Allow Details properties for the exact displayed Saved scenario view

crates/oa-desktop/src/app.rs

@@ -10,13 +10,15 @@ mod hosted;
 mod reference_authoring;
 #[cfg(test)]
 mod review_navigation_tests;
+mod scenario_diagram;
+mod scenario_spacing;
 pub(crate) mod source_rename;
 mod source_symbols;
 #[cfg(test)]
 mod transition_context_tests;
 #[cfg(test)]
 mod view_copy_tests;
-pub(crate) const SAVED_SCENARIO_UNAVAILABLE: &str = "Saved Scenario layout rendering and canvas editing are not available yet. Select the Scenario in Behavior to use its existing semantic preview.";
+pub(crate) const SAVED_SCENARIO_UNAVAILABLE: &str = "This action uses architecture diagram tools and is unavailable for a saved Scenario. Open the view in Behavior; saved positions are preserved.";
 use crate::forms::Draft;
 use crate::{
     behavior,
@@ -530,6 +532,7 @@ pub struct App {
     pub(crate) diagram_navigation_focus: Option<crate::diagram_usage::Focus>,
     source_diagram_job: Option<Id>,
     diagram_lookup_in_flight: Option<Id>,
+    pending_scenario_reveal_visit: Option<Id>,
     pending_diagram_reveal: Option<(
         crate::diagram_usage::Context,
         crate::diagram_usage::Usage,
@@ -651,6 +654,7 @@ impl App {
             source_diagram_job: None,
             diagram_lookup_in_flight: None,
             pending_diagram_reveal: None,
+            pending_scenario_reveal_visit: None,
             model_issues,
             migration: None,
             source_version: 0,
@@ -665,6 +669,7 @@ impl App {
             workflow: None,
         };
         app.route_state_diagram_workspace();
+        app.reconcile_scenario_workspace();
         app.last_workspace_page = app.page;
         app
     }
@@ -775,6 +780,17 @@ impl App {
         self.sync_with_alias_editor(None);
     }
     fn sync_with_alias_editor(&mut self, hint: Option<source_rename::EditorRefresh<'_>>) {
+        // A saved view may be retargeted across layers by one source transaction.
+        // Follow that explicit identity before generic active-view normalization.
+        if let Some(rep @ behavior::scenario_layout::Representation::Saved { diagram }) =
+            self.behavior.scenario.representation()
+            && self.active_diagram == Some(diagram)
+            && let Some(owner) =
+                behavior::scenario_layout::presentation::checked_owner(self.project(), rep)
+        {
+            self.layer = self.project().elements[&owner].layer();
+            self.behavior.active_owner = Some(owner);
+        }
         self.explorer_index = crate::explorer::Index::new(self.project(), self.layer);
         self.model_issues = validate(self.project());
         self.normalize_creation();
@@ -879,6 +895,26 @@ impl App {
                 .map_err(|e| e.to_string())
         }) {
             Ok(id) => {
+                if self.behavior.scenario.representation()
+                    == Some(behavior::scenario_layout::Representation::Saved { diagram: original })
+                    && id != original
+                {
+                    let representation =
+                        behavior::scenario_layout::Representation::Saved { diagram: id };
+                    if let Some(owner) = behavior::scenario_layout::presentation::checked_owner(
+                        self.project(),
+                        representation,
+                    ) {
+                        self.behavior.scenario.enter_representation(
+                            self.canvas_document,
+                            owner,
+                            representation,
+                        );
+                        if self.page != Page::Behavior {
+                            self.behavior.scenario.leave();
+                        }
+                    }
+                }
                 if self.active_diagram == Some(original) {
                     self.active_diagram = Some(id);
                 }
@@ -1083,6 +1119,17 @@ impl App {
             && let Some(owner) = crate::behavior::selected_behavior(self.project(), id)
         {
             self.behavior.active_owner = Some(owner);
+            if self.behavior.scenario.representation().is_some_and(|rep| {
+                behavior::scenario_layout::presentation::checked_owner(self.project(), rep)
+                    != Some(owner)
+            }) && self.project().elements[&owner].kind() == Kind::Scenario
+            {
+                self.enter_scenario_representation(
+                    behavior::scenario_layout::Representation::Derived { owner },
+                );
+            } else if self.project().elements[&owner].kind() != Kind::Scenario {
+                self.behavior.scenario.forget_view();
+            }
         }
         if self.reset_state_view_after_navigation(previous_state_view)
             && self.page == Page::Behavior
@@ -1225,6 +1272,9 @@ impl App {
         ])
     }
     pub fn update(&mut self, message: Message) -> Task<Message> {
+        if let Message::ScenarioCanvas(behavior::scenario::CanvasEvent::Spacing(event)) = &message {
+            return self.scenario_spacing(*event);
+        }
         // Reject stale rename intents before camera/reveal reconciliation or
         // source interaction can disturb a newer navigation destination.
         if let Message::SourceRename(event) = &message
@@ -1232,6 +1282,53 @@ impl App {
         {
             return Task::none();
         }
+        // Prior view visits are inert before they can retire a newer reveal,
+        // camera lifetime or focus operation. Passive events may relax epoch,
+        // but never the destination identity.
+        if let Message::ScenarioCanvas(event) = &message {
+            let captured = event.context();
+            if self.scenario_context().is_none_or(|current| {
+                current.document != captured.document
+                    || current.scenario != captured.scenario
+                    || current.representation != captured.representation
+                    || current.visit != captured.visit
+                    || (!matches!(event, behavior::scenario::CanvasEvent::Restored(..))
+                        && current.revision != captured.revision)
+            }) {
+                return Task::none();
+            }
+            if let behavior::scenario::CanvasEvent::Camera(_, lifetime, _) = event
+                && *lifetime != self.camera_epoch
+            {
+                return Task::none();
+            }
+            // A retained Details button may belong to an earlier selection or
+            // canvas epoch. Refuse it before retiring any newer reveal or draft.
+            if let behavior::scenario::CanvasEvent::Properties(_, id) = event
+                && (self.scenario_context() != Some(captured)
+                    || self.selected != *id
+                    || !self.project().contains(*id)
+                    || !behavior::scenario::properties_target(self.project(), captured, *id)
+                    || self.behavior.has_pending()
+                    || self.draft_dirty()
+                    || self.source_dirty()
+                    || self.source_rename.open()
+                    || !behavior::canvas_workspace::keyboard_enabled(self))
+            {
+                return Task::none();
+            }
+        }
+        if let Message::BehaviorControl(intent) = &message
+            && behavior::canvas_workspace::Scope::current(self).is_none_or(|scope| {
+                scope.document != intent.scope.document
+                    || scope.owner != intent.scope.owner
+                    || scope.scenario_view != intent.scope.scenario_view
+                    || scope.revision != intent.scope.revision
+                    || scope.epoch != intent.scope.epoch
+            })
+        {
+            return Task::none();
+        }
         let usage_viewport = self.diagram_reveal_viewport(&message);
         let window_resized = matches!(&message, Message::WindowResized(_));
         // Reject stale measurements before legacy viewport handlers can change
@@ -1252,6 +1349,7 @@ impl App {
                 | Message::TopologyCanvas(crate::behavior::topology::CanvasEvent::Camera(..))
         );
         let before = self.camera_boundary();
+        let spacing_selected = self.selected;
         let task = self.update_inner(message);
         if window_resized && let Some((_, _, epoch)) = &mut self.pending_diagram_reveal {
             *epoch = self.canvas_epoch;
@@ -1266,6 +1364,13 @@ impl App {
         {
             self.diagram_navigation_focus = None;
         }
+        if (self.camera_boundary() != before
+            || self.selected != spacing_selected
+            || !self.spacing_enabled())
+            && self.behavior.scenario.cancel_spacing()
+        {
+            self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+        }
         if !camera && self.camera_boundary() != before {
             self.camera_epoch = self.camera_epoch.wrapping_add(1);
             self.camera_boundary_epoch = self.canvas_epoch;
@@ -1284,6 +1389,7 @@ impl App {
         let valid_scenario = |c: behavior::scenario::Context| {
             c.document == scope.document
                 && c.scenario == scope.owner
+                && scope.scenario_view == Some((c.representation, c.visit))
                 && c.revision == scope.revision
                 && self.camera_toolbar_epoch(c.epoch)
         };
@@ -1299,6 +1405,9 @@ impl App {
             Message::ScenarioCanvas(Scenario::Camera(c, lifetime, Camera::Focus))
                 if valid_scenario(*c) && *lifetime == scope.epoch =>
             {
+                if self.behavior.scenario.cancel_spacing() {
+                    self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+                }
                 return canvas_workspace::focus_task(scope, Camera::Focus);
             }
             Message::TopologyCanvas(Process::Camera(c, lifetime, Camera::Focus))
@@ -1324,6 +1433,9 @@ impl App {
             _ => return Task::none(),
         }
         let task = self.update(message);
+        if self.behavior.scenario.cancel_spacing() {
+            self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+        }
         // Reapplying Fit or a tool also ends a held gesture. Focus is stamped
         // after the action, for Iced's final-view ordering.
         if self.camera_epoch == scope.epoch {
@@ -1667,6 +1779,7 @@ impl App {
         self.refresh_source_rename_context();
         self.reconcile_reference_chooser();
         self.route_state_diagram_workspace();
+        self.reconcile_scenario_workspace();
         if self.page != Page::Home {
             self.last_workspace_page = self.page;
         }
@@ -1675,11 +1788,6 @@ impl App {
                 .topology
                 .enter(context.document, context.owner);
         }
-        if let Some(context) = self.scenario_context() {
-            self.behavior
-                .scenario
-                .enter(context.document, context.scenario);
-        }
         if self.connection.as_ref().is_some_and(|session| {
             Some(session.context) != self.route_context()
                 || self.page != Page::Diagram
@@ -1723,15 +1831,23 @@ impl App {
         }
     }
     pub(crate) fn scenario_context(&self) -> Option<crate::behavior::scenario::Context> {
-        let scenario = crate::behavior::selected_owner(self)?;
-        (self.page == Page::Behavior
-            && self.project().elements.get(&scenario)?.kind() == Kind::Scenario)
-            .then_some(crate::behavior::scenario::Context {
-                document: self.canvas_document,
-                scenario,
-                revision: self.document.revision(),
-                epoch: self.canvas_epoch,
-            })
+        if self.page != Page::Behavior {
+            return None;
+        }
+        let scenario = if matches!(
+            self.behavior.scenario.representation(),
+            Some(behavior::scenario_layout::Representation::Saved { .. })
+        ) {
+            self.behavior.scenario.owner()?
+        } else {
+            crate::behavior::selected_owner(self)?
+        };
+        self.behavior.scenario.context(
+            self.canvas_document,
+            scenario,
+            self.document.revision(),
+            self.canvas_epoch,
+        )
     }
     pub(crate) fn scenario_focus_owner(&self) -> Option<crate::behavior::scenario::focus::Stamp> {
         if self.busy
@@ -1759,10 +1875,7 @@ impl App {
             .active_diagram
             .is_some_and(|id| self.saved_scenario_diagram(id));
         match message {
-            Message::Diagram(choice) => self.saved_scenario_diagram(choice.id),
-            Message::RevealInDiagram(diagram, _) | Message::Command(Command::Layout(diagram)) => {
-                self.saved_scenario_diagram(*diagram)
-            }
+            Message::Command(Command::Layout(diagram)) => self.saved_scenario_diagram(*diagram),
             Message::Projection(projection) => active || projection.scenario().is_some(),
             Message::SelectNode(_)
             | Message::PlaceSelected
@@ -1811,6 +1924,8 @@ impl App {
                     if self.scenario_context().is_some_and(|current| {
                         current.document == context.document
                             && current.scenario == context.scenario
+                            && current.representation == context.representation
+                            && current.visit == context.visit
                             && current.revision == context.revision
                     }) && self.scenario_focus_owner().is_some()
                         && self.behavior.scenario.take_form_focus(mount)
@@ -1823,6 +1938,8 @@ impl App {
                     if self.scenario_context().is_some_and(|current| {
                         current.document == context.document
                             && current.scenario == context.scenario
+                            && current.representation == context.representation
+                            && current.visit == context.visit
                             && current.revision == context.revision
                     }) && self.behavior.scenario.viewport(size)
                     {
@@ -1832,7 +1949,10 @@ impl App {
                 }
                 if let CanvasEvent::Restored(_, token, area, offset) = event {
                     if self.scenario_context().is_some_and(|current| {
-                        current.document == context.document && current.scenario == context.scenario
+                        current.document == context.document
+                            && current.scenario == context.scenario
+                            && current.representation == context.representation
+                            && current.visit == context.visit
                     }) && self
                         .behavior
                         .scenario
@@ -1849,6 +1969,8 @@ impl App {
                     if self.scenario_context().is_some_and(|current| {
                         current.document == context.document
                             && current.scenario == context.scenario
+                            && current.representation == context.representation
+                            && current.visit == context.visit
                             && current.revision == context.revision
                     }) && self.behavior.scenario.scrolled(area, offset)
                     {
@@ -1862,6 +1984,8 @@ impl App {
                         || !self.scenario_context().is_some_and(|c| {
                             c.document == context.document
                                 && c.scenario == context.scenario
+                                && c.representation == context.representation
+                                && c.visit == context.visit
                                 && c.revision == context.revision
                         })
                     {
@@ -1870,6 +1994,7 @@ impl App {
                     let scope = canvas_workspace::Scope {
                         document: context.document,
                         owner: context.scenario,
+                        scenario_view: Some((context.representation, context.visit)),
                         revision: context.revision,
                         epoch: lifetime,
                     };
@@ -1880,6 +2005,9 @@ impl App {
                     {
                         return Task::none();
                     }
+                    if self.behavior.scenario.cancel_spacing() {
+                        self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+                    }
                     match input {
                         Event::Focus
                         | Event::Traverse(_)
@@ -1892,7 +2020,10 @@ impl App {
                             self.canvas_epoch = self.canvas_epoch.wrapping_add(1)
                         }
                         input => {
-                            if self.behavior.scenario.camera(input) {
+                            let mut state = std::mem::take(&mut self.behavior.scenario);
+                            let changed = state.camera(self.project(), context.scenario, input);
+                            self.behavior.scenario = state;
+                            if changed {
                                 self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
                             }
                         }
@@ -1903,6 +2034,32 @@ impl App {
                     return Task::none();
                 }
                 match event {
+                    CanvasEvent::Representation(_, requested) => {
+                        use behavior::scenario_layout::{
+                            Representation, presentation::checked_owner,
+                        };
+                        if checked_owner(self.project(), requested) != Some(context.scenario) {
+                            return Task::none();
+                        }
+                        if !self.apply() {
+                            return Task::none();
+                        }
+                        let requested = match requested {
+                            Representation::Saved { diagram }
+                                if context.representation
+                                    == (Representation::Saved { diagram }) =>
+                            {
+                                Representation::Saved {
+                                    diagram: self.active_diagram.unwrap_or(diagram),
+                                }
+                            }
+                            Representation::Derived { owner } => Representation::Derived {
+                                owner: self.behavior.active_owner.unwrap_or(owner),
+                            },
+                            other => other,
+                        };
+                        self.enter_scenario_representation(requested);
+                    }
                     CanvasEvent::Focus(_) => {
                         self.behavior.scenario.toggle_focus();
                         self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
@@ -1911,6 +2068,13 @@ impl App {
                         self.behavior.scenario.toggle_shelf(shelf);
                         self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
                     }
+                    CanvasEvent::Properties(_, _) => {
+                        // The checked action opens the current record only: no
+                        // select()/Apply side effect or representation change.
+                        self.behavior.scenario.show_properties();
+                        self.inspector_tab = crate::navigation::InspectorTab::Properties;
+                        self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+                    }
                     CanvasEvent::Zoom(_, scale) => {
                         let mut state = std::mem::take(&mut self.behavior.scenario);
                         if state.camera_zoom(self.project(), context.scenario, scale) {
@@ -1931,7 +2095,11 @@ impl App {
                             Ok(target) => {
                                 // A command can preselect this target while the
                                 // caller remains visible, bypassing select below.
-                                self.behavior.active_owner = Some(target);
+                                self.enter_scenario_representation(
+                                    behavior::scenario_layout::Representation::Derived {
+                                        owner: target,
+                                    },
+                                );
                                 self.select(target);
                                 self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
                             }
@@ -1953,7 +2121,7 @@ impl App {
                             // A command may already have selected this UUID while
                             // leaving the referenced definition open. select's
                             // same-UUID fast path must not keep that old owner.
-                            self.behavior.active_owner = Some(caller.owner);
+                            self.enter_scenario_representation(caller.representation);
                             self.select(caller.occurrence);
                             self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
                             if let Some(context) = self.scenario_context() {
@@ -1981,6 +2149,15 @@ impl App {
                         }
                     }
                     CanvasEvent::Choose(_, tool) => {
+                        if tool != scenario::CanvasTool::Select
+                            && !self
+                                .behavior
+                                .scenario
+                                .coordinate_input(self.project(), context)
+                        {
+                            self.status = "Canvas insertion and reordering are unavailable for this presentation.".into();
+                            return Task::none();
+                        }
                         if self.behavior.has_pending() || self.draft_dirty() || self.source_dirty()
                         {
                             self.status =
@@ -1992,6 +2169,17 @@ impl App {
                         self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
                     }
                     mutation => {
+                        if !behavior::scenario_layout::presentation::present(
+                            self.project(),
+                            context.representation,
+                            self.selected,
+                        )
+                        .capabilities()
+                        .coordinate_input
+                        {
+                            self.status = "Layout editing is unavailable for this presentation. Saved positions are preserved.".into();
+                            return Task::none();
+                        }
                         if self.behavior.has_pending() || self.draft_dirty() || self.source_dirty()
                         {
                             self.status =
@@ -2092,6 +2280,13 @@ impl App {
                     })
                 {
                     self.behavior.active_owner = Some(choice.id);
+                    if self.project().elements[&choice.id].kind() == Kind::Scenario {
+                        self.enter_scenario_representation(
+                            behavior::scenario_layout::Representation::Derived { owner: choice.id },
+                        );
+                    } else {
+                        self.behavior.scenario.forget_view();
+                    }
                     self.behavior.diagram = Default::default();
                     self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
                     self.select(choice.id);
@@ -2457,6 +2652,15 @@ impl App {
                             crate::behavior::selected_behavior(self.project(), self.selected)
                         {
                             self.behavior.active_owner = Some(owner);
+                            if self.project().elements[&owner].kind() == Kind::Scenario
+                                && self.behavior.scenario.owner() != Some(owner)
+                            {
+                                self.enter_scenario_representation(
+                                    behavior::scenario_layout::Representation::Derived { owner },
+                                );
+                            } else if self.project().elements[&owner].kind() != Kind::Scenario {
+                                self.behavior.scenario.forget_view();
+                            }
                         }
                         self.behavior.active_owner = crate::behavior::selected_owner(self);
                         self.reset_state_view_after_navigation(previous_state_view);
@@ -2693,6 +2897,7 @@ impl App {
             }
             Message::Layer(layer) => {
                 if self.apply() {
+                    self.behavior.scenario.forget_view();
                     let previous_state_view = self.state_view_identity();
                     self.layer = layer;
                     self.create_kind = if layer == Layer::Oa {
@@ -2865,6 +3070,9 @@ impl App {
                 }
             }
             Message::RevealInDiagram(diagram, selected) => {
+                if self.saved_scenario_diagram(diagram) {
+                    return self.reveal_saved_scenario(diagram, selected);
+                }
                 let original = self.selected;
                 if !self.apply() {
                     return Task::none();
@@ -3096,6 +3304,16 @@ impl App {
                     self.status = "Diagram no longer exists.".into();
                     return Task::none();
                 }
+                if self.saved_scenario_diagram(choice.id)
+                    && behavior::scenario_layout::presentation::checked_owner(
+                        self.project(),
+                        behavior::scenario_layout::Representation::Saved { diagram: choice.id },
+                    )
+                    .is_none()
+                {
+                    self.status = "This Scenario view has an incompatible or missing owner.".into();
+                    return Task::none();
+                }
                 let previous_diagram = self.active_diagram;
                 let follow_view = previous_diagram == Some(self.selected);
                 if self.apply() {
@@ -3115,7 +3333,14 @@ impl App {
                     }
                     self.selected_node = None;
                     self.refresh_draft();
-                    self.fit();
+                    if self.saved_scenario_diagram(diagram) {
+                        self.enter_scenario_representation(
+                            behavior::scenario_layout::Representation::Saved { diagram },
+                        );
+                    } else {
+                        self.page = Page::Diagram;
+                        self.fit();
+                    }
                 }
             }
             Message::Projection(projection) => {
@@ -5748,12 +5973,17 @@ mod saved_scenario_dispatch_tests {
     }
 
     #[test]
-    fn unsupported_saved_picker_and_reveal_do_not_apply_pending_properties() {
+    fn saved_picker_with_invalid_properties_and_reveal_with_pending_properties_do_not_apply() {
         for reveal in [false, true] {
             let (mut app, architecture, saved, owner) = fixture();
             let _ = app.update(Message::Field(
-                "/name".into(),
-                "Unapplied scenario name".into(),
+                if reveal { "/name" } else { "/id" }.into(),
+                if reveal {
+                    "Unapplied scenario name"
+                } else {
+                    "-"
+                }
+                .into(),
             ));
             assert!(app.draft_dirty());
             let before = app.document.bundle().clone();
@@ -5773,7 +6003,6 @@ mod saved_scenario_dispatch_tests {
             assert_eq!(app.active_diagram, Some(architecture));
             assert_eq!(app.selected, selected);
             assert!(app.draft_dirty());
-            assert_eq!(app.status, SAVED_SCENARIO_UNAVAILABLE);
         }
     }
 

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

@@ -1,5 +1,6 @@
 //! Complete a navigation camera after the destination reports its real viewport.
 use super::*;
+use crate::behavior::scenario_layout::Representation;
 use crate::diagram_usage::{Context, Surface};
 #[cfg(test)]
 mod tests;
@@ -47,11 +48,23 @@ impl App {
                     && c.epoch == *epoch,
             ),
             Message::ScenarioCanvas(behavior::scenario::CanvasEvent::Viewport(c, size)) => (
-                Surface::Scenario(c.scenario),
+                match c.representation {
+                    Representation::Derived { owner } => Surface::Scenario(owner),
+                    Representation::Saved { diagram } => Surface::Saved(diagram),
+                },
                 *size,
                 c.document == context.document
                     && c.revision == context.revision
-                    && c.epoch == *epoch,
+                    && c.epoch == *epoch
+                    && self.pending_scenario_reveal_visit == Some(c.visit)
+                    && self.page == Page::Behavior
+                    && self.behavior.active_owner == Some(c.scenario)
+                    && self.behavior.scenario.context(
+                        self.canvas_document,
+                        c.scenario,
+                        self.document.revision(),
+                        self.canvas_epoch,
+                    ) == Some(*c),
             ),
             Message::StateDiagram(behavior::state_edit::Event::Viewport(c, size)) => (
                 Surface::Saved(c.diagram),
@@ -91,6 +104,7 @@ impl App {
                 | Message::StateDiagram(behavior::state_edit::Event::Viewport(..))
         ) {
             self.pending_diagram_reveal = None;
+            self.pending_scenario_reveal_visit = None;
             if !Self::is_navigation_camera(message) {
                 self.diagram_navigation_focus = None;
             }
@@ -142,5 +156,6 @@ impl App {
             self.reveal_diagram_usage(&usage);
         }
         self.pending_diagram_reveal = None;
+        self.pending_scenario_reveal_visit = None;
     }
 }

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

@@ -144,6 +144,7 @@ fn measurement(
     epoch: u64,
     surface: Surface,
     size: Size,
+    visit: Id,
 ) -> Message {
     match canvas {
         Canvas::Architecture => Message::DiagramRevealViewport(context, epoch, size),
@@ -160,6 +161,10 @@ fn measurement(
             behavior::scenario::Context {
                 document: context.document,
                 scenario: surface.id(),
+                representation: Representation::Derived {
+                    owner: surface.id(),
+                },
+                visit,
                 revision: context.revision,
                 epoch,
             },
@@ -177,12 +182,16 @@ fn measurement(
     }
 }
 
-fn stamp(app: &App) -> (Context, u64) {
+fn stamp(app: &App) -> (Context, u64, Id) {
     let (context, _, epoch) = app
         .pending_diagram_reveal
         .as_ref()
         .expect("reveal awaits measured destination");
-    (*context, *epoch)
+    (
+        *context,
+        *epoch,
+        app.pending_scenario_reveal_visit.unwrap_or(Id::nil()),
+    )
 }
 
 fn assert_centered(app: &App, canvas: Canvas, target: &Usage) {
@@ -220,7 +229,11 @@ fn assert_centered(app: &App, canvas: Canvas, target: &Usage) {
             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));
+            expected.camera(
+                app.project(),
+                target.surface.id(),
+                behavior::canvas_workspace::Event::Pan(pan),
+            );
             assert!(app.behavior.scenario.camera_boundary() == expected.camera_boundary());
         }
     }
@@ -239,10 +252,10 @@ fn all_reveal_surfaces_recenter_once_after_the_real_viewport_and_preserve_author
             app.document.dirty(),
         );
         assert!(app.reveal_diagram_usage(&target));
-        let (context, epoch) = stamp(&app);
+        let (context, epoch, visit) = stamp(&app);
         send(
             &mut app,
-            measurement(canvas, context, epoch, target.surface, ACTUAL),
+            measurement(canvas, context, epoch, target.surface, ACTUAL, visit),
         );
         assert!(app.pending_diagram_reveal.is_none());
         assert_centered(&app, canvas, &target);
@@ -261,7 +274,7 @@ fn all_reveal_surfaces_recenter_once_after_the_real_viewport_and_preserve_author
         let camera = app.camera_boundary();
         send(
             &mut app,
-            measurement(canvas, context, epoch, target.surface, ACTUAL),
+            measurement(canvas, context, epoch, target.surface, ACTUAL, visit),
         );
         assert!(app.pending_diagram_reveal.is_none());
         assert!(app.camera_boundary() == camera);
@@ -275,7 +288,7 @@ fn malformed_or_wrong_stamp_measurements_cannot_poison_a_pending_reveal() {
         for invalid in 0..6 {
             let (mut app, target) = fixture(canvas);
             assert!(app.reveal_diagram_usage(&target));
-            let (context, epoch) = stamp(&app);
+            let (context, epoch, visit) = stamp(&app);
             let camera = app.camera_boundary();
             let mut stale = context;
             let mut wrong_epoch = epoch;
@@ -290,13 +303,13 @@ fn malformed_or_wrong_stamp_measurements_cannot_poison_a_pending_reveal() {
             }
             send(
                 &mut app,
-                measurement(canvas, stale, wrong_epoch, target.surface, size),
+                measurement(canvas, stale, wrong_epoch, target.surface, size, visit),
             );
             assert!(
                 app.pending_diagram_reveal.is_some(),
                 "{canvas:?} invalid case {invalid}"
             );
-            assert_eq!(stamp(&app), (context, epoch));
+            assert_eq!(stamp(&app), (context, epoch, visit));
             assert_eq!(app.canvas_epoch, epoch);
             assert!(
                 app.camera_boundary() == camera,
@@ -304,7 +317,7 @@ fn malformed_or_wrong_stamp_measurements_cannot_poison_a_pending_reveal() {
             );
             send(
                 &mut app,
-                measurement(canvas, context, epoch, target.surface, ACTUAL),
+                measurement(canvas, context, epoch, target.surface, ACTUAL, visit),
             );
             assert!(app.pending_diagram_reveal.is_none());
             assert_centered(&app, canvas, &target);
@@ -318,9 +331,10 @@ fn actual_window_resize_before_first_measurement_retains_focus_for_the_new_conte
         let (mut app, target) = fixture(canvas);
         let accepted = app.document.snapshot();
         assert!(app.reveal_diagram_usage(&target));
-        let (context, old_epoch) = stamp(&app);
+        let (context, old_epoch, visit) = stamp(&app);
         send(&mut app, Message::WindowResized(Size::new(1100., 700.)));
-        let (current, epoch) = stamp(&app);
+        let (current, epoch, current_visit) = stamp(&app);
+        assert_eq!(current_visit, visit);
         assert_eq!(current, context);
         assert_eq!(epoch, app.canvas_epoch);
         if matches!(canvas, Canvas::Process | Canvas::Scenario) {
@@ -328,14 +342,14 @@ fn actual_window_resize_before_first_measurement_retains_focus_for_the_new_conte
             let camera = app.camera_boundary();
             send(
                 &mut app,
-                measurement(canvas, context, old_epoch, target.surface, ACTUAL),
+                measurement(canvas, context, old_epoch, target.surface, ACTUAL, visit),
             );
-            assert_eq!(stamp(&app), (current, epoch));
+            assert_eq!(stamp(&app), (current, epoch, visit));
             assert!(app.camera_boundary() == camera);
         }
         send(
             &mut app,
-            measurement(canvas, current, epoch, target.surface, ACTUAL),
+            measurement(canvas, current, epoch, target.surface, ACTUAL, visit),
         );
         assert!(app.pending_diagram_reveal.is_none());
         assert_centered(&app, canvas, &target);
@@ -350,7 +364,7 @@ fn user_camera_edit_and_navigation_cancel_deferred_focus_without_late_snapping()
             let (mut app, target) = fixture(canvas);
             let accepted = app.document.snapshot();
             assert!(app.reveal_diagram_usage(&target));
-            let (context, epoch) = stamp(&app);
+            let (context, epoch, visit) = stamp(&app);
             let event = match action {
                 0 => match canvas {
                     Canvas::Architecture => Message::Pan(Vector::new(31., -17.)),
@@ -387,7 +401,7 @@ fn user_camera_edit_and_navigation_cancel_deferred_focus_without_late_snapping()
             // restore the old navigation camera after deliberate user input.
             send(
                 &mut app,
-                measurement(canvas, context, epoch, target.surface, WIDE),
+                measurement(canvas, context, epoch, target.surface, WIDE, visit),
             );
             assert!(app.pending_diagram_reveal.is_none());
             assert!(

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

@@ -1,5 +1,6 @@
 //! Navigation-only adapter: validates destinations before changing presentation.
 use super::*;
+use crate::behavior::scenario_layout::{Representation, presentation};
 use crate::diagram_usage::{self as usage, Context, Event, Panel, Surface, Target, Usage};
 #[cfg(test)]
 mod tests;
@@ -58,10 +59,6 @@ impl App {
                     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."));
@@ -168,6 +165,7 @@ impl App {
             // Only an accepted new chooser supersedes the previous reveal.
             // Rejected/stale panel envelopes leave its first measurement intact.
             self.pending_diagram_reveal = None;
+            self.pending_scenario_reveal_visit = None;
             self.diagram_navigation_focus = None;
             self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
             return Task::batch([
@@ -290,14 +288,78 @@ impl App {
         Task::none()
     }
 
