consumer name: {}",
+                    crate::views::short(&d.name, 60)
+                ))
+                .size(12),
+                child.map(|e| event(Event::Source(e)))
+            ]
+            .spacing(6)
+            .height(Fill)
+            .into();
         } else {
-            if let Some(link) = d.insertion.link.and_then(|id| p.relations.get(&id)) {
-                let guard = if let RelationBody::SequenceLink { guard, .. } = &link.body {
-                    guard.as_str()
-                } else {
-                    ""
-                };
-                form = form.push(label(format!(
-                    "Insert on {} → {} · preserve path identity and condition [{}]",
-                    p.named(link.source()),
-                    p.named(link.target()),
-                    guard
-                )));
-            } else if d.fixed && ordered {
-                form = form.push(label(match (d.before, d.after) {
-                    (Some(before), Some(after)) => format!(
-                        "Insert between {} → {} · preserve the ordered path",
-                        p.named(before),
-                        p.named(after)
-                    ),
-                    (Some(before), None) => format!("Continue after {}", p.named(before)),
-                    (None, Some(after)) => format!("Insert before {}", p.named(after)),
-                    _ => "Start the ordered path".into(),
-                }));
-            } else if d.fixed
-                && d.tool == Tool::Exchange
-                && let Some(before) = d.before
-            {
-                form = form.push(label(format!(
-                    "Append after {} → new exchange · Create adds an explicit sequence link",
-                    p.named(before)
-                )));
-            } else if d.fixed && d.tool != Tool::Connect {
-                form = form.push(label(
-                    d.insertion
-                        .before
-                        .map_or("Append an unconnected contribution".into(), |id| {
-                            format!("Unconnected contribution before {}", p.named(id))
-                        }),
-                ));
-            }
-            if !legacy_order(p, owner).is_empty() {
-                form = form.push(label(
+            let mut form = column![text(d.tool.title()).size(16)].spacing(8);
+            if let Some(contextual) = &d.contextual {
+                form = form
+                    .push(
+                        text_input("Link name (retain current when blank)", &d.name)
+                            .on_input(|v| event(Event::Name(v)))
+                            .padding(8)
+                            .size(12),
+                    )
+                    .push(super::contextual::view(p, owner, contextual));
+            } else {
+                if let Some(link) = d.insertion.link.and_then(|id| p.relations.get(&id)) {
+                    let guard = if let RelationBody::SequenceLink { guard, .. } = &link.body {
+                        guard.as_str()
+                    } else {
+                        ""
+                    };
+                    form = form.push(label(format!(
+                        "Insert on {} → {} · preserve path identity and condition [{}]",
+                        p.named(link.source()),
+                        p.named(link.target()),
+                        guard
+                    )));
+                } else if d.fixed && ordered {
+                    form = form.push(label(match (d.before, d.after) {
+                        (Some(before), Some(after)) => format!(
+                            "Insert between {} → {} · preserve the ordered path",
+                            p.named(before),
+                            p.named(after)
+                        ),
+                        (Some(before), None) => format!("Continue after {}", p.named(before)),
+                        (None, Some(after)) => format!("Insert before {}", p.named(after)),
+                        _ => "Start the ordered path".into(),
+                    }));
+                } else if d.fixed
+                    && d.tool == Tool::Exchange
+                    && let Some(before) = d.before
+                {
+                    form = form.push(label(format!(
+                        "Append after {} → new exchange · Create adds an explicit sequence link",
+                        p.named(before)
+                    )));
+                } else if d.fixed && d.tool != Tool::Connect {
+                    form = form.push(label(
+                        d.insertion
+                            .before
+                            .map_or("Append an unconnected contribution".into(), |id| {
+                                format!("Unconnected contribution before {}", p.named(id))
+                            }),
+                    ));
+                }
+                if d.tool == Tool::Work {
+                    if let Some(title) = d.source.label(d.target) {
+                        form = form.push(label(title)).push(label("Create commits the new work and contribution together at the chosen path position."));
+                    }
+                    form = form.push(button("Create new source…").on_press(event(Event::Source(
+                        super::super::source_draft::Event::Open(d.invocation),
+                    ))));
+                }
+                if !legacy_order(p, owner).is_empty() {
+                    form = form.push(label(
                     "This edit preserves the ordered path as explicit links in the same undo step.",
                 ));
-            }
-            if matches!(
-                d.tool,
-                Tool::Work | Tool::Exchange | Tool::Reuse | Tool::Branch
-            ) {
-                let choices = targets(p, owner, d.tool)
-                    .into_iter()
-                    .filter(|c| compatible_source(p, d, c.id))
-                    .collect();
-                if d.tool == Tool::Branch {
-                    form = form.push(label("First path work"));
                 }
-                form = form.push(picker(
-                    choices,
-                    d,
-                    0,
-                    d.target,
+                if matches!(
+                    d.tool,
+                    Tool::Work | Tool::Exchange | Tool::Reuse | Tool::Branch
+                ) {
+                    let choices = targets(p, owner, d.tool)
+                        .into_iter()
+                        .filter(|c| compatible_source(p, d, c.id))
+                        .collect();
                     if d.tool == Tool::Branch {
-                        "Choose first path work…"
+                        form = form.push(label("First path work"));
+                    }
+                    form = form.push(picker(
+                        choices,
+                        d,
+                        0,
+                        d.target,
+                        if d.tool == Tool::Branch {
+                            "Choose first path work…"
+                        } else {
+                            "Choose existing source…"
+                        },
+                        Event::Target,
+                    ));
+                }
+                if d.tool != Tool::Connect {
+                    form = form.push(
+                        text_input("Contribution name (defaults to source)", &d.name)
+                            .on_input(|v| event(Event::Name(v)))
+                            .padding(8)
+                            .size(12),
+                    );
+                }
+                if matches!(d.tool, Tool::Control | Tool::Branch) {
+                    let kinds = if d.tool == Tool::Branch {
+                        vec![ControlKind::Choice, ControlKind::Fork]
                     } else {
-                        "Choose existing source…"
-                    },
-                    Event::Target,
-                ));
-            }
-            if d.tool != Tool::Connect {
-                form = form.push(
-                    text_input("Contribution name (defaults to source)", &d.name)
-                        .on_input(|v| event(Event::Name(v)))
+                        vec![
+                            ControlKind::Choice,
+                            ControlKind::Merge,
+                            ControlKind::Fork,
+                            ControlKind::Join,
+                            ControlKind::Loop,
+                        ]
+                    };
+                    form = form.push(
+                        pick_list(
+                            kinds.into_iter().map(ControlChoice).collect::<Vec<_>>(),
+                            Some(ControlChoice(d.control)),
+                            |v| event(Event::Control(v)),
+                        )
+                        .padding(8)
+                        .text_size(12),
+                    );
+                }
+                if d.tool == Tool::Branch {
+                    form = form.push(label("Second path work")).push(picker(
+                        targets(p, owner, Tool::Work),
+                        d,
+                        1,
+                        d.alternate,
+                        "Second path work…",
+                        Event::Alternate,
+                    ));
+                    if d.control != ControlKind::Fork {
+                        form = form
+                            .push(label("First path guard"))
+                            .push(
+                                text_input("First path guard", &d.guard)
+                                    .on_input(|v| event(Event::Guard(v)))
+                                    .padding(8),
+                            )
+                            .push(label("Second path guard"))
+                            .push(
+                                text_input("Second path guard (e.g. else)", &d.alternate_guard)
+                                    .on_input(|v| event(Event::AlternateGuard(v)))
+                                    .padding(8),
+                            );
+                    }
+                }
+                if d.fixed {
+                    if let (Some(a), Some(b)) = (d.before, d.after) {
+                        form = form.push(label(format!("{} → {}", p.named(a), p.named(b))));
+                    }
+                } else {
+                    form = form
+                        .push(label("Preceding contribution"))
+                        .push(picker(
+                            contributions(p, owner),
+                            d,
+                            2,
+                            d.before,
+                            "After contribution…",
+                            Event::Before,
+                        ))
+                        .push(button("Clear preceding").on_press(event(Event::ClearBefore)))
+                        .push(label("Following contribution"))
+                        .push(picker(
+                            contributions(p, owner),
+                            d,
+                            3,
+                            d.after,
+                            "Before contribution…",
+                            Event::After,
+                        ))
+                        .push(button("Clear following").on_press(event(Event::ClearAfter)));
+                }
+                if d.tool != Tool::Branch
+                    && d.insertion.link.is_none()
+                    && (d.before.is_some() || d.tool == Tool::Connect)
+                {
+                    form = form.push(
+                        text_input(
+                            "Path condition (empty remains a Choice / Loop warning)",
+                            &d.guard,
+                        )
+                        .on_input(|v| event(Event::Guard(v)))
                         .padding(8)
                         .size(12),
-                );
+                    );
+                }
             }
-            if matches!(d.tool, Tool::Control | Tool::Branch) {
-                let kinds = if d.tool == Tool::Branch {
-                    vec![ControlKind::Choice, ControlKind::Fork]
+            let valid = match d.command(p) {
+                Ok(_) => true,
+                Err(problem) => {
+                    form = form.push(label(problem));
+                    false
+                }
+            };
+            let actions = row![
+                button(if d.contextual.is_some() {
+                    "Apply link"
                 } else {
-                    vec![
-                        ControlKind::Choice,
-                        ControlKind::Merge,
-                        ControlKind::Fork,
-                        ControlKind::Join,
-                        ControlKind::Loop,
-                    ]
-                };
-                form = form.push(
-                    pick_list(
-                        kinds.into_iter().map(ControlChoice).collect::<Vec<_>>(),
-                        Some(ControlChoice(d.control)),
-                        |v| event(Event::Control(v)),
-                    )
-                    .padding(8)
-                    .text_size(12),
-                );
-            }
-            if d.tool == Tool::Branch {
-                form = form.push(label("Second path work")).push(picker(
-                    targets(p, owner, Tool::Work),
-                    d,
-                    1,
-                    d.alternate,
-                    "Second path work…",
-                    Event::Alternate,
-                ));
-                if d.control != ControlKind::Fork {
-                    form = form
-                        .push(label("First path guard"))
-                        .push(
-                            text_input("First path guard", &d.guard)
-                                .on_input(|v| event(Event::Guard(v)))
-                                .padding(8),
-                        )
-                        .push(label("Second path guard"))
-                        .push(
-                            text_input("Second path guard (e.g. else)", &d.alternate_guard)
-                                .on_input(|v| event(Event::AlternateGuard(v)))
-                                .padding(8),
-                        );
-                }
-            }
-            if d.fixed {
-                if let (Some(a), Some(b)) = (d.before, d.after) {
-                    form = form.push(label(format!("{} → {}", p.named(a), p.named(b))));
-                }
-            } else {
-                form = form
-                    .push(label("Preceding contribution"))
-                    .push(picker(
-                        contributions(p, owner),
-                        d,
-                        2,
-                        d.before,
-                        "After contribution…",
-                        Event::Before,
-                    ))
-                    .push(button("Clear preceding").on_press(event(Event::ClearBefore)))
-                    .push(label("Following contribution"))
-                    .push(picker(
-                        contributions(p, owner),
-                        d,
-                        3,
-                        d.after,
-                        "Before contribution…",
-                        Event::After,
-                    ))
-                    .push(button("Clear following").on_press(event(Event::ClearAfter)));
-            }
-            if d.tool != Tool::Branch
-                && d.insertion.link.is_none()
-                && (d.before.is_some() || d.tool == Tool::Connect)
-            {
-                form = form.push(
-                    text_input(
-                        "Path condition (empty remains a Choice / Loop warning)",
-                        &d.guard,
-                    )
-                    .on_input(|v| event(Event::Guard(v)))
-                    .padding(8)
-                    .size(12),
-                );
-            }
+                    "Create"
+                })
+                .on_press_maybe(valid.then(|| event(Event::Submit))),
+                button("Cancel").on_press(event(Event::Cancel))
+            ]
+            .spacing(7);
+            form_panel = editor_panel(d.invocation, actions.into(), form.into());
         }
-        let valid = match d.command(p) {
-            Ok(_) => true,
-            Err(problem) => {
-                form = form.push(label(problem));
-                false
-            }
-        };
-        let actions = row![
-            button(if d.contextual.is_some() {
-                "Apply link"
-            } else {
-                "Create"
-            })
-            .on_press_maybe(valid.then(|| event(Event::Submit))),
-            button("Cancel").on_press(event(Event::Cancel))
-        ]
-        .spacing(7);
-        form_panel = editor_panel(actions.into(), form.into());
     }
-    panes(diagram, form_panel, pending)
-}
-
-/// A permanent three-slot tree: variable controls never remount the canvas.
-/// The shelf scrolls independently; the canvas receives actual remaining height.
-fn explicit_pane<'a, R: iced::advanced::text::Renderer + 'a>(
-    header: iced::Element<'a, Message, iced::Theme, R>,
-    details: iced::Element<'a, Message, iced::Theme, R>,
-    canvas: iced::Element<'a, Message, iced::Theme, R>,
-    show_details: bool,
-    pending: bool,
-) -> iced::Element<'a, Message, iced::Theme, R> {
-    // Column::push drops Fixed(0) children. from_vec retains the closed shelf
-    // slot so its disclosure cannot move/remount the following canvas tree.
-    Column::from_vec(vec![
-        container(header).width(Fill).into(),
-        scrollable(details)
-            .id("process-details")
-            .width(Fill)
-            .height(if show_details {
-                if pending { 64. } else { 112. }
-            } else {
-                0.
-            })
-            .into(),
-        container(canvas).width(Fill).height(Fill).into(),
-    ])
-    .spacing(6)
-    .padding(8)
-    .width(Fill)
-    .height(Fill)
-    .into()
-}
-
-/// Keep the diagram mounted while an independent editor uses the remaining
-/// workspace height. The editor must never be clipped by the page scrollable.
-fn panes<'a, R: iced::advanced::Renderer + 'a>(
-    diagram: iced::Element<'a, Message, iced::Theme, R>,
-    form: iced::Element<'a, Message, iced::Theme, R>,
-    pending: bool,
-) -> iced::Element<'a, Message, iced::Theme, R> {
-    column![
-        container(diagram).width(Fill).height(if pending {
-            iced::Length::FillPortion(1)
-        } else {
-            Fill
-        }),
-        container(form).width(Fill).height(if pending {
-            iced::Length::FillPortion(1)
-        } else {
-            iced::Length::Shrink
-        }),
-    ]
-    .width(Fill)
-    .height(Fill)
-    .into()
+    let editor = if pending {
+        Some(form_panel)
+    } else {
+        state.shelf.map(|_| details)
+    };
+    super::super::canvas_workspace::host(header.into(), palette, canvas, editor)
 }
 