+    /// Explicit saved-Scenario reveal runs before generic Apply. An absent target
+    /// never selects the owner or another saved arrangement as a fallback.
+    pub(super) fn reveal_saved_scenario(&mut self, diagram: Id, selected: Id) -> Task<Message> {
+        if self.diagram_usages.is_some() || !self.usage_navigation_available() {
+            self.status = "Apply or revert pending edits before revealing a saved Scenario. Your inputs are retained.".into();
+            return Task::none();
+        }
+        if presentation::checked_owner(self.project(), Representation::Saved { diagram }).is_none()
+        {
+            return Task::none();
+        }
+        let Some(found) = self
+            .current_surface_usages(selected, Surface::Saved(diagram))
+            .into_iter()
+            .find(|row| matches!(row.target, Target::Whole | Target::ScenarioObject(_)))
+        else {
+            self.status = "This object has no visible target in that saved Scenario.".into();
+            return Task::none();
+        };
+        self.reveal_diagram_usage(&found);
+        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 scenario_representation = match usage.surface {
+            Surface::Saved(diagram) if self.saved_scenario_diagram(diagram) => {
+                Some(Representation::Saved { diagram })
+            }
+            Surface::Scenario(owner) => Some(Representation::Derived { owner }),
+            _ => None,
+        };
+        if let Some(representation) = scenario_representation {
+            let Some(owner) = presentation::checked_owner(self.project(), representation) else {
+                return false;
+            };
+            if !self
+                .behavior
+                .scenario
+                .representation_usages(self.project(), representation, usage.subject)
+                .iter()
+                .any(|row| row == usage)
+            {
+                return false;
+            }
+            // Finish target/camera admission before changing the App route. The
+            // checked immutable owner also makes the following entry infallible.
+            let revealed = match representation {
+                Representation::Derived { .. } => self.behavior.scenario.reveal_usage(
+                    self.document.project(),
+                    self.canvas_document,
+                    owner,
+                    &usage.target,
+                ),
+                Representation::Saved { .. } => self.behavior.scenario.reveal_representation_usage(
+                    self.document.project(),
+                    self.canvas_document,
+                    owner,
+                    representation,
+                    &usage.target,
+                ),
+            };
+            if !revealed {
+                return false;
+            }
+            if !self.enter_scenario_representation(representation) {
+                return false;
+            }
+        }
         let p = self.document.project();
         let (selected, placement) = match &usage.target {
             Target::Whole => (usage.surface.id(), None),
@@ -337,7 +399,10 @@ impl App {
                 };
                 self.layer = diagram.layer;
                 self.active_diagram = Some(id);
-                if let Some(machine) = diagram.projection.state_machine() {
+                if let Some(owner) = diagram.projection.scenario() {
+                    self.behavior.active_owner = Some(owner);
+                    self.page = Page::Behavior;
+                } else 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.),
@@ -379,19 +444,14 @@ impl App {
                 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;
             }
         }
+        if scenario_representation.is_none() {
+            self.behavior.scenario.forget_view();
+        }
         self.selected = selected;
         self.selected_node = placement;
         self.model_menu = None;
@@ -418,6 +478,18 @@ impl App {
             usage: usage.clone(),
             selected,
         });
+        self.pending_scenario_reveal_visit = scenario_representation.and_then(|representation| {
+            let owner = presentation::checked_owner(self.project(), representation)?;
+            self.behavior
+                .scenario
+                .context(
+                    self.canvas_document,
+                    owner,
+                    self.document.revision(),
+                    self.canvas_epoch,
+                )
+                .map(|context| context.visit)
+        });
         self.pending_diagram_reveal = Some((
             Context {
                 document: self.canvas_document,
@@ -437,12 +509,21 @@ impl App {
         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)
+                    && (!self.saved_scenario_diagram(id)
+                        || (self.page == Page::Behavior
+                            && self.behavior.scenario.representation()
+                                == Some(Representation::Saved { diagram: id })))
             }
-            Surface::Process(owner) | Surface::Scenario(owner) => {
+            Surface::Process(owner) => {
                 self.page == Page::Behavior && self.behavior.active_owner == Some(owner)
             }
+            Surface::Scenario(owner) => {
+                self.page == Page::Behavior
+                    && self.behavior.active_owner == Some(owner)
+                    && self.behavior.scenario.representation()
+                        == Some(Representation::Derived { owner })
+            }
         };
         (current_surface
             && focus.usage.surface == surface

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

@@ -1401,3 +1401,5 @@ fn completion_releases_worker_behind_busy_modal_without_navigation() {
     assert_eq!(location(&app), prior);
     assert_eq!(authored(&app), before);
 }
+
+mod saved_scenario;

crates/oa-desktop/src/app/diagram_usages/tests/saved_scenario.arcadia

@@ -0,0 +1,108 @@
+arcadia 7;
+project incident_workspace "Incident report review" id "70200000-0000-4000-8000-000000000001" {
+    // Two operational activities, with one lifeline appearance per Scenario.
+    oa_activity report_incident "Report incident" id "70200000-0000-4000-8000-000000000002" {}
+    oa_activity assess_incident "Assess incident" id "70200000-0000-4000-8000-000000000003" {}
+    interaction incident_report "Incident report" id "70200000-0000-4000-8000-000000000004" {
+        source @report_incident;
+        target @assess_incident;
+    }
+
+    oa_scenario incident_response "Review a reported incident" id "70200000-0000-4000-8000-000000000010" {
+        viewpoint OperationalActivity;
+        steps [@initial_report, @updated_report, @assess_call, @assess_reply, @unfinished_notice, @use_review];
+    }
+    oa_lifeline reporter "Reporting activity" id "70200000-0000-4000-8000-000000000011" {
+        parent @incident_response; represented @report_incident;
+    }
+    oa_lifeline assessor "Assessment activity" id "70200000-0000-4000-8000-000000000012" {
+        parent @incident_response; represented @assess_incident;
+    }
+    // Both appearances reuse one definition. Navigation must retain the occurrence.
+    oa_occurrence initial_report "Initial incident report" id "70200000-0000-4000-8000-000000000020" {
+        parent @incident_response;
+        body { Exchange { exchange @incident_report; sender @reporter; receiver @assessor; message_kind Asynchronous; }; };
+    }
+    oa_occurrence updated_report "Updated incident report" id "70200000-0000-4000-8000-000000000021" {
+        parent @incident_response;
+        body { Exchange { exchange @incident_report; sender @reporter; receiver @assessor; message_kind Asynchronous; }; };
+    }
+    // A correlated self call/reply with deliberately unassigned exchange definitions.
+    oa_occurrence assess_call "Assess report details" id "70200000-0000-4000-8000-000000000022" {
+        parent @incident_response;
+        body { Exchange { exchange none; sender @assessor; receiver @assessor; message_kind Call; }; };
+    }
+    oa_occurrence assess_reply "Assessment ready" id "70200000-0000-4000-8000-000000000023" {
+        parent @incident_response;
+        body { Exchange { exchange none; sender @assessor; receiver @assessor; message_kind Reply; reply_to @assess_call; }; };
+    }
+    // Intentional unfinished work: no receiver and therefore no fabricated arrow.
+    oa_occurrence unfinished_notice "Follow-up recipient undecided" id "70200000-0000-4000-8000-000000000024" {
+        parent @incident_response;
+        body { Exchange { exchange @incident_report; sender @reporter; receiver none; message_kind Asynchronous; }; };
+    }
+    oa_occurrence use_review "Use the reviewed reporting procedure" id "70200000-0000-4000-8000-000000000025" {
+        parent @incident_response;
+        body { ScenarioUse {
+            bindings [{ local @reporter; referenced @review_reporter; }, { local @assessor; referenced @review_assessor; }];
+            scenario @reporting_review;
+        }; };
+    }
+
+    // This definition stays opaque in the caller. Open it, then Back to the saved view.
+    oa_scenario reporting_review "Reporting procedure detail" id "70200000-0000-4000-8000-000000000030" {
+        viewpoint OperationalActivity;
+        steps [@review_delivery];
+    }
+    oa_lifeline review_reporter "Reporting activity in detail" id "70200000-0000-4000-8000-000000000031" {
+        parent @reporting_review; represented @report_incident;
+    }
+    oa_lifeline review_assessor "Assessment activity in detail" id "70200000-0000-4000-8000-000000000032" {
+        parent @reporting_review; represented @assess_incident;
+    }
+    oa_occurrence review_delivery "Check the incident report" id "70200000-0000-4000-8000-000000000033" {
+        parent @reporting_review;
+        body { Exchange { exchange @incident_report; sender @review_reporter; receiver @review_assessor; message_kind Asynchronous; }; };
+    }
+
+    diagram incident_readable "A - Incident review readable" id "70200000-0000-4000-8000-000000000040" {
+        layer Oa;
+        projection { Scenario { scenario @incident_response; }; };
+        layout { Scenario {
+            lanes [{ lifeline @reporter; x 160; }, { lifeline @assessor; x 640; }];
+            messages [
+                { address { references []; occurrence @initial_report; }; send_y 160; },
+                { address { references []; occurrence @updated_report; }; send_y 252; },
+                { address { references []; occurrence @assess_call; }; send_y 344; },
+                { address { references []; occurrence @assess_reply; }; send_y 436; }
+            ];
+        }; };
+    }
+    diagram incident_wide "B - Incident review negative and far" id "70200000-0000-4000-8000-000000000041" {
+        layer Oa;
+        projection { Scenario { scenario @incident_response; }; };
+        layout { Scenario {
+            lanes [{ lifeline @reporter; x -500; }, { lifeline @assessor; x 50000; }];
+            messages [
+                { address { references []; occurrence @initial_report; }; send_y 160; },
+                { address { references []; occurrence @updated_report; }; send_y 252; },
+                { address { references []; occurrence @assess_call; }; send_y 344; },
+                { address { references []; occurrence @assess_reply; }; send_y 436; }
+            ];
+        }; };
+    }
+    diagram incident_repair "C - Incident review needs layout repair" id "70200000-0000-4000-8000-000000000042" {
+        layer Oa;
+        projection { Scenario { scenario @incident_response; }; };
+        layout { Scenario {
+            // These valid authored lanes must remain saved during complete fallback.
+            lanes [{ lifeline @reporter; x 900; }, { lifeline @assessor; x -500; }];
+            messages [
+                // REPAIR: change only this 300 to 424, then Undo and Redo the edit.
+                { address { references []; occurrence @assess_reply; }; send_y 300; },
+                // This authored value stays latent while the receiver is missing.
+                { address { references []; occurrence @unfinished_notice; }; send_y 2000; }
+            ];
+        }; };
+    }
+}

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

@@ -0,0 +1,356 @@
+//! Actual App chooser/explicit-reveal checks for saved Scenario identity and source history.
+use super::*;
+use crate::behavior::scenario::{CanvasEvent, State};
+use crate::behavior::scenario_layout::{
+    Representation,
+    presentation::{self, PresentationStatus},
+};
+use iced::{Size, Vector};
+
+fn fixture() -> App {
+    let p = language::parse(include_str!("saved_scenario.arcadia")).unwrap();
+    let errors: Vec<_> = oa_core::validation::validate(&p)
+        .into_iter()
+        .filter(|d| d.severity == oa_core::validation::Severity::Error)
+        .collect();
+    assert!(errors.is_empty(), "{errors:?}");
+    App::with_project(p)
+}
+fn id(app: &App, alias: &str) -> Id {
+    app.project()
+        .identities()
+        .into_iter()
+        .find(|(_, a)| *a == alias)
+        .unwrap()
+        .0
+}
+fn representation(view: Id) -> Representation {
+    Representation::Saved { diagram: view }
+}
+fn find(app: &App, subject: Id, view: Id) -> Usage {
+    usage::saved_usages_for(app.project(), subject, Some(view))
+        .into_iter()
+        .find(|row| row.target == Target::ScenarioObject(subject))
+        .expect("exact saved occurrence")
+}
+fn context(app: &App) -> behavior::scenario::Context {
+    let owner = app.behavior.active_owner.unwrap();
+    app.behavior
+        .scenario
+        .context(
+            app.canvas_document,
+            owner,
+            app.document.revision(),
+            app.canvas_epoch,
+        )
+        .unwrap()
+}
+fn navigate(app: &mut App, subject: Id, view: Id) -> Id {
+    let (token, rows) = open(app, subject);
+    let found = rows
+        .into_iter()
+        .find(|u| u.surface == Surface::Saved(view) && u.target == Target::ScenarioObject(subject))
+        .expect("saved chooser destination");
+    choose(app, token, found);
+    assert!(app.diagram_usages.is_none());
+    assert_eq!(app.page, Page::Behavior);
+    assert_eq!(app.active_diagram, Some(view));
+    assert_eq!(
+        app.behavior.scenario.representation(),
+        Some(representation(view))
+    );
+    assert_eq!(app.selected, subject);
+    token
+}
+
+#[test]
+fn saved_queries_use_each_actual_presentation_and_keep_repeated_appearances_and_references_opaque()
+{
+    let app = fixture();
+    let owner = id(&app, "incident_response");
+    let first = id(&app, "initial_report");
+    let second = id(&app, "updated_report");
+    let exchange = id(&app, "incident_report");
+    let latent = id(&app, "unfinished_notice");
+    let callee_message = id(&app, "review_delivery");
+    let views = ["incident_readable", "incident_wide", "incident_repair"].map(|a| id(&app, a));
+    let derived = app
+        .behavior
+        .scenario
+        .diagram_usages(app.project(), owner, first)
+        .pop()
+        .unwrap();
+    let rows = views.map(|view| find(&app, first, view));
+    assert_eq!(rows[0].bounds.y - derived.bounds.y, 12.);
+    assert_ne!(rows[0].bounds, rows[1].bounds);
+    assert_eq!(
+        rows[2].bounds, derived.bounds,
+        "complete fallback cannot retain the authored lane override"
+    );
+    for view in views {
+        let represented = usage::saved_usages_for(app.project(), exchange, Some(view));
+        assert_eq!(represented.len(), 2);
+        assert!(
+            represented
+                .iter()
+                .any(|u| u.target == Target::ScenarioObject(first))
+        );
+        assert!(
+            represented
+                .iter()
+                .any(|u| u.target == Target::ScenarioObject(second))
+        );
+        assert!(
+            represented
+                .iter()
+                .all(|u| u.surface == Surface::Saved(view))
+        );
+        assert!(usage::saved_usages_for(app.project(), callee_message, Some(view)).is_empty());
+        assert_eq!(
+            find(&app, latent, view).target,
+            Target::ScenarioObject(latent)
+        );
+        let shown = presentation::present(app.project(), representation(view), owner);
+        let whole = usage::saved_usages_for(app.project(), view, Some(view));
+        assert_eq!(whole.len(), 1);
+        assert_eq!(whole[0].target, Target::Whole);
+        assert_eq!(Some(whole[0].bounds), shown.bounds());
+    }
+    let wide = presentation::present(app.project(), representation(views[1]), owner)
+        .bounds()
+        .unwrap();
+    assert!(wide.x < -500. && wide.x + wide.width > 50000.);
+    let fallback = presentation::present(app.project(), representation(views[2]), owner);
+    assert!(matches!(
+        fallback.status(),
+        PresentationStatus::Fallback { .. }
+    ));
+    assert_eq!(fallback.latent_messages(), &[latent]);
+    assert!(!fallback.capabilities().coordinate_input);
+}
+
+#[test]
+fn saved_chooser_and_explicit_reveal_preserve_complete_source_and_actual_undo_redo() {
+    for alias in ["incident_readable", "incident_wide", "incident_repair"] {
+        let mut app = fixture();
+        let view = id(&app, alias);
+        let first = id(&app, "initial_report");
+        let owner = id(&app, "incident_response");
+        let original = app.document.snapshot();
+        app.document
+            .execute(Command::Rename(first, "Reviewed incident report".into()))
+            .unwrap();
+        let edited = app.document.snapshot();
+        app.sync_source();
+        app.refresh_draft();
+        let before = authored(&app);
+        navigate(&mut app, first, view);
+        assert_eq!(app.behavior.active_owner, Some(owner));
+        assert_eq!(authored(&app), before);
+        send(&mut app, Message::RevealInDiagram(view, first));
+        assert_eq!(app.active_diagram, Some(view));
+        assert_eq!(authored(&app), before);
+        assert!(app.document.undo());
+        assert_eq!(app.project(), &original.decoded.project);
+        assert_eq!(app.document.bundle(), &original.bundle);
+        assert!(app.document.redo());
+        assert_eq!(app.project(), &edited.decoded.project);
+        assert_eq!(app.document.bundle(), &edited.bundle);
+    }
+}
+
+#[test]
+fn saved_reveal_and_chooser_refuse_source_property_and_behavior_drafts() {
+    for chooser in [false, true] {
+        for block in 0..3 {
+            let mut app = fixture();
+            let view = id(&app, "incident_repair");
+            let first = id(&app, "initial_report");
+            let choice = chooser.then(|| {
+                let (token, rows) = open(&mut app, first);
+                (
+                    token,
+                    rows.into_iter()
+                        .find(|u| u.surface == Surface::Saved(view))
+                        .unwrap(),
+                )
+            });
+            match block {
+                0 => {
+                    let cursor = app.source_editor.cursor();
+                    app.source_workspace
+                        .edit("? preserve unfinished source".into(), cursor);
+                }
+                1 => {
+                    app.draft
+                        .as_mut()
+                        .unwrap()
+                        .input("/name", "Unapplied inspector value".into());
+                    assert!(app.draft_dirty());
+                }
+                _ => {
+                    let p = app.project().clone();
+                    app.behavior
+                        .creation
+                        .update(&p, behavior::creation::Event::Open(Layer::Oa))
+                        .unwrap();
+                    assert!(app.behavior.has_pending());
+                }
+            }
+            let before = authored(&app);
+            let prior = location(&app);
+            let draft = app
+                .draft
+                .as_ref()
+                .map(|d| serde_json::to_value(d.recovery_snapshot()).unwrap());
+            if let Some((token, row)) = choice {
+                choose(&mut app, token, row);
+            } else {
+                send(&mut app, Message::RevealInDiagram(view, first));
+            }
+            assert_eq!(authored(&app), before);
+            assert_eq!(location(&app), prior);
+            assert_eq!(
+                app.draft
+                    .as_ref()
+                    .map(|d| serde_json::to_value(d.recovery_snapshot()).unwrap()),
+                draft
+            );
+        }
+    }
+}
+
+#[test]
+fn saved_a_b_a_rejects_old_visit_and_panel_callbacks_before_deferred_measurement() {
+    let mut app = fixture();
+    let a = id(&app, "incident_readable");
+    let b = id(&app, "incident_wide");
+    let first = id(&app, "initial_report");
+    let before = authored(&app);
+    let old_token = navigate(&mut app, first, a);
+    let old = context(&app);
+    navigate(&mut app, first, b);
+    navigate(&mut app, first, a);
+    let current = context(&app);
+    assert_ne!(old.visit, current.visit);
+    let held = behavior::scenario::Context {
+        epoch: current.epoch,
+        ..old
+    };
+    let camera = app.behavior.scenario.camera_boundary();
+    send(
+        &mut app,
+        Message::ScenarioCanvas(CanvasEvent::Viewport(held, Size::new(900., 900.))),
+    );
+    send(&mut app, Message::ScenarioCanvas(CanvasEvent::Focus(held)));
+    send(
+        &mut app,
+        Message::DiagramUsage(Event::Search(old_token, "obsolete filter".into())),
+    );
+    send(&mut app, Message::DiagramUsage(Event::Close(old_token)));
+    assert_eq!(app.pending_scenario_reveal_visit, Some(current.visit));
+    assert!(app.pending_diagram_reveal.is_some());
+    assert!(app.behavior.scenario.camera_boundary() == camera);
+    let bounds = find(&app, first, a).bounds;
+    send(
+        &mut app,
+        Message::ScenarioCanvas(CanvasEvent::Viewport(current, Size::new(500., 300.))),
+    );
+    assert!(app.pending_diagram_reveal.is_none());
+    assert_eq!(context(&app).visit, current.visit);
+    let mut expected = State::default();
+    expected.enter_representation(app.canvas_document, current.scenario, representation(a));
+    expected.viewport(Size::new(500., 300.));
+    expected.zoom(Some(1.25));
+    expected.camera(
+        app.project(),
+        current.scenario,
+        behavior::canvas_workspace::Event::Pan(Vector::new(
+            250. - bounds.center_x() * 1.25,
+            150. - bounds.center_y() * 1.25,
+        )),
+    );
+    assert!(app.behavior.scenario.camera_boundary() == expected.camera_boundary());
+    assert_eq!(authored(&app), before);
+}
+
+#[test]
+fn retargeted_saved_view_cannot_reveal_a_former_owner_occurrence() {
+    let mut app = fixture();
+    let first = id(&app, "initial_report");
+    let view = id(&app, "incident_readable");
+    let other = id(&app, "reporting_review");
+    let (token, rows) = open(&mut app, first);
+    let old = rows
+        .into_iter()
+        .find(|u| u.surface == Surface::Saved(view))
+        .unwrap();
+    let mut replacement = app.project().diagrams[&view].clone();
+    replacement.projection = ProjectionKind::Scenario { scenario: other };
+    replacement.layout = None;
+    app.document
+        .execute(Command::EditDiagram(view, replacement))
+        .unwrap();
+    app.sync_source();
+    app.refresh_draft();
+    let before = authored(&app);
+    let prior = location(&app);
+    choose(&mut app, token, old);
+    assert_eq!(location(&app), prior);
+    assert_eq!(authored(&app), before);
+    finish_lookup(&mut app);
+    let token = app.diagram_usages.as_ref().unwrap().token;
+    assert!(
+        app.diagram_usages
+            .as_ref()
+            .unwrap()
+            .usages
+            .iter()
+            .all(|u| u.surface != Surface::Saved(view))
+    );
+    send(&mut app, Message::DiagramUsage(Event::Close(token)));
+    send(&mut app, Message::RevealInDiagram(view, first));
+    assert_eq!(location(&app), prior);
+    assert_eq!(authored(&app), before);
+}
+
+#[test]
+fn explicit_saved_layout_repair_undo_redo_requeries_authored_and_fallback_geometry_without_extra_history()
+ {
+    let mut app = fixture();
+    let view = id(&app, "incident_repair");
+    let first = id(&app, "initial_report");
+    let reply = id(&app, "assess_reply");
+    let before = app.document.snapshot();
+    let fallback = find(&app, first, view);
+    app.document
+        .execute(Command::SetScenarioMessagePosition {
+            diagram: view,
+            position: oa_core::ScenarioMessagePosition {
+                address: oa_core::OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence: reply,
+                },
+                send_y: 424.,
+            },
+        })
+        .unwrap();
+    app.sync_source();
+    app.refresh_draft();
+    let repaired = app.document.snapshot();
+    let authored_row = find(&app, first, view);
+    assert_ne!(authored_row.bounds, fallback.bounds);
+    navigate(&mut app, first, view);
+    assert!(app.document.undo());
+    app.sync_source();
+    app.refresh_draft();
+    assert_eq!(app.project(), &before.decoded.project);
+    assert_eq!(app.document.bundle(), &before.bundle);
+    assert_eq!(find(&app, first, view).bounds, fallback.bounds);
+    assert!(app.document.redo());
+    app.sync_source();
+    app.refresh_draft();
+    assert_eq!(app.project(), &repaired.decoded.project);
+    assert_eq!(app.document.bundle(), &repaired.bundle);
+    assert_eq!(find(&app, first, view).bounds, authored_row.bounds);
+}

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

@@ -65,6 +65,7 @@ impl App {
                 owner: context.owner,
                 revision: context.revision,
                 epoch: lifetime,
+                scenario_view: None,
             };
             if self.behavior.has_pending()
                 || self.draft_dirty()

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

@@ -0,0 +1,96 @@
+//! Saved Scenario navigation is presentation state, never a document edit.
+use super::*;
+use crate::behavior::scenario_layout::{Representation, presentation::checked_owner};
+
+impl App {
+    pub(super) fn enter_scenario_representation(&mut self, representation: Representation) -> bool {
+        let Some(owner) = checked_owner(self.project(), representation) else {
+            self.status =
+                "This Scenario view is no longer available or has an incompatible owner.".into();
+            return false;
+        };
+        self.layer = self.project().elements[&owner].layer();
+        self.page = Page::Behavior;
+        self.behavior.active_owner = Some(owner);
+        match representation {
+            Representation::Saved { diagram } => self.active_diagram = Some(diagram),
+            Representation::Derived { .. } => {
+                if self
+                    .active_diagram
+                    .is_some_and(|id| self.saved_scenario_diagram(id))
+                {
+                    self.active_diagram = None;
+                }
+            }
+        }
+        self.selected_node = None;
+        if self
+            .behavior
+            .scenario
+            .enter_representation(self.canvas_document, owner, representation)
+        {
+            self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+        }
+        true
+    }
+
+    /// Reconcile after navigation/adoption without selecting or applying a draft.
+    /// A retained invalid Saved identity remains unavailable; it must not silently
+    /// turn into a different automatic Scenario or another saved arrangement.
+    pub(super) fn reconcile_scenario_workspace(&mut self) {
+        if self.page == Page::Diagram
+            && !self.behavior.has_pending()
+            && let Some(diagram) = self
+                .active_diagram
+                .filter(|id| self.saved_scenario_diagram(*id))
+        {
+            self.enter_scenario_representation(Representation::Saved { diagram });
+        }
+        if self.page != Page::Behavior {
+            self.behavior.scenario.leave();
+            return;
+        }
+        if let Some(rep @ Representation::Saved { diagram }) =
+            self.behavior.scenario.representation()
+        {
+            // The requested view is authoritative until explicit navigation
+            // retires it. This also recovers the same view when Undo restores it.
+            if let Some(owner) = checked_owner(self.project(), rep) {
+                self.active_diagram = Some(diagram);
+                self.layer = self.project().elements[&owner].layer();
+                self.behavior.active_owner = Some(owner);
+                self.behavior
+                    .scenario
+                    .enter_representation(self.canvas_document, owner, rep);
+            } else if let Some(owner) = self.behavior.scenario.owner() {
+                self.behavior
+                    .scenario
+                    .enter_representation(self.canvas_document, owner, rep);
+            }
+            return;
+        }
+        let Some(owner) = behavior::selected_owner(self) else {
+            self.behavior.scenario.leave();
+            return;
+        };
+        if self
+            .project()
+            .elements
+            .get(&owner)
+            .is_some_and(|e| e.kind() == Kind::Scenario)
+        {
+            self.behavior.scenario.enter(self.canvas_document, owner);
+        } else {
+            self.behavior.scenario.leave();
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;
+
+#[cfg(test)]
+mod adoption_tests;
+
+#[cfg(test)]
+mod owner_navigation_tests;

crates/oa-desktop/src/app/scenario_diagram/adoption_tests.rs

@@ -0,0 +1,264 @@
+//! Independent adoption oracles: expected Projects are edited directly in the
+//! fixture, then admitted through the actual source editor/Document transaction.
+//! Navigation is checked separately from the expected authored mutation.
+use super::*;
+use crate::behavior::canvas_workspace::tests::Mounted;
+use iced::advanced::widget;
+use iced::widget::text_editor;
+use oa_core::language;
+use std::sync::Arc;
+
+struct Fixture {
+    app: App,
+    owner: Id,
+    same_layer: Id,
+    other_layer: Id,
+    view: Id,
+    spare_view: Id,
+}
+
+fn fixture() -> Fixture {
+    let mut project = Project::empty();
+    let owner = project
+        .add_element(Kind::Scenario, Layer::Oa, "Original owner", None)
+        .unwrap();
+    let same_layer = project
+        .add_element(Kind::Scenario, Layer::Oa, "Other OA owner", None)
+        .unwrap();
+    let other_layer = project
+        .add_element(Kind::Scenario, Layer::Sa, "SA owner", None)
+        .unwrap();
+    // A remaining topology makes silent fallback observably different from the
+    // required unavailable Saved view after its owner is deleted.
+    project
+        .add_element(Kind::Process, Layer::Oa, "Remaining process", None)
+        .unwrap();
+    let mut make_view = |alias: &str, name: &str, owner| {
+        let id = Id::new_v4();
+        project.diagrams.insert(
+            id,
+            Diagram {
+                id,
+                alias: alias.into(),
+                name: name.into(),
+                description: String::new(),
+                layer: Layer::Oa,
+                projection: ProjectionKind::Scenario { scenario: owner },
+                layout: None,
+                nodes: Default::default(),
+                routes: vec![],
+                view_options: Default::default(),
+            },
+        );
+        id
+    };
+    let view = make_view("retained_view", "Retained arrangement", owner);
+    let spare_view = make_view("spare_view", "Spare arrangement", same_layer);
+    let mut app = App::with_project(project);
+    let _ = app.update(Message::Select(owner));
+    choose(&mut app, view);
+    assert_saved(&app, view, owner, Layer::Oa);
+    assert!(!app.document.can_undo());
+    Fixture {
+        app,
+        owner,
+        same_layer,
+        other_layer,
+        view,
+        spare_view,
+    }
+}
+
+fn choose(app: &mut App, id: Id) {
+    let _ = app.update(Message::Diagram(Choice {
+        id,
+        label: "Previously captured picker item".into(),
+    }));
+}
+
+fn assert_saved(app: &App, view: Id, owner: Id, layer: Layer) {
+    assert_eq!(app.page, Page::Behavior);
+    assert_eq!(app.layer, layer);
+    assert_eq!(app.active_diagram, Some(view));
+    let context = app
+        .scenario_context()
+        .expect("saved owner remains the visible context");
+    assert_eq!(context.scenario, owner);
+    assert_eq!(
+        context.representation,
+        Representation::Saved { diagram: view }
+    );
+    assert!(!context.visit.is_nil());
+}
+
+fn adopt_from_source(app: &mut App, expected: &Project) {
+    let text = language::format(expected);
+    // Parser equality is a fixture precondition, not the navigation oracle.
+    assert_eq!(language::parse(&text).unwrap(), *expected);
+    let _ = app.update(Message::Page(Page::Text));
+    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)),
+    )));
+    assert!(app.source_dirty());
+    let _ = app.update(Message::ApplySource);
+    assert!(!app.source_dirty(), "{}", app.status);
+    assert_eq!(
+        app.project(),
+        expected,
+        "actual source transaction must adopt exactly the fixture change"
+    );
+    let _ = app.update(Message::Page(Page::Behavior));
+}
+
+fn retarget(cross_layer: bool) {
+    let mut f = fixture();
+    let before = f.app.document.snapshot();
+    let old_context = f.app.scenario_context().unwrap();
+    let revision = f.app.document.revision();
+    let target = if cross_layer {
+        f.other_layer
+    } else {
+        f.same_layer
+    };
+    let layer = if cross_layer { Layer::Sa } else { Layer::Oa };
+    let mut expected = before.decoded.project.clone();
+    let view = expected.diagrams.get_mut(&f.view).unwrap();
+    view.projection = ProjectionKind::Scenario { scenario: target };
+    view.layer = layer;
+
+    adopt_from_source(&mut f.app, &expected);
+    assert_saved(&f.app, f.view, target, layer);
+    assert_ne!(f.app.scenario_context().unwrap().visit, old_context.visit);
+    assert_eq!(
+        f.app.document.revision(),
+        revision + 1,
+        "routing must not create a second transaction"
+    );
+    assert_eq!(
+        f.app.project().diagrams[&f.spare_view],
+        before.decoded.project.diagrams[&f.spare_view]
+    );
+    let adopted_bundle = f.app.document.bundle().clone();
+
+    let _ = f.app.update(Message::Undo);
+    assert_saved(&f.app, f.view, f.owner, Layer::Oa);
+    assert_eq!(f.app.project(), &before.decoded.project);
+    assert_eq!(f.app.document.bundle(), &before.bundle);
+    assert!(
+        !f.app.document.can_undo(),
+        "exactly one authored adoption must be undone"
+    );
+    let _ = f.app.update(Message::Redo);
+    assert_saved(&f.app, f.view, target, layer);
+    assert_eq!(f.app.project(), &expected);
+    assert_eq!(f.app.document.bundle(), &adopted_bundle);
+    assert!(!f.app.document.can_redo());
+}
+
+#[test]
+fn source_same_layer_owner_retarget_undo_redo_keeps_requested_saved_uuid() {
+    retarget(false);
+}
+
+#[test]
+fn source_cross_layer_owner_retarget_undo_redo_keeps_requested_saved_uuid() {
+    retarget(true);
+}
+
+#[tokio::test]
+async fn source_deleted_owner_and_saved_view_mount_unavailable_instead_of_another_behavior() {
+    let mut f = fixture();
+    let before = f.app.document.snapshot();
+    let mut expected = before.decoded.project.clone();
+    assert!(expected.elements.remove(&f.owner).is_some());
+    assert!(expected.diagrams.remove(&f.view).is_some());
+    assert!(expected.elements.contains_key(&f.same_layer));
+    assert!(
+        expected
+            .elements
+            .values()
+            .any(|e| e.kind() == Kind::Process)
+    );
+    adopt_from_source(&mut f.app, &expected);
+    assert_eq!(
+        f.app.behavior.scenario.representation(),
+        Some(Representation::Saved { diagram: f.view })
+    );
+    let adopted = f.app.document.snapshot();
+    let revision = f.app.document.revision();
+    let mut mounted = Mounted::new(&mut f.app).await;
+    let geometry = mounted.geometry(&f.app);
+    assert!(
+        geometry
+            .containers
+            .contains_key(&widget::Id::from("scenario-viewport-unavailable"))
+    );
+    assert!(
+        !geometry
+            .containers
+            .contains_key(&widget::Id::from("scenario-viewport"))
+    );
+    assert_eq!(f.app.project(), &expected);
+    assert_eq!(f.app.document.bundle(), &adopted.bundle);
+    assert_eq!(
+        f.app.document.revision(),
+        revision,
+        "mounting unavailable must remain passive"
+    );
+
+    let _ = f.app.update(Message::Undo);
+    assert_saved(&f.app, f.view, f.owner, Layer::Oa);
+    assert_eq!(f.app.document.bundle(), &before.bundle);
+    let _ = f.app.update(Message::Redo);
+    assert_eq!(
+        f.app.behavior.scenario.representation(),
+        Some(Representation::Saved { diagram: f.view })
+    );
+    mounted.settle(&mut f.app).await;
+    assert!(
+        mounted
+            .geometry(&f.app)
+            .containers
+            .contains_key(&widget::Id::from("scenario-viewport-unavailable"))
+    );
+    assert_eq!(f.app.project(), &expected);
+    assert_eq!(f.app.document.bundle(), &adopted.bundle);
+}
+
+#[test]
+fn missing_and_deleted_picker_ids_cannot_apply_an_unrelated_valid_property_draft() {
+    let mut f = fixture();
+    let mut expected = f.app.project().clone();
+    expected.diagrams.remove(&f.spare_view).unwrap();
+    adopt_from_source(&mut f.app, &expected);
+    let _ = f.app.update(Message::Select(f.owner));
+    let _ = f.app.update(Message::Field(
+        "/name".into(),
+        "Pending valid owner rename".into(),
+    ));
+    assert!(f.app.draft_dirty());
+    let before = f.app.document.snapshot();
+    let revision = f.app.document.revision();
+    let selected = f.app.selected;
+    for invalid in [Id::nil(), f.spare_view] {
+        choose(&mut f.app, invalid);
+        assert_saved(&f.app, f.view, f.owner, Layer::Oa);
+        assert_eq!(f.app.selected, selected);
+        assert!(f.app.draft_dirty());
+        assert_eq!(f.app.project(), &before.decoded.project);
+        assert_eq!(f.app.document.bundle(), &before.bundle);
+        assert_eq!(f.app.document.revision(), revision);
+    }
+    // Establish that the retained draft really was valid, not merely refused by
+    // the property validator: explicit Apply commits it in exactly one step.
+    assert!(f.app.apply(), "{}", f.app.status);
+    assert_eq!(
+        f.app.project().elements[&f.owner].name,
+        "Pending valid owner rename"
+    );
+    assert_eq!(f.app.document.revision(), revision + 1);
+    let _ = f.app.update(Message::Undo);
+    assert_eq!(f.app.project(), &before.decoded.project);
+    assert_eq!(f.app.document.bundle(), &before.bundle);
+}

crates/oa-desktop/src/app/scenario_diagram/owner_navigation_tests.rs

@@ -0,0 +1,113 @@
+//! Explicit owner navigation must retire a retained Saved Scenario, including
+//! when selection was made on a different page. These are real App events.
+use super::*;
+use crate::behavior::scenario::CanvasEvent;
+
+fn setup(kind: Kind) -> (App, Id, Id) {
+    let mut project = Project::empty();
+    let scenario = project
+        .add_element(Kind::Scenario, Layer::Oa, "Incident review", None)
+        .unwrap();
+    let target = project
+        .add_element(kind, Layer::Oa, "Explicit destination", None)
+        .unwrap();
+    let view = Id::new_v4();
+    project.diagrams.insert(
+        view,
+        Diagram {
+            id: view,
+            alias: "incident_saved".into(),
+            name: "Incident saved arrangement".into(),
+            description: String::new(),
+            layer: Layer::Oa,
+            projection: ProjectionKind::Scenario { scenario },
+            layout: None,
+            nodes: Default::default(),
+            routes: vec![],
+            view_options: Default::default(),
+        },
+    );
+    let errors: Vec<_> = oa_core::validation::validate(&project)
+        .into_iter()
+        .filter(|issue| issue.severity == oa_core::validation::Severity::Error)
+        .collect();
+    assert!(errors.is_empty(), "{errors:?}");
+    let mut app = App::with_project(project);
+    let _ = app.update(Message::Select(scenario));
+    let _ = app.update(Message::Diagram(Choice {
+        id: view,
+        label: "Incident saved arrangement".into(),
+    }));
+    assert_eq!(app.page, Page::Behavior);
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        Representation::Saved { diagram: view }
+    );
+    assert_eq!(app.selected, scenario);
+    (app, scenario, target)
+}
+
+fn assert_destination(app: &App, target: Id) {
+    assert_eq!(app.page, Page::Behavior);
+    assert_eq!(app.selected, target);
+    assert_eq!(app.behavior.active_owner, Some(target));
+    assert_eq!(behavior::selected_owner(app), Some(target));
+    assert_eq!(
+        app.behavior.scenario.representation(),
+        None,
+        "explicit non-Scenario destination must not retain an overriding Saved request"
+    );
+    assert!(app.scenario_context().is_none());
+}
+
+fn exercise(via_guide: bool) {
+    for kind in [Kind::Process, Kind::StateMachine] {
+        let (mut app, scenario, target) = setup(kind);
+        assert_ne!(scenario, target);
+        let held = app.scenario_context().unwrap();
+        let accepted = app.document.snapshot();
+        let drafts = app.source_workspace.bundle();
+        let revision = app.document.revision();
+        let dirty = (app.document.dirty(), app.dirty(), app.source_dirty());
+        assert!(!app.document.can_undo() && !app.document.can_redo());
+        if via_guide {
+            let _ = app.update(Message::Page(Page::Guide));
+            assert_eq!(app.page, Page::Guide);
+            assert!(app.scenario_context().is_none());
+        }
+        let _ = app.update(Message::Select(target));
+        if via_guide {
+            assert_eq!(
+                app.page,
+                Page::Guide,
+                "explorer selection must not itself switch the page"
+            );
+            let _ = app.update(Message::Page(Page::Behavior));
+        }
+        assert_destination(&app, target);
+        let camera = app.camera_boundary();
+        // The prior saved canvas cannot regain focus after either owner route.
+        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Focus(held)));
+        assert_destination(&app, target);
+        assert!(app.camera_boundary() == camera);
+        assert_eq!(app.project(), &accepted.decoded.project);
+        assert_eq!(app.document.bundle(), &accepted.bundle);
+        assert_eq!(app.source_workspace.bundle(), drafts);
+        assert_eq!(app.document.revision(), revision);
+        assert_eq!(
+            (app.document.dirty(), app.dirty(), app.source_dirty()),
+            dirty
+        );
+        assert!(!app.document.can_undo() && !app.document.can_redo());
+    }
+}
+
+#[test]
+fn saved_scenario_guide_selection_returns_to_explicit_process_or_state_owner() {
+    exercise(true);
+}
+
+#[test]
+fn saved_scenario_direct_behavior_selection_enters_explicit_process_or_state_owner() {
+    exercise(false);
+}

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

@@ -0,0 +1,205 @@
+use super::*;
+use crate::behavior::scenario::{CanvasEvent, ScrollArea};
+
+fn saved(p: &mut Project, owner: Id, name: &str) -> Id {
+    let id = Id::new_v4();
+    p.diagrams.insert(
+        id,
+        Diagram {
+            id,
+            alias: format!("view_{}", p.diagrams.len()),
+            name: name.into(),
+            description: String::new(),
+            layer: Layer::Oa,
+            projection: ProjectionKind::Scenario { scenario: owner },
+            layout: None,
+            routes: vec![],
+            nodes: Default::default(),
+            view_options: Default::default(),
+        },
+    );
+    id
+}
+fn setup() -> (App, Id, Id, Id, Id) {
+    let (mut p, [owner, callee, _], [reference, _, _]) =
+        behavior::scenario::direct_tests::navigation_fixture();
+    let a = saved(&mut p, owner, "Review A");
+    let b = saved(&mut p, owner, "Review B");
+    let mut app = App::with_project(p);
+    app.select(owner);
+    (app, a, b, reference, callee)
+}
+fn choose(app: &mut App, diagram: Id) {
+    let _ = app.update(Message::Diagram(Choice {
+        id: diagram,
+        label: "Captured view".into(),
+    }));
+}
+fn event(app: &mut App, f: impl FnOnce(behavior::scenario::Context) -> CanvasEvent) {
+    let context = app.scenario_context().unwrap();
+    let _ = app.update(Message::ScenarioCanvas(f(context)));
+}
+#[test]
+fn saved_view_switches_are_distinct_passive_visits_and_preserve_actual_history() {
+    let (mut app, a, b, _, _) = setup();
+    let original = app.document.snapshot();
+    let owner = app.selected;
+    assert!(app.execute(Command::Rename(owner, "Previously edited caller".into())));
+    let edited = app.document.snapshot();
+    let edited_revision = app.document.revision();
+    choose(&mut app, a);
+    let first = app.scenario_context().unwrap();
+    choose(&mut app, b);
+    let second = app.scenario_context().unwrap();
+    choose(&mut app, a);
+    let third = app.scenario_context().unwrap();
+    assert_eq!(first.scenario, owner);
+    assert_eq!(first.representation, Representation::Saved { diagram: a });
+    assert_eq!(second.representation, Representation::Saved { diagram: b });
+    assert_ne!(first.visit, second.visit);
+    assert_ne!(first.visit, third.visit);
+    assert_eq!(app.page, Page::Behavior);
+    assert_eq!(app.selected, owner);
+    assert_eq!(app.document.bundle(), &edited.bundle);
+    assert_eq!(app.project(), &edited.decoded.project);
+    assert_eq!(app.document.revision(), edited_revision);
+    let _ = app.update(Message::Undo);
+    assert_eq!(app.document.bundle(), &original.bundle);
+    assert_eq!(app.project(), &original.decoded.project);
+    let _ = app.update(Message::Redo);
+    assert_eq!(app.document.bundle(), &edited.bundle);
+    assert_eq!(app.project(), &edited.decoded.project);
+}
+#[test]
+fn saved_view_return_rejects_old_passive_events_without_an_intermediate_frame() {
+    let (mut app, a, b, _, _) = setup();
+    choose(&mut app, a);
+    let old = app.scenario_context().unwrap();
+    choose(&mut app, b);
+    choose(&mut app, a);
+    let current = app.scenario_context().unwrap();
+    let camera = app.behavior.scenario.camera_boundary();
+    let before = app.document.snapshot();
+    for stale in [
+        CanvasEvent::Viewport(old, iced::Size::new(432., 321.)),
+        CanvasEvent::Scrolled(old, ScrollArea::Page, iced::Vector::new(0., 800.)),
+        CanvasEvent::FormShown(old, Id::new_v4()),
+        CanvasEvent::Restored(
+            old,
+            Id::new_v4(),
+            ScrollArea::Page,
+            iced::Vector::new(0., 800.),
+        ),
+        CanvasEvent::Camera(
+            old,
+            app.camera_epoch,
+            behavior::canvas_workspace::Event::Pan(iced::Vector::new(90., 80.)),
+        ),
+    ] {
+        let _ = app.update(Message::ScenarioCanvas(stale));
+        assert_eq!(app.scenario_context(), Some(current));
+        assert!(app.behavior.scenario.camera_boundary() == camera);
+        assert_eq!(app.document.bundle(), &before.bundle);
+    }
+}
+#[test]
+fn saved_reference_back_restores_exact_view_with_a_fresh_visit() {
+    let (mut app, a, _, reference, callee) = setup();
+    choose(&mut app, a);
+    let caller = app.scenario_context().unwrap();
+    let before = app.document.snapshot();
+    event(&mut app, |ctx| CanvasEvent::OpenUse(ctx, reference));
+    let target = app.scenario_context().unwrap();
+    assert_eq!(target.scenario, callee);
+    assert_eq!(
+        target.representation,
+        Representation::Derived { owner: callee }
+    );
+    assert_eq!(app.active_diagram, None);
+    event(&mut app, CanvasEvent::Back);
+    let returned = app.scenario_context().unwrap();
+    assert_eq!(returned.representation, caller.representation);
+    assert_eq!(app.active_diagram, Some(a));
+    assert_eq!(app.selected, reference);
+    assert_ne!(returned.visit, caller.visit);
+    assert_eq!(app.document.bundle(), &before.bundle);
+    assert_eq!(app.project(), &before.decoded.project);
+    assert!(!app.document.can_undo());
+}
+#[test]
+fn saved_picker_applies_valid_old_draft_and_uuid_edit_follows_that_same_view() {
+    let (mut app, a, b, _, _) = setup();
+    choose(&mut app, a);
+    let _ = app.update(Message::Select(a));
+    let before = app.document.snapshot();
+    let _ = app.update(Message::Field("/name".into(), "Renamed A".into()));
+    choose(&mut app, b);
+    assert_eq!(app.project().diagrams[&a].name, "Renamed A");
+    assert_eq!(app.selected, b);
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        Representation::Saved { diagram: b }
+    );
+    let _ = app.update(Message::Undo);
+    assert_eq!(app.document.bundle(), &before.bundle);
+    choose(&mut app, a);
+    let replacement = Id::new_v4();
+    let _ = app.update(Message::Field("/id".into(), replacement.to_string()));
+    choose(&mut app, a);
+    assert!(!app.project().diagrams.contains_key(&a));
+    assert_eq!(app.active_diagram, Some(replacement));
+    assert_eq!(app.selected, replacement);
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        Representation::Saved {
+            diagram: replacement
+        }
+    );
+}
+#[test]
+fn leaving_and_reentering_saved_view_preserves_source_and_retires_passive_visit() {
+    let (mut app, a, _, _, _) = setup();
+    choose(&mut app, a);
+    let old = app.scenario_context().unwrap();
+    let before = app.document.snapshot();
+    let _ = app.update(Message::Page(Page::Guide));
+    assert!(app.scenario_context().is_none());
+    let _ = app.update(Message::Page(Page::Behavior));
+    let fresh = app.scenario_context().unwrap();
+    assert_eq!(fresh.representation, old.representation);
+    assert_ne!(fresh.visit, old.visit);
+    assert_eq!(app.document.bundle(), &before.bundle);
+}
+
+#[test]
+fn arrangement_picker_rejects_previous_visit_and_switches_automatic_without_model_changes() {
+    let (mut app, a, b, _, _) = setup();
+    choose(&mut app, a);
+    let stale = app.scenario_context().unwrap();
+    choose(&mut app, b);
+    let current = app.scenario_context().unwrap();
+    let before = app.document.snapshot();
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Representation(
+        stale,
+        Representation::Saved { diagram: a },
+    )));
+    assert_eq!(app.scenario_context(), Some(current));
+    event(&mut app, |context| {
+        CanvasEvent::Representation(
+            context,
+            Representation::Derived {
+                owner: context.scenario,
+            },
+        )
+    });
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        Representation::Derived {
+            owner: current.scenario
+        }
+    );
+    assert_eq!(app.active_diagram, None);
+    assert_eq!(app.document.bundle(), &before.bundle);
+    assert_eq!(app.project(), &before.decoded.project);
+    assert!(!app.document.can_undo());
+}

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

@@ -0,0 +1,88 @@
+//! Admit spacing packets before ordinary navigation can retire a newer reveal.
+use super::*;
+use behavior::scenario::spacing::{Event, controller::Finish};
+
+#[cfg(test)]
+mod tests;
+
+impl App {
+    pub(super) fn spacing_enabled(&self) -> bool {
+        self.pending_diagram_reveal.is_none()
+            && !self.behavior.has_pending()
+            && !self.draft_dirty()
+            && !self.source_dirty()
+            && !self.source_rename.open()
+            && behavior::canvas_workspace::keyboard_enabled(self)
+    }
+
+    pub(super) fn scenario_spacing(&mut self, event: Event) -> Task<Message> {
+        let stamp = event.stamp();
+        if self.scenario_context() != Some(stamp.context) || self.camera_epoch != stamp.camera_epoch
+        {
+            return Task::none();
+        }
+        let state = &self.behavior.scenario;
+        let matches =
+            state.spacing_token() == Some(event.token()) && state.spacing_stamp() == Some(stamp);
+        if match event {
+            Event::Begin { token, .. } => token.is_nil() || state.spacing_token().is_some(),
+            _ => !matches,
+        } {
+            return Task::none();
+        }
+        if matches!(event, Event::Cancel { .. }) || !self.spacing_enabled() {
+            if self.behavior.scenario.cancel_spacing() {
+                self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+            }
+            return Task::none();
+        }
+        match event {
+            Event::Begin { .. } => {
+                let mut state = std::mem::take(&mut self.behavior.scenario);
+                let result = state.begin_spacing(self.project(), event);
+                self.behavior.scenario = state;
+                if result.is_err() {
+                    self.status = "The drag could not start in this view. Try again.".into();
+                }
+            }
+            Event::Move { screen, .. } => self.behavior.scenario.move_spacing(screen),
+            Event::Finish { screen, .. } => {
+                let finished = self.behavior.scenario.finish_spacing(screen);
+                // Retire queued packets even for zero motion or a refused finish.
+                self.canvas_epoch = self.canvas_epoch.wrapping_add(1);
+                match finished {
+                    Ok(Finish::Click(target)) => self.select(target),
+                    Ok(Finish::Noop) => {}
+                    Ok(Finish::Commit {
+                        command,
+                        selected,
+                        scale,
+                        pan,
+                    }) => {
+                        // Document prepares and writes the source candidate before
+                        // committing its snapshot. Failure leaves camera/selection
+                        // and source/history at their accepted values.
+                        match self.document.execute(command) {
+                            Ok(_) => {
+                                self.selected = selected;
+                                self.selected_node = None;
+                                self.diagram_navigation_focus = None;
+                                self.behavior.scenario.accept_spacing_camera(scale, pan);
+                                self.sync();
+                                self.status = "Scenario spacing updated.".into();
+                            }
+                            Err(error) => self.status = format!("Spacing was not applied: {error}"),
+                        }
+                    }
+                    Err(_) => {
+                        self.status =
+                            "That position cannot be applied. The saved arrangement is unchanged."
+                                .into()
+                    }
+                }
+            }
+            Event::Cancel { .. } => unreachable!(),
+        }
+        Task::none()
+    }
+}

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

@@ -0,0 +1,272 @@
+use super::*;
+use behavior::scenario::{
+    CanvasEvent,
+    spacing::{
+        Target,
+        controller::tests::{fixture, packet},
+    },
+};
+use iced::{Point, Size, Vector};
+
+fn setup() -> (App, Id, Id) {
+    let (document, owner, diagram, lane, message) = fixture();
+    let mut app = App::with_project(document.project().clone());
+    let _ = app.update(Message::Select(owner));
+    let _ = app.update(Message::Diagram(Choice {
+        id: diagram,
+        label: "Saved".into(),
+    }));
+    let c = app.scenario_context().unwrap();
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Viewport(
+        c,
+        Size::new(900., 600.),
+    )));
+    assert!(app.spacing_enabled());
+    (app, lane, message)
+}
+fn begin(app: &mut App, target: Target) -> (Event, Point, f32) {
+    let event = packet(
+        app.project(),
+        &app.behavior.scenario,
+        app.scenario_context().unwrap(),
+        app.camera_epoch,
+        target,
+    );
+    let Event::Begin {
+        press_screen,
+        scale,
+        ..
+    } = event
+    else {
+        unreachable!()
+    };
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Spacing(event)));
+    assert_eq!(app.behavior.scenario.spacing_token(), Some(event.token()));
+    (event, press_screen, scale)
+}
+fn send(app: &mut App, event: Event) {
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Spacing(event)));
+}
+fn move_to(app: &mut App, begin: Event, screen: Point) {
+    send(
+        app,
+        Event::Move {
+            stamp: begin.stamp(),
+            token: begin.token(),
+            screen,
+        },
+    );
+}
+fn finish(app: &mut App, begin: Event, screen: Point) {
+    send(
+        app,
+        Event::Finish {
+            stamp: begin.stamp(),
+            token: begin.token(),
+            screen,
+        },
+    );
+}
+
+#[test]
+fn same_batch_preview_is_immutable_and_one_commit_undo_redo_has_exact_source_parity() {
+    let (mut app, lane, _) = setup();
+    let original = app.document.snapshot();
+    let source = app.source_workspace.bundle();
+    let selected = app.selected;
+    let epoch = app.canvas_epoch;
+    let (event, start, scale) = begin(&mut app, Target::Lane(lane));
+    move_to(&mut app, event, start + Vector::new(40., 300.));
+    assert_eq!(app.selected, selected);
+    assert_eq!(app.canvas_epoch, epoch);
+    assert_eq!(app.project(), &original.decoded.project);
+    assert_eq!(app.source_workspace.bundle(), source);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+    finish(&mut app, event, start + Vector::new(40., 300.));
+    assert_eq!(app.selected, lane);
+    assert!(app.document.can_undo() && !app.document.can_redo());
+    let accepted = app.document.snapshot();
+    assert_ne!(accepted.bundle, original.bundle);
+    let expected = behavior::scenario::spacing::controller::tests::expected(
+        &original.decoded.project,
+        match event.stamp().context.representation {
+            behavior::scenario_layout::Representation::Saved { diagram } => diagram,
+            _ => unreachable!(),
+        },
+        Target::Lane(lane),
+        40. / scale,
+    );
+    assert_eq!(app.project(), &expected);
+    let _ = app.update(Message::ShortcutUndo(false));
+    assert_eq!(app.project(), &original.decoded.project);
+    assert_eq!(app.document.bundle(), &original.bundle);
+    assert!(!app.document.can_undo() && app.document.can_redo());
+    let _ = app.update(Message::ShortcutUndo(true));
+    assert_eq!(app.project(), &accepted.decoded.project);
+    assert_eq!(app.document.bundle(), &accepted.bundle);
+}
+
+#[test]
+fn click_selects_but_crossed_return_and_cancel_preserve_selection_camera_and_history() {
+    let (mut app, lane, message) = setup();
+    let original = app.document.snapshot();
+    let camera = app.behavior.scenario.camera_boundary();
+    let (event, start, _) = begin(&mut app, Target::Message(message));
+    finish(&mut app, event, start + Vector::new(30., 2.));
+    assert_eq!(app.selected, message);
+    assert!(camera == app.behavior.scenario.camera_boundary());
+    for cancel in [false, true] {
+        let (event, start, _) = begin(&mut app, Target::Lane(lane));
+        move_to(&mut app, event, start + Vector::new(30., 0.));
+        if cancel {
+            send(
+                &mut app,
+                Event::Cancel {
+                    stamp: event.stamp(),
+                    token: event.token(),
+                },
+            );
+        } else {
+            finish(&mut app, event, start);
+        }
+        assert_eq!(app.selected, message);
+        assert!(camera == app.behavior.scenario.camera_boundary());
+        assert_eq!(app.document.bundle(), &original.bundle);
+        assert_eq!(app.project(), &original.decoded.project);
+        assert!(!app.document.can_undo() && !app.document.can_redo());
+    }
+}
+
+#[test]
+fn stale_finish_after_new_view_and_forged_token_are_inert_before_reveal_reconciliation() {
+    let (mut app, lane, _) = setup();
+    let (event, start, _) = begin(&mut app, Target::Lane(lane));
+    let held_epoch = app.canvas_epoch;
+    send(
+        &mut app,
+        Event::Finish {
+            stamp: event.stamp(),
+            token: Id::new_v4(),
+            screen: start + Vector::new(30., 0.),
+        },
+    );
+    assert_eq!(app.canvas_epoch, held_epoch);
+    assert_eq!(app.behavior.scenario.spacing_token(), Some(event.token()));
+    let owner = event.stamp().context.scenario;
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Representation(
+        event.stamp().context,
+        behavior::scenario_layout::Representation::Derived { owner },
+    )));
+    let current = app.scenario_context();
+    let epoch = app.canvas_epoch;
+    let original = app.document.snapshot();
+    finish(&mut app, event, start + Vector::new(50., 0.));
+    assert_eq!(app.scenario_context(), current);
+    assert_eq!(app.canvas_epoch, epoch);
+    assert!(app.behavior.scenario.spacing_token().is_none());
+    assert_eq!(app.document.bundle(), &original.bundle);
+}
+
+#[test]
+fn source_write_failure_cannot_commit_candidate_or_materialize_camera() {
+    let (mut app, lane, _) = setup();
+    let bundle = app.document.bundle().clone();
+    let mut limits = oa_core::source_project::ProjectLimits::default();
+    limits.model.max_source_bytes = bundle.files.values().map(String::len).sum();
+    app.document = Document::from_bundle(bundle, limits).unwrap();
+    app.sync();
+    let original = app.document.snapshot();
+    let selected = app.selected;
+    let camera = app.behavior.scenario.camera_boundary();
+    let (event, start, _) = begin(&mut app, Target::Lane(lane));
+    move_to(&mut app, event, start + Vector::new(40., 0.));
+    finish(&mut app, event, start + Vector::new(40., 0.));
+    assert!(
+        app.status.starts_with("Spacing was not applied:"),
+        "{}",
+        app.status
+    );
+    assert_eq!(app.selected, selected);
+    assert!(camera == app.behavior.scenario.camera_boundary());
+    assert_eq!(app.project(), &original.decoded.project);
+    assert_eq!(app.document.bundle(), &original.bundle);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+    assert!(app.behavior.scenario.spacing_token().is_none());
+}
+
+#[test]
+fn pending_semantic_draft_and_source_edit_cancel_and_reject_held_finish() {
+    for source in [false, true] {
+        let (mut app, lane, _) = setup();
+        let original = app.document.snapshot();
+        let selected = app.selected;
+        let (event, start, _) = begin(&mut app, Target::Lane(lane));
+        move_to(&mut app, event, start + Vector::new(30., 0.));
+        if source {
+            let _ = app.update(Message::SourceEdit(text_editor::Action::Edit(
+                text_editor::Edit::Insert(' '),
+            )));
+            assert!(app.source_dirty());
+        } else {
+            let _ = app.update(Message::Behavior(behavior::Event::Scenario(
+                behavior::scenario::Event::Start(
+                    event.stamp().context.scenario,
+                    behavior::scenario::Tool::Lifeline,
+                ),
+            )));
+            assert!(app.behavior.has_pending());
+        }
+        let draft = app.source_workspace.bundle();
+        assert!(app.behavior.scenario.spacing_token().is_none());
+        finish(&mut app, event, start + Vector::new(30., 0.));
+        assert_eq!(app.project(), &original.decoded.project);
+        assert_eq!(app.document.bundle(), &original.bundle);
+        assert_eq!(app.source_workspace.bundle(), draft);
+        assert_eq!(app.selected, selected);
+        assert!(!app.document.can_undo());
+    }
+}
+
+#[test]
+fn stale_finish_cannot_remove_new_same_view_deferred_reveal() {
+    let (mut app, lane, message) = setup();
+    let (event, start, _) = begin(&mut app, Target::Lane(lane));
+    let behavior::scenario_layout::Representation::Saved { diagram } =
+        event.stamp().context.representation
+    else {
+        unreachable!()
+    };
+    let _ = app.update(Message::RevealInDiagram(diagram, message));
+    assert!(app.pending_diagram_reveal.is_some());
+    let epoch = app.canvas_epoch;
+    let selected = app.selected;
+    let visit = app.pending_scenario_reveal_visit;
+    let original = app.document.snapshot();
+    finish(&mut app, event, start + Vector::new(50., 0.));
+    assert_eq!(app.canvas_epoch, epoch);
+    assert_eq!(app.pending_scenario_reveal_visit, visit);
+    assert!(app.pending_diagram_reveal.is_some());
+    assert_eq!(app.selected, selected);
+    assert_eq!(app.document.bundle(), &original.bundle);
+    assert!(!app.document.can_undo());
+}
+
+#[test]
+fn modal_open_cancels_preview_and_captured_begin_stays_retired_after_close() {
+    let (mut app, lane, _) = setup();
+    let original = app.document.snapshot();
+    let camera = app.behavior.scenario.camera_boundary();
+    let (event, start, _) = begin(&mut app, Target::Lane(lane));
+    move_to(&mut app, event, start + Vector::new(30., 0.));
+    let _ = app.update(Message::Delete);
+    assert!(app.delete_pending);
+    assert!(app.behavior.scenario.spacing_token().is_none());
+    finish(&mut app, event, start + Vector::new(30., 0.));
+    let _ = app.update(Message::CancelDelete);
+    send(&mut app, event);
+    assert!(app.behavior.scenario.spacing_token().is_none());
+    assert_eq!(app.project(), &original.decoded.project);
+    assert_eq!(app.document.bundle(), &original.bundle);
+    assert!(camera == app.behavior.scenario.camera_boundary());
+    assert!(!app.document.can_undo());
+}