 fn editor_panel<'a, R: iced::advanced::text::Renderer + 'a>(
+    session: Id,
     actions: iced::Element<'a, Message, iced::Theme, R>,
     fields: iced::Element<'a, Message, iced::Theme, R>,
 ) -> iced::Element<'a, Message, iced::Theme, R> {
     container(
-        container(column![actions, scrollable(fields).id("process-form").height(Fill)].spacing(8))
-            .width(Fill)
-            .height(Fill)
-            .padding(12)
-            .style(style::card),
+        container(
+            column![
+                container(actions).id("process-actions"),
+                super::super::form_session::reset_on_change(
+                    session,
+                    scrollable(fields).id("process-form").height(Fill)
+                )
+            ]
+            .spacing(8),
+        )
+        .width(Fill)
+        .height(Fill)
+        .padding(12)
+        .style(style::card),
     )
     .width(Fill)
     .height(Fill)

crates/oa-desktop/src/diagram.rs

@@ -41,6 +41,8 @@ pub struct DiagramCanvas<'a> {
     pub view_index: Option<&'a oa_core::view_options::ViewIndex>,
     pub diagram: Id,
     pub selected: Id,
+    /// Presentation-only navigation marker; never used by hit tests or edits.
+    pub navigation_focus: Option<Rectangle>,
     pub zoom: f32,
     pub pan: Vector,
     pub context: Context,
@@ -1193,6 +1195,14 @@ impl canvas::Program<Message> for DiagramCanvas<'_> {
                 f.fill(&Path::circle(center, 1.5), color);
             }
         }
+        if let Some(bounds) = self.navigation_focus {
+            f.stroke(
+                &Path::rectangle(bounds.position(), bounds.size()),
+                Stroke::default()
+                    .with_color(style::TEAL)
+                    .with_width(2.5 / self.zoom),
+            );
+        }
         if let Some(edge) = scene.routed.edges.get(&self.selected)
             && !edge.custom_suspended
         {
@@ -1584,11 +1594,32 @@ fn hex(c: Color) -> String {
         (c.b * 255.) as u8
     )
 }
-pub fn export_svg(p: &Project, diagram: Id) -> String {
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ExportError {
+    MissingDiagram(Id),
+    UnsupportedScenario(Id),
+}
+impl std::fmt::Display for ExportError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::MissingDiagram(id) => write!(f, "Cannot export: diagram {id} no longer exists."),
+            Self::UnsupportedScenario(_) => {
+                f.write_str("SVG export of saved Scenario views is not available yet.")
+            }
+        }
+    }
+}
+impl std::error::Error for ExportError {}
+
+pub fn export_svg(p: &Project, diagram: Id) -> Result<String, ExportError> {
+    let d = p
+        .diagrams
+        .get(&diagram)
+        .ok_or(ExportError::MissingDiagram(diagram))?;
+    if d.projection.scenario().is_some() {
+        return Err(ExportError::UnsupportedScenario(diagram));
+    }
     let view = project_view(p, diagram);
-    let Some(d) = p.diagrams.get(&diagram) else {
-        return String::new();
-    };
     let routed = route_diagram(p, d, &view);
     let left = routed.bounds.position.x - 30.;
     let top = routed.bounds.position.y - 30.;
@@ -1727,7 +1758,7 @@ pub fn export_svg(p: &Project, diagram: Id) -> String {
         svg.push_str("</g>");
     }
     svg.push_str("</svg>");
-    svg
+    Ok(svg)
 }
 
 #[cfg(test)]
@@ -1737,6 +1768,83 @@ mod pointer_tests;
 #[cfg(test)]
 mod tests {
     use super::*;
+
+    #[test]
+    fn svg_rejects_saved_scenario_with_absent_or_authored_layout_without_mutation() {
+        let f = crate::behavior::scenario::direct_tests::fixture();
+        let mut p = f.project;
+        let diagram = p.ensure_diagram(Layer::Oa);
+        let d = p.diagrams.get_mut(&diagram).unwrap();
+        d.projection = ProjectionKind::Scenario { scenario: f.owner };
+        d.nodes.clear();
+        d.routes.clear();
+        for layout in [
+            None,
+            Some(DiagramLayout::Scenario(ScenarioLayout {
+                lanes: vec![ScenarioLanePosition {
+                    lifeline: f.sender,
+                    x: 240.,
+                }],
+                messages: vec![ScenarioMessagePosition {
+                    address: OccurrenceEndpoint {
+                        references: vec![],
+                        occurrence: f.call,
+                    },
+                    send_y: 180.,
+                }],
+            })),
+        ] {
+            p.diagrams.get_mut(&diagram).unwrap().layout = layout;
+            let admitted = execute_batch(&p, &[]).expect("valid saved Scenario fixture");
+            assert_eq!(admitted, p);
+            let before = p.clone();
+            assert_eq!(
+                export_svg(&p, diagram),
+                Err(ExportError::UnsupportedScenario(diagram))
+            );
+            assert_eq!(p, before);
+        }
+    }
+
+    #[test]
+    fn svg_rejects_missing_diagram_without_mutation() {
+        let p = Project::demo();
+        let missing = Id::new_v4();
+        let before = p.clone();
+        assert_eq!(
+            export_svg(&p, missing),
+            Err(ExportError::MissingDiagram(missing))
+        );
+        assert_eq!(p, before);
+    }
+
+    #[test]
+    fn svg_accepts_populated_and_empty_architecture_views() {
+        let mut p = Project::demo();
+        let diagram = p
+            .diagrams
+            .values()
+            .find(|d| d.projection.is_architecture() && !d.nodes.is_empty())
+            .unwrap()
+            .id;
+        let before = p.clone();
+        let svg = export_svg(&p, diagram).expect("populated architecture");
+        assert!(svg.starts_with("<svg "));
+        assert!(svg.contains("<text "));
+        assert!(svg.ends_with("</svg>"));
+        assert_eq!(p, before);
+        let d = p.diagrams.get_mut(&diagram).unwrap();
+        d.projection = ProjectionKind::Overview;
+        d.nodes.clear();
+        d.routes.clear();
+        assert_eq!(execute_batch(&p, &[]).expect("valid empty architecture"), p);
+        let before = p.clone();
+        let svg = export_svg(&p, diagram).expect("empty architecture is supported");
+        assert!(svg.contains("viewBox=\"-30 -30 60 60\""));
+        assert!(svg.ends_with("</svg>"));
+        assert_eq!(p, before);
+    }
+
     #[test]
     fn typed_function_glyphs_and_unoriented_standard_connections_have_distinct_svg() {
         let p = Project::demo();
@@ -1770,7 +1878,7 @@ mod tests {
             .find(|d| d.layer == Layer::Sa && d.projection == ProjectionKind::Allocation)
             .unwrap()
             .id;
-        let svg = export_svg(&p, diagram);
+        let svg = export_svg(&p, diagram).expect("supported diagram");
         let title = format!("<title>{}</title>", escape(&boundary.name));
         let edge_path = svg
             .split(&title)
@@ -1844,7 +1952,7 @@ mod tests {
                 p.place(diagram, id, Position { x: 60., y: 60. });
             }
             let p = execute_batch(&p, &[Command::Layout(diagram)]).unwrap();
-            let svg = export_svg(&p, diagram);
+            let svg = export_svg(&p, diagram).expect("supported diagram");
             let group = svg
                 .split("<g>")
                 .find(|g| g.contains(">Grouped work</text>"))
@@ -1902,6 +2010,7 @@ mod tests {
             connection: None,
             diagram,
             selected: p.id,
+            navigation_focus: None,
             zoom: 1.,
             pan: Vector::ZERO,
         };
@@ -1933,7 +2042,7 @@ mod tests {
             .unwrap()
             .id;
         let view = project_view(&p, diagram);
-        let svg = export_svg(&p, diagram);
+        let svg = export_svg(&p, diagram).expect("supported diagram");
         for edge in &view.edges {
             assert!(svg.contains(&format!(">{}</text>", escape(&short(p.named(edge.id), 32)))));
         }
@@ -1948,7 +2057,7 @@ mod tests {
         p.place(d, a, Position { x: 0., y: 0. });
         p.place(d, b, Position { x: 400., y: 0. });
         p.relate(RelationKind::CapabilityInclude, "Uses", a, b);
-        let svg = export_svg(&p, d);
+        let svg = export_svg(&p, d).expect("supported diagram");
         assert!(svg.contains("«include»</text>"));
         assert!(svg.contains("stroke-dasharray=\"6 4\""));
     }
@@ -1976,6 +2085,7 @@ mod tests {
             connection: None,
             diagram,
             selected: p.id,
+            navigation_focus: None,
             zoom: 0.6,
             pan: Vector::new(10., 20.),
         };
@@ -2034,7 +2144,7 @@ mod tests {
             .unwrap();
         assert_eq!(moved.position.x, port.position.x + 100.);
         assert_eq!(moved.position.y, port.position.y + 70.);
-        let svg = export_svg(&p, diagram);
+        let svg = export_svg(&p, diagram).expect("supported diagram");
         for port in &view.ports {
             assert!(svg.contains(&format!("<title>{}</title>", escape(p.named(port.element)))));
         }
@@ -2092,6 +2202,7 @@ mod tests {
                 diagram,
                 context,
                 selected: p.id,
+                navigation_focus: None,
                 selected_bend: None,
                 zoom,
                 pan: Vector::new(20., 30.),
@@ -2259,6 +2370,7 @@ mod tests {
                 view_index: None,
                 diagram,
                 selected: edge,
+                navigation_focus: None,
                 zoom,
                 pan: Vector::new(150., 300.),
                 context: Context {
@@ -2334,6 +2446,7 @@ mod tests {
             view_index: None,
             diagram,
             selected: edge,
+            navigation_focus: None,
             zoom: 0.5,
             pan: Vector::new(150., 300.),
             context: Context {
@@ -2430,6 +2543,7 @@ mod tests {
             view_index: None,
             diagram,
             selected: edge,
+            navigation_focus: None,
             zoom: 1.,
             pan: Vector::new(150., 300.),
             context: Context {
@@ -2487,7 +2601,7 @@ mod tests {
         });
         let view = project_view(&p, diagram);
         let geometry = route_diagram(&p, &p.diagrams[&diagram], &view);
-        let svg = export_svg(&p, diagram);
+        let svg = export_svg(&p, diagram).expect("supported diagram");
         let route = &geometry.edges[&edge];
         let path = route
             .points
@@ -2547,7 +2661,7 @@ mod tests {
             let routed = route_diagram(&p, &p.diagrams[&diagram], &projected);
             let ends = routing::association_end_geometry(&p.relations[&edge], &routed.edges[&edge]);
             assert_eq!(ends.len(), 2);
-            let svg = export_svg(&p, diagram);
+            let svg = export_svg(&p, diagram).expect("supported diagram");
             assert!(svg.contains("parent [0..1]</text>"));
             assert!(svg.contains("children [0..*]</text>"));
             assert!(!svg.contains("data-navigation=\"source\""));
@@ -2557,6 +2671,7 @@ mod tests {
                 view_index: None,
                 diagram,
                 selected: edge,
+                navigation_focus: None,
                 zoom: 0.7,
                 pan: Vector::new(350., 350.),
                 context: Context {
@@ -2610,6 +2725,7 @@ mod tests {
             view_index: None,
             diagram,
             selected: p.id,
+            navigation_focus: None,
             zoom: 1.,
             pan: Vector::new(100., 400.),
             context: Context {
@@ -2683,6 +2799,7 @@ mod tests {
             view_index: None,
             diagram,
             selected: edge,
+            navigation_focus: None,
             zoom: 1.,
             pan: Vector::new(100., 400.),
             context: Context {
@@ -2715,6 +2832,7 @@ mod tests {
             view_index: None,
             diagram,
             selected,
+            navigation_focus: None,
             zoom: 1.,
             pan: Vector::ZERO,
             context: Context {

crates/oa-desktop/src/diagram/lifecycle_tests.rs

@@ -57,6 +57,7 @@ fn canvas(app: &App) -> DiagramCanvas<'_> {
         view_index: None,
         diagram: app.active_diagram.unwrap(),
         selected: app.selected,
+        navigation_focus: None,
         zoom: 1.,
         pan: app.pan,
         context: app.route_context().unwrap(),

crates/oa-desktop/src/diagram/pointer_tests.rs

@@ -65,6 +65,7 @@ fn canvas(app: &App, zoom: f32) -> DiagramCanvas<'_> {
         view_index: None,
         diagram: app.active_diagram.unwrap(),
         selected: app.selected,
+        navigation_focus: None,
         zoom,
         pan: app.pan,
         context: app.route_context().unwrap(),

crates/oa-desktop/src/diagram/port_hit_tests.rs

@@ -6,6 +6,7 @@ fn canvas(project: &Project, diagram: Id, zoom: f32) -> DiagramCanvas<'_> {
         view_index: None,
         diagram,
         selected: Id::nil(),
+        navigation_focus: None,
         zoom,
         pan: Vector::new(17., 23.),
         context: Context {