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

@@ -24,6 +24,7 @@ impl App {
         if self.behavior.has_pending() {
             return;
         }
+        self.behavior.scenario.forget_view();
         self.layer = layer;
         self.page = Page::Behavior;
         self.behavior.active_owner = Some(machine);

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

@@ -49,11 +49,28 @@ fn fixture(layer: Layer, kind: Kind) -> (App, Id, Id, Id) {
     p.diagrams.get_mut(&view).unwrap().name = "Unrelated architecture".into();
     p.place(view, reused, Position { x: 873., y: 421. });
     let mut app = App::with_project(p);
-    app.layer = layer;
-    app.page = Page::Behavior;
-    app.selected = root;
-    app.behavior.active_owner = Some(root);
-    app.refresh_draft();
+    let accepted = app.document.snapshot();
+    // Enter through the actual navigation path: assigning Page/owner alone does
+    // not create the representation and live visit required by canvas events.
+    send(&mut app, Message::Select(root));
+    send(&mut app, Message::Page(Page::Behavior));
+    assert_eq!(app.layer, layer);
+    assert_eq!(app.page, Page::Behavior);
+    assert_eq!(app.selected, root);
+    assert_eq!(app.behavior.active_owner, Some(root));
+    if kind == Kind::Scenario {
+        let context = app.scenario_context().unwrap();
+        assert_eq!(context.document, app.canvas_document);
+        assert_eq!(context.scenario, root);
+        assert_eq!(
+            context.representation,
+            crate::behavior::scenario_layout::Representation::Derived { owner: root }
+        );
+        assert!(!context.visit.is_nil());
+    }
+    assert!(Arc::ptr_eq(&accepted, &app.document.snapshot()));
+    assert_eq!(app.source_workspace.bundle(), accepted.bundle);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
     (app, root, work, reused)
 }
 

crates/oa-desktop/src/behavior.rs

@@ -21,9 +21,11 @@ pub(crate) mod creation;
 mod form_session;
 pub(crate) mod scenario;
 mod scenario_activation;
+#[cfg(test)]
+mod scenario_hit_tests;
 // Pure saved-geometry bridge; workspace integration is a separate checkpoint.
 #[allow(dead_code)]
-mod scenario_layout;
+pub(crate) mod scenario_layout;
 mod scenario_lifecycle;
 pub(crate) mod source_draft;
 pub(crate) mod state_canvas;
@@ -62,9 +64,18 @@ mod scenario_scroll {
         process: bool,
         restore: Option<scenario::ScrollRestore>,
     }
-    type Report = Option<(bool, Id, Id, Vector)>;
+    type Identity = (Id, Id, scenario_layout::Representation, Id);
+    fn identity(context: scenario::Context) -> Identity {
+        (
+            context.document,
+            context.scenario,
+            context.representation,
+            context.visit,
+        )
+    }
+    type Report = Option<(bool, Identity, Vector)>;
     struct ObservedScroll {
-        identity: (Id, Id),
+        identity: Identity,
         report: Report,
         restored: Option<Id>,
     }
@@ -115,8 +126,12 @@ mod scenario_scroll {
         ) {
             let restore = self.restore.filter(|request| {
                 !self.process
-                    && (request.document, request.owner)
-                        == (self.context.document, self.context.scenario)
+                    && (
+                        request.document,
+                        request.owner,
+                        request.representation,
+                        request.visit,
+                    ) == identity(self.context)
                     && tree.state.downcast_ref::<ObservedScroll>().restored != Some(request.token)
             });
             let receipt = restore.and_then(|request| {
@@ -140,12 +155,7 @@ mod scenario_scroll {
                 &mut offset,
             );
             if let Some(offset) = offset.0 {
-                let next = Some((
-                    self.process,
-                    self.context.document,
-                    self.context.scenario,
-                    offset,
-                ));
+                let next = Some((self.process, identity(self.context), offset));
                 let state = tree.state.downcast_mut::<ObservedScroll>();
                 if let Some(token) = receipt {
                     state.restored = Some(token);
@@ -189,7 +199,7 @@ mod scenario_scroll {
         }
         fn state(&self) -> widget::tree::State {
             widget::tree::State::new(ObservedScroll {
-                identity: (self.context.document, self.context.scenario),
+                identity: identity(self.context),
                 report: None,
                 restored: None,
             })
@@ -198,9 +208,7 @@ mod scenario_scroll {
             vec![widget::Tree::new(self.content.as_widget())]
         }
         fn diff(&self, tree: &mut widget::Tree) {
-            if tree.state.downcast_ref::<ObservedScroll>().identity
-                != (self.context.document, self.context.scenario)
-            {
+            if tree.state.downcast_ref::<ObservedScroll>().identity != identity(self.context) {
                 // A new owner/document needs fresh real scroll state, not merely
                 // cleared mirrored offsets. Edits and tool/form changes retain it.
                 tree.state = self.state();
@@ -489,17 +497,25 @@ mod scenario_scroll {
         }
         #[test]
         fn direct_scenario_restore_cannot_scroll_another_document_owner_or_process_view() {
-            for mismatch in 0..3 {
+            for mismatch in 0..5 {
                 let context = scenario::direct_tests::context(Id::new_v4());
                 let mut request = scenario::ScrollRestore {
                     document: context.document,
                     owner: context.scenario,
+                    representation: context.representation,
+                    visit: context.visit,
                     token: Id::new_v4(),
                     offset: Vector::new(0., 180.),
                 };
                 match mismatch {
                     0 => request.document = Id::new_v4(),
                     1 => request.owner = Id::new_v4(),
+                    3 => {
+                        request.representation = scenario_layout::Representation::Saved {
+                            diagram: Id::new_v4(),
+                        }
+                    }
+                    4 => request.visit = Id::new_v4(),
                     _ => {}
                 }
                 let mut view = observer(600., context);
@@ -586,7 +602,7 @@ mod scenario_scroll {
             use widget::operation::scrollable::{AbsoluteOffset, scroll_to};
             for process in [false, true] {
                 let area = scenario::ScrollArea::Page;
-                for change in 0..4 {
+                for change in 0..6 {
                     let context = scenario::direct_tests::context(Id::new_v4());
                     let mut view = observer(600., context);
                     view.process = process;
@@ -615,6 +631,12 @@ mod scenario_scroll {
                             next.revision += 1;
                             next.epoch += 5;
                         }
+                        4 => {
+                            next.representation = scenario_layout::Representation::Saved {
+                                diagram: Id::new_v4(),
+                            }
+                        }
+                        5 => next.visit = Id::new_v4(),
                         _ => {}
                     }
                     view = observer(if change == 3 { 800. } else { 600. }, next);
@@ -662,7 +684,7 @@ mod scenario_scroll {
                         .collect::<Vec<_>>();
                     assert_eq!(
                         actual,
-                        vec![if change < 2 {
+                        vec![if change < 2 || change >= 4 {
                             Vector::ZERO
                         } else {
                             Vector::new(0., 180.)
@@ -976,6 +998,19 @@ pub fn view(app: &App) -> Element<'_, Message> {
             return container(out).padding(16).width(Fill).height(Fill).into();
         }
     }
+    // A requested saved view remains the destination even after its model is removed.
+    // The shared display adapter reports unavailable instead of choosing another behavior.
+    if matches!(
+        app.behavior.scenario.representation(),
+        Some(scenario_layout::Representation::Saved { .. })
+    ) && let Some(owner) = app.behavior.scenario.owner()
+        && !p
+            .elements
+            .get(&owner)
+            .is_some_and(|element| element.kind() == Kind::Scenario && element.layer() == app.layer)
+    {
+        return scenario::view(app, owner, column![].spacing(6));
+    }
     let choices = p
         .elements
         .values()
@@ -987,7 +1022,14 @@ pub fn view(app: &App) -> Element<'_, Message> {
             label: format!("{} · {}", e.kind(), e.name),
         })
         .collect::<Vec<_>>();
-    let owner = selected_owner(app);
+    let owner = if matches!(
+        app.behavior.scenario.representation(),
+        Some(scenario_layout::Representation::Saved { .. })
+    ) {
+        app.behavior.scenario.owner()
+    } else {
+        selected_owner(app)
+    };
     let selected = owner
         .and_then(|id| choices.iter().find(|c| c.id == id))
         .or(choices.first())
@@ -1121,8 +1163,27 @@ fn in_machine(p: &Project, id: Id, machine: Id) -> bool {
     false
 }
 
+/// Identifies the drawn primitive that won selection, not an authoring permission.
+/// In particular an activation and its message can share an occurrence UUID.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum SceneHitRole {
+    LifelineHeader,
+    MessageBody,
+    MessageLabel,
+    Activation,
+    LifecycleMarker,
+    LifelineGuide,
+    Box,
+    OtherLine,
+}
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+struct SceneHit {
+    id: Id,
+    role: SceneHitRole,
+}
 struct BoxItem {
     id: Id,
+    role: SceneHitRole,
     rect: Rectangle,
     title: String,
     detail: String,
@@ -1155,6 +1216,7 @@ fn box_text_clip(
 
 struct Line {
     id: Id,
+    role: SceneHitRole,
     points: Vec<Point>,
     label: String,
     label_at: Point,
@@ -1180,6 +1242,8 @@ struct Scene {
     scale: f32,
     camera_pan: iced::Vector,
     interaction: Option<(scenario::Context, scenario::CanvasTool, bool)>,
+    spacing_stamp: Option<scenario::spacing::Stamp>,
+    coordinate_input: bool,
     pending_placement: Option<(scenario::Slot, Option<Id>)>,
     lanes: BTreeMap<Id, f32>,
     // Exact render coordinates include unassigned lanes; do not derive from cards.
@@ -1207,6 +1271,10 @@ struct SequenceInput {
 }
 #[derive(Clone, Copy)]
 enum SequencePress {
+    Spacing {
+        stamp: scenario::spacing::Stamp,
+        token: Id,
+    },
     Occurrence {
         tool: scenario::Tool,
         slot: scenario::Slot,
@@ -1227,6 +1295,19 @@ enum SequencePress {
     },
 }
 impl SequenceInput {
+    fn cancel_spacing(&mut self) -> Option<Action<Message>> {
+        let cancel = match self.press {
+            Some(SequencePress::Spacing { stamp, token }) => Some(
+                Action::publish(Message::ScenarioCanvas(scenario::CanvasEvent::Spacing(
+                    scenario::spacing::Event::Cancel { stamp, token },
+                )))
+                .and_capture(),
+            ),
+            _ => None,
+        };
+        self.cancel();
+        cancel
+    }
     fn cancel(&mut self) {
         self.source = None;
         self.press = None;
@@ -1252,6 +1333,8 @@ impl Scene {
             layout_origin: Point::ORIGIN,
             selected,
             interaction: None,
+            spacing_stamp: None,
+            coordinate_input: true,
             pending_placement: None,
             lanes: BTreeMap::new(),
             render_lanes: BTreeMap::new(),
@@ -1408,6 +1491,7 @@ impl Scene {
                     0,
                     Line {
                         id,
+                        role: SceneHitRole::LifelineGuide,
                         points: vec![Point::new(x, 85.), Point::new(x, scene.size.height - 20.)],
                         label: String::new(),
                         label_at: Point::ORIGIN,
@@ -1417,6 +1501,11 @@ impl Scene {
             }
             scene.boxes.push(BoxItem {
                 id,
+                role: if scenario {
+                    SceneHitRole::LifelineHeader
+                } else {
+                    SceneHitRole::Box
+                },
                 rect: Rectangle::new(Point::new(x - 102., 15.), Size::new(204., 70.)),
                 title: if scenario {
                     format!("Lane · {name}")
@@ -1510,6 +1599,7 @@ impl Scene {
                         0,
                         BoxItem {
                             id: *id,
+                            role: SceneHitRole::Box,
                             rect,
                             title: format!("{operator:?} · {}", e.name),
                             detail: String::new(),
@@ -1521,6 +1611,7 @@ impl Scene {
                 OccurrenceBody::Branch { guard, .. } => {
                     self.boxes.push(BoxItem {
                         id: *id,
+                        role: SceneHitRole::Box,
                         rect: Rectangle::new(
                             Point::new(36. + depth as f32 * 10., *y),
                             Size::new(self.size.width - 85. - depth as f32 * 20., 43.),
@@ -1604,6 +1695,7 @@ impl Scene {
                         }
                         self.lines.push(Line {
                             id: *id,
+                            role: SceneHitRole::MessageBody,
                             points,
                             label: format!("{}. {kind}{}", index + 1, message_label),
                             label_at: Point::new(a.min(*b) + 12., *y - 26.),
@@ -1612,6 +1704,7 @@ impl Scene {
                     } else {
                         self.boxes.push(BoxItem {
                             id: *id,
+                            role: SceneHitRole::Box,
                             rect: Rectangle::new(
                                 Point::new(65., *y - 20.),
                                 Size::new(self.size.width - 130., 65.),
@@ -1634,6 +1727,7 @@ impl Scene {
                         .unwrap_or(180.);
                     self.boxes.push(BoxItem {
                         id: *id,
+                        role: SceneHitRole::Box,
                         rect: Rectangle::new(Point::new(x - 110., *y - 20.), Size::new(220., 70.)),
                         title: e.name.clone(),
                         detail: action
@@ -1646,6 +1740,7 @@ impl Scene {
                 OccurrenceBody::Control { kind } => {
                     self.boxes.push(BoxItem {
                         id: *id,
+                        role: SceneHitRole::Box,
                         rect: Rectangle::new(Point::new(65., *y - 20.), Size::new(240., 70.)),
                         title: format!("{kind:?} · {}", e.name),
                         detail: "Contextual process control".into(),
@@ -1656,6 +1751,7 @@ impl Scene {
                 OccurrenceBody::SequenceReference { sequence } => {
                     self.boxes.push(BoxItem {
                         id: *id,
+                        role: SceneHitRole::Box,
                         rect: Rectangle::new(Point::new(65., *y - 20.), Size::new(280., 70.)),
                         title: e.name.clone(),
                         detail: sequence
@@ -1668,6 +1764,7 @@ impl Scene {
                 OccurrenceBody::ScenarioUse { scenario, bindings } => {
                     self.boxes.push(BoxItem {
                         id: *id,
+                        role: SceneHitRole::Box,
                         rect: Rectangle::new(
                             Point::new(65., *y - 20.),
                             Size::new(self.size.width - 130., 70.),
@@ -1733,11 +1830,21 @@ impl Scene {
         ))
     }
     fn hit(&self, point: Point) -> Option<Id> {
+        self.hit_item(point).map(|hit| hit.id)
+    }
+
+    /// Preserve the semantic selection order and tolerance while retaining the
+    /// primitive's identity. Future spacing admission must also validate the
+    /// saved view, owner and core occurrence kind; a hit alone grants no edit.
+    fn hit_item(&self, point: Point) -> Option<SceneHit> {
         if !point.x.is_finite() || !point.y.is_finite() {
             return None;
         }
         if let Some(id) = self.lifecycle.marker_at(point) {
-            return Some(id);
+            return Some(SceneHit {
+                id,
+                role: SceneHitRole::LifecycleMarker,
+            });
         }
         self.boxes
             .iter()
@@ -1747,7 +1854,10 @@ impl Scene {
                     && b.rect.contains(point)
                     && (b.marker != Some(Kind::Occurrence) || point.y < b.rect.y + 38.)
             })
-            .map(|b| b.id)
+            .map(|b| SceneHit {
+                id: b.id,
+                role: b.role,
+            })
             .or_else(|| {
                 self.lines
                     .iter()
@@ -1757,36 +1867,51 @@ impl Scene {
                                 crate::diagram::distance_to_segment(point, p[0], p[1]) < 1.5
                             })
                     })
-                    .map(|line| line.id)
+                    .map(|line| SceneHit {
+                        id: line.id,
+                        role: line.role,
+                    })
             })
             .or_else(|| {
                 self.activations
                     .iter()
                     .rev()
                     .find(|b| b.rect.contains(point))
-                    .map(|b| b.call)
+                    .map(|b| SceneHit {
+                        id: b.call,
+                        role: SceneHitRole::Activation,
+                    })
             })
             .or_else(|| {
                 self.lines
                     .iter()
-                    .find(|line| {
-                        !line.label.is_empty()
-                            && Rectangle::new(
-                                line.label_at,
-                                Size::new(
-                                    (line.label.chars().count() as f32 * 6.8 + 8.).min(225.),
-                                    25.,
-                                ),
-                            )
-                            .contains(point)
+                    .find(|line| !line.label.is_empty() && line.label_bounds().contains(point))
+                    .map(|line| SceneHit {
+                        id: line.id,
+                        role: if line.role == SceneHitRole::MessageBody {
+                            SceneHitRole::MessageLabel
+                        } else {
+                            SceneHitRole::OtherLine
+                        },
                     })
-                    .map(|line| line.id)
             })
             // The generous message tolerance must not steal the exposed
             // shoulder of another call's execution when the view is zoomed out.
             .or_else(|| self.near_sequence_item(point))
-            .or_else(|| self.lifecycle.lane_at(point, self.scale))
-            .or_else(|| self.lane_at(point))
+            .or_else(|| {
+                self.lifecycle
+                    .lane_at(point, self.scale)
+                    .map(|id| SceneHit {
+                        id,
+                        role: SceneHitRole::LifelineGuide,
+                    })
+            })
+            .or_else(|| {
+                self.lane_at(point).map(|id| SceneHit {
+                    id,
+                    role: SceneHitRole::LifelineGuide,
+                })
+            })
             .or_else(|| {
                 self.lines
                     .iter()
@@ -1797,11 +1922,14 @@ impl Scene {
                                     < 8. / self.scale
                             })
                     })
-                    .map(|line| line.id)
+                    .map(|line| SceneHit {
+                        id: line.id,
+                        role: line.role,
+                    })
             })
     }
 
-    fn near_sequence_item(&self, point: Point) -> Option<Id> {
+    fn near_sequence_item(&self, point: Point) -> Option<SceneHit> {
         if !self.scale.is_finite() || self.scale <= 0. {
             return None;
         }
@@ -1815,17 +1943,32 @@ impl Scene {
                     .windows(2)
                     .map(|p| crate::diagram::distance_to_segment(point, p[0], p[1]))
                     .fold(f32::INFINITY, f32::min);
-                (line.id, distance)
+                (
+                    SceneHit {
+                        id: line.id,
+                        role: line.role,
+                    },
+                    distance,
+                )
             });
         // Compare broad message and lifecycle-marker tolerance together after
         // exact shapes, so dense minimum-Fit rows choose the nearer item.
         self.lifecycle
             .nearest_marker(point)
+            .map(|(id, distance)| {
+                (
+                    SceneHit {
+                        id,
+                        role: SceneHitRole::LifecycleMarker,
+                    },
+                    distance,
+                )
+            })
             .into_iter()
             .chain(messages)
             .filter(|(_, distance)| *distance <= 8. / self.scale)
-            .min_by(|a, b| a.1.total_cmp(&b.1).then_with(|| a.0.cmp(&b.0)))
-            .map(|(id, _)| id)
+            .min_by(|a, b| a.1.total_cmp(&b.1).then_with(|| a.0.id.cmp(&b.0.id)))
+            .map(|(hit, _)| hit)
     }
 }
 impl canvas::Program<Message> for Scene {
@@ -1853,15 +1996,33 @@ impl canvas::Program<Message> for Scene {
         // captured insertion slot belongs to the previous view, even if the
         // pointer itself did not move and the semantic context is unchanged.
         if state.bounds.is_some_and(|previous| previous != bounds) {
-            state.cancel();
+            let cancelled = state.cancel_spacing();
             state.pointer = None;
+            state.bounds = Some(bounds);
+            if cancelled.is_some() {
+                return cancelled;
+            }
         }
         state.bounds = Some(bounds);
-        if !editable {
-            state.cancel();
+        if (!editable || !self.coordinate_input)
+            && let Some(cancelled) = state.cancel_spacing()
+        {
+            return Some(cancelled);
         }
         // The viewport masks input outside its visible canvas bounds.
         let visible = cursor.position().is_some();
+        if !visible
+            && matches!(state.press, Some(SequencePress::Spacing { .. }))
+            && matches!(
+                event,
+                canvas::Event::Mouse(
+                    mouse::Event::CursorMoved { .. }
+                        | mouse::Event::ButtonReleased(mouse::Button::Left)
+                )
+            )
+        {
+            return state.cancel_spacing();
+        }
         if !visible
             && matches!(
                 event,
@@ -1880,7 +2041,7 @@ impl canvas::Program<Message> for Scene {
                         | SequencePress::Reorder { start, moved, .. } => {
                             *moved |= position.distance(*start) >= 3.
                         }
-                        SequencePress::Occurrence { .. } => {}
+                        SequencePress::Occurrence { .. } | SequencePress::Spacing { .. } => {}
                     }
                 }
                 mouse::Cursor::Available(*position)
@@ -1889,9 +2050,9 @@ impl canvas::Program<Message> for Scene {
             | canvas::Event::Window(iced::window::Event::Resized(_))
             | canvas::Event::Mouse(mouse::Event::CursorLeft)
             | canvas::Event::Window(iced::window::Event::Unfocused) => {
-                state.cancel();
+                let cancelled = state.cancel_spacing();
                 state.pointer = None;
-                return Some(Action::request_redraw());
+                return cancelled.or_else(|| Some(Action::request_redraw()));
             }
             canvas::Event::Mouse(
                 mouse::Event::ButtonPressed(_) | mouse::Event::ButtonReleased(_),
@@ -1904,8 +2065,9 @@ impl canvas::Program<Message> for Scene {
                 key: iced::keyboard::Key::Named(iced::keyboard::key::Named::Escape),
                 ..
             }) if state.source.is_some() || state.press.is_some() => {
-                state.cancel();
-                return Some(Action::request_redraw().and_capture());
+                return state
+                    .cancel_spacing()
+                    .or_else(|| Some(Action::request_redraw().and_capture()));
             }
             _ => cursor,
         };
@@ -1925,6 +2087,14 @@ impl canvas::Program<Message> for Scene {
                     if !editable {
                         return None;
                     }
+                    if !self.coordinate_input {
+                        return self.hit(point).map(|id| {
+                            Action::publish(Message::ScenarioCanvas(CanvasEvent::Select(
+                                context, id,
+                            )))
+                            .and_capture()
+                        });
+                    }
                     if let CanvasTool::Message(_) = tool {
                         let first = state.source.is_none();
                         let (source, slot) = state.source.or_else(|| {
@@ -1951,6 +2121,48 @@ impl canvas::Program<Message> for Scene {
                         });
                         return Some(Action::request_redraw().and_capture());
                     }
+                    if matches!(
+                        context.representation,
+                        scenario_layout::Representation::Saved { .. }
+                    ) {
+                        let hit = self.hit_item(point)?;
+                        let target = match hit.role {
+                            SceneHitRole::LifelineHeader => {
+                                Some(scenario::spacing::Target::Lane(hit.id))
+                            }
+                            SceneHitRole::MessageBody | SceneHitRole::MessageLabel => {
+                                Some(scenario::spacing::Target::Message(hit.id))
+                            }
+                            _ => None,
+                        };
+                        if let Some((target, stamp)) = target.zip(self.spacing_stamp)
+                            && stamp.context == context
+                        {
+                            let token = Id::new_v4();
+                            state.press = Some(SequencePress::Spacing { stamp, token });
+                            return Some(
+                                Action::publish(Message::ScenarioCanvas(CanvasEvent::Spacing(
+                                    scenario::spacing::Event::Begin {
+                                        stamp,
+                                        token,
+                                        target,
+                                        press_screen: cursor.position()?,
+                                        canvas_bounds: bounds,
+                                        scale: self.scale,
+                                        pan: self.camera_pan,
+                                    },
+                                )))
+                                .and_capture(),
+                            );
+                        }
+                        // Saved spacing never silently changes the shared Scenario order.
+                        return Some(
+                            Action::publish(Message::ScenarioCanvas(CanvasEvent::Select(
+                                context, hit.id,
+                            )))
+                            .and_capture(),
+                        );
+                    }
                     if let Some(occurrence) = self
                         .hit(point)
                         .filter(|id| self.rows.contains_key(id))
@@ -1980,6 +2192,22 @@ impl canvas::Program<Message> for Scene {
                 let press = state.press.take()?;
                 let context = context?;
                 match press {
+                    SequencePress::Spacing { stamp, token } => {
+                        state.source = None;
+                        let event = if world.is_some() {
+                            scenario::spacing::Event::Finish {
+                                stamp,
+                                token,
+                                screen: cursor.position()?,
+                            }
+                        } else {
+                            scenario::spacing::Event::Cancel { stamp, token }
+                        };
+                        return Some(
+                            Action::publish(Message::ScenarioCanvas(CanvasEvent::Spacing(event)))
+                                .and_capture(),
+                        );
+                    }
                     SequencePress::Occurrence {
                         tool: captured,
                         slot,
@@ -2071,6 +2299,18 @@ impl canvas::Program<Message> for Scene {
                 Some(Action::request_redraw().and_capture())
             }
             canvas::Event::Mouse(mouse::Event::CursorMoved { .. }) if context.is_some() => {
+                if let Some(SequencePress::Spacing { stamp, token }) = state.press {
+                    return Some(
+                        Action::publish(Message::ScenarioCanvas(CanvasEvent::Spacing(
+                            scenario::spacing::Event::Move {
+                                stamp,
+                                token,
+                                screen: cursor.position()?,
+                            },
+                        )))
+                        .and_capture(),
+                    );
+                }
                 Some(Action::request_redraw())
             }
             _ => None,
@@ -2252,7 +2492,10 @@ impl canvas::Program<Message> for Scene {
         self.lifecycle
             .draw_markers(&mut f, self.selected, self.scale, self.camera_pan);
         if let Some((context, tool, editable)) = self.interaction {
-            let active = editable && state.context == Some(context) && state.tool == tool;
+            let active = editable
+                && self.coordinate_input
+                && state.context == Some(context)
+                && state.tool == tool;
             let point = cursor.position_in(bounds).map(|p| {
                 Point::new(
                     (p.x - self.camera_pan.x) / self.scale,
@@ -2268,7 +2511,12 @@ impl canvas::Program<Message> for Scene {
                 }
             });
             if editable
+                && self.coordinate_input
                 && tool == scenario::CanvasTool::Select
+                && matches!(
+                    context.representation,
+                    scenario_layout::Representation::Derived { .. }
+                )
                 && let Some(handle) = self.reorder_handle()
             {
                 f.fill_rectangle(handle.position(), handle.size(), style::TEAL);

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

@@ -50,7 +50,7 @@ pub fn controls<'a>(
             tooltip::Position::Bottom),
         control("Fit", "Fit", Some(zoom(None))),
         control("ZoomOut", "−", Some(zoom(Some(scale / 1.25)))),
-        text(format!("{:.0}%", scale * 100.)).size(12),
+        text(zoom_label(scale)).size(12),
         control("ZoomIn", "+", Some(zoom(Some(scale * 1.25)))),
         control("ActualSize", "100%", Some(zoom(Some(1.)))),
     ].spacing(4).align_y(iced::Center).into()
@@ -58,6 +58,7 @@ pub fn controls<'a>(
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct Scope {
+    pub(crate) scenario_view: Option<(super::scenario_layout::Representation, Id)>,
     pub document: Id,
     pub owner: Id,
     pub revision: u64,
@@ -69,6 +70,7 @@ impl Scope {
             Some(Self {
                 document: context.document,
                 owner: context.scenario,
+                scenario_view: Some((context.representation, context.visit)),
                 revision: context.revision,
                 epoch: app.camera_epoch,
             })
@@ -77,6 +79,7 @@ impl Scope {
             Some(Self {
                 document: context.document,
                 owner: context.owner,
+                scenario_view: None,
                 revision: context.revision,
                 epoch: app.camera_epoch,
             })
@@ -96,8 +99,8 @@ impl Scope {
 
     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
+            "behavior-control:{}:{}:{}:{:?}:{name}",
+            self.document, self.owner, self.revision, self.scenario_view
         ))
     }
 }
@@ -131,6 +134,20 @@ pub enum Event {
 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 {
+    change_with_minimum(pan, zoom, fit, event, 0.05)
+}
+
+/// Scenario extents can require scales below the topology canvas's 5% floor.
+pub(super) fn change_with_minimum(
+    pan: &mut Vector,
+    zoom: &mut Option<f32>,
+    fit: &mut bool,
+    event: Event,
+    minimum: f32,
+) -> bool {
+    if !minimum.is_finite() || minimum <= 0. || minimum > 3. {
+        return false;
+    }
     match event {
         Event::Pan(delta) if delta.x.is_finite() && delta.y.is_finite() => {
             let next = *pan + delta;
@@ -150,7 +167,10 @@ pub fn change(pan: &mut Vector, zoom: &mut Option<f32>, fit: &mut bool, event: E
                 && at.y.is_finite() =>
         {
             let old = if *fit { base } else { zoom.unwrap_or(base) };
-            let next = (old * factor).clamp(0.05, 3.);
+            if !old.is_finite() || old <= 0. {
+                return false;
+            }
+            let next = (old * factor).clamp(minimum, 3.);
             if old == next {
                 return false;
             }
@@ -168,6 +188,51 @@ pub fn change(pan: &mut Vector, zoom: &mut Option<f32>, fit: &mut bool, event: E
     }
 }
 