crates/oa-desktop/src/diagram/port_labels.rs

@@ -178,6 +178,7 @@ mod tests {
             view_index: None,
             diagram: app.active_diagram.unwrap(),
             selected: app.selected,
+            navigation_focus: None,
             zoom: 1.,
             pan: Vector::ZERO,
             context: app.route_context().unwrap(),

crates/oa-desktop/src/diagram/view_options_tests.rs

@@ -27,7 +27,7 @@ fn communication_svg_uses_saved_visibility_labels_and_direction() {
     validate_candidate(&p).unwrap();
     let initial = p.clone();
     let path_key = format!("<path data-edge=\"{edge}\"");
-    let svg = export_svg(&p, diagram);
+    let svg = export_svg(&p, diagram).expect("supported diagram");
     let edge_path = svg
         .split(&path_key)
         .nth(1)
@@ -46,7 +46,7 @@ fn communication_svg_uses_saved_visibility_labels_and_direction() {
         .unwrap()
         .view_options
         .exchange_labels = ExchangeLabels::Items;
-    let items_svg = export_svg(&p, diagram);
+    let items_svg = export_svg(&p, diagram).expect("supported diagram");
     assert!(items_svg.contains("Data &amp; status"));
     let RelationBody::CommunicationMean { oriented, .. } =
         &mut p.relations.get_mut(&edge).unwrap().body
@@ -54,7 +54,7 @@ fn communication_svg_uses_saved_visibility_labels_and_direction() {
         unreachable!()
     };
     *oriented = true;
-    let svg = export_svg(&p, diagram);
+    let svg = export_svg(&p, diagram).expect("supported diagram");
     assert!(
         svg.split(&path_key)
             .nth(1)
@@ -71,7 +71,11 @@ fn communication_svg_uses_saved_visibility_labels_and_direction() {
         .view_options
         .hidden_edges
         .push(edge);
-    assert!(!export_svg(&p, diagram).contains(&path_key));
+    assert!(
+        !export_svg(&p, diagram)
+            .expect("supported diagram")
+            .contains(&path_key)
+    );
     p.diagrams
         .get_mut(&diagram)
         .unwrap()
@@ -83,7 +87,11 @@ fn communication_svg_uses_saved_visibility_labels_and_direction() {
         .unwrap()
         .view_options
         .relation_kinds = RelationKinds::Only(vec![]);
-    assert!(!export_svg(&p, diagram).contains(&path_key));
+    assert!(
+        !export_svg(&p, diagram)
+            .expect("supported diagram")
+            .contains(&path_key)
+    );
     assert_eq!(p.diagrams[&diagram].nodes, placements);
     assert_eq!(language::parse(&language::format(&p)).unwrap(), p);
 }

crates/oa-desktop/src/diagram_usage.rs

@@ -0,0 +1,472 @@
+//! Read-only identities for objects actually represented by a diagram renderer.
+use iced::Rectangle;
+use oa_core::{Id, OccurrenceEndpoint, Project, projection, routing, view_options::ViewIndex};
+pub(crate) mod view;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct Context {
+    pub document: Id,
+    pub revision: u64,
+    pub subject: Id,
+}
+
+#[derive(Debug, Clone)]
+pub(crate) enum Event {
+    Open(Context),
+    Close(Id),
+    Search(Id, String),
+    Page(Id, usize),
+    Destination(Id, Option<Surface>),
+    Choose(Id, Usage),
+    Move(Id, i8),
+    Activate(Id),
+}
+
+/// One completed immutable accepted-model lookup. The token owns one worker slot.
+#[derive(Debug, Clone)]
+pub(crate) struct Completion {
+    pub token: Id,
+    pub context: Context,
+    pub result: Result<Vec<Usage>, String>,
+}
+
+pub(crate) struct Panel {
+    pub token: Id,
+    pub context: Context,
+    pub usages: Vec<Usage>,
+    pub loading: bool,
+    pub search: String,
+    pub page: usize,
+    pub cursor: usize,
+    pub destination: Option<Surface>,
+    pub notice: Option<String>,
+}
+
+impl Panel {
+    pub fn new(context: Context, usages: Vec<Usage>) -> Self {
+        Self {
+            token: Id::new_v4(),
+            context,
+            usages,
+            loading: false,
+            search: String::new(),
+            page: 0,
+            cursor: 0,
+            destination: None,
+            notice: None,
+        }
+    }
+
+    pub fn matches<'a>(&'a self, p: &Project) -> Vec<&'a Usage> {
+        let query = self.search.to_lowercase();
+        if query.is_empty() {
+            return self.usages.iter().collect();
+        }
+        self.usages
+            .iter()
+            .filter(|usage| {
+                let surface = usage.surface;
+                let searchable = format!(
+                    "{} {} {} {} {}",
+                    surface.category(p),
+                    p.named(surface.id()),
+                    alias(p, surface.id()),
+                    target_name(p, usage),
+                    usage.role
+                );
+                searchable.to_lowercase().contains(&query)
+            })
+            .collect()
+    }
+
+    pub fn choices(&self, p: &Project) -> Vec<Event> {
+        if self.loading {
+            return Vec::new();
+        }
+        let matches = self.matches(p);
+        if let Some(surface) = self.destination {
+            matches
+                .into_iter()
+                .filter(|u| u.surface == surface)
+                .map(|u| Event::Choose(self.token, u.clone()))
+                .collect()
+        } else {
+            let mut seen = std::collections::BTreeSet::new();
+            matches
+                .into_iter()
+                .filter(|u| seen.insert(u.surface))
+                .map(|u| Event::Destination(self.token, Some(u.surface)))
+                .collect()
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+pub(crate) enum Surface {
+    Saved(Id),
+    Process(Id),
+    Scenario(Id),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum Target {
+    Whole,
+    Placement(Id),
+    Port {
+        port: Id,
+        placement: Id,
+    },
+    Edge(Id),
+    StateRow {
+        placement: Id,
+        relation: Id,
+    },
+    AllocationGrouping {
+        relation: Id,
+        work_placement: Id,
+        performer_placement: Id,
+    },
+    ProcessOccurrence(OccurrenceEndpoint),
+    ProcessLink(Id),
+    ProcessPreviewLink {
+        relation: Id,
+        source: OccurrenceEndpoint,
+        target: OccurrenceEndpoint,
+    },
+    ScenarioObject(Id),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) struct Usage {
+    pub subject: Id,
+    pub surface: Surface,
+    pub target: Target,
+    /// Concise, truthful explanation, e.g. "action occurrence" or "entry action".
+    pub role: String,
+    /// Actual current renderer coordinates. Recompute before activation.
+    pub bounds: Rectangle,
+}
+
+/// A navigation highlight is presentation state, never an edit/Delete target.
+pub(crate) struct Focus {
+    pub context: Context,
+    pub usage: Usage,
+    pub selected: Id,
+}
+
+impl Surface {
+    pub fn id(self) -> Id {
+        match self {
+            Self::Saved(id) | Self::Process(id) | Self::Scenario(id) => id,
+        }
+    }
+
+    pub fn category(self, p: &Project) -> &'static str {
+        match self {
+            Self::Saved(id)
+                if p.diagrams
+                    .get(&id)
+                    .is_some_and(|d| d.projection.state_machine().is_some()) =>
+            {
+                "State views"
+            }
+            Self::Saved(_) => "Architecture",
+            Self::Process(_) => "Processes and chains",
+            Self::Scenario(_) => "Scenarios",
+        }
+    }
+}
+
+pub(crate) fn collect(
+    p: &Project,
+    subject: Id,
+    process: &crate::behavior::topology::State,
+    scenario: &crate::behavior::scenario::State,
+) -> Vec<Usage> {
+    let mut usages = saved_usages(p, subject);
+    for element in p.elements.values() {
+        match element.kind() {
+            oa_core::Kind::Process | oa_core::Kind::FunctionalChain => {
+                usages.extend(process.diagram_usages(p, element.id, subject));
+            }
+            oa_core::Kind::Scenario => {
+                usages.extend(scenario.diagram_usages(p, element.id, subject));
+            }
+            _ => {}
+        }
+    }
+    usages.sort_by_cached_key(|u| {
+        (
+            u.surface.category(p),
+            p.named(u.surface.id()).to_lowercase(),
+            u.surface,
+            target_name(p, u).to_lowercase(),
+        )
+    });
+    usages
+        .dedup_by(|a, b| a.subject == b.subject && a.surface == b.surface && a.target == b.target);
+    usages
+}
+
+pub(crate) fn alias(p: &Project, id: Id) -> &str {
+    p.elements
+        .get(&id)
+        .map(|e| e.alias.as_str())
+        .or_else(|| p.relations.get(&id).map(|r| r.alias.as_str()))
+        .or_else(|| p.diagrams.get(&id).map(|d| d.alias.as_str()))
+        .or_else(|| p.traces.get(&id).map(|t| t.alias.as_str()))
+        .or_else(|| {
+            p.diagrams
+                .values()
+                .find_map(|d| d.nodes.get(&id).map(|n| n.alias.as_str()))
+        })
+        .unwrap_or("")
+}
+
+pub(crate) fn target_name(p: &Project, usage: &Usage) -> String {
+    let id = match &usage.target {
+        Target::Whole => usage.surface.id(),
+        Target::Placement(id) => p
+            .diagrams
+            .get(&usage.surface.id())
+            .and_then(|d| d.nodes.get(id))
+            .map_or(*id, |n| n.element),
+        Target::Port { port, .. } => *port,
+        Target::Edge(id)
+        | Target::StateRow { relation: id, .. }
+        | Target::AllocationGrouping { relation: id, .. }
+        | Target::ProcessLink(id)
+        | Target::ScenarioObject(id) => *id,
+        Target::ProcessOccurrence(endpoint) => {
+            return endpoint
+                .references
+                .iter()
+                .copied()
+                .chain([endpoint.occurrence])
+                .map(|id| format!("{} (@{})", p.named(id), alias(p, id)))
+                .collect::<Vec<_>>()
+                .join(" / ");
+        }
+        Target::ProcessPreviewLink {
+            relation, source, ..
+        } => {
+            return source
+                .references
+                .iter()
+                .copied()
+                .chain([*relation])
+                .map(|id| format!("{} (@{})", p.named(id), alias(p, id)))
+                .collect::<Vec<_>>()
+                .join(" / ");
+        }
+    };
+    format!("{} (@{})", p.named(id), alias(p, id))
+}
+
+/// Saved view membership is the renderer's final projection, including folds,
+/// projection-kind exclusions and explicit view filters. Stored route metadata
+/// and merely having both relation endpoints placed do not imply visibility.
+pub(crate) fn saved_usages(p: &Project, subject: Id) -> Vec<Usage> {
+    saved_usages_for(p, subject, None)
+}
+
+/// Revalidate only the requested saved surface before activation. The optional
+/// filter is applied before projection and routing, never after a whole lookup.
+pub(crate) fn saved_usages_for(p: &Project, subject: Id, only_diagram: Option<Id>) -> Vec<Usage> {
+    if only_diagram.is_some_and(|id| !p.diagrams.contains_key(&id)) {
+        return Vec::new();
+    }
+    let index = ViewIndex::new(p);
+    let mut usages = Vec::new();
+    for diagram in p
+        .diagrams
+        .values()
+        .filter(|diagram| only_diagram.is_none_or(|id| diagram.id == id))
+    {
+        let view = projection::project_diagram_with_index(p, diagram, &index);
+        let surface = Surface::Saved(diagram.id);
+        if subject == diagram.id || diagram.projection.state_machine() == Some(subject) {
+            usages.push(Usage {
+                subject,
+                surface,
+                target: Target::Whole,
+                role: if subject == diagram.id {
+                    "diagram"
+                } else {
+                    "state machine view"
+                }
+                .into(),
+                bounds: routed_bounds(routing::route_diagram(p, diagram, &view).bounds),
+            });
+        }
+        for node in &view.nodes {
+            if subject == node.element || subject == node.id {
+                usages.push(Usage {
+                    subject,
+                    surface,
+                    target: Target::Placement(node.id),
+                    role: "node".into(),
+                    bounds: Rectangle {
+                        x: node.position.x,
+                        y: node.position.y,
+                        // Reveal the labelled header, not the empty interior of
+                        // a large expanded container at the minimum zoom.
+                        width: node.size.width.min(420.),
+                        height: node.size.height.min(64.),
+                    },
+                });
+            }
+        }
+        for port in &view.ports {
+            if subject == port.element {
+                usages.push(Usage {
+                    subject,
+                    surface,
+                    target: Target::Port {
+                        port: port.element,
+                        placement: port.owner,
+                    },
+                    role: "port".into(),
+                    bounds: Rectangle {
+                        x: port.position.x - 12.,
+                        y: port.position.y - 12.,
+                        width: 24.,
+                        height: 24.,
+                    },
+                });
+            }
+        }
+        // Allocation arrows are suppressed in this projection. A direct
+        // relation is represented only by its actual visible containment chain;
+        // aggregate summaries never manufacture inherited relations.
+        if diagram.projection == oa_core::ProjectionKind::Allocation
+            && let Some(relation) = p.relations.get(&subject)
+            && relation.kind() == oa_core::RelationKind::Allocation
+        {
+            let placements: std::collections::BTreeMap<_, _> =
+                view.nodes.iter().map(|node| (node.id, node)).collect();
+            for work in view.nodes.iter().filter(|n| n.element == relation.target()) {
+                let mut parent = work.visual_parent;
+                let mut seen = std::collections::BTreeSet::new();
+                while let Some(id) = parent.filter(|id| seen.insert(*id)) {
+                    let Some(performer) = placements.get(&id) else {
+                        break;
+                    };
+                    if performer.element == relation.source() {
+                        usages.push(Usage {
+                            subject,
+                            surface,
+                            target: Target::AllocationGrouping {
+                                relation: subject,
+                                work_placement: work.id,
+                                performer_placement: performer.id,
+                            },
+                            role: "allocation grouping".into(),
+                            bounds: Rectangle {
+                                x: work.position.x,
+                                y: work.position.y,
+                                width: work.size.width.min(420.),
+                                height: work.size.height.min(64.),
+                            },
+                        });
+                        break;
+                    }
+                    parent = performer.visual_parent;
+                }
+            }
+        }
+        if view.edges.iter().any(|edge| edge.id == subject)
+            && let Some(edge) = routing::route_diagram(p, diagram, &view)
+                .edges
+                .get(&subject)
+        {
+            usages.push(Usage {
+                subject,
+                surface,
+                target: Target::Edge(subject),
+                role: "relationship".into(),
+                bounds: edge_focus_bounds(edge),
+            });
+        }
+        if diagram.projection.state_machine().is_some() {
+            usages.extend(crate::behavior::state_canvas::diagram_usages(
+                p, diagram, &view, subject,
+            ));
+        }
+    }
+    usages
+}
+
+pub(crate) fn routed_bounds(bounds: routing::RoutingBounds) -> Rectangle {
+    Rectangle {
+        x: bounds.position.x,
+        y: bounds.position.y,
+        width: bounds.size.width,
+        height: bounds.size.height,
+    }
+}
+
+/// Focus a named edge at its label. For an unlabelled line, focus its middle
+/// segment instead of shrinking a long connector to fit the whole diagram.
+pub(crate) fn edge_focus_bounds(edge: &routing::RoutedEdge) -> Rectangle {
+    if !edge.label.text.is_empty() {
+        return routed_bounds(edge.label.bounds);
+    }
+    let point = edge
+        .points
+        .get(edge.points.len() / 2)
+        .copied()
+        .unwrap_or(edge.label.center);
+    Rectangle {
+        x: point.x - 40.,
+        y: point.y - 24.,
+        width: 80.,
+        height: 48.,
+    }
+}
+
+/// Whole-canvas navigation fits its entire extent; an individual target keeps
+/// the readable minimum zoom of `camera` rather than shrinking unrelated space.
+pub(crate) fn camera_for(
+    target: &Target,
+    bounds: Rectangle,
+    viewport: iced::Size,
+) -> (f32, iced::Vector) {
+    if !matches!(target, Target::Whole) {
+        return camera(bounds, viewport);
+    }
+    let available = iced::Size::new(
+        (viewport.width - 64.).max(1.),
+        (viewport.height - 64.).max(1.),
+    );
+    let zoom = (available.width / bounds.width.max(1.))
+        .min(available.height / bounds.height.max(1.))
+        .clamp(0.0001, 1.25);
+    let pan = iced::Vector::new(
+        viewport.width / 2. - bounds.center_x() * zoom,
+        viewport.height / 2. - bounds.center_y() * zoom,
+    );
+    (zoom, pan)
+}
+
+/// Return a readable, centered camera without modifying authored geometry.
+pub(crate) fn camera(bounds: Rectangle, viewport: iced::Size) -> (f32, iced::Vector) {
+    let available = iced::Size::new(
+        (viewport.width - 64.).max(1.),
+        (viewport.height - 64.).max(1.),
+    );
+    let zoom = (available.width / bounds.width.max(1.))
+        .min(available.height / bounds.height.max(1.))
+        .clamp(0.5, 1.25);
+    let pan = iced::Vector::new(
+        viewport.width / 2. - bounds.center_x() * zoom,
+        viewport.height / 2. - bounds.center_y() * zoom,
+    );
+    (zoom, pan)
+}
+
+#[cfg(test)]
+mod tests;
+
+#[cfg(test)]
+mod coverage_tests;