+fn zoom_label(scale: f32) -> String {
+    let percent = f64::from(scale) * 100.;
+    if !percent.is_finite() || percent <= 0. {
+        return "—".into();
+    }
+    if percent >= 1. {
+        format!("{percent:.0}%")
+    } else if percent >= 0.01 {
+        format!("{percent:.3}%")
+    } else {
+        format!("{percent:.2e}%")
+    }
+}
+
+#[cfg(test)]
+mod camera_policy_tests {
+    use super::*;
+
+    #[test]
+    fn topology_retains_five_percent_floor() {
+        let (mut pan, mut zoom, mut fit) = (Vector::ZERO, Some(0.06), false);
+        assert!(change(
+            &mut pan,
+            &mut zoom,
+            &mut fit,
+            Event::Zoom {
+                factor: 0.1,
+                at: Point::ORIGIN,
+                base: 0.06,
+            }
+        ));
+        assert_eq!(zoom, Some(0.05));
+    }
+
+    #[test]
+    fn tiny_zoom_label_is_nonzero_and_changes_with_zoom() {
+        assert_eq!(zoom_label(1.), "100%");
+        assert_eq!(zoom_label(0.05), "5%");
+        assert_eq!(zoom_label(0.00034193), "0.034%");
+        assert_eq!(zoom_label(0.00034193 * 1.25), "0.043%");
+        assert_eq!(zoom_label(1e-7), "1.00e-5%");
+        assert_ne!(zoom_label(f32::from_bits(1)), "0%");
+    }
+}
+
 /// Constant-width labelled palette. Arming a tool never reallocates the canvas.
 pub fn palette<'a>(
     scope: Scope,

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

@@ -368,6 +368,7 @@ fn relative_camera_zoom_keeps_the_cursor_world_point_and_rejects_nonfinite_input
 fn viewport_ordered_batch_uses_each_event_position_and_cancels_before_camera_motion() {
     use iced::widget::Space;
     let scope = Scope {
+        scenario_view: None,
         document: Id::new_v4(),
         owner: Id::new_v4(),
         revision: 2,
@@ -427,6 +428,7 @@ pub(crate) fn scope(app: &App) -> Scope {
         Scope {
             document: context.document,
             owner: context.scenario,
+            scenario_view: Some((context.representation, context.visit)),
             revision: context.revision,
             epoch: app.camera_epoch,
         }
@@ -435,6 +437,7 @@ pub(crate) fn scope(app: &App) -> Scope {
         Scope {
             document: context.document,
             owner: context.owner,
+            scenario_view: None,
             revision: context.revision,
             epoch: app.camera_epoch,
         }

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

@@ -893,11 +893,14 @@ fn contextual_source_empty_palette_lifeline_cannot_open_a_previous_owner_or_laye
         .add_element(Kind::Scenario, Layer::Oa, "Second scenario", None)
         .unwrap();
     let mut app = App::with_project(p.clone());
-    app.page = Page::Behavior;
-    app.layer = Layer::Oa;
-    app.behavior.active_owner = Some(a);
-    app.selected = a;
+    // Capture the context created by actual navigation, including its visit.
+    // Merely assigning active_owner/selected does not mount a Scenario anymore.
+    let _ = app.update(Message::Select(a));
+    let _ = app.update(Message::Page(Page::Behavior));
     let context = app.scenario_context().unwrap();
+    assert_eq!(context.scenario, a);
+    assert!(!context.visit.is_nil());
+    let snapshot = app.document.snapshot();
     let source = app.document.bundle().clone();
     let begin = |context| scenario::CanvasEvent::BeginOccurrence {
         context,
@@ -908,23 +911,40 @@ fn contextual_source_empty_palette_lifeline_cannot_open_a_previous_owner_or_laye
         },
         lifeline: None,
     };
-    app.behavior.active_owner = Some(b);
-    app.selected = b;
+    let _ = app.update(Message::Select(b));
+    let second = app.scenario_context().unwrap();
+    assert_eq!(second.scenario, b);
+    assert_ne!(second.visit, context.visit);
     let _ = app.update(Message::ScenarioCanvas(begin(context)));
     assert!(!app.behavior.has_pending());
     assert_eq!(app.project(), &p);
-    app.behavior.active_owner = Some(a);
-    app.selected = a;
-    app.layer = Layer::Sa;
-    let _ = app.update(Message::ScenarioCanvas(begin(context)));
+
+    let _ = app.update(Message::Select(a));
+    let before_layer_change = app.scenario_context().unwrap();
+    assert_eq!(before_layer_change.scenario, a);
+    assert_ne!(before_layer_change.visit, context.visit);
+    let _ = app.update(Message::Layer(Layer::Sa));
+    assert_eq!(app.layer, Layer::Sa);
+    assert!(app.scenario_context().is_none());
+    let _ = app.update(Message::ScenarioCanvas(begin(before_layer_change)));
     assert!(!app.behavior.has_pending());
-    app.layer = Layer::Oa;
+
+    let _ = app.update(Message::Layer(Layer::Oa));
+    let _ = app.update(Message::Select(a));
     let current = app.scenario_context().unwrap();
+    assert_eq!(current.scenario, a);
+    assert_ne!(current.visit, before_layer_change.visit);
+    // Returning to the same owner/layer must not revive either retired packet.
+    for retired in [context, before_layer_change] {
+        let _ = app.update(Message::ScenarioCanvas(begin(retired)));
+        assert!(!app.behavior.has_pending());
+    }
+    assert!(std::sync::Arc::ptr_eq(&snapshot, &app.document.snapshot()));
     let _ = app.update(Message::ScenarioCanvas(begin(current)));
     assert_eq!(app.behavior.pending_owner(), Some(a));
     assert_eq!(app.project(), &p);
     assert_eq!(app.document.bundle(), &source);
-    assert!(!app.document.can_undo());
+    assert!(!app.document.can_undo() && !app.document.can_redo());
 }
 
 #[test]

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

@@ -4,12 +4,28 @@ use super::topology::{occurrence, unique_batch};
 use super::*;
 use iced::widget::{Column, column, text_input};
 use std::{cell::RefCell, collections::BTreeSet};
+mod camera;
 pub(crate) mod focus;
+pub(crate) mod spacing;
+use super::scenario_layout::{
+    Representation,
+    presentation::{self, ScenarioPresentation},
+};
+#[cfg(test)]
+mod presentation_tests;
 mod usage;
 mod workspace;
 pub(crate) use workspace::NAME_INPUT;
 pub use workspace::{Shelf, view};
 
+// A picker may select the Saved diagram record itself. Another view of the
+// same Scenario is not the property target of this displayed representation.
+pub(crate) fn properties_target(p: &Project, context: Context, id: Id) -> bool {
+    super::selected_behavior(p, id) == Some(context.scenario)
+        || matches!(context.representation, Representation::Saved { diagram } if diagram == id)
+            && presentation::checked_owner(p, context.representation) == Some(context.scenario)
+}
+
 #[cfg(test)]
 #[path = "scenario_operation_tests.rs"]
 mod operation_tests;
@@ -71,6 +87,8 @@ impl std::fmt::Display for MessageStyle {
 pub struct Context {
     pub document: Id,
     pub scenario: Id,
+    pub representation: Representation,
+    pub visit: Id,
     pub revision: u64,
     pub epoch: u64,
 }
@@ -97,6 +115,7 @@ impl std::fmt::Display for CanvasTool {
 }
 #[derive(Debug, Clone)]
 pub enum CanvasEvent {
+    Spacing(spacing::Event),
     Scrolled(Context, ScrollArea, iced::Vector),
     Restored(Context, Id, ScrollArea, iced::Vector),
     Viewport(Context, Size),
@@ -105,9 +124,11 @@ pub enum CanvasEvent {
     Camera(Context, u64, super::canvas_workspace::Event),
     Focus(Context),
     Shelf(Context, Shelf),
+    Properties(Context, Id),
     OpenUse(Context, Id),
     Back(Context),
     Choose(Context, CanvasTool),
+    Representation(Context, Representation),
     Select(Context, Id),
     Begin {
         context: Context,
@@ -136,6 +157,7 @@ pub enum ScrollArea {
 impl CanvasEvent {
     pub fn context(&self) -> Context {
         match self {
+            Self::Spacing(event) => event.stamp().context,
             Self::Scrolled(context, _, _)
             | Self::Restored(context, ..)
             | Self::Viewport(context, _)
@@ -144,9 +166,11 @@ impl CanvasEvent {
             | Self::Camera(context, ..)
             | Self::Focus(context)
             | Self::Shelf(context, _)
+            | Self::Properties(context, _)
             | Self::OpenUse(context, _)
             | Self::Back(context)
             | Self::Choose(context, _)
+            | Self::Representation(context, _)
             | Self::Select(context, _)
             | Self::Begin { context, .. }
             | Self::BeginOccurrence { context, .. }
@@ -203,6 +227,7 @@ pub enum ValueSection {
 const VALUE_PAGE_SIZE: usize = 24;
 #[derive(Default)]
 pub struct State {
+    spacing: Option<spacing::controller::Session>,
     draft: Option<Draft>,
     form_session: Id,
     form_mount: Id,
@@ -218,6 +243,7 @@ const CALLER_LIMIT: usize = 32;
 pub(crate) struct Caller {
     document: Id,
     pub owner: Id,
+    pub representation: Representation,
     pub occurrence: Id,
     target: Id,
     tool: CanvasTool,
@@ -227,6 +253,8 @@ pub(crate) struct Caller {
 struct DetailsRestore {
     document: Id,
     owner: Id,
+    representation: Representation,
+    visit: Id,
     token: Id,
     offset: iced::Vector,
 }
@@ -234,6 +262,8 @@ struct DetailsRestore {
 pub(super) struct ScrollRestore {
     pub document: Id,
     pub owner: Id,
+    pub representation: Representation,
+    pub visit: Id,
     pub token: Id,
     pub offset: iced::Vector,
 }
@@ -327,42 +357,149 @@ impl State {
     }
 
     pub(crate) fn enter(&mut self, document: Id, owner: Id) {
-        if self.presentation.identity != Some((document, owner)) {
+        self.enter_representation(document, owner, Representation::Derived { owner });
+    }
+    /// App validates requested identity with checked_owner before entering.
+    pub(crate) fn enter_representation(
+        &mut self,
+        document: Id,
+        owner: Id,
+        representation: Representation,
+    ) -> bool {
+        if matches!(representation, Representation::Derived { owner: requested } if requested != owner)
+        {
+            return false;
+        }
+        let changed = self.presentation.identity != Some((document, owner))
+            || self.presentation.representation != Some(representation);
+        if changed {
             self.presentation = workspace::Presentation {
                 identity: Some((document, owner)),
+                representation: Some(representation),
                 focused: self.presentation.focused,
+                fit: matches!(representation, Representation::Saved { .. }),
                 ..Default::default()
             };
             self.details_offset = iced::Vector::ZERO;
-            self.restore = None;
+            self.canvas_tool = Some((owner, CanvasTool::Select));
         }
+        if changed || self.presentation.visit.is_nil() {
+            self.spacing = None;
+            self.presentation.visit = Id::new_v4();
+            self.restore = None;
+            return true;
+        }
+        false
+    }
+    /// Suspend captured events while preserving this destination's camera state.
+    pub(crate) fn leave(&mut self) {
+        self.spacing = None;
+        self.presentation.visit = Id::nil();
+        self.restore = None;
+    }
+    pub(crate) fn forget_view(&mut self) {
+        self.spacing = None;
+        self.presentation.identity = None;
+        self.presentation.representation = None;
+        self.presentation.visit = Id::nil();
+        self.restore = None;
+    }
+    pub(crate) fn representation(&self) -> Option<Representation> {
+        self.presentation.representation
+    }
+    pub(crate) fn owner(&self) -> Option<Id> {
+        self.presentation.identity.map(|(_, owner)| owner)
+    }
+    pub(crate) fn context(
+        &self,
+        document: Id,
+        owner: Id,
+        revision: u64,
+        epoch: u64,
+    ) -> Option<Context> {
+        if self.presentation.identity != Some((document, owner)) || self.presentation.visit.is_nil()
+        {
+            return None;
+        }
+        Some(Context {
+            document,
+            scenario: owner,
+            representation: self.representation()?,
+            visit: self.presentation.visit,
+            revision,
+            epoch,
+        })
+    }
+    pub(crate) fn display(
+        &self,
+        p: &Project,
+        owner: Id,
+        selected: Id,
+    ) -> Option<ScenarioPresentation> {
+        let (_, current_owner) = self.presentation.identity?;
+        let representation = self.representation()?;
+        (current_owner == owner).then(|| presentation::present(p, representation, selected))
+    }
+    pub(crate) fn coordinate_input(&self, p: &Project, context: Context) -> bool {
+        self.context(
+            context.document,
+            context.scenario,
+            context.revision,
+            context.epoch,
+        ) == Some(context)
+            && self
+                .display(p, context.scenario, context.scenario)
+                .is_some_and(|shown| shown.capabilities().coordinate_input)
     }
     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 {
+    pub(crate) fn camera(
+        &mut self,
+        project: &Project,
+        owner: Id,
+        event: super::canvas_workspace::Event,
+    ) -> bool {
+        let Some(bounds) = self
+            .display(project, owner, owner)
+            .and_then(|shown| shown.bounds())
+        else {
+            return false;
+        };
         let p = &mut self.presentation;
-        super::canvas_workspace::change(&mut p.pan, &mut p.zoom, &mut p.fit, event)
+        camera::change(
+            &mut p.pan,
+            &mut p.zoom,
+            &mut p.fit,
+            p.viewport,
+            bounds,
+            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);
+        let Some(bounds) = self
+            .display(p, owner, owner)
+            .and_then(|shown| shown.bounds())
+        else {
+            return false;
+        };
         if let Some(next) = zoom {
+            let current = self.presentation.camera(bounds);
             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,
-            })
+            self.camera(
+                p,
+                owner,
+                super::canvas_workspace::Event::Zoom {
+                    factor: next / current.scale,
+                    at: Point::new(viewport.width / 2., viewport.height / 2.),
+                    base: current.scale,
+                },
+            )
         } else {
-            self.zoom(None);
-            let fitted = self.presentation.scale(size);
-            self.zoom(Some(fitted));
-            self.presentation.pan = iced::Vector::ZERO;
-            true
+            self.zoom(None)
         }
     }
     pub(crate) fn focused(&self) -> bool {
@@ -374,6 +511,12 @@ impl State {
     pub(crate) fn toggle_shelf(&mut self, shelf: Shelf) {
         self.presentation.shelf = (self.presentation.shelf != Some(shelf)).then_some(shelf);
     }
+    pub(crate) fn show_properties(&mut self) {
+        // Properties belong to the inspector. Restore that panel and dismiss
+        // the competing outline without replacing this view or its camera.
+        self.presentation.focused = false;
+        self.presentation.shelf = None;
+    }
     pub(crate) fn open_use(
         &mut self,
         p: &Project,
@@ -390,6 +533,7 @@ impl State {
         self.return_to.push(Caller {
             document: context.document,
             owner: context.scenario,
+            representation: context.representation,
             occurrence,
             target,
             tool: self.canvas_tool(context.scenario),
@@ -404,6 +548,7 @@ impl State {
     fn valid_caller(p: &Project, context: Context, frame: &Caller) -> bool {
         frame.document == context.document
             && frame.target == context.scenario
+            && presentation::checked_owner(p, frame.representation) == Some(frame.owner)
             && referenced_scenario(p, frame.owner, frame.occurrence) == Some(frame.target)
     }
     pub(super) fn can_back(&self, p: &Project, context: Context) -> bool {
@@ -420,16 +565,23 @@ impl State {
         None
     }
     pub(crate) fn restore_caller(&mut self, context: Context, frame: Caller) {
-        if context.document != frame.document || context.scenario != frame.owner {
+        if context.document != frame.document
+            || context.scenario != frame.owner
+            || context.representation != frame.representation
+        {
             return;
         }
         self.canvas_tool = Some((frame.owner, frame.tool));
         self.details_offset = frame.details_offset;
         self.presentation = frame.presentation;
         self.presentation.identity = Some((context.document, context.scenario));
+        self.presentation.representation = Some(frame.representation);
+        self.presentation.visit = context.visit;
         self.restore = Some(DetailsRestore {
             document: context.document,
             owner: frame.owner,
+            representation: frame.representation,
+            visit: context.visit,
             token: Id::new_v4(),
             offset: frame.details_offset,
         });
@@ -439,13 +591,17 @@ impl State {
         context: Context,
         ScrollArea::Page: ScrollArea,
     ) -> Option<ScrollRestore> {
-        let restore = self
-            .restore
-            .as_ref()
-            .filter(|r| r.document == context.document && r.owner == context.scenario)?;
+        let restore = self.restore.as_ref().filter(|r| {
+            r.document == context.document
+                && r.owner == context.scenario
+                && r.representation == context.representation
+                && r.visit == context.visit
+        })?;
         Some(ScrollRestore {
             document: restore.document,
             owner: restore.owner,
+            representation: restore.representation,
+            visit: restore.visit,
             token: restore.token,
             offset: restore.offset,
         })
@@ -458,7 +614,11 @@ impl State {
         offset: iced::Vector,
     ) -> bool {
         if !self.restore.as_ref().is_some_and(|r| {
-            r.document == context.document && r.owner == context.scenario && r.token == token
+            r.document == context.document
+                && r.owner == context.scenario
+                && r.representation == context.representation
+                && r.visit == context.visit
+                && r.token == token
         }) {
             return false;
         }
@@ -1931,6 +2091,8 @@ pub(crate) mod direct_tests {
         Context {
             document: Id::new_v4(),
             scenario: owner,
+            representation: Representation::Derived { owner },
+            visit: Id::new_v4(),
             revision: 0,
             epoch: 0,
         }

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

@@ -0,0 +1,282 @@
+//! Scenario camera policy. Bounds are from the exact displayed presentation,
+//! including its origin and automatic fallback; no model geometry is authored.
+use crate::behavior::canvas_workspace::{self, Event};
+use iced::{Rectangle, Size, Vector};
+
+pub(super) const MIN_SCALE: f32 = f32::from_bits(1);
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub(super) struct Camera {
+    pub(super) scale: f32,
+    pub(super) pan: Vector,
+}
+
+/// Fit never enlarges above 100%. Use f64 intermediates so a valid f32 origin
+/// and size cannot overflow while finding the center. Unrepresentable cameras
+/// are refused rather than silently clamped to an unrelated minimum scale.
+pub(super) fn fit(bounds: Rectangle, viewport: Size) -> Option<Camera> {
+    if [
+        bounds.x,
+        bounds.y,
+        bounds.width,
+        bounds.height,
+        viewport.width,
+        viewport.height,
+    ]
+    .iter()
+    .any(|n| !n.is_finite())
+        || bounds.width < 0.
+        || bounds.height < 0.
+        || viewport.width <= 0.
+        || viewport.height <= 0.
+    {
+        return None;
+    }
+    let width = f64::from(viewport.width);
+    let height = f64::from(viewport.height);
+    let scale = ((width - 2. * (width / 4.).min(8.)) / f64::from(bounds.width).max(1.))
+        .min((height - 2. * (height / 4.).min(8.)) / f64::from(bounds.height).max(1.))
+        .min(1.) as f32;
+    if !scale.is_finite() || scale <= 0. {
+        return None;
+    }
+    let x = width / 2. - (f64::from(bounds.x) + f64::from(bounds.width) / 2.) * f64::from(scale);
+    let y = height / 2. - (f64::from(bounds.y) + f64::from(bounds.height) / 2.) * f64::from(scale);
+    let pan = Vector::new(x as f32, y as f32);
+    (pan.x.is_finite() && pan.y.is_finite()).then_some(Camera { scale, pan })
+}
+
+pub(super) fn effective_camera(
+    pan: Vector,
+    zoom: Option<f32>,
+    fitting: bool,
+    viewport: Option<Size>,
+    bounds: Rectangle,
+) -> Camera {
+    if fitting && let Some(camera) = viewport.and_then(|size| fit(bounds, size)) {
+        return camera;
+    }
+    Camera {
+        scale: zoom.unwrap_or(1.),
+        pan,
+    }
+}
+
+/// None preserves Fit as a mode, including before the first viewport arrives.
+pub(super) fn set_zoom(
+    pan: &mut Vector,
+    zoom: &mut Option<f32>,
+    fitting: &mut bool,
+    scale: Option<f32>,
+) -> bool {
+    if scale.is_some_and(|value| !value.is_finite() || value <= 0.) {
+        return false;
+    }
+    let next = scale.map(|value| value.min(3.));
+    let next_pan = if scale.is_none() { Vector::ZERO } else { *pan };
+    let changed = *zoom != next || *fitting != scale.is_none() || *pan != next_pan;
+    *zoom = next;
+    *fitting = scale.is_none();
+    *pan = next_pan;
+    changed
+}
+
+/// Materialize the visible fitted camera only when a camera gesture succeeds.
+/// A zero-motion or rejected event preserves the original mode and fields.
+pub(super) fn change(
+    pan: &mut Vector,
+    zoom: &mut Option<f32>,
+    fitting: &mut bool,
+    viewport: Option<Size>,
+    bounds: Rectangle,
+    event: Event,
+) -> bool {
+    let camera = effective_camera(*pan, *zoom, *fitting, viewport, bounds);
+    let (mut next_pan, mut next_zoom, mut next_fit) = (camera.pan, Some(camera.scale), false);
+    let event = match event {
+        Event::Zoom { base, .. } if !base.is_finite() || base <= 0. => return false,
+        Event::Zoom { factor, at, .. } => Event::Zoom {
+            factor,
+            at,
+            base: camera.scale,
+        },
+        event => event,
+    };
+    if !canvas_workspace::change_with_minimum(
+        &mut next_pan,
+        &mut next_zoom,
+        &mut next_fit,
+        event,
+        MIN_SCALE,
+    ) {
+        return false;
+    }
+    *pan = next_pan;
+    *zoom = next_zoom;
+    *fitting = next_fit;
+    true
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use iced::Point;
+
+    fn bounds() -> Rectangle {
+        Rectangle {
+            x: -1_000_160.,
+            y: -200.,
+            width: 2_000_400.,
+            height: 1_000.,
+        }
+    }
+    fn near(actual: f32, expected: f32, tolerance: f32) {
+        assert!(
+            (actual - expected).abs() <= tolerance,
+            "{actual} != {expected}"
+        );
+    }
+    fn projected(camera: Camera, point: Point) -> Point {
+        Point::new(
+            point.x * camera.scale + camera.pan.x,
+            point.y * camera.scale + camera.pan.y,
+        )
+    }
+
+    #[test]
+    fn negative_origin_fit_contains_independently_known_extremes() {
+        let camera = fit(bounds(), Size::new(700., 500.)).unwrap();
+        near(camera.scale, 0.0003419316, 1e-10);
+        near(camera.pan.x, 349.98633, 0.0001);
+        near(
+            projected(camera, Point::new(-1_000_160., -200.)).x,
+            8.,
+            0.0001,
+        );
+        near(
+            projected(camera, Point::new(1_000_240., 800.)).x,
+            692.,
+            0.0001,
+        );
+        near(projected(camera, Point::new(40., 300.)).y, 250., 0.0001);
+    }
+
+    #[test]
+    fn fit_remains_active_across_first_and_changed_viewport() {
+        let (mut pan, mut zoom, mut fitting) = (Vector::new(50., 80.), Some(0.8), false);
+        assert!(set_zoom(&mut pan, &mut zoom, &mut fitting, None));
+        let retained = effective_camera(pan, zoom, fitting, Some(Size::new(1200., 500.)), bounds());
+        let actual = effective_camera(pan, zoom, fitting, Some(Size::new(500., 500.)), bounds());
+        assert!(actual.scale < retained.scale);
+        near(
+            projected(actual, Point::new(-1_000_160., -200.)).x,
+            8.,
+            0.0001,
+        );
+        near(
+            projected(actual, Point::new(1_000_240., 800.)).x,
+            492.,
+            0.0001,
+        );
+        assert_eq!((pan, zoom, fitting), (Vector::ZERO, None, true));
+    }
+
+    #[test]
+    fn tiny_fit_zoom_in_out_preserves_pointer_world_anchor_without_floor_jump() {
+        let viewport = Some(Size::new(700., 500.));
+        let start = fit(bounds(), viewport.unwrap()).unwrap();
+        let (mut pan, mut zoom, mut fitting) = (Vector::ZERO, None, true);
+        let at = Point::new(210., 180.);
+        let world = Point::new(
+            (at.x - start.pan.x) / start.scale,
+            (at.y - start.pan.y) / start.scale,
+        );
+        for factor in [1.25, 0.8] {
+            let prior_scale = zoom.unwrap_or(start.scale);
+            assert!(change(
+                &mut pan,
+                &mut zoom,
+                &mut fitting,
+                viewport,
+                bounds(),
+                Event::Zoom {
+                    factor,
+                    at,
+                    base: start.scale,
+                }
+            ));
+            let camera = effective_camera(pan, zoom, fitting, viewport, bounds());
+            near(camera.scale, prior_scale * factor, 1e-10);
+            assert!(camera.scale < 0.001);
+            near(projected(camera, world).x, at.x, 0.0001);
+            near(projected(camera, world).y, at.y, 0.0001);
+        }
+        near(zoom.unwrap(), start.scale, 1e-10);
+        near(pan.x, start.pan.x, 0.0001);
+        assert!(!fitting);
+    }
+
+    #[test]
+    fn pan_leaves_fit_from_displayed_position_and_zero_motion_preserves_fit() {
+        let viewport = Some(Size::new(700., 500.));
+        let (mut pan, mut zoom, mut fitting) = (Vector::ZERO, None, true);
+        for event in [
+            Event::Pan(Vector::ZERO),
+            Event::Zoom {
+                factor: 1.,
+                at: Point::ORIGIN,
+                base: 1.,
+            },
+        ] {
+            assert!(!change(
+                &mut pan,
+                &mut zoom,
+                &mut fitting,
+                viewport,
+                bounds(),
+                event
+            ));
+            assert_eq!((pan, zoom, fitting), (Vector::ZERO, None, true));
+        }
+        let start = fit(bounds(), viewport.unwrap()).unwrap();
+        assert!(change(
+            &mut pan,
+            &mut zoom,
+            &mut fitting,
+            viewport,
+            bounds(),
+            Event::Pan(Vector::new(20., -30.))
+        ));
+        assert_eq!(pan, start.pan + Vector::new(20., -30.));
+        assert_eq!(zoom, Some(start.scale));
+        assert!(!fitting);
+    }
+
+    #[test]
+    fn invalid_inputs_are_passive_and_large_finite_bounds_do_not_overflow_center() {
+        assert!(fit(bounds(), Size::new(f32::NAN, 500.)).is_none());
+        let extreme = Rectangle {
+            x: f32::MAX,
+            y: 0.,
+            width: f32::MAX,
+            height: 100.,
+        };
+        let camera = fit(extreme, Size::new(700., 500.)).unwrap();
+        assert!(camera.scale > 0. && camera.scale < 1e-30 && camera.pan.x.is_finite());
+        let (mut pan, mut zoom, mut fitting) = (Vector::ZERO, None, true);
+        assert!(!set_zoom(&mut pan, &mut zoom, &mut fitting, Some(f32::NAN)));
+        assert!(!change(
+            &mut pan,
+            &mut zoom,
+            &mut fitting,
+            Some(Size::new(700., 500.)),
+            bounds(),
+            Event::Zoom {
+                factor: 1.25,
+                at: Point::ORIGIN,
+                base: f32::NAN
+            }
+        ));
+        assert_eq!((pan, zoom, fitting), (Vector::ZERO, None, true));
+    }
+}

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

@@ -11,6 +11,8 @@ use std::collections::BTreeMap;
 pub(crate) struct Stamp {
     document: ModelId,
     owner: ModelId,
+    representation: super::Representation,
+    visit: ModelId,
     revision: u64,
     session: ModelId,
     mount: ModelId,
@@ -20,6 +22,8 @@ impl Stamp {
         Self {
             document: context.document,
             owner: context.scenario,
+            representation: context.representation,
+            visit: context.visit,
             revision: context.revision,
             session,
             mount,
@@ -28,10 +32,12 @@ impl Stamp {
 }
 pub(crate) fn name_id(stamp: Stamp) -> Id {
     Id::from(format!(
-        "{}:{}:{}:{}:{}:{}",
+        "{}:{}:{}:{:?}:{}:{}:{}:{}",
         super::NAME_INPUT,
         stamp.document,
         stamp.owner,
+        stamp.representation,
+        stamp.visit,
         stamp.revision,
         stamp.session,
         stamp.mount