crates/oa-desktop/src/diagram_usage/coverage_tests.rs

@@ -0,0 +1,386 @@
+//! Independent allocation membership oracles. Expected targets and coordinates
+//! come from handwritten fixtures, never from the usage predicate under test.
+use super::{Surface, Target, Usage, saved_usages, saved_usages_for};
+use iced::Rectangle;
+use oa_core::{
+    Id, Kind, Layer, Position, Project, ProjectionKind, RelationKind, Size, projection, validation,
+};
+
+struct AllocationFixture {
+    project: Project,
+    diagram: Id,
+    performer: Id,
+    work: Id,
+    relation: Id,
+    performer_node: Id,
+    work_node: Id,
+}
+
+fn assert_valid(project: &Project) {
+    let errors: Vec<_> = validation::validate(project)
+        .into_iter()
+        .filter(|issue| issue.severity == validation::Severity::Error)
+        .collect();
+    assert!(
+        errors.is_empty(),
+        "fixture must be structurally valid: {errors:?}"
+    );
+}
+
+fn fixture() -> AllocationFixture {
+    let mut project = Project::empty();
+    let performer = project
+        .add_element(Kind::Entity, Layer::Oa, "Rescue team", None)
+        .unwrap();
+    let work = project
+        .add_element(Kind::Activity, Layer::Oa, "Dispatch", None)
+        .unwrap();
+    let relation = project.relate(RelationKind::Allocation, "Performs", performer, work);
+    let diagram = project.ensure_diagram(Layer::Oa);
+    project.diagrams.get_mut(&diagram).unwrap().projection = ProjectionKind::Allocation;
+    let performer_node = project.place(diagram, performer, Position { x: 20., y: 40. });
+    let work_node = project.place(diagram, work, Position { x: 240., y: 320. });
+    project
+        .diagrams
+        .get_mut(&diagram)
+        .unwrap()
+        .nodes
+        .get_mut(&work_node)
+        .unwrap()
+        .size = Size {
+        width: 320.,
+        height: 110.,
+    };
+    assert_valid(&project);
+    AllocationFixture {
+        project,
+        diagram,
+        performer,
+        work,
+        relation,
+        performer_node,
+        work_node,
+    }
+}
+
+fn expected(f: &AllocationFixture) -> Usage {
+    Usage {
+        subject: f.relation,
+        surface: Surface::Saved(f.diagram),
+        target: Target::AllocationGrouping {
+            relation: f.relation,
+            work_placement: f.work_node,
+            performer_placement: f.performer_node,
+        },
+        role: "allocation grouping".into(),
+        bounds: Rectangle {
+            x: 240.,
+            y: 320.,
+            width: 320.,
+            height: 64.,
+        },
+    }
+}
+
+/// Two semantic decomposition levels, both summaries of the one allocated leaf.
+/// No Allocation relation targets either summary.
+fn nest_under_summaries(f: &mut AllocationFixture) -> (Id, Id, Id, Id) {
+    let top = f
+        .project
+        .add_element(Kind::Activity, Layer::Oa, "Respond", None)
+        .unwrap();
+    let middle = f
+        .project
+        .add_element(Kind::Activity, Layer::Oa, "Coordinate", Some(top))
+        .unwrap();
+    f.project.elements.get_mut(&f.work).unwrap().parent = Some(middle);
+    let top_node = f
+        .project
+        .place(f.diagram, top, Position { x: 70., y: 120. });
+    let middle_node = f
+        .project
+        .place(f.diagram, middle, Position { x: 130., y: 210. });
+    assert_valid(&f.project);
+    (top, middle, top_node, middle_node)
+}
+
+#[test]
+fn allocation_grouping_has_exact_relation_placements_and_readable_work_geometry() {
+    let f = fixture();
+    let before = f.project.clone();
+    let view = projection::project_view(&f.project, f.diagram);
+    let work = view
+        .nodes
+        .iter()
+        .find(|node| node.id == f.work_node)
+        .unwrap();
+    assert_eq!(work.visual_parent, Some(f.performer_node));
+    assert_eq!(work.position, Position { x: 240., y: 320. });
+    assert_eq!(
+        work.size,
+        Size {
+            width: 320.,
+            height: 110.
+        }
+    );
+    assert!(!view.edges.iter().any(|edge| edge.id == f.relation));
+
+    assert_eq!(saved_usages(&f.project, f.relation), vec![expected(&f)]);
+    assert_eq!(
+        saved_usages_for(&f.project, f.relation, Some(f.diagram)),
+        vec![expected(&f)]
+    );
+    assert!(saved_usages_for(&f.project, f.relation, Some(Id::new_v4())).is_empty());
+    // The semantic work and its placement remain ordinary node selections.
+    for subject in [f.work, f.work_node] {
+        let usages = saved_usages(&f.project, subject);
+        assert_eq!(usages.len(), 1);
+        assert_eq!(usages[0].target, Target::Placement(f.work_node));
+    }
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn allocation_grouping_walks_two_visible_summary_levels_without_inventing_allocations() {
+    let mut f = fixture();
+    let (top, middle, top_node, middle_node) = nest_under_summaries(&mut f);
+    let before = f.project.clone();
+    let view = projection::project_view(&f.project, f.diagram);
+    for (node_id, parent, summary) in [
+        (f.work_node, Some(middle_node), false),
+        (middle_node, Some(top_node), true),
+        (top_node, Some(f.performer_node), true),
+    ] {
+        let node = view.nodes.iter().find(|node| node.id == node_id).unwrap();
+        assert_eq!(node.visual_parent, parent);
+        assert_eq!(node.allocation_summary, summary);
+    }
+    assert_eq!(f.project.relations.len(), 1);
+    assert_eq!(saved_usages(&f.project, f.relation), vec![expected(&f)]);
+    for (element, node) in [(top, top_node), (middle, middle_node)] {
+        let usages = saved_usages(&f.project, element);
+        assert_eq!(usages.len(), 1);
+        assert_eq!(usages[0].target, Target::Placement(node));
+    }
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn folded_summary_or_performer_does_not_substitute_a_visible_ancestor_for_the_leaf() {
+    let mut f = fixture();
+    let (_, _, top_node, middle_node) = nest_under_summaries(&mut f);
+    for folded in [f.performer_node, top_node, middle_node] {
+        let mut project = f.project.clone();
+        project
+            .diagrams
+            .get_mut(&f.diagram)
+            .unwrap()
+            .nodes
+            .get_mut(&folded)
+            .unwrap()
+            .collapsed = true;
+        assert_valid(&project);
+        let before = project.clone();
+        let view = projection::project_view(&project, f.diagram);
+        assert!(view.nodes.iter().any(|node| node.id == folded));
+        assert!(!view.nodes.iter().any(|node| node.id == f.work_node));
+        assert!(saved_usages(&project, f.relation).is_empty());
+        assert_eq!(project, before);
+    }
+}
+
+#[test]
+fn absent_endpoint_placements_and_hidden_performer_do_not_create_grouping_targets() {
+    let mut f = fixture();
+    let (_, _, top_node, _) = nest_under_summaries(&mut f);
+    for absent in [f.performer_node, f.work_node] {
+        let mut project = f.project.clone();
+        project
+            .diagrams
+            .get_mut(&f.diagram)
+            .unwrap()
+            .nodes
+            .remove(&absent);
+        assert_valid(&project);
+        let before = project.clone();
+        let view = projection::project_view(&project, f.diagram);
+        // The aggregate card remains visible even when the actual leaf or its
+        // actual performer has no placement. It cannot stand in for that end.
+        assert!(
+            view.nodes
+                .iter()
+                .any(|node| node.id == top_node && node.allocation_summary)
+        );
+        assert!(saved_usages(&project, f.relation).is_empty());
+        assert_eq!(project, before);
+    }
+
+    let outer = f
+        .project
+        .add_element(Kind::Entity, Layer::Oa, "Organization", None)
+        .unwrap();
+    f.project.elements.get_mut(&f.performer).unwrap().parent = Some(outer);
+    let outer_node = f
+        .project
+        .place(f.diagram, outer, Position { x: -40., y: -60. });
+    f.project
+        .diagrams
+        .get_mut(&f.diagram)
+        .unwrap()
+        .nodes
+        .get_mut(&outer_node)
+        .unwrap()
+        .collapsed = true;
+    assert_valid(&f.project);
+    let before = f.project.clone();
+    let view = projection::project_view(&f.project, f.diagram);
+    assert!(view.nodes.iter().any(|node| node.id == outer_node));
+    assert!(!view.nodes.iter().any(|node| node.id == f.performer_node));
+    assert!(saved_usages(&f.project, f.relation).is_empty());
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn collapsed_leaf_and_edge_filter_still_leave_the_actual_nesting_visible() {
+    let mut f = fixture();
+    let diagram = f.project.diagrams.get_mut(&f.diagram).unwrap();
+    diagram.nodes.get_mut(&f.work_node).unwrap().collapsed = true;
+    // hidden_edges controls arrows. Allocation is drawn as nesting, which is
+    // still visible; do not mistake the filter for a hidden node/grouping.
+    diagram.view_options.hidden_edges.push(f.relation);
+    assert_valid(&f.project);
+    let before = f.project.clone();
+    let view = projection::project_view(&f.project, f.diagram);
+    let work = view
+        .nodes
+        .iter()
+        .find(|node| node.id == f.work_node)
+        .unwrap();
+    assert!(work.collapsed);
+    assert_eq!(work.visual_parent, Some(f.performer_node));
+    assert_eq!(saved_usages(&f.project, f.relation), vec![expected(&f)]);
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn other_projections_do_not_report_allocation_nesting_when_only_an_arrow_or_nothing_is_drawn() {
+    let mut f = fixture();
+    f.project.diagrams.get_mut(&f.diagram).unwrap().projection = ProjectionKind::Overview;
+    assert_valid(&f.project);
+    let before = f.project.clone();
+    let view = projection::project_view(&f.project, f.diagram);
+    assert!(view.edges.iter().any(|edge| edge.id == f.relation));
+    assert!(view.nodes.iter().all(|node| node.visual_parent.is_none()));
+    let usages = saved_usages(&f.project, f.relation);
+    assert_eq!(usages.len(), 1);
+    assert_eq!(usages[0].subject, f.relation);
+    assert_eq!(usages[0].surface, Surface::Saved(f.diagram));
+    assert_eq!(usages[0].target, Target::Edge(f.relation));
+    assert_eq!(f.project, before);
+
+    f.project.diagrams.get_mut(&f.diagram).unwrap().projection = ProjectionKind::FunctionalDataflow;
+    assert_valid(&f.project);
+    let before = f.project.clone();
+    let view = projection::project_view(&f.project, f.diagram);
+    assert!(view.nodes.iter().any(|node| node.id == f.work_node));
+    assert!(!view.nodes.iter().any(|node| node.id == f.performer_node));
+    assert!(saved_usages(&f.project, f.relation).is_empty());
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn repeated_saved_views_keep_allocation_placement_identity_and_geometry_independent() {
+    let mut f = fixture();
+    // The first diagram is Allocation, so this creates a different Overview.
+    let second = f.project.ensure_diagram(Layer::Oa);
+    assert_ne!(second, f.diagram);
+    f.project.diagrams.get_mut(&second).unwrap().projection = ProjectionKind::Allocation;
+    let second_performer = f
+        .project
+        .place(second, f.performer, Position { x: 900., y: 600. });
+    let second_work = f
+        .project
+        .place(second, f.work, Position { x: 1000., y: 700. });
+    f.project
+        .diagrams
+        .get_mut(&second)
+        .unwrap()
+        .nodes
+        .get_mut(&second_work)
+        .unwrap()
+        .size = Size {
+        width: 520.,
+        height: 130.,
+    };
+    assert_ne!(second_performer, f.performer_node);
+    assert_ne!(second_work, f.work_node);
+    assert_valid(&f.project);
+    let before = f.project.clone();
+    let other = Usage {
+        subject: f.relation,
+        surface: Surface::Saved(second),
+        target: Target::AllocationGrouping {
+            relation: f.relation,
+            work_placement: second_work,
+            performer_placement: second_performer,
+        },
+        role: "allocation grouping".into(),
+        bounds: Rectangle {
+            x: 1000.,
+            y: 700.,
+            width: 420.,
+            height: 64.,
+        },
+    };
+    let usages = saved_usages(&f.project, f.relation);
+    assert_eq!(usages.len(), 2);
+    assert!(usages.contains(&expected(&f)));
+    assert!(usages.contains(&other));
+    assert_eq!(
+        saved_usages_for(&f.project, f.relation, Some(second)),
+        vec![other]
+    );
+    assert_eq!(f.project, before);
+}
+
+#[test]
+fn role_derived_nesting_without_a_direct_allocation_does_not_invent_one() {
+    let mut f = fixture();
+    f.project.relations.remove(&f.relation);
+    let role = f
+        .project
+        .add_element(Kind::Role, Layer::Oa, "Dispatcher", None)
+        .unwrap();
+    let realization = f.project.relate(
+        RelationKind::RoleRealization,
+        "Realizes dispatcher",
+        f.performer,
+        role,
+    );
+    let assignment = f
+        .project
+        .relate(RelationKind::RoleAssignment, "Dispatches", role, f.work);
+    assert_valid(&f.project);
+    let before = f.project.clone();
+    let view = projection::project_view(&f.project, f.diagram);
+    let work = view
+        .nodes
+        .iter()
+        .find(|node| node.id == f.work_node)
+        .unwrap();
+    assert_eq!(work.visual_parent, Some(f.performer_node));
+    assert!(work.allocation_summary);
+    assert!(
+        f.project
+            .relations
+            .values()
+            .all(|relation| relation.kind() != RelationKind::Allocation)
+    );
+    for subject in [f.relation, realization, assignment] {
+        assert!(saved_usages(&f.project, subject).is_empty());
+    }
+    let usages = saved_usages(&f.project, f.work);
+    assert_eq!(usages.len(), 1);
+    assert_eq!(usages[0].target, Target::Placement(f.work_node));
+    assert_eq!(f.project, before);
+}

crates/oa-desktop/src/diagram_usage/tests.rs

@@ -0,0 +1,196 @@
+use super::*;
+use oa_core::{Kind, Layer, Position, RelationKind};
+
+#[test]
+fn saved_membership_respects_filters_and_does_not_change_project() {
+    let mut p = Project::empty();
+    let first = p.add(Kind::Activity, "Same name", 20., 20.);
+    let second = p.add(Kind::Activity, "Same name", 340., 20.);
+    let relation = p.relate(RelationKind::Interaction, "Handoff", first, second);
+    let shown = p.ensure_diagram(Layer::Oa);
+    let mut hidden = p.diagrams[&shown].clone();
+    hidden.id = Id::new_v4();
+    hidden.alias = "filtered_copy".into();
+    hidden.nodes = hidden
+        .nodes
+        .into_values()
+        .map(|mut node| {
+            node.id = Id::new_v4();
+            node.alias = format!("filtered_{}", node.alias);
+            (node.id, node)
+        })
+        .collect();
+    hidden.view_options.hidden_edges.push(relation);
+    let hidden_id = hidden.id;
+    p.diagrams.insert(hidden_id, hidden);
+    let before = p.clone();
+
+    let hits = saved_usages(&p, relation);
+    assert_eq!(hits.len(), 1);
+    assert_eq!(hits[0].surface, Surface::Saved(shown));
+    assert_eq!(hits[0].target, Target::Edge(relation));
+    let hits = saved_usages(&p, first);
+    assert_eq!(hits.len(), 2);
+    assert!(hits.iter().all(|hit| match hit.target {
+        Target::Placement(node) => p.diagrams[&hit.surface.id()].nodes[&node].element == first,
+        _ => false,
+    }));
+    assert_eq!(p, before);
+}
+
+#[test]
+fn folded_child_is_not_a_visible_node_and_placement_identity_stays_exact() {
+    let mut p = Project::empty();
+    let parent = p.add(Kind::Activity, "Container", 20., 20.);
+    let child = p
+        .add_element(Kind::Activity, Layer::Oa, "Nested", Some(parent))
+        .unwrap();
+    let diagram = p.ensure_diagram(Layer::Oa);
+    let child_node = p.place(diagram, child, Position { x: 50., y: 100. });
+    let parent_node = p.diagrams[&diagram]
+        .nodes
+        .values()
+        .find(|n| n.element == parent)
+        .unwrap()
+        .id;
+    let hits = saved_usages(&p, child_node);
+    assert_eq!(hits.len(), 1);
+    assert_eq!(hits[0].target, Target::Placement(child_node));
+    p.diagrams
+        .get_mut(&diagram)
+        .unwrap()
+        .nodes
+        .get_mut(&parent_node)
+        .unwrap()
+        .collapsed = true;
+    let before = p.clone();
+    assert!(saved_usages(&p, child).is_empty());
+    assert!(saved_usages(&p, child_node).is_empty());
+    assert_eq!(saved_usages(&p, parent).len(), 1);
+    assert_eq!(p, before);
+}
+
+#[test]
+fn ports_are_found_at_the_visible_owner_and_unplaced_elements_do_not_match_names() {
+    let mut p = Project::empty();
+    let owner = p.add(Kind::Function, "Compute", 20., 20.);
+    let port = Id::new_v4();
+    let element = oa_core::ports::make_port(
+        &p,
+        port,
+        owner,
+        "Input",
+        oa_core::PortContract::FunctionInput {
+            incoming_items: vec![],
+        },
+    )
+    .unwrap();
+    p = oa_core::execute_batch(&p, &[oa_core::Command::CreateElement(element)]).unwrap();
+    let unrelated = p
+        .add_element(Kind::Function, Layer::Sa, "Compute", None)
+        .unwrap();
+    let hits = saved_usages(&p, port);
+    assert_eq!(hits.len(), 1);
+    let view = projection::project_view(&p, hits[0].surface.id());
+    let painted = view
+        .ports
+        .iter()
+        .find(|shown| shown.element == port)
+        .unwrap();
+    assert_eq!(
+        hits[0].target,
+        Target::Port {
+            port,
+            placement: painted.owner
+        }
+    );
+    assert_eq!(
+        hits[0].bounds.center(),
+        iced::Point::new(painted.position.x, painted.position.y)
+    );
+    assert!(saved_usages(&p, unrelated).is_empty());
+    assert!(saved_usages(&p, Id::new_v4()).is_empty());
+}
+
+#[test]
+fn reveal_camera_centers_target_without_whole_view_shrink() {
+    let bounds = Rectangle {
+        x: 100_000.,
+        y: -50_000.,
+        width: 224.,
+        height: 94.,
+    };
+    let viewport = iced::Size::new(700., 500.);
+    let (zoom, pan) = camera(bounds, viewport);
+    assert_eq!(zoom, 1.25);
+    assert!((bounds.center_x() * zoom + pan.x - 350.).abs() < 0.01);
+    assert!((bounds.center_y() * zoom + pan.y - 250.).abs() < 0.01);
+}
+
+#[test]
+fn oversized_container_reveal_targets_its_labelled_header() {
+    let mut p = Project::empty();
+    let container = p.add(Kind::Activity, "Large enclosing activity", 40., 70.);
+    let diagram = p.ensure_diagram(Layer::Oa);
+    let node = p
+        .diagrams
+        .get_mut(&diagram)
+        .unwrap()
+        .nodes
+        .values_mut()
+        .next()
+        .unwrap();
+    node.size = oa_core::Size {
+        width: 4000.,
+        height: 4000.,
+    };
+    let before = p.clone();
+    let hits = saved_usages(&p, container);
+    assert_eq!(hits.len(), 1);
+    assert_eq!(hits[0].bounds.x, 40.);
+    assert_eq!(hits[0].bounds.y, 70.);
+    assert!(hits[0].bounds.width <= 420.);
+    assert!(hits[0].bounds.height <= 64.);
+    let (zoom, pan) = camera(hits[0].bounds, iced::Size::new(500., 300.));
+    assert!((hits[0].bounds.center_x() * zoom + pan.x - 250.).abs() < 0.01);
+    assert!(70. * zoom + pan.y >= 0.);
+    assert_eq!(p, before);
+}
+
+#[test]
+fn state_machine_owner_finds_its_view_without_a_machine_placement() {
+    let mut p = Project::empty();
+    let machine = p
+        .add_element(Kind::StateMachine, Layer::Sa, "Monitor", None)
+        .unwrap();
+    let unrelated = p
+        .add_element(Kind::StateMachine, Layer::Sa, "Other", None)
+        .unwrap();
+    let diagram = p.ensure_diagram(Layer::Sa);
+    p.diagrams.get_mut(&diagram).unwrap().projection =
+        oa_core::ProjectionKind::StateMachine { machine };
+    let before = p.clone();
+    let hits = saved_usages(&p, machine);
+    assert_eq!(hits.len(), 1);
+    assert_eq!(hits[0].surface, Surface::Saved(diagram));
+    assert_eq!(hits[0].target, Target::Whole);
+    assert_eq!(hits[0].role, "state machine view");
+    assert!(saved_usages(&p, unrelated).is_empty());
+    assert_eq!(p, before);
+}
+
+#[test]
+fn whole_diagram_camera_fits_large_bounds_instead_of_individual_object_scale() {
+    let bounds = Rectangle {
+        x: 2000.,
+        y: -4000.,
+        width: 100_000.,
+        height: 80_000.,
+    };
+    let (zoom, pan) = camera_for(&Target::Whole, bounds, iced::Size::new(500., 300.));
+    assert!(zoom < 0.01);
+    assert!(bounds.x * zoom + pan.x >= 0.);
+    assert!(bounds.y * zoom + pan.y >= 0.);
+    assert!((bounds.x + bounds.width) * zoom + pan.x <= 500.);
+    assert!((bounds.y + bounds.height) * zoom + pan.y <= 300.);
+}