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

@@ -0,0 +1,348 @@
+//! Controller identity and actual presentation input, independent of App routing.
+use super::*;
+use oa_core::{Diagram, DiagramLayout, ProjectionKind, ScenarioLanePosition, ScenarioLayout};
+
+fn saved(p: &mut Project, owner: Id, lanes: &[(Id, f32)]) -> Representation {
+    let id = Id::new_v4();
+    p.diagrams.insert(
+        id,
+        Diagram {
+            id,
+            alias: format!("saved_{}", p.diagrams.len()),
+            name: "Saved scenario".into(),
+            description: String::new(),
+            layer: p.elements[&owner].layer(),
+            projection: ProjectionKind::Scenario { scenario: owner },
+            view_options: Default::default(),
+            nodes: Default::default(),
+            routes: vec![],
+            layout: Some(DiagramLayout::Scenario(ScenarioLayout {
+                lanes: lanes
+                    .iter()
+                    .map(|&(lifeline, x)| ScenarioLanePosition { lifeline, x })
+                    .collect(),
+                messages: vec![],
+            })),
+        },
+    );
+    let errors: Vec<_> = oa_core::validation::validate(p)
+        .into_iter()
+        .filter(|issue| issue.severity == oa_core::validation::Severity::Error)
+        .collect();
+    assert!(errors.is_empty(), "{errors:?}");
+    Representation::Saved { diagram: id }
+}
+
+#[test]
+fn saved_visits_distinguish_same_owner_roundtrips_and_suspended_return_without_editing() {
+    let mut f = direct_tests::fixture();
+    let a = saved(&mut f.project, f.owner, &[(f.sender, -500.)]);
+    let b = saved(&mut f.project, f.owner, &[(f.sender, 900.)]);
+    let original = f.project.clone();
+    let document = Id::new_v4();
+    let mut state = State::default();
+    assert!(state.enter_representation(document, f.owner, a));
+    let first = state.context(document, f.owner, 7, 9).unwrap();
+    assert!(!state.enter_representation(document, f.owner, a));
+    assert_eq!(state.context(document, f.owner, 7, 9), Some(first));
+    state.presentation.pan = iced::Vector::new(23., -17.);
+    state.leave();
+    assert_eq!(state.representation(), Some(a));
+    assert_eq!(state.owner(), Some(f.owner));
+    assert!(state.context(document, f.owner, 7, 9).is_none());
+    assert!(state.enter_representation(document, f.owner, a));
+    let returned = state.context(document, f.owner, 7, 9).unwrap();
+    assert_ne!(returned.visit, first.visit);
+    assert_eq!(state.presentation.pan, iced::Vector::new(23., -17.));
+    assert!(state.enter_representation(document, f.owner, b));
+    let middle = state.context(document, f.owner, 7, 9).unwrap();
+    assert!(state.enter_representation(document, f.owner, a));
+    let last = state.context(document, f.owner, 7, 9).unwrap();
+    assert_ne!(last.visit, returned.visit);
+    assert_ne!(last.visit, middle.visit);
+    assert!(!state.coordinate_input(&f.project, first));
+    assert!(state.coordinate_input(&f.project, last));
+    let session = Id::new_v4();
+    let mount = Id::new_v4();
+    assert_ne!(
+        focus::Stamp::new(first, session, mount),
+        focus::Stamp::new(last, session, mount)
+    );
+    assert_eq!(f.project, original);
+    state.forget_view();
+    assert_eq!(state.representation(), None);
+    assert_eq!(state.owner(), None);
+    assert!(state.context(document, f.owner, 7, 9).is_none());
+}
+
+#[test]
+fn saved_caller_restores_exact_representation_with_fresh_visit_and_rejects_deleted_view() {
+    let (mut project, [a, b, _], [reference, _, _]) = direct_tests::navigation_fixture();
+    let view = saved(&mut project, a, &[]);
+    let original = project.clone();
+    let document = Id::new_v4();
+    let mut state = State::default();
+    state.enter_representation(document, a, view);
+    let initial = state.context(document, a, 0, 0).unwrap();
+    state.presentation.pan = iced::Vector::new(11., 29.);
+    state.details_offset = iced::Vector::new(0., 71.);
+    assert_eq!(state.open_use(&project, initial, reference).unwrap(), b);
+    state.enter(document, b);
+    let callee = state.context(document, b, 0, 0).unwrap();
+    let frame = state.back(&project, callee).unwrap();
+    assert_eq!(frame.representation, view);
+    state.enter_representation(document, a, frame.representation);
+    let returned = state.context(document, a, 0, 0).unwrap();
+    state.restore_caller(returned, frame);
+    assert_ne!(returned.visit, initial.visit);
+    assert_eq!(state.representation(), Some(view));
+    assert_eq!(state.presentation.pan, iced::Vector::new(11., 29.));
+    assert!(state.scroll_restore(initial, ScrollArea::Page).is_none());
+    assert_eq!(
+        state
+            .scroll_restore(returned, ScrollArea::Page)
+            .unwrap()
+            .offset,
+        iced::Vector::new(0., 71.)
+    );
+    assert_eq!(project, original);
+    state.open_use(&project, returned, reference).unwrap();
+    state.enter(document, b);
+    let Representation::Saved { diagram } = view else {
+        unreachable!()
+    };
+    project.diagrams.remove(&diagram);
+    let callee = state.context(document, b, 0, 0).unwrap();
+    assert!(state.back(&project, callee).is_none());
+}
+
+#[test]
+fn complete_fallback_scene_selects_but_cannot_capture_or_finish_coordinate_gestures() {
+    let mut f = direct_tests::fixture();
+    // Equal authored lane centers are structurally valid, but cannot render a distinct-endpoint call.
+    let rep = saved(
+        &mut f.project,
+        f.owner,
+        &[(f.sender, 900.), (f.receiver, 900.)],
+    );
+    let original = f.project.clone();
+    let mut state = State::default();
+    state.enter_representation(Id::new_v4(), f.owner, rep);
+    let document = state.presentation.identity.unwrap().0;
+    let context = state.context(document, f.owner, 0, 0).unwrap();
+    let shown = state.display(&f.project, f.owner, f.call).unwrap();
+    assert!(matches!(
+        shown.status(),
+        presentation::PresentationStatus::Fallback { .. }
+    ));
+    assert!(!state.coordinate_input(&f.project, context));
+    let automatic = presentation::present(
+        &f.project,
+        Representation::Derived { owner: f.owner },
+        f.call,
+    );
+    let automatic = automatic.scene().unwrap();
+    assert_eq!(shown.scene().unwrap().render_lanes, automatic.render_lanes);
+    assert_eq!(shown.scene().unwrap().activations, automatic.activations);
+    assert!(!automatic.activations.is_empty());
+    let mut scene = shown.into_scene().unwrap();
+    scene.coordinate_input = false;
+    let line = scene.lines.iter().find(|line| line.id == f.call).unwrap();
+    let point = Point::new(
+        (line.points[0].x + line.points.last().unwrap().x) / 2.,
+        line.points[0].y,
+    );
+    assert_eq!(scene.hit(point), Some(f.call));
+    let bounds = Rectangle::with_size(Size::new(1600., 1000.));
+    for tool in [
+        CanvasTool::Select,
+        CanvasTool::Message(MessageStyle::CallReply),
+        CanvasTool::Add(Tool::Reuse),
+    ] {
+        scene.interaction = Some((context, tool, true));
+        let mut input = SequenceInput::default();
+        let mut messages = vec![];
+        for event in [
+            mouse::Event::CursorMoved { position: point },
+            mouse::Event::ButtonPressed(mouse::Button::Left),
+            mouse::Event::CursorMoved {
+                position: Point::new(point.x, point.y + 100.),
+            },
+            mouse::Event::ButtonReleased(mouse::Button::Left),
+        ] {
+            if let Some(message) = canvas::Program::update(
+                &scene,
+                &mut input,
+                &canvas::Event::Mouse(event),
+                bounds,
+                mouse::Cursor::Available(point),
+            )
+            .and_then(|action| action.into_inner().0)
+            {
+                messages.push(message);
+            }
+        }
+        assert_eq!(messages.len(), 1);
+        assert!(
+            matches!(messages[0], Message::ScenarioCanvas(CanvasEvent::Select(c, id)) if c == context && id == f.call)
+        );
+        assert!(input.press.is_none() && input.source.is_none());
+    }
+    // Capture from an actual Ready presentation, then revoke coordinate input
+    // with the complete fallback frame of the same Saved representation.
+    let Representation::Saved { diagram } = rep else {
+        unreachable!()
+    };
+    let mut ready_project = f.project.clone();
+    ready_project.diagrams.get_mut(&diagram).unwrap().layout =
+        Some(DiagramLayout::Scenario(ScenarioLayout::default()));
+    let ready_original = ready_project.clone();
+    let ready = state.display(&ready_project, f.owner, f.call).unwrap();
+    assert!(matches!(
+        ready.status(),
+        presentation::PresentationStatus::Ready
+    ));
+    let mut ready_scene = ready.into_scene().unwrap();
+    let line = ready_scene
+        .lines
+        .iter()
+        .find(|line| line.id == f.call)
+        .unwrap();
+    let ready_point = Point::new(
+        (line.points[0].x + line.points.last().unwrap().x) / 2.,
+        line.points[0].y,
+    );
+    let hit = ready_scene.hit_item(ready_point).unwrap();
+    assert_eq!(hit.id, f.call);
+    assert_eq!(hit.role, SceneHitRole::MessageBody);
+    let stamp = spacing::Stamp {
+        context,
+        camera_epoch: 17,
+    };
+    ready_scene.coordinate_input = true;
+    ready_scene.interaction = Some((context, CanvasTool::Select, true));
+    ready_scene.spacing_stamp = Some(stamp);
+    let mut input = SequenceInput::default();
+    let begin = canvas::Program::update(
+        &ready_scene,
+        &mut input,
+        &canvas::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)),
+        bounds,
+        mouse::Cursor::Available(ready_point),
+    )
+    .and_then(|action| action.into_inner().0)
+    .unwrap();
+    let Message::ScenarioCanvas(CanvasEvent::Spacing(spacing::Event::Begin {
+        stamp: captured_stamp,
+        token,
+        target: spacing::Target::Message(target),
+        ..
+    })) = begin
+    else {
+        panic!("Ready Saved message must begin a stamped spacing gesture");
+    };
+    assert_eq!(captured_stamp, stamp);
+    assert_eq!(target, f.call);
+    assert!(matches!(input.press, Some(SequencePress::Spacing {
+        stamp: held_stamp, token: held_token
+    }) if held_stamp == stamp && held_token == token));
+    scene.interaction = Some((context, CanvasTool::Select, true));
+    assert!(!scene.coordinate_input && scene.spacing_stamp.is_none());
+    let release = canvas::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left));
+    let result = canvas::Program::update(
+        &scene,
+        &mut input,
+        &release,
+        bounds,
+        mouse::Cursor::Available(ready_point),
+    )
+    .and_then(|action| action.into_inner().0);
+    assert!(
+        matches!(result, Some(Message::ScenarioCanvas(CanvasEvent::Spacing(
+        spacing::Event::Cancel { stamp: cancelled_stamp, token: cancelled_token }
+    ))) if cancelled_stamp == stamp && cancelled_token == token)
+    );
+    assert!(input.press.is_none() && input.source.is_none());
+    assert!(
+        canvas::Program::update(
+            &scene,
+            &mut input,
+            &release,
+            bounds,
+            mouse::Cursor::Available(ready_point),
+        )
+        .and_then(|action| action.into_inner().0)
+        .is_none()
+    );
+    assert_eq!(ready_project, ready_original);
+    assert_eq!(f.project, original);
+}
+
+#[test]
+fn saved_camera_fits_actual_negative_origin_and_tiny_scale_without_authored_mutation() {
+    let mut f = direct_tests::fixture();
+    let rep = saved(
+        &mut f.project,
+        f.owner,
+        &[(f.sender, -1_000_000.), (f.receiver, 1_000_000.)],
+    );
+    let original = f.project.clone();
+    let mut state = State::default();
+    state.enter_representation(Id::new_v4(), f.owner, rep);
+    state.viewport(Size::new(700., 500.));
+    assert!(
+        state.presentation.fit,
+        "new saved views await their real viewport in Fit mode"
+    );
+    assert!(
+        !state.camera_zoom(&f.project, f.owner, None),
+        "already-active Fit is idempotent"
+    );
+    let shown = state.display(&f.project, f.owner, f.owner).unwrap();
+    assert!(matches!(
+        shown.status(),
+        presentation::PresentationStatus::Ready
+    ));
+    let bounds = shown.bounds().unwrap();
+    assert!(bounds.x < -1_000_000. && bounds.x + bounds.width > 1_000_000.);
+    let fitted = state.presentation.camera(bounds);
+    assert!(fitted.scale > 0. && fitted.scale < 0.001);
+    let left = bounds.x * fitted.scale + fitted.pan.x;
+    let right = (bounds.x + bounds.width) * fitted.scale + fitted.pan.x;
+    assert!((left - 8.).abs() < 0.001 && (right - 692.).abs() < 0.001);
+    assert!(state.camera(
+        &f.project,
+        f.owner,
+        super::super::canvas_workspace::Event::Pan(iced::Vector::new(13., -7.))
+    ));
+    let moved = state.presentation.camera(bounds);
+    assert_eq!(moved.scale, fitted.scale);
+    assert_eq!(moved.pan, fitted.pan + iced::Vector::new(13., -7.));
+    assert!(!state.presentation.fit);
+    assert_eq!(f.project, original);
+}
+
+#[test]
+fn deleted_saved_identity_remains_unavailable_and_never_falls_into_derived_geometry() {
+    let mut f = direct_tests::fixture();
+    let rep = saved(&mut f.project, f.owner, &[]);
+    let mut state = State::default();
+    let document = Id::new_v4();
+    state.enter_representation(document, f.owner, rep);
+    let Representation::Saved { diagram } = rep else {
+        unreachable!()
+    };
+    f.project.diagrams.remove(&diagram);
+    let original = f.project.clone();
+    let shown = state.display(&f.project, f.owner, f.owner).unwrap();
+    assert_eq!(shown.requested(), rep);
+    assert!(matches!(
+        shown.status(),
+        presentation::PresentationStatus::Unavailable { .. }
+    ));
+    assert!(shown.scene().is_none() && shown.bounds().is_none());
+    assert_eq!(state.owner(), Some(f.owner));
+    assert!(state.context(document, f.owner, 0, 0).is_some());
+    assert!(!state.camera_zoom(&f.project, f.owner, None));
+    assert_eq!(f.project, original);
+}

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

@@ -0,0 +1,160 @@
+//! Pure Saved-only spacing preparation. Delta is measured from the original
+//! pointer in the captured camera's world coordinates, never from the last
+//! preview. The controller must own document/revision/visit, camera and hit-role
+//! admission; this module neither dispatches commands nor changes selection.
+use crate::behavior::scenario_layout::{
+    GeometryIssue, Representation, ResolvedScenarioPlan, presentation::checked_owner, resolve,
+};
+use oa_core::{
+    Command, Id, Kind, OccurrenceBody, OccurrenceEndpoint, Project, ScenarioLanePosition,
+    ScenarioMessagePosition, SharedBody, execute_batch,
+};
+
+pub(crate) mod controller;
+#[cfg(test)]
+mod tests;
+pub(crate) use controller::{Event, Stamp};
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Target {
+    Lane(Id),
+    Message(Id),
+}
+impl Target {
+    pub(crate) fn id(self) -> Id {
+        match self {
+            Self::Lane(id) | Self::Message(id) => id,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub(crate) enum Refusal {
+    InvalidSavedView(Id),
+    TargetNotRendered(Target),
+    InvalidDelta,
+    InvalidGesture,
+    CameraChanged,
+    TargetNotHit(Target),
+    Command(String),
+    Geometry(Vec<GeometryIssue>),
+}
+
+pub(super) struct Drag {
+    original: Project,
+    diagram: Id,
+    target: Target,
+    origin: f32,
+    original_geometry: ResolvedScenarioPlan,
+}
+
+pub(super) struct Preview {
+    pub(super) command: Command,
+    #[cfg(test)]
+    pub(super) project: Project,
+    pub(super) geometry: ResolvedScenarioPlan,
+}
+
+/// Capture an accepted, actually drawn target. A Saved view displaying automatic
+/// fallback is not an editable original, even if the target appears in fallback.
+pub(super) fn capture(project: &Project, diagram: Id, target: Target) -> Result<Drag, Refusal> {
+    let representation = Representation::Saved { diagram };
+    let owner = checked_owner(project, representation).ok_or(Refusal::InvalidSavedView(diagram))?;
+    let geometry = resolve(project, representation, target.id()).map_err(Refusal::Geometry)?;
+    let element = project.elements.get(&target.id());
+    let origin = match target {
+        Target::Lane(id)
+            if element.is_some_and(|e| e.kind() == Kind::Lifeline && e.parent == Some(owner)) =>
+        {
+            // Unassigned lifelines still have drawn headers. `scene.lanes`
+            // excludes them only from semantic message-endpoint hit testing.
+            geometry.scene.render_lanes.get(&id).copied()
+        }
+        Target::Message(id)
+            if element.is_some_and(|e| {
+                matches!(
+                    e.shared(),
+                    Some(SharedBody::Occurrence {
+                        body: OccurrenceBody::Exchange { .. },
+                        ..
+                    })
+                )
+            }) =>
+        {
+            // A lifecycle row can denote receive y; the public position means
+            // send y. Read the actual outgoing endpoint, including self calls.
+            geometry
+                .scene
+                .lines
+                .iter()
+                .find(|line| line.id == id)
+                .and_then(|line| line.points.first())
+                .map(|point| point.y)
+        }
+        _ => None,
+    }
+    .ok_or(Refusal::TargetNotRendered(target))?;
+    if !origin.is_finite() {
+        return Err(Refusal::TargetNotRendered(target));
+    }
+    Ok(Drag {
+        original: project.clone(),
+        diagram,
+        target,
+        origin,
+        original_geometry: geometry,
+    })
+}
+
+impl Drag {
+    /// None means there is no command to commit. In particular +0/-0, return to
+    /// start, and sub-precision motion never materialize a missing override or
+    /// normalize an existing explicit value. Document/redo are never touched.
+    pub(super) fn prepare(&self, original_delta: f32) -> Result<Option<Preview>, Refusal> {
+        if !original_delta.is_finite() {
+            return Err(Refusal::InvalidDelta);
+        }
+        if original_delta == 0. {
+            return Ok(None);
+        }
+        let position = (f64::from(self.origin) + f64::from(original_delta)) as f32;
+        if position == self.origin {
+            return Ok(None);
+        }
+        let command = match self.target {
+            Target::Lane(lifeline) => Command::SetScenarioLanePosition {
+                diagram: self.diagram,
+                position: ScenarioLanePosition {
+                    lifeline,
+                    x: position,
+                },
+            },
+            Target::Message(occurrence) => Command::SetScenarioMessagePosition {
+                diagram: self.diagram,
+                position: ScenarioMessagePosition {
+                    address: OccurrenceEndpoint {
+                        references: vec![],
+                        occurrence,
+                    },
+                    send_y: position,
+                },
+            },
+        };
+        let project = execute_batch(&self.original, std::slice::from_ref(&command))
+            .map_err(|error| Refusal::Command(error.to_string()))?;
+        let geometry = resolve(
+            &project,
+            Representation::Saved {
+                diagram: self.diagram,
+            },
+            self.target.id(),
+        )
+        .map_err(Refusal::Geometry)?;
+        Ok(Some(Preview {
+            command,
+            #[cfg(test)]
+            project,
+            geometry,
+        }))
+    }
+}

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

@@ -0,0 +1,300 @@
+//! One press owns one immutable accepted Project and one frozen display camera.
+use super::*;
+use crate::behavior::{
+    Scene, SceneHitRole,
+    scenario::{CanvasTool, Context, State},
+    scenario_layout::Diagnostic,
+};
+use iced::{Point, Rectangle, Vector};
+
+#[cfg(test)]
+pub(crate) mod tests;
+#[cfg(test)]
+mod timing_tests;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct Stamp {
+    pub(crate) context: Context,
+    pub(crate) camera_epoch: u64,
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum Event {
+    Begin {
+        stamp: Stamp,
+        token: Id,
+        target: Target,
+        press_screen: Point,
+        canvas_bounds: Rectangle,
+        scale: f32,
+        pan: Vector,
+    },
+    Move {
+        stamp: Stamp,
+        token: Id,
+        screen: Point,
+    },
+    Finish {
+        stamp: Stamp,
+        token: Id,
+        screen: Point,
+    },
+    Cancel {
+        stamp: Stamp,
+        token: Id,
+    },
+}
+impl Event {
+    pub(crate) fn stamp(self) -> Stamp {
+        match self {
+            Self::Begin { stamp, .. }
+            | Self::Move { stamp, .. }
+            | Self::Finish { stamp, .. }
+            | Self::Cancel { stamp, .. } => stamp,
+        }
+    }
+    pub(crate) fn token(self) -> Id {
+        match self {
+            Self::Begin { token, .. }
+            | Self::Move { token, .. }
+            | Self::Finish { token, .. }
+            | Self::Cancel { token, .. } => token,
+        }
+    }
+}
+
+pub(crate) struct Session {
+    stamp: Stamp,
+    token: Id,
+    press_screen: Point,
+    scale: f32,
+    pan: Vector,
+    drag: Drag,
+    preview: Option<Preview>,
+    refusal: Option<Refusal>,
+    ever_crossed: bool,
+}
+
+pub(in crate::behavior) struct Paint<'a> {
+    pub(in crate::behavior) scene: &'a Scene,
+    #[cfg(test)]
+    pub(in crate::behavior) bounds: Rectangle,
+    pub(in crate::behavior) refusal: Option<&'a Refusal>,
+    pub(in crate::behavior) original_diagnostics: &'a [Diagnostic],
+    pub(in crate::behavior) original_latent: &'a [Id],
+    pub(in crate::behavior) diagnostics: &'a [Diagnostic],
+}
+
+pub(crate) enum Finish {
+    Click(Id),
+    Noop,
+    Commit {
+        command: Command,
+        selected: Id,
+        scale: f32,
+        pan: Vector,
+    },
+}
+
+impl Session {
+    fn configure(&self, scene: &mut Scene) {
+        scene.selected = self.drag.target.id();
+        scene.scale = self.scale;
+        scene.camera_pan = self.pan;
+        scene.interaction = Some((self.stamp.context, CanvasTool::Select, true));
+        scene.spacing_stamp = Some(self.stamp);
+        scene.coordinate_input = true;
+        scene.pending_placement = None;
+    }
+    fn update(&mut self, screen: Point) {
+        self.preview = None;
+        self.refusal = None;
+        if !screen.x.is_finite() || !screen.y.is_finite() {
+            self.refusal = Some(Refusal::InvalidDelta);
+            return;
+        }
+        let distance = match self.drag.target {
+            Target::Lane(_) => screen.x - self.press_screen.x,
+            Target::Message(_) => screen.y - self.press_screen.y,
+        };
+        self.ever_crossed |= distance.abs() >= 3.;
+        if !self.ever_crossed {
+            return;
+        }
+        match self.drag.prepare(distance / self.scale) {
+            Ok(Some(mut preview)) => {
+                self.configure(&mut preview.geometry.scene);
+                self.preview = Some(preview);
+            }
+            Ok(None) => {}
+            Err(error) => self.refusal = Some(error),
+        }
+    }
+}
+
+impl State {
+    pub(crate) fn spacing_token(&self) -> Option<Id> {
+        self.spacing.as_ref().map(|s| s.token)
+    }
+    pub(crate) fn spacing_stamp(&self) -> Option<Stamp> {
+        self.spacing.as_ref().map(|s| s.stamp)
+    }
+    pub(crate) fn cancel_spacing(&mut self) -> bool {
+        self.spacing.take().is_some()
+    }
+
+    pub(in crate::behavior) fn spacing_paint(
+        &self,
+        context: Context,
+        camera_epoch: u64,
+    ) -> Option<Paint<'_>> {
+        let session = self.spacing.as_ref()?;
+        if session.stamp
+            != (Stamp {
+                context,
+                camera_epoch,
+            })
+        {
+            return None;
+        }
+        let original = &session.drag.original_geometry;
+        let shown = session.preview.as_ref().map_or(original, |p| &p.geometry);
+        Some(Paint {
+            scene: &shown.scene,
+            #[cfg(test)]
+            bounds: shown.bounds,
+            refusal: session.refusal.as_ref(),
+            original_diagnostics: &original.plan.diagnostics,
+            original_latent: &original.latent_messages,
+            diagnostics: &shown.plan.diagnostics,
+        })
+    }
+
+    pub(crate) fn begin_spacing(&mut self, project: &Project, event: Event) -> Result<(), Refusal> {
+        let Event::Begin {
+            stamp,
+            token,
+            target,
+            press_screen,
+            canvas_bounds,
+            scale,
+            pan,
+        } = event
+        else {
+            return Err(Refusal::InvalidGesture);
+        };
+        let context = stamp.context;
+        if self.spacing.is_some()
+            || token.is_nil()
+            || self.context(
+                context.document,
+                context.scenario,
+                context.revision,
+                context.epoch,
+            ) != Some(context)
+            || self.canvas_tool(context.scenario) != CanvasTool::Select
+            || ![
+                press_screen.x,
+                press_screen.y,
+                canvas_bounds.x,
+                canvas_bounds.y,
+                canvas_bounds.width,
+                canvas_bounds.height,
+                scale,
+                pan.x,
+                pan.y,
+            ]
+            .into_iter()
+            .all(f32::is_finite)
+            || scale <= 0.
+            || canvas_bounds.width <= 0.
+            || canvas_bounds.height <= 0.
+            || !canvas_bounds.contains(press_screen)
+        {
+            return Err(Refusal::InvalidGesture);
+        }
+        let Representation::Saved { diagram } = context.representation else {
+            return Err(Refusal::InvalidGesture);
+        };
+        let mut drag = capture(project, diagram, target)?;
+        let camera = self.presentation.camera(drag.original_geometry.bounds);
+        if self.presentation.viewport != Some(canvas_bounds.size())
+            || camera.scale != scale
+            || camera.pan != pan
+        {
+            return Err(Refusal::CameraChanged);
+        }
+        let world = Point::new(
+            (press_screen.x - canvas_bounds.x - pan.x) / scale,
+            (press_screen.y - canvas_bounds.y - pan.y) / scale,
+        );
+        // Hit tolerance is measured in displayed pixels, just like the widget.
+        drag.original_geometry.scene.scale = scale;
+        drag.original_geometry.scene.camera_pan = pan;
+        let hit = drag.original_geometry.scene.hit_item(world);
+        if !hit.is_some_and(|hit| {
+            hit.id == target.id()
+                && match target {
+                    Target::Lane(_) => hit.role == SceneHitRole::LifelineHeader,
+                    Target::Message(_) => matches!(
+                        hit.role,
+                        SceneHitRole::MessageBody | SceneHitRole::MessageLabel
+                    ),
+                }
+        }) {
+            return Err(Refusal::TargetNotHit(target));
+        }
+        // Configure baseline without changing the persistent camera or selection.
+        let scene = &mut drag.original_geometry.scene;
+        scene.selected = target.id();
+        scene.scale = scale;
+        scene.camera_pan = pan;
+        scene.interaction = Some((context, CanvasTool::Select, true));
+        scene.spacing_stamp = Some(stamp);
+        scene.coordinate_input = true;
+        scene.pending_placement = None;
+        self.spacing = Some(Session {
+            stamp,
+            token,
+            press_screen,
+            scale,
+            pan,
+            drag,
+            preview: None,
+            refusal: None,
+            ever_crossed: false,
+        });
+        Ok(())
+    }
+    pub(crate) fn move_spacing(&mut self, screen: Point) {
+        if let Some(session) = &mut self.spacing {
+            session.update(screen);
+        }
+    }
+    pub(crate) fn finish_spacing(&mut self, screen: Point) -> Result<Finish, Refusal> {
+        let Some(mut session) = self.spacing.take() else {
+            return Err(Refusal::InvalidGesture);
+        };
+        session.update(screen);
+        if let Some(error) = session.refusal {
+            return Err(error);
+        }
+        if !session.ever_crossed {
+            return Ok(Finish::Click(session.drag.target.id()));
+        }
+        Ok(match session.preview {
+            None => Finish::Noop,
+            Some(preview) => Finish::Commit {
+                command: preview.command,
+                selected: session.drag.target.id(),
+                scale: session.scale,
+                pan: session.pan,
+            },
+        })
+    }
+    pub(crate) fn accept_spacing_camera(&mut self, scale: f32, pan: Vector) {
+        self.presentation.zoom = Some(scale);
+        self.presentation.pan = pan;
+        self.presentation.fit = false;
+    }
+}