crates/oa-desktop/src/diagram_usage/view.rs

@@ -0,0 +1,220 @@
+use super::*;
+use crate::{
+    app::{App, Message},
+    style,
+    views::{action, short},
+};
+use iced::{
+    Element, Fill,
+    widget::{self, column, container, row, text, text_input, tooltip},
+};
+use std::collections::BTreeSet;
+
+const PAGE_SIZE: usize = 6;
+
+pub(crate) fn overlay<'a>(app: &'a App, base: Element<'a, Message>) -> Element<'a, Message> {
+    let Some(panel) = &app.diagram_usages else {
+        return base;
+    };
+    let p = app.project();
+    let token = panel.token;
+    let message = |event| Message::DiagramUsage(event);
+    let matched = panel.matches(p);
+    let mut surfaces = Vec::new();
+    let mut seen = BTreeSet::new();
+    for usage in &matched {
+        if seen.insert(usage.surface) {
+            surfaces.push(usage.surface);
+        }
+    }
+    let targets: Vec<_> = matched
+        .iter()
+        .copied()
+        .filter(|usage| Some(usage.surface) == panel.destination)
+        .collect();
+    let count = if panel.destination.is_some() {
+        targets.len()
+    } else {
+        surfaces.len()
+    };
+    let last = count.saturating_sub(1) / PAGE_SIZE;
+    let page = panel.page.min(last);
+    let total_surfaces = panel
+        .usages
+        .iter()
+        .map(|u| u.surface)
+        .collect::<BTreeSet<_>>()
+        .len();
+    let mut content = column![
+        row![
+            text("Show in diagrams").size(22).width(Fill),
+            action("Close", message(Event::Close(token)))
+        ]
+        .spacing(12),
+        tooltip(
+            text(format!(
+                "{}  ·  @{}",
+                short(p.named(panel.context.subject), 48),
+                short(alias(p, panel.context.subject), 48)
+            ))
+            .size(14),
+            container(
+                widget::scrollable(
+                    text(format!(
+                        "{}\n@{}",
+                        p.named(panel.context.subject),
+                        alias(p, panel.context.subject)
+                    ))
+                    .size(13)
+                )
+                .height(220)
+            )
+            .padding(10)
+            .width(620)
+            .style(style::card),
+            tooltip::Position::Bottom
+        ),
+        text(if panel.loading {
+            "Searching rendered objects…".into()
+        } else {
+            format!(
+                "{} diagram destinations · {} representations",
+                total_surfaces,
+                panel.usages.len()
+            )
+        })
+        .size(12)
+        .color(style::MUTED),
+        text_input("Filter diagram, occurrence, or alias", &panel.search)
+            .id(format!("diagram-usage-filter-{}", panel.token))
+            .padding(9)
+            .on_input(move |value| Message::DiagramUsage(Event::Search(token, value)))
+            .on_submit(message(Event::Activate(token))),
+    ]
+    .spacing(10);
+    if let Some(notice) = &panel.notice {
+        content = content.push(text(notice).size(13));
+    }
+    if let Some(surface) = panel.destination {
+        content = content.push(
+            row![
+                action("All diagrams", message(Event::Destination(token, None))),
+                text(short(p.named(surface.id()), 55)).size(15),
+            ]
+            .spacing(10),
+        );
+        for (index, usage) in targets
+            .into_iter()
+            .enumerate()
+            .skip(page * PAGE_SIZE)
+            .take(PAGE_SIZE)
+        {
+            let name = target_name(p, usage);
+            content = content.push(tooltip(
+                action(
+                    &format!("{} · {}", usage.role, short(&name, 70)),
+                    message(Event::Choose(token, usage.clone())),
+                )
+                .width(Fill)
+                .style(if panel.cursor == index {
+                    style::selected
+                } else {
+                    style::nav
+                }),
+                container(text(name).size(13))
+                    .padding(10)
+                    .max_width(680)
+                    .style(style::card),
+                tooltip::Position::Top,
+            ));
+        }
+    } else {
+        for (index, surface) in surfaces
+            .into_iter()
+            .enumerate()
+            .skip(page * PAGE_SIZE)
+            .take(PAGE_SIZE)
+        {
+            let targets = matched.iter().filter(|u| u.surface == surface).count();
+            let name = format!(
+                "{} · {} (@{}) · {} representations",
+                surface.category(p),
+                p.named(surface.id()),
+                alias(p, surface.id()),
+                targets
+            );
+            let layer = p
+                .diagrams
+                .get(&surface.id())
+                .map(|d| d.layer)
+                .or_else(|| p.layer_of(surface.id()))
+                .map(|l| l.to_string())
+                .unwrap_or_default();
+            content = content.push(tooltip(
+                action(
+                    &format!(
+                        "{} · {} · {} · {}",
+                        surface.category(p),
+                        layer,
+                        short(p.named(surface.id()), 34),
+                        targets
+                    ),
+                    message(Event::Destination(token, Some(surface))),
+                )
+                .width(Fill)
+                .style(if panel.cursor == index {
+                    style::selected
+                } else {
+                    style::nav
+                }),
+                container(text(name).size(13))
+                    .padding(10)
+                    .max_width(680)
+                    .style(style::card),
+                tooltip::Position::Top,
+            ));
+        }
+    }
+    if panel.loading {
+        content = content.push(text("Finding diagram representations…").size(13));
+    } else if count == 0 {
+        content = content.push(text(if panel.usages.is_empty() {
+            "No currently rendered representation found. Folded or filtered objects and unexpanded reuse contents are excluded."
+        } else { "No results match this filter." }).size(13));
+    }
+    let mut paging = row![
+        text(format!(
+            "Page {} of {} · {} matches",
+            page + 1,
+            last + 1,
+            count
+        ))
+        .size(12)
+        .width(Fill)
+    ]
+    .spacing(8);
+    if page > 0 {
+        paging = paging.push(action("Previous", message(Event::Page(token, page - 1))));
+    }
+    if page < last {
+        paging = paging.push(action("Next", message(Event::Page(token, page + 1))));
+    }
+    content = content.push(paging).push(text("↑ ↓ choose · Enter opens · Escape closes. Source and saved view settings are preserved.").size(12).color(style::MUTED));
+    widget::stack![
+        base,
+        widget::opaque(
+            container(
+                container(content)
+                    .padding(22)
+                    .width((app.window_size.width - 80.).clamp(620., 820.))
+                    .style(style::card)
+            )
+            .center(Fill)
+            .style(|_| container::Style {
+                background: Some(iced::Color::from_rgba(0.08, 0.12, 0.18, 0.38).into()),
+                ..Default::default()
+            })
+        )
+    ]
+    .into()
+}