crates/oa-desktop/src/behavior/scenario/spacing/controller/tests.rs

@@ -0,0 +1,421 @@
+use super::*;
+use crate::document::Document;
+use iced::Size;
+use oa_core::{Diagram, Layer, ProjectionKind, language, source_project::ProjectLimits};
+
+pub(crate) fn fixture() -> (Document, Id, Id, Id, Id) {
+    let mut p = language::parse(r#"arcadia 7;
+project spacing "Spacing" {
+ oa_activity work "Work" {}
+ oa_activity response "Response" {}
+ oa_scenario incident "Incident" { viewpoint OperationalActivity; steps [@first, @second]; }
+ oa_lifeline reporter "Reporter" { parent @incident; represented @work; }
+ oa_lifeline operator "Operator" { parent @incident; represented @response; }
+ oa_occurrence first "First" { parent @incident; body { Exchange { exchange none; sender @reporter; receiver @operator; message_kind Asynchronous; }; }; }
+ oa_occurrence second "Second" { parent @incident; body { Exchange { exchange none; sender @operator; receiver @reporter; message_kind Asynchronous; }; }; }
+}"#).unwrap();
+    let id = |name: &str| {
+        p.identities()
+            .into_iter()
+            .find(|(_, alias)| *alias == name)
+            .unwrap()
+            .0
+    };
+    let (owner, lane, message) = (id("incident"), id("reporter"), id("first"));
+    let diagram = Id::new_v4();
+    p.diagrams.insert(
+        diagram,
+        Diagram {
+            id: diagram,
+            alias: "saved".into(),
+            name: "Saved".into(),
+            description: String::new(),
+            layer: Layer::Oa,
+            projection: ProjectionKind::Scenario { scenario: owner },
+            nodes: Default::default(),
+            routes: vec![],
+            view_options: Default::default(),
+            layout: None,
+        },
+    );
+    (
+        Document::from_project(p, ProjectLimits::default()).unwrap(),
+        owner,
+        diagram,
+        lane,
+        message,
+    )
+}
+
+pub(crate) fn expected(p: &Project, diagram: Id, target: Target, delta: f32) -> Project {
+    capture(p, diagram, target)
+        .unwrap()
+        .prepare(delta)
+        .unwrap()
+        .unwrap()
+        .project
+}
+
+pub(crate) fn packet(
+    p: &Project,
+    state: &State,
+    context: Context,
+    camera_epoch: u64,
+    target: Target,
+) -> Event {
+    let geometry = resolve(p, context.representation, target.id()).unwrap();
+    let world = match target {
+        Target::Lane(id) => geometry
+            .scene
+            .boxes
+            .iter()
+            .find(|item| item.id == id && item.role == SceneHitRole::LifelineHeader)
+            .unwrap()
+            .rect
+            .center(),
+        Target::Message(id) => {
+            let line = geometry
+                .scene
+                .lines
+                .iter()
+                .find(|line| line.id == id)
+                .unwrap();
+            Point::new((line.points[0].x + line.points[1].x) / 2., line.points[0].y)
+        }
+    };
+    assert!(
+        geometry
+            .scene
+            .hit_item(world)
+            .is_some_and(|hit| hit.id == target.id())
+    );
+    let camera = state.presentation.camera(geometry.bounds);
+    let canvas_bounds = Rectangle::new(Point::new(17., 23.), state.presentation.viewport.unwrap());
+    Event::Begin {
+        stamp: Stamp {
+            context,
+            camera_epoch,
+        },
+        token: Id::new_v4(),
+        target,
+        press_screen: Point::new(
+            canvas_bounds.x + world.x * camera.scale + camera.pan.x,
+            canvas_bounds.y + world.y * camera.scale + camera.pan.y,
+        ),
+        canvas_bounds,
+        scale: camera.scale,
+        pan: camera.pan,
+    }
+}
+fn setup(target_message: bool) -> (Document, State, Event) {
+    let (doc, owner, diagram, lane, message) = fixture();
+    let mut state = State::default();
+    state.enter_representation(Id::new_v4(), owner, Representation::Saved { diagram });
+    state.presentation.viewport = Some(Size::new(900., 600.));
+    let context = state
+        .context(
+            state.presentation.identity.unwrap().0,
+            owner,
+            doc.revision(),
+            4,
+        )
+        .unwrap();
+    let target = if target_message {
+        Target::Message(message)
+    } else {
+        Target::Lane(lane)
+    };
+    let event = packet(doc.project(), &state, context, 9, target);
+    (doc, state, event)
+}
+fn press(event: Event) -> Point {
+    let Event::Begin { press_screen, .. } = event else {
+        unreachable!()
+    };
+    press_screen
+}
+
+#[test]
+fn real_preview_moves_only_active_axis_from_original_and_never_changes_document() {
+    for message in [false, true] {
+        let (doc, mut state, begin) = setup(message);
+        let original = doc.snapshot();
+        let camera = state.camera_boundary();
+        let start = press(begin);
+        state.begin_spacing(doc.project(), begin).unwrap();
+        let first = if message {
+            Vector::new(500., 30.)
+        } else {
+            Vector::new(30., 500.)
+        };
+        state.move_spacing(start + first);
+        let session = state.spacing.as_ref().unwrap();
+        let candidate = session.preview.as_ref().unwrap();
+        let delta = 30. / session.scale;
+        let actual_anchor = match session.drag.target {
+            Target::Lane(id) => candidate.geometry.scene.render_lanes[&id],
+            Target::Message(id) => {
+                candidate
+                    .geometry
+                    .scene
+                    .lines
+                    .iter()
+                    .find(|line| line.id == id)
+                    .unwrap()
+                    .points[0]
+                    .y
+            }
+        };
+        let wanted = (f64::from(session.drag.origin) + f64::from(delta)) as f32;
+        assert_eq!(actual_anchor.to_bits(), wanted.to_bits());
+        let expected = session.drag.prepare(delta).unwrap().unwrap();
+        assert_eq!(candidate.project, expected.project);
+        assert_eq!(candidate.geometry.scene.rows, expected.geometry.scene.rows);
+        assert_eq!(
+            candidate.geometry.scene.render_lanes,
+            expected.geometry.scene.render_lanes
+        );
+        state.move_spacing(start + first * 2.);
+        let session = state.spacing.as_ref().unwrap();
+        assert_eq!(
+            session.preview.as_ref().unwrap().project,
+            session.drag.prepare(delta * 2.).unwrap().unwrap().project
+        );
+        assert_eq!(doc.project(), &original.decoded.project);
+        assert_eq!(doc.compiled().bundle, original.bundle);
+        assert!(!doc.dirty() && !doc.can_undo() && !doc.can_redo());
+        assert!(camera == state.camera_boundary());
+    }
+}
+
+#[test]
+fn click_threshold_is_active_axis_and_return_to_zero_is_not_a_click() {
+    let (doc, mut state, begin) = setup(false);
+    let start = press(begin);
+    state.begin_spacing(doc.project(), begin).unwrap();
+    state.move_spacing(start + Vector::new(2., 100.));
+    assert!(matches!(
+        state.finish_spacing(start).unwrap(),
+        Finish::Click(_)
+    ));
+    state.begin_spacing(doc.project(), begin).unwrap();
+    state.move_spacing(start + Vector::new(4., 0.));
+    assert!(matches!(state.finish_spacing(start).unwrap(), Finish::Noop));
+    assert!(!doc.can_undo());
+}
+
+#[test]
+fn invalid_move_discards_prior_candidate_and_finish_rechecks_final_pointer() {
+    let (doc, mut state, begin) = setup(false);
+    let start = press(begin);
+    state.begin_spacing(doc.project(), begin).unwrap();
+    state.move_spacing(start + Vector::new(20., 0.));
+    state.move_spacing(Point::new(f32::NAN, start.y));
+    let paint = state.spacing_paint(begin.stamp().context, 9).unwrap();
+    assert!(matches!(paint.refusal, Some(Refusal::InvalidDelta)));
+    assert_eq!(
+        paint.scene.render_lanes,
+        state
+            .spacing
+            .as_ref()
+            .unwrap()
+            .drag
+            .original_geometry
+            .scene
+            .render_lanes
+    );
+    assert!(matches!(
+        state.finish_spacing(Point::new(f32::NAN, start.y)),
+        Err(Refusal::InvalidDelta)
+    ));
+    assert!(state.spacing_token().is_none());
+}
+
+#[test]
+fn forged_camera_hit_role_and_retired_visit_cannot_capture() {
+    let (doc, mut state, begin) = setup(false);
+    let Event::Begin {
+        stamp,
+        token,
+        target,
+        press_screen,
+        canvas_bounds,
+        scale,
+        pan,
+    } = begin
+    else {
+        unreachable!()
+    };
+    assert!(matches!(
+        state.begin_spacing(
+            doc.project(),
+            Event::Begin {
+                stamp,
+                token,
+                target,
+                press_screen,
+                canvas_bounds,
+                scale: scale * 2.,
+                pan
+            }
+        ),
+        Err(Refusal::CameraChanged)
+    ));
+    assert!(matches!(
+        state.begin_spacing(
+            doc.project(),
+            Event::Begin {
+                stamp,
+                token,
+                target,
+                press_screen: canvas_bounds.center(),
+                canvas_bounds,
+                scale,
+                pan
+            }
+        ),
+        Err(Refusal::TargetNotHit(_))
+    ));
+    state.leave();
+    assert!(matches!(
+        state.begin_spacing(doc.project(), begin),
+        Err(Refusal::InvalidGesture)
+    ));
+}
+
+#[test]
+fn zoomed_out_message_tolerance_matches_actual_canvas_hit() {
+    let (doc, mut state, _) = setup(true);
+    state.presentation.fit = false;
+    state.presentation.zoom = Some(0.25);
+    state.presentation.pan = Vector::ZERO;
+    let context = state
+        .context(
+            state.presentation.identity.unwrap().0,
+            state.owner().unwrap(),
+            doc.revision(),
+            4,
+        )
+        .unwrap();
+    let message = doc
+        .project()
+        .identities()
+        .into_iter()
+        .find(|(_, alias)| *alias == "first")
+        .map(|(id, _)| id)
+        .unwrap();
+    let Event::Begin {
+        stamp,
+        token,
+        target,
+        press_screen,
+        canvas_bounds,
+        scale,
+        pan,
+    } = packet(doc.project(), &state, context, 9, Target::Message(message))
+    else {
+        unreachable!()
+    };
+    let event = Event::Begin {
+        stamp,
+        token,
+        target,
+        press_screen: press_screen + Vector::new(0., 3.),
+        canvas_bounds,
+        scale,
+        pan,
+    };
+    state.begin_spacing(doc.project(), event).unwrap();
+    assert_eq!(state.spacing_token(), Some(token));
+}
+
+#[test]
+fn fractional_screen_packet_preserves_subpixel_motion_in_preview_and_finish() {
+    let (doc, owner, diagram, _, message) = fixture();
+    let original = doc.snapshot();
+    assert!(doc.project().diagrams[&diagram].layout.is_none());
+    let mut state = State::default();
+    let document = Id::new_v4();
+    state.enter_representation(document, owner, Representation::Saved { diagram });
+    state.presentation.viewport = Some(Size::new(900., 600.));
+    state.presentation.fit = false;
+    state.presentation.zoom = Some(0.5);
+    // 406 + 2^-15 puts the press just below the 512 screen-coordinate boundary.
+    state.presentation.pan = Vector::new(0., f32::from_bits(0x43cb_0001));
+    let camera = state.camera_boundary();
+    let context = state.context(document, owner, doc.revision(), 4).unwrap();
+    let baseline = resolve(doc.project(), context.representation, message).unwrap();
+    let line = baseline
+        .scene
+        .lines
+        .iter()
+        .find(|line| line.id == message)
+        .unwrap();
+    assert_eq!(line.points[0].y, 148.);
+    let begin = packet(doc.project(), &state, context, 9, Target::Message(message));
+    let Event::Begin {
+        press_screen,
+        canvas_bounds,
+        scale,
+        pan,
+        ..
+    } = begin
+    else {
+        unreachable!()
+    };
+    assert_eq!(canvas_bounds.y, 23.);
+    assert_eq!(scale, 0.5);
+    assert_eq!(pan.y.to_bits(), 0x43cb_0001);
+    assert_eq!(press_screen.y.to_bits(), 0x43fb_8001); // 503 + 2^-15.
+    let end = press_screen + Vector::new(0., 10.);
+    assert_eq!(end.y, 513.);
+    assert!(canvas_bounds.contains(press_screen) && canvas_bounds.contains(end));
+    // The submitted f32 displacement is 10 - 2^-15, not exactly 10.
+    assert_eq!((end.y - press_screen.y).to_bits(), 0x411f_ffe0);
+    assert_eq!(((end.y - press_screen.y) / scale).to_bits(), 0x419f_ffe0);
+    // Independent oracle: 148 + (10 - 2^-15) / .5 = 168 - 2^-14.
+    let expected_y = f32::from_bits(0x4327_fffc);
+    let mut expected = original.decoded.project.clone();
+    expected.diagrams.get_mut(&diagram).unwrap().layout =
+        Some(oa_core::DiagramLayout::Scenario(oa_core::ScenarioLayout {
+            lanes: vec![],
+            messages: vec![oa_core::ScenarioMessagePosition {
+                address: oa_core::OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence: message,
+                },
+                send_y: expected_y,
+            }],
+        }));
+    state.begin_spacing(doc.project(), begin).unwrap();
+    state.move_spacing(end);
+    let preview = state.spacing.as_ref().unwrap().preview.as_ref().unwrap();
+    assert_eq!(preview.project, expected);
+    let line = preview
+        .geometry
+        .scene
+        .lines
+        .iter()
+        .find(|line| line.id == message)
+        .unwrap();
+    assert_eq!(line.points[0].y.to_bits(), expected_y.to_bits());
+    let Finish::Commit {
+        command,
+        selected,
+        scale,
+        pan,
+    } = state.finish_spacing(end).unwrap()
+    else {
+        panic!("fractional motion must remain a commit")
+    };
+    assert_eq!(selected, message);
+    assert_eq!(scale, 0.5);
+    assert_eq!(pan.y.to_bits(), 0x43cb_0001);
+    let committed = oa_core::execute_batch(doc.project(), &[command]).unwrap();
+    assert_eq!(committed, expected);
+    assert!(state.spacing_token().is_none());
+    assert_eq!(doc.project(), &original.decoded.project);
+    assert_eq!(doc.compiled().bundle, original.bundle);
+    assert!(!doc.dirty() && !doc.can_undo() && !doc.can_redo());
+    assert!(camera == state.camera_boundary());
+}

crates/oa-desktop/src/behavior/scenario/spacing/controller/timing_tests.rs

@@ -0,0 +1,304 @@
+//! Diagnostic only: production capture/prepare, excluding fixture construction,
+//! oracle work, App source writes, widget rebuilds, text shaping and GPU paint.
+use super::*;
+use crate::document::Document;
+use oa_core::{
+    DiagramLayout, Layer, MessageKind, RelationKind, ScenarioLayout, source_project::ProjectLimits,
+};
+use serde_json::{Value, json};
+use std::{collections::BTreeSet, sync::Arc, time::Instant};
+
+const MESSAGE_COUNT: usize = 1000;
+const TARGET_INDEX: usize = 500;
+
+fn large_fixture() -> (Document, Id, [Id; 3], Vec<Id>, Vec<Id>) {
+    let (seed, owner, a, reporter, first) = super::tests::fixture();
+    let mut p = seed.project().clone();
+    let old_steps = p.elements[&owner].steps().unwrap().clone();
+    let template = p.elements[&first].clone();
+    let work = |alias: &str| {
+        p.identities()
+            .into_iter()
+            .find(|(_, name)| *name == alias)
+            .unwrap()
+            .0
+    };
+    let (source, target) = (work("work"), work("response"));
+    let operator = work("operator");
+    let relation = p.relate(
+        RelationKind::Interaction,
+        "Repeated incident report",
+        source,
+        target,
+    );
+    let mut lanes = vec![];
+    for index in 0..20 {
+        let original = if index < 10 { reporter } else { operator };
+        let mut lane = p.elements[&original].clone();
+        lane.id = Id::new_v4();
+        lane.alias = format!("timing_lane_{index:02}");
+        lane.name = format!("Review participant {index:02}");
+        lanes.push(lane.id);
+        p.elements.insert(lane.id, lane);
+    }
+    p.elements.remove(&reporter);
+    p.elements.remove(&operator);
+    for id in old_steps {
+        p.elements.remove(&id);
+    }
+    let mut messages = vec![];
+    for index in 0..MESSAGE_COUNT {
+        let mut occurrence = template.clone();
+        occurrence.id = Id::new_v4();
+        occurrence.alias = format!("timing_message_{index:04}");
+        occurrence.name = format!("Validate incident report {index:04}");
+        *occurrence.shared_mut().unwrap() = SharedBody::Occurrence {
+            body: OccurrenceBody::Exchange {
+                exchange: Some(relation),
+                sender: Some(lanes[index % 10]),
+                receiver: Some(lanes[10 + index % 10]),
+                message_kind: MessageKind::Asynchronous,
+                operation: None,
+                reply_to: None,
+                values: vec![],
+            },
+            precondition: String::new(),
+            postcondition: String::new(),
+        };
+        messages.push(occurrence.id);
+        p.elements.insert(occurrence.id, occurrence);
+    }
+    *p.elements.get_mut(&owner).unwrap().steps_mut().unwrap() = messages.clone();
+    p.diagrams.get_mut(&a).unwrap().layout = Some(DiagramLayout::Scenario(ScenarioLayout {
+        lanes: lanes
+            .iter()
+            .enumerate()
+            .map(|(i, &lifeline)| ScenarioLanePosition {
+                lifeline,
+                x: 160. + i as f32 * 240.,
+            })
+            .collect(),
+        messages: vec![],
+    }));
+    let mut views = [a, Id::nil(), Id::nil()];
+    for (index, x, offset) in [(1, -500., 12.), (2, 6500., -12.)] {
+        let mut view = p.diagrams[&a].clone();
+        view.id = Id::new_v4();
+        view.alias = format!("timing_saved_{index}");
+        view.name = format!("Review arrangement {index}");
+        view.layout = Some(DiagramLayout::Scenario(ScenarioLayout {
+            lanes: vec![ScenarioLanePosition {
+                lifeline: lanes[0],
+                x,
+            }],
+            messages: vec![ScenarioMessagePosition {
+                address: OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence: messages[TARGET_INDEX],
+                },
+                send_y: 148. + TARGET_INDEX as f32 * 92. + offset,
+            }],
+        }));
+        views[index] = view.id;
+        p.diagrams.insert(view.id, view);
+    }
+    let document = Document::from_project(p, ProjectLimits::default()).unwrap();
+    assert_eq!(
+        document
+            .project()
+            .children(owner)
+            .filter(|e| e.kind() == Kind::Lifeline)
+            .count(),
+        20
+    );
+    assert_eq!(document.project().elements[&owner].layer(), Layer::Oa);
+    assert_eq!(document.project().diagrams.len(), 3);
+    (document, owner, views, lanes, messages)
+}
+
+fn assert_scene(
+    scene: &Scene,
+    lanes: &[Id],
+    messages: &[Id],
+    moved_message: Option<(Id, f32)>,
+    moved_lane: Option<(Id, f32)>,
+) {
+    assert_eq!(scene.render_lanes.len(), 20);
+    assert_eq!(
+        scene
+            .boxes
+            .iter()
+            .filter(|b| b.role == SceneHitRole::LifelineHeader)
+            .count(),
+        20
+    );
+    assert_eq!(scene.lines.len(), MESSAGE_COUNT);
+    assert_eq!(
+        scene
+            .lines
+            .iter()
+            .map(|line| line.id)
+            .collect::<BTreeSet<_>>(),
+        messages.iter().copied().collect::<BTreeSet<_>>()
+    );
+    assert!(scene.activations.is_empty() && scene.open_calls.is_empty());
+    let x = |index: usize| {
+        160. + index as f32 * 240.
+            + moved_lane
+                .filter(|(id, _)| *id == lanes[index])
+                .map_or(0., |(_, delta)| delta)
+    };
+    for (index, &lane) in lanes.iter().enumerate() {
+        assert_eq!(scene.render_lanes[&lane], x(index));
+    }
+    for (index, (line, &id)) in scene.lines.iter().zip(messages).enumerate() {
+        let y = 148.
+            + index as f32 * 92.
+            + moved_message
+                .filter(|(target, _)| *target == id)
+                .map_or(0., |(_, delta)| delta);
+        assert_eq!(line.id, id);
+        assert_eq!(
+            line.points,
+            vec![
+                Point::new(x(index % 10), y),
+                Point::new(x(10 + index % 10), y)
+            ]
+        );
+    }
+}
+
+fn summary(samples: &[Value], phase: &str) -> Value {
+    let mut times: Vec<u64> = samples
+        .iter()
+        .filter(|sample| sample["phase"] == phase)
+        .map(|sample| sample["elapsed_ns"].as_u64().unwrap())
+        .collect();
+    times.sort_unstable();
+    let n = times.len();
+    let median = if n.is_multiple_of(2) {
+        ((u128::from(times[n / 2 - 1]) + u128::from(times[n / 2])) / 2) as u64
+    } else {
+        times[n / 2]
+    };
+    json!({"samples": n, "min_ns": times[0], "median_ns": median, "max_ns": times[n-1]})
+}
+
+#[test]
+#[ignore = "Diagnostic timing only; run alone with --exact --ignored --nocapture after correctness gates; no latency acceptance threshold"]
+fn saved_spacing_capture_prepare_20_lanes_1000_messages_3_views() {
+    let (document, owner, views, lanes, messages) = large_fixture();
+    let original = document.snapshot();
+    let target = messages[TARGET_INDEX];
+    let mut samples = vec![];
+    let mut retained = None;
+    for iteration in 0..4 {
+        let start = Instant::now();
+        let result = capture(document.project(), views[0], Target::Message(target));
+        let elapsed_ns = u64::try_from(start.elapsed().as_nanos()).unwrap();
+        let drag = result.expect("complete asynchronous fixture must resolve");
+        samples.push(json!({"phase":"capture_message", "iteration":iteration,
+            "first_in_probe":iteration==0, "elapsed_ns":elapsed_ns, "outcome":"captured"}));
+        assert_scene(&drag.original_geometry.scene, &lanes, &messages, None, None);
+        if iteration == 0 {
+            retained = Some(drag);
+        }
+    }
+    let drag = retained.unwrap();
+    // Every sample is relative to the original press, including duplicate,
+    // reverse and return-to-start samples. Oracle work is outside each timer.
+    let deltas = [
+        4., 8., 12., 16., 20., 24., 28., 32., 32., 28., 24., 20., 16., 12., 8., 4., -4., -8., -4.,
+        0.,
+    ];
+    for (iteration, delta) in deltas.into_iter().enumerate() {
+        let start = Instant::now();
+        let result = drag.prepare(delta);
+        let elapsed_ns = u64::try_from(start.elapsed().as_nanos()).unwrap();
+        let candidate = result.expect("these isolated asynchronous offsets are feasible");
+        samples.push(json!({"phase":"prepare_message", "iteration":iteration,
+            "delta_world":delta, "elapsed_ns":elapsed_ns, "outcome":if candidate.is_some(){"preview"}else{"noop"}}));
+        if delta == 0. {
+            assert!(candidate.is_none());
+        } else {
+            let candidate = candidate.unwrap();
+            let mut expected = original.decoded.project.clone();
+            let Some(DiagramLayout::Scenario(layout)) =
+                &mut expected.diagrams.get_mut(&views[0]).unwrap().layout
+            else {
+                panic!()
+            };
+            layout.messages.push(ScenarioMessagePosition {
+                address: OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence: target,
+                },
+                send_y: 148. + TARGET_INDEX as f32 * 92. + delta,
+            });
+            assert_eq!(candidate.project, expected);
+            assert_scene(
+                &candidate.geometry.scene,
+                &lanes,
+                &messages,
+                Some((target, delta)),
+                None,
+            );
+        }
+        assert_eq!(
+            document.project().elements[&owner].steps().unwrap(),
+            &messages
+        );
+        assert_eq!(document.project(), &original.decoded.project);
+        assert!(Arc::ptr_eq(&original, &document.snapshot()));
+    }
+    let lane = lanes[10];
+    let start = Instant::now();
+    let result = capture(document.project(), views[0], Target::Lane(lane));
+    let elapsed_ns = u64::try_from(start.elapsed().as_nanos()).unwrap();
+    let drag = result.unwrap();
+    samples.push(json!({"phase":"capture_lane", "iteration":0, "elapsed_ns":elapsed_ns, "outcome":"captured"}));
+    for (iteration, delta) in [20., 40., -20.].into_iter().enumerate() {
+        let start = Instant::now();
+        let result = drag.prepare(delta);
+        let elapsed_ns = u64::try_from(start.elapsed().as_nanos()).unwrap();
+        let candidate = result.unwrap().unwrap();
+        samples.push(json!({"phase":"prepare_lane", "iteration":iteration,
+            "delta_world":delta, "elapsed_ns":elapsed_ns, "outcome":"preview"}));
+        let mut expected = original.decoded.project.clone();
+        let Some(DiagramLayout::Scenario(layout)) =
+            &mut expected.diagrams.get_mut(&views[0]).unwrap().layout
+        else {
+            panic!()
+        };
+        layout.lanes[10].x = 2560. + delta;
+        assert_eq!(candidate.project, expected);
+        assert_scene(
+            &candidate.geometry.scene,
+            &lanes,
+            &messages,
+            None,
+            Some((lane, delta)),
+        );
+    }
+    assert_eq!(document.project(), &original.decoded.project);
+    assert_eq!(document.bundle(), &original.bundle);
+    for view in views {
+        assert_eq!(
+            document.project().diagrams[&view],
+            original.decoded.project.diagrams[&view]
+        );
+    }
+    assert_eq!(document.revision(), 0);
+    assert!(!document.dirty() && !document.can_undo() && !document.can_redo());
+    let report = json!({
+        "schema":"scenario_spacing_timing_v1",
+        "fixture":{"lanes":20,"messages":MESSAGE_COUNT,"saved_views":3,"target_index":TARGET_INDEX,"distinct_message_ids":messages.iter().copied().collect::<BTreeSet<_>>().len()},
+        "profile_context":{"debug_assertions":cfg!(debug_assertions),"os":std::env::consts::OS,"arch":std::env::consts::ARCH,
+            "source_pin_from_runner":std::env::var("SCENARIO_SPACING_SOURCE_PIN").ok(),"source_binary_toolchain_binding":"external gate receipt required"},
+        "summaries":{"capture_message":summary(&samples,"capture_message"),"prepare_message":summary(&samples,"prepare_message"),"capture_lane":summary(&samples,"capture_lane"),"prepare_lane":summary(&samples,"prepare_lane")},
+        "samples":samples,
+        "invariant_status":"passed",
+        "limits":"First capture is first in this probe, not cold OS caches. Timers exclude construction/oracles, prior-preview disposal, source write/history, widget rebuild, label shaping, GPU paint and queued input; no responsiveness acceptance or latency threshold. All messages asynchronous; no nested frame/lifecycle stress."
+    });
+    println!("SPACING_TIMING_JSON={report}");
+}

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

@@ -0,0 +1,522 @@
+use super::*;
+use crate::behavior::scenario_layout::Diagnostic;
+use crate::document::Document;
+use oa_core::{
+    Diagram, DiagramLayout, ProjectionKind, ScenarioLayout, language, source_project::ProjectLimits,
+};
+
+fn id(project: &Project, alias: &str) -> Id {
+    project
+        .identities()
+        .into_iter()
+        .find(|(_, name)| *name == alias)
+        .unwrap()
+        .0
+}
+
+fn fixture(layout: Option<ScenarioLayout>) -> (Document, Id, Id) {
+    let mut project = language::parse(FIXTURE).unwrap();
+    let owner = id(&project, "conversation");
+    let mut add = |alias: &str, layout: Option<ScenarioLayout>| {
+        let diagram = Id::new_v4();
+        project.diagrams.insert(
+            diagram,
+            Diagram {
+                id: diagram,
+                alias: alias.into(),
+                name: alias.into(),
+                description: String::new(),
+                layer: oa_core::Layer::Oa,
+                projection: ProjectionKind::Scenario { scenario: owner },
+                nodes: Default::default(),
+                routes: vec![],
+                view_options: Default::default(),
+                layout: layout.map(DiagramLayout::Scenario),
+            },
+        );
+        diagram
+    };
+    let a = add("saved_a", layout);
+    let b = add("saved_b", Some(ScenarioLayout::default()));
+    let document = Document::from_project(project, ProjectLimits::default()).unwrap();
+    (document, a, b)
+}
+
+fn resolved(project: &Project, diagram: Id, selected: Id) -> ResolvedScenarioPlan {
+    resolve(project, Representation::Saved { diagram }, selected).unwrap()
+}
+
+fn same_geometry(a: &ResolvedScenarioPlan, b: &ResolvedScenarioPlan) {
+    assert_eq!(a.bounds, b.bounds);
+    assert_eq!(a.lanes, b.lanes);
+    assert_eq!(a.plan.frames, b.plan.frames);
+    assert_eq!(a.plan.scopes, b.plan.scopes);
+    let (a, b) = (&a.scene, &b.scene);
+    assert_eq!(a.rows, b.rows);
+    assert_eq!(a.sequence_bounds, b.sequence_bounds);
+    assert_eq!(a.size, b.size);
+    assert_eq!(a.layout_origin, b.layout_origin);
+    assert_eq!(a.lanes, b.lanes);
+    assert_eq!(a.render_lanes, b.render_lanes);
+    assert_eq!(a.activations, b.activations);
+    assert_eq!(a.lifecycle, b.lifecycle);
+    assert_eq!(a.open_calls, b.open_calls);
+    let slots = |scene: &crate::behavior::Scene| {
+        scene
+            .slots
+            .iter()
+            .map(|item| {
+                (
+                    item.slot.parent,
+                    item.slot.before,
+                    item.y,
+                    item.label.clone(),
+                )
+            })
+            .collect::<Vec<_>>()
+    };
+    assert_eq!(slots(a), slots(b));
+    let lines = |scene: &crate::behavior::Scene| {
+        scene
+            .lines
+            .iter()
+            .map(|line| {
+                (
+                    line.id,
+                    line.points.clone(),
+                    line.label_at,
+                    line.label.clone(),
+                    line.dashed,
+                )
+            })
+            .collect::<Vec<_>>()
+    };
+    let boxes = |scene: &crate::behavior::Scene| {
+        scene
+            .boxes
+            .iter()
+            .map(|item| {
+                (
+                    item.id,
+                    item.rect,
+                    item.title.clone(),
+                    item.detail.clone(),
+                    item.marker,
+                )
+            })
+            .collect::<Vec<_>>()
+    };
+    assert_eq!(lines(a), lines(b));
+    assert_eq!(boxes(a), boxes(b));
+}
+
+fn expected_message(project: &Project, diagram: Id, occurrence: Id, y: f32) -> Project {
+    // Independent expected mutation: tests begin with no message overrides.
+    let mut expected = project.clone();
+    expected.diagrams.get_mut(&diagram).unwrap().layout =
+        Some(DiagramLayout::Scenario(ScenarioLayout {
+            lanes: vec![],
+            messages: vec![ScenarioMessagePosition {
+                address: OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence,
+                },
+                send_y: y,
+            }],
+        }));
+    expected
+}
+
+#[test]
+fn one_repeated_message_moves_in_one_view_with_exact_document_undo_redo_and_reopen() {
+    let (mut document, a, b) = fixture(None);
+    let original = document.snapshot();
+    let before = document.project().clone();
+    let first = id(&before, "first");
+    let second = id(&before, "second");
+    let baseline = resolved(&before, a, second);
+    assert_eq!(baseline.scene.rows[&first].1, 148.);
+    assert_eq!(baseline.scene.rows[&second].1, 240.);
+    let untouched = resolved(&before, b, second);
+    let drag = capture(&before, a, Target::Message(second)).unwrap();
+    let preview = drag.prepare(-40.).unwrap().unwrap();
+    let expected = expected_message(&before, a, second, 200.);
+    assert_eq!(preview.project, expected);
+    assert_eq!(preview.geometry.scene.rows[&first].1, 148.);
+    assert_eq!(preview.geometry.scene.rows[&second].1, 200.);
+    let line = preview
+        .geometry
+        .scene
+        .lines
+        .iter()
+        .find(|line| line.id == second)
+        .unwrap();
+    assert_eq!(line.points.first().unwrap().y, 200.);
+    assert_eq!(line.points.last().unwrap().y, 200.);
+    assert_eq!(
+        preview.geometry.scene.activations,
+        baseline.scene.activations
+    );
+    assert_eq!(preview.geometry.scene.lifecycle, baseline.scene.lifecycle);
+    same_geometry(&resolved(&preview.project, b, second), &untouched);
+    assert_eq!(drag.original, before);
+    assert!(std::sync::Arc::ptr_eq(&original, &document.snapshot()));
+    assert!(!document.can_undo());
+
+    let returned_selection = document.execute(preview.command).unwrap();
+    assert_eq!(
+        returned_selection,
+        Some(a),
+        "controller must preserve the dragged semantic selection separately"
+    );
+    assert_eq!(document.project(), &expected);
+    assert_eq!(document.revision(), 1);
+    let accepted = document.bundle().clone();
+    same_geometry(&resolved(document.project(), a, second), &preview.geometry);
+    assert!(document.undo());
+    assert_eq!(document.project(), &before);
+    assert_eq!(document.bundle(), &original.bundle);
+    assert!(!document.can_undo());
+    assert!(document.redo());
+    assert_eq!(document.project(), &expected);
+    assert_eq!(document.bundle(), &accepted);
+    let reopened = Document::from_bundle(accepted, ProjectLimits::default()).unwrap();
+    assert_eq!(reopened.project(), &expected);
+    same_geometry(&resolved(reopened.project(), a, second), &preview.geometry);
+    assert!(!reopened.dirty() && !reopened.can_undo());
+}
+
+#[test]
+fn horizontal_lane_move_changes_actual_header_and_attached_endpoints_only_in_selected_view() {
+    let (document, a, b) = fixture(None);
+    let before = document.project();
+    let right = id(before, "right");
+    let first = id(before, "first");
+    let other = resolved(before, b, right);
+    let preview = capture(before, a, Target::Lane(right))
+        .unwrap()
+        .prepare(100.)
+        .unwrap()
+        .unwrap();
+    let mut expected = before.clone();
+    expected.diagrams.get_mut(&a).unwrap().layout = Some(DiagramLayout::Scenario(ScenarioLayout {
+        lanes: vec![ScenarioLanePosition {
+            lifeline: right,
+            x: 500.,
+        }],
+        messages: vec![],
+    }));
+    assert_eq!(preview.project, expected);
+    assert_eq!(preview.geometry.scene.lanes[&right], 500.);
+    let header = preview
+        .geometry
+        .scene
+        .boxes
+        .iter()
+        .find(|item| item.id == right)
+        .unwrap();
+    assert_eq!(header.rect.center_x(), 500.);
+    let line = preview
+        .geometry
+        .scene
+        .lines
+        .iter()
+        .find(|line| line.id == first)
+        .unwrap();
+    assert_eq!(line.points.first().unwrap().x, 160.);
+    assert_eq!(line.points.last().unwrap().x, 500.);
+    assert!(line.points.iter().all(|point| point.y == 148.));
+    same_geometry(&resolved(&preview.project, b, right), &other);
+    assert_eq!(document.project(), before);
+    assert!(!document.dirty() && !document.can_undo());
+}
+
+#[test]
+fn drawn_unassigned_lifeline_can_move_without_assigning_a_semantic_participant() {
+    let (document, a, _) = fixture(None);
+    let mut project = document.project().clone();
+    let owner = id(&project, "conversation");
+    let lane = project
+        .add_element(
+            Kind::Lifeline,
+            oa_core::Layer::Oa,
+            "Unassigned header",
+            Some(owner),
+        )
+        .unwrap();
+    let document = Document::from_project(project, ProjectLimits::default()).unwrap();
+    let baseline = resolved(document.project(), a, lane);
+    assert!(!baseline.scene.lanes.contains_key(&lane));
+    let before_header = baseline
+        .scene
+        .boxes
+        .iter()
+        .find(|item| item.id == lane)
+        .unwrap()
+        .rect;
+    let preview = capture(document.project(), a, Target::Lane(lane))
+        .unwrap()
+        .prepare(70.)
+        .unwrap()
+        .unwrap();
+    let after_header = preview
+        .geometry
+        .scene
+        .boxes
+        .iter()
+        .find(|item| item.id == lane)
+        .unwrap()
+        .rect;
+    assert_eq!(after_header.x, before_header.x + 70.);
+    assert_eq!(after_header.y, before_header.y);
+    assert_eq!(after_header.size(), before_header.size());
+    assert_eq!(preview.project.elements, document.project().elements);
+    assert_eq!(preview.project.relations, document.project().relations);
+    assert!(!document.can_undo());
+}
+
+#[test]
+fn self_call_spacing_uses_send_y_and_preserves_reply_and_actual_activation_finish() {
+    let (document, a, _) = fixture(None);
+    let before = document.project();
+    let call = id(before, "call");
+    let reply = id(before, "reply");
+    let baseline = resolved(before, a, call);
+    let preview = capture(before, a, Target::Message(call))
+        .unwrap()
+        .prepare(-22.)
+        .unwrap()
+        .unwrap();
+    assert_eq!(preview.project, expected_message(before, a, call, 310.));
+    let line = preview
+        .geometry
+        .scene
+        .lines
+        .iter()
+        .find(|line| line.id == call)
+        .unwrap();
+    assert_eq!(line.points.first().unwrap().y, 310.);
+    assert_eq!(line.points.last().unwrap().y, 334.);
+    assert_eq!(preview.geometry.scene.rows[&reply].1, 424.);
+    assert_eq!(preview.geometry.scene.activations.len(), 1);
+    let mut expected_activation = baseline.scene.activations.clone();
+    expected_activation[0].rect.y = 334.;
+    expected_activation[0].rect.height = 90.;
+    assert_eq!(preview.geometry.scene.activations, expected_activation);
+    assert_eq!(preview.geometry.scene.lifecycle, baseline.scene.lifecycle);
+}
+
+#[test]
+fn feasible_spacing_crossing_remains_authored_with_diagnostic_and_unchanged_steps() {
+    let (document, a, _) = fixture(None);
+    let before = document.project();
+    let first = id(before, "first");
+    let second = id(before, "second");
+    let owner = id(before, "conversation");
+    let preview = capture(before, a, Target::Message(second))
+        .unwrap()
+        .prepare(-120.)
+        .unwrap()
+        .unwrap();
+    assert_eq!(preview.project, expected_message(before, a, second, 120.));
+    assert_eq!(preview.geometry.scene.rows[&second].1, 120.);
+    assert_eq!(preview.geometry.scene.rows[&first].1, 148.);
+    assert_eq!(
+        preview.project.elements[&owner].steps(),
+        before.elements[&owner].steps()
+    );
+    let shown = crate::behavior::scenario_layout::presentation::present(
+        &preview.project,
+        Representation::Saved { diagram: a },
+        second,
+    );
+    assert!(shown.capabilities().coordinate_input);
+    assert!(
+        shown
+            .diagnostics()
+            .contains(&Diagnostic::SourceOrderCrossing {
+                scope: owner,
+                before: first,
+                after: second
+            })
+    );
+}
+
+#[test]
+fn unsupported_self_call_move_is_refused_and_automatic_fallback_is_not_editable_capture() {
+    let (document, a, _) = fixture(None);
+    let before = document.project();
+    let call = id(before, "call");
+    let drag = capture(before, a, Target::Message(call)).unwrap();
+    let Err(Refusal::Geometry(issues)) = drag.prepare(118.) else {
+        panic!("send450 / receive474 after reply424 must be refused")
+    };
+    assert!(issues.iter().any(|issue| matches!(issue, GeometryIssue::TypedActivationCrossingNotSupported { call: id, .. } if *id == call)));
+    assert_eq!(&drag.original, before);
+    let invalid_geometry = expected_message(before, a, call, 450.);
+    let shown = crate::behavior::scenario_layout::presentation::present(
+        &invalid_geometry,
+        Representation::Saved { diagram: a },
+        call,
+    );
+    assert!(shown.capabilities().geometry_navigation && !shown.capabilities().coordinate_input);
+    assert!(matches!(
+        capture(&invalid_geometry, a, Target::Message(call)),
+        Err(Refusal::Geometry(_))
+    ));
+    assert!(!document.dirty() && !document.can_undo());
+}
+
+#[test]
+fn invalid_view_foreign_identity_and_latent_message_are_not_spacing_targets() {
+    let (document, a, b) = fixture(None);
+    let p = document.project();
+    let unfinished = id(p, "unfinished");
+    let source = id(p, "source");
+    assert!(matches!(
+        capture(p, Id::nil(), Target::Lane(source)),
+        Err(Refusal::InvalidSavedView(_))
+    ));
+    for target in [
+        Target::Lane(source),
+        Target::Lane(b),
+        Target::Message(source),
+        Target::Message(unfinished),
+    ] {
+        assert!(
+            matches!(capture(p, a, target), Err(Refusal::TargetNotRendered(found)) if found == target)
+        );
+    }
+    // A stored latent coordinate is not permission to fabricate a painted arrow.
+    let mut latent = expected_message(p, a, unfinished, 2000.);
+    let foreign_owner = latent
+        .add_element(Kind::Scenario, oa_core::Layer::Oa, "Foreign", None)
+        .unwrap();
+    let foreign_lane = latent
+        .add_element(
+            Kind::Lifeline,
+            oa_core::Layer::Oa,
+            "Foreign lane",
+            Some(foreign_owner),
+        )
+        .unwrap();
+    *latent
+        .elements
+        .get_mut(&foreign_lane)
+        .unwrap()
+        .shared_mut()
+        .unwrap() = SharedBody::Lifeline {
+        represented: Some(source),
+    };
+    let latent_document = Document::from_project(latent, ProjectLimits::default()).unwrap();
+    assert!(matches!(
+        capture(latent_document.project(), a, Target::Message(unfinished)),
+        Err(Refusal::TargetNotRendered(_))
+    ));
+    assert!(matches!(
+        capture(latent_document.project(), a, Target::Lane(foreign_lane)),
+        Err(Refusal::TargetNotRendered(_))
+    ));
+}
+
+#[test]
+fn zero_motion_return_to_start_and_subprecision_preserve_sparse_intent_and_real_redo() {
+    let parsed = language::parse(FIXTURE).unwrap();
+    let left = id(&parsed, "left");
+    let second = id(&parsed, "second");
+    let layouts = [
+        None,
+        Some(ScenarioLayout::default()),
+        Some(ScenarioLayout {
+            lanes: vec![],
+            messages: vec![ScenarioMessagePosition {
+                address: OccurrenceEndpoint {
+                    references: vec![],
+                    occurrence: second,
+                },
+                send_y: 240.,
+            }],
+        }),
+        Some(ScenarioLayout {
+            lanes: vec![ScenarioLanePosition {
+                lifeline: left,
+                x: -0.,
+            }],
+            messages: vec![],
+        }),
+    ];
+    for (index, layout) in layouts.into_iter().enumerate() {
+        let (mut document, a, _) = fixture(layout);
+        let owner = id(document.project(), "conversation");
+        document
+            .execute(Command::Rename(owner, "A real redo entry".into()))
+            .unwrap();
+        let redo = document.snapshot();
+        assert!(document.undo());
+        let before = document.snapshot();
+        let revision = document.revision();
+        let target = if index == 3 {
+            Target::Lane(left)
+        } else {
+            Target::Message(second)
+        };
+        let drag = capture(document.project(), a, target).unwrap();
+        if index == 3 {
+            let Some(DiagramLayout::Scenario(layout)) = &drag.original.diagrams[&a].layout else {
+                panic!()
+            };
+            assert_eq!(layout.lanes[0].x.to_bits(), (-0_f32).to_bits());
+        }
+        assert!(drag.prepare(10.).unwrap().is_some());
+        for delta in [0., -0.] {
+            assert!(drag.prepare(delta).unwrap().is_none());
+        }
+        if index != 3 {
+            assert!(drag.prepare(f32::from_bits(1)).unwrap().is_none());
+        }
+        assert_eq!(
+            serde_json::to_vec(&drag.original).unwrap(),
+            serde_json::to_vec(document.project()).unwrap()
+        );
+        assert!(std::sync::Arc::ptr_eq(&before, &document.snapshot()));
+        assert_eq!(document.bundle(), &before.bundle);
+        assert_eq!(document.revision(), revision);
+        assert!(document.can_redo());
+        assert!(document.redo());
+        assert_eq!(document.project(), &redo.decoded.project);
+        assert_eq!(document.bundle(), &redo.bundle);
+    }
+}
+
+#[test]
+fn malformed_or_out_of_range_motion_cannot_mutate_original() {
+    let (document, a, _) = fixture(None);
+    let drag = capture(
+        document.project(),
+        a,
+        Target::Message(id(document.project(), "second")),
+    )
+    .unwrap();
+    for delta in [f32::NAN, f32::INFINITY, f32::NEG_INFINITY] {
+        assert!(matches!(drag.prepare(delta), Err(Refusal::InvalidDelta)));
+    }
+    assert!(matches!(drag.prepare(f32::MAX), Err(Refusal::Command(_))));
+    assert_eq!(&drag.original, document.project());
+    assert!(!document.dirty() && !document.can_undo());
+}
+
+const FIXTURE: &str = r#"arcadia 7;
+project spacing_probe "Saved spacing probe" id "71000000-0000-4000-8000-000000000001" {
+ oa_activity source "Source" id "71000000-0000-4000-8000-000000000002" {}
+ oa_activity target "Target" id "71000000-0000-4000-8000-000000000003" {}
+ interaction exchange "Repeated exchange" id "71000000-0000-4000-8000-000000000004" { source @source; target @target; }
+ oa_scenario conversation "Conversation" id "71000000-0000-4000-8000-000000000005" { viewpoint OperationalActivity; steps [@first, @second, @call, @reply, @unfinished]; }
+ oa_lifeline left "Left" id "71000000-0000-4000-8000-000000000006" { parent @conversation; represented @source; }
+ oa_lifeline right "Right" id "71000000-0000-4000-8000-000000000007" { parent @conversation; represented @target; }
+ oa_occurrence first "First" id "71000000-0000-4000-8000-000000000008" { parent @conversation; body { Exchange { exchange @exchange; sender @left; receiver @right; message_kind Asynchronous; }; }; }
+ oa_occurrence second "Second" id "71000000-0000-4000-8000-000000000009" { parent @conversation; body { Exchange { exchange @exchange; sender @left; receiver @right; message_kind Asynchronous; }; }; }
+ oa_occurrence call "Call" id "71000000-0000-4000-8000-00000000000a" { parent @conversation; body { Exchange { exchange none; sender @right; receiver @right; message_kind Call; }; }; }
+ oa_occurrence reply "Reply" id "71000000-0000-4000-8000-00000000000b" { parent @conversation; body { Exchange { exchange none; sender @right; receiver @right; message_kind Reply; reply_to @call; }; }; }
+ oa_occurrence unfinished "Unfinished" id "71000000-0000-4000-8000-00000000000c" { parent @conversation; body { Exchange { exchange @exchange; sender @left; receiver none; message_kind Asynchronous; }; }; }
+}
+"#;

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

@@ -1,5 +1,6 @@
 //! Navigation is derived from the same opaque-reference scene that is painted.
 use super::*;
+use crate::behavior::scenario_layout::{Representation, presentation};
 use crate::diagram_usage::{Surface, Target, Usage};
 
 /// The renderer collapses whitespace before shortening. Require at least one
@@ -22,7 +23,14 @@ fn label_field_visible(full: &str, prefix: &str, value: &str) -> bool {
     start < retained
 }
 
-fn usages(p: &Project, owner: Id, subject: Id, scene: &Scene) -> Vec<Usage> {
+fn usages(
+    p: &Project,
+    owner: Id,
+    subject: Id,
+    surface: Surface,
+    bounds: Rectangle,
+    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;
@@ -33,7 +41,7 @@ fn usages(p: &Project, owner: Id, subject: Id, scene: &Scene) -> Vec<Usage> {
         {
             result.push(Usage {
                 subject,
-                surface: Surface::Scenario(owner),
+                surface,
                 target: Target::ScenarioObject(id),
                 role: role.into(),
                 bounds,
@@ -137,15 +145,15 @@ fn usages(p: &Project, owner: Id, subject: Id, scene: &Scene) -> Vec<Usage> {
             }
         }
     }
-    if subject == owner {
+    if subject == owner || subject == surface.id() {
         result.insert(
             0,
             Usage {
                 subject,
-                surface: Surface::Scenario(owner),
+                surface,
                 target: Target::Whole,
                 role: "scenario".into(),
-                bounds: Rectangle::new(Point::ORIGIN, scene.size),
+                bounds,
             },
         );
     }
@@ -153,15 +161,29 @@ fn usages(p: &Project, owner: Id, subject: Id, scene: &Scene) -> Vec<Usage> {
 }
 
 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)
-        {
+    /// Membership comes from the complete presentation chosen for this exact view,
+    /// including automatic fallback geometry while retaining its Saved identity.
+    pub(crate) fn representation_usages(
+        &self,
+        p: &Project,
+        representation: Representation,
+        subject: Id,
+    ) -> Vec<Usage> {
+        let shown = presentation::present(p, representation, subject);
+        let (Some(owner), Some(bounds), Some(scene)) =
+            (shown.owner(), shown.bounds(), shown.scene())
+        else {
             return vec![];
-        }
-        usages(p, owner, subject, &Scene::sequence(p, owner, subject))
+        };
+        let surface = match representation {
+            Representation::Derived { owner } => Surface::Scenario(owner),
+            Representation::Saved { diagram } => Surface::Saved(diagram),
+        };
+        usages(p, owner, subject, surface, bounds, scene)
+    }
+
+    pub(crate) fn diagram_usages(&self, p: &Project, owner: Id, subject: Id) -> Vec<Usage> {
+        self.representation_usages(p, Representation::Derived { owner }, subject)
     }
 
     pub(crate) fn reveal_usage(
@@ -171,12 +193,24 @@ impl State {
         owner: Id,
         target: &Target,
     ) -> bool {
-        if self.draft.is_some()
-            || !p
-                .elements
-                .get(&owner)
-                .is_some_and(|e| e.kind() == Kind::Scenario)
-        {
+        self.reveal_representation_usage(
+            p,
+            document,
+            owner,
+            Representation::Derived { owner },
+            target,
+        )
+    }
+
+    pub(crate) fn reveal_representation_usage(
+        &mut self,
+        p: &Project,
+        document: Id,
+        owner: Id,
+        representation: Representation,
+        target: &Target,
+    ) -> bool {
+        if self.draft.is_some() || presentation::checked_owner(p, representation) != Some(owner) {
             return false;
         }
         let id = match target {
@@ -185,7 +219,7 @@ impl State {
             _ => return false,
         };
         let Some(usage) = self
-            .diagram_usages(p, owner, id)
+            .representation_usages(p, representation, id)
             .into_iter()
             .find(|u| &u.target == target)
         else {
@@ -193,11 +227,29 @@ impl State {
         };
         // 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);
+        if !viewport.width.is_finite()
+            || !viewport.height.is_finite()
+            || viewport.width <= 0.
+            || viewport.height <= 0.
+        {
+            return false;
+        }
+        let (zoom, pan) = if matches!(target, Target::Whole) {
+            let Some(camera) = super::camera::fit(usage.bounds, viewport) else {
+                return false;
+            };
+            (None, camera.pan)
+        } else {
+            let (zoom, pan) = crate::diagram_usage::camera_for(target, usage.bounds, viewport);
+            if !zoom.is_finite() || !pan.x.is_finite() || !pan.y.is_finite() {
+                return false;
+            }
+            (Some(zoom), pan)
+        };
+        self.enter_representation(document, owner, representation);
         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.zoom(zoom);
         self.presentation.pan = pan;
         true
     }

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

@@ -13,6 +13,8 @@ pub enum Shelf {
 #[derive(Clone, Default)]
 pub(super) struct Presentation {
     pub(super) identity: Option<(Id, Id)>,
+    pub(super) representation: Option<Representation>,
+    pub(super) visit: Id,
     pub(super) viewport: Option<Size>,
     pub(super) focused: bool,
     pub(super) shelf: Option<Shelf>,
@@ -20,7 +22,6 @@ pub(super) struct Presentation {
     pub(super) zoom: Option<f32>,
     pub(super) fit: bool,
 }
-const MIN_SCALE: f32 = 0.05;
 impl Presentation {
     pub(super) fn viewport(&mut self, size: Size) -> bool {
         if !size.width.is_finite()
@@ -35,29 +36,26 @@ impl Presentation {
         true
     }
     pub(super) fn zoom(&mut self, scale: Option<f32>) -> bool {
-        if scale.is_some_and(|value| !value.is_finite() || value <= 0.) {
-            return false;
-        }
-        let next = scale.map(|value| value.clamp(MIN_SCALE, 3.));
-        let changed = self.zoom != next || self.fit != scale.is_none();
-        self.zoom = next;
-        self.fit = scale.is_none();
-        changed
+        camera::set_zoom(&mut self.pan, &mut self.zoom, &mut self.fit, scale)
     }
-    fn fit_scale(&self, scene: Size) -> Option<f32> {
-        let viewport = self.viewport?;
-        // Fit uses the actual mounted viewport with a small visual gutter.
-        Some(
-            ((viewport.width - 16.).max(1.) / scene.width.max(1.))
-                .min((viewport.height - 16.).max(1.) / scene.height.max(1.)),
-        )
+    pub(super) fn camera(&self, bounds: Rectangle) -> camera::Camera {
+        camera::effective_camera(self.pan, self.zoom, self.fit, self.viewport, bounds)
     }
-    pub(super) fn scale(&self, scene: Size) -> f32 {
-        if self.fit {
-            self.fit_scale(scene).unwrap_or(1.).clamp(MIN_SCALE, 1.)
-        } else {
-            self.zoom.unwrap_or(1.)
-        }
+    // Legacy tests call size-only scale; actual display always passes full bounds.
+    #[cfg(test)]
+    pub(super) fn scale(&self, size: Size) -> f32 {
+        self.camera(Rectangle::new(Point::ORIGIN, size)).scale
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+struct ArrangementChoice {
+    representation: Representation,
+    label: String,
+}
+impl std::fmt::Display for ArrangementChoice {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.label)
     }
 }
 
@@ -69,43 +67,136 @@ pub fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Element<'a
         .draft
         .as_ref()
         .is_some_and(|draft| draft.owner == owner);
-    let context = app.scenario_context().expect("visible scenario context");
+    let Some(context) = app.scenario_context() else {
+        return column![
+            out,
+            text("Scenario view is unavailable."),
+            button("Open selected source").on_press(Message::SourceForSelection)
+        ]
+        .spacing(8)
+        .into();
+    };
     let tool = state.canvas_tool(owner);
     let clean = !app.behavior.has_pending() && !app.draft_dirty() && !app.source_dirty();
-    let mut scene = Scene::sequence(p, owner, app.selected);
-    let scale = presentation.scale(scene.size);
-    scene.scale = scale;
-    scene.camera_pan = presentation.pan;
-    scene.interaction = Some((context, tool, clean));
-    scene.pending_placement = state.pending_placement(owner);
+    // Resolve once per accepted view. An active spacing session owns its exact
+    // prepared geometry; borrowing it also retains the canvas input state.
+    let preview = state.spacing_paint(context, app.camera_epoch);
+    let shown = preview
+        .is_none()
+        .then(|| presentation::present(p, context.representation, app.selected));
+    let capabilities = shown.as_ref().map_or(
+        presentation::PresentationCapabilities {
+            geometry_navigation: true,
+            coordinate_input: true,
+        },
+        ScenarioPresentation::capabilities,
+    );
+    let coordinate_input = clean && capabilities.coordinate_input;
+    let notice = if let Some(paint) = &preview {
+        display_notice_parts(
+            p,
+            context.representation,
+            &presentation::PresentationStatus::Ready,
+            paint.original_diagnostics,
+            paint.original_latent,
+        )
+    } else {
+        display_notice(p, shown.as_ref().expect("normal presentation"))
+    };
+    let camera_state = preview
+        .as_ref()
+        .map(|paint| camera::Camera {
+            scale: paint.scene.scale,
+            pan: paint.scene.camera_pan,
+        })
+        .or_else(|| {
+            shown
+                .as_ref()
+                .and_then(ScenarioPresentation::bounds)
+                .map(|bounds| presentation.camera(bounds))
+        });
+    let scale = camera_state.map_or(1., |camera| camera.scale);
     let scope = super::super::canvas_workspace::Scope {
         document: context.document,
         owner,
         revision: context.revision,
         epoch: app.camera_epoch,
+        scenario_view: Some((context.representation, context.visit)),
     };
-    let keyboard = clean && super::super::canvas_workspace::keyboard_enabled(app);
+    let keyboard = clean
+        && capabilities.geometry_navigation
+        && super::super::canvas_workspace::keyboard_enabled(app);
     let camera = move |e| Message::ScenarioCanvas(CanvasEvent::Camera(context, scope.epoch, e));
-    let canvas = container(
-        sensor(
-            super::super::canvas_workspace::Viewport::new(
-                canvas::Canvas::new(scene).width(Fill).height(Fill),
-                scope,
-                scale,
-                keyboard,
-                camera,
-            )
-            .pan_background(tool == CanvasTool::Select),
+    let raw_canvas: Option<Element<'a, Message>> = if let Some(paint) = &preview {
+        Some(
+            canvas::Canvas::new(paint.scene)
+                .width(Fill)
+                .height(Fill)
+                .into(),
         )
-        .key((context.document, owner))
-        .on_show(move |size| Message::ScenarioCanvas(CanvasEvent::Viewport(context, size)))
-        .on_resize(move |size| Message::ScenarioCanvas(CanvasEvent::Viewport(context, size))),
-    )
-    .id("scenario-viewport")
-    .width(Fill)
-    .height(Fill)
-    .style(style::card)
-    .into();
+    } else if let Some(mut scene) = shown.and_then(ScenarioPresentation::into_scene) {
+        let camera_state = camera_state.expect("displayed Scene has complete bounds");
+        scene.scale = camera_state.scale;
+        scene.camera_pan = camera_state.pan;
+        scene.interaction = Some((context, tool, clean));
+        scene.spacing_stamp = (coordinate_input
+            && !app.source_rename.open()
+            && keyboard
+            && matches!(context.representation, Representation::Saved { .. }))
+        .then_some(spacing::Stamp {
+            context,
+            camera_epoch: app.camera_epoch,
+        });
+        scene.coordinate_input = capabilities.coordinate_input;
+        scene.pending_placement = coordinate_input
+            .then(|| state.pending_placement(owner))
+            .flatten();
+        Some(canvas::Canvas::new(scene).width(Fill).height(Fill).into())
+    } else {
+        None
+    };
+    let canvas: Element<'a, Message> = if let Some(raw_canvas) = raw_canvas {
+        // Keep this Stack in both branches: replacing the Canvas with a wrapper
+        // on Begin would discard its pointer capture before Move/Finish.
+        let mut layers = iced::widget::stack![raw_canvas];
+        if let Some(paint) = &preview {
+            let feedback = spacing_feedback(p, paint.refusal, paint.diagnostics);
+            layers = layers.push(
+                container(
+                    container(text(feedback).size(12))
+                        .padding(6)
+                        .width(Fill)
+                        .style(style::card),
+                )
+                .width(Fill)
+                .align_bottom(Fill)
+                .padding(8),
+            );
+        }
+        container(
+            sensor(
+                super::super::canvas_workspace::Viewport::new(
+                    layers, scope, scale, keyboard, camera,
+                )
+                .pan_background(tool == CanvasTool::Select || !capabilities.coordinate_input),
+            )
+            .key((
+                context.document,
+                format!("{:?}", context.representation),
+                context.visit,
+            ))
+            .on_show(move |size| Message::ScenarioCanvas(CanvasEvent::Viewport(context, size)))
+            .on_resize(move |size| Message::ScenarioCanvas(CanvasEvent::Viewport(context, size))),
+        )
+        .id("scenario-viewport")
+        .width(Fill)
+        .height(Fill)
+        .style(style::card)
+        .into()
+    } else {
+        container(text("No supported canvas geometry is available. Inspect the model or open its source to repair this view."))
+            .id("scenario-viewport-unavailable").padding(16).width(Fill).height(Fill).style(style::card).into()
+    };
     let mut navigation = row![
         out.width(Fill),
         super::super::canvas_workspace::Control::new(
@@ -141,9 +232,47 @@ pub fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Element<'a
                 clean.then_some(Message::ScenarioCanvas(CanvasEvent::Back(context))),
             ));
     }
-    let header = column![
-        navigation,
-        super::super::canvas_workspace::controls(
+    let mut header = column![navigation, notice].spacing(4);
+    let saved_views = p
+        .diagrams
+        .values()
+        .filter(|diagram| {
+            presentation::checked_owner(
+                p,
+                Representation::Saved {
+                    diagram: diagram.id,
+                },
+            ) == Some(owner)
+        })
+        .map(|diagram| ArrangementChoice {
+            representation: Representation::Saved {
+                diagram: diagram.id,
+            },
+            label: short(&diagram.name, 64),
+        })
+        .collect::<Vec<_>>();
+    if !saved_views.is_empty() {
+        let mut choices = vec![ArrangementChoice {
+            representation: Representation::Derived { owner },
+            label: "Automatic arrangement".into(),
+        }];
+        choices.extend(saved_views);
+        let selected = choices
+            .iter()
+            .find(|choice| choice.representation == context.representation)
+            .cloned();
+        header = header.push(
+            pick_list(choices, selected, move |choice: ArrangementChoice| {
+                Message::ScenarioCanvas(CanvasEvent::Representation(context, choice.representation))
+            })
+            .placeholder("Choose arrangement")
+            .text_size(12)
+            .padding(5)
+            .width(Fill),
+        );
+    }
+    if capabilities.geometry_navigation {
+        header = header.push(super::super::canvas_workspace::controls(
             scope,
             keyboard,
             scale,
@@ -151,15 +280,22 @@ pub fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Element<'a
             clean.then_some(Message::ScenarioCanvas(CanvasEvent::Camera(
                 context,
                 scope.epoch,
-                super::super::canvas_workspace::Event::Focus
+                super::super::canvas_workspace::Event::Focus,
             ))),
             move |zoom| Message::ScenarioCanvas(CanvasEvent::Zoom(context, zoom)),
-            camera
-        )
-    ]
-    .spacing(4);
+            camera,
+        ));
+    }
     let entries = [
-        ("S", "Select / reorder occurrences", CanvasTool::Select),
+        (
+            "S",
+            if matches!(context.representation, Representation::Saved { .. }) {
+                "Select / move messages and lifelines"
+            } else {
+                "Select / reorder occurrences"
+            },
+            CanvasTool::Select,
+        ),
         (
             "L",
             "Lifeline: click to choose represented work or participant",
@@ -226,16 +362,21 @@ pub fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Element<'a
                 glyph,
                 label,
                 choice == tool,
-                clean.then_some(Message::ScenarioCanvas(CanvasEvent::Choose(
-                    context, choice,
-                ))),
+                (clean && (choice == CanvasTool::Select || capabilities.coordinate_input))
+                    .then_some(Message::ScenarioCanvas(CanvasEvent::Choose(
+                        context, choice,
+                    ))),
             )
         }),
     );
     let mut details = column![
         text(format!("Selected: {}", p.named(app.selected))).size(12),
-        button(text("Properties").size(12))
-            .on_press_maybe(clean.then_some(Message::EditProperties(app.selected)))
+        container(button(text("Properties").size(12)).on_press_maybe(
+            (clean && properties_target(p, context, app.selected)).then_some(
+                Message::ScenarioCanvas(CanvasEvent::Properties(context, app.selected)),
+            ),
+        ))
+        .id("scenario-properties")
     ]
     .spacing(6);
     if referenced_scenario(p, owner, app.selected).is_some() {
@@ -246,6 +387,10 @@ pub fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Element<'a
             ))),
         ));
     }
+    details = details.push(text("Scenario order").size(13));
+    if matches!(context.representation, Representation::Saved { .. }) {
+        details = details.push(text("↑ and ↓ change the shared Scenario order. Saved message positions are retained; automatically placed items may move.").size(11));
+    }
     let details = details_pane(
         context,
         state.scroll_restore(context, ScrollArea::Page),
@@ -575,6 +720,153 @@ pub fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Element<'a
     super::super::canvas_workspace::host(header.into(), palette, canvas, editor)
 }
 
+fn display_notice<'a>(p: &Project, shown: &ScenarioPresentation) -> Element<'a, Message> {
+    display_notice_parts(
+        p,
+        shown.requested(),
+        shown.status(),
+        shown.diagnostics(),
+        shown.latent_messages(),
+    )
+}
+
+fn display_notice_parts<'a>(
+    p: &Project,
+    requested: Representation,
+    status: &presentation::PresentationStatus,
+    diagnostics: &[super::super::scenario_layout::Diagnostic],
+    latent_messages: &[Id],
+) -> Element<'a, Message> {
+    use super::super::scenario_layout::{Diagnostic, presentation::PresentationStatus};
+    let title = match requested {
+        Representation::Saved { diagram } => p.diagrams.get(&diagram).map_or_else(
+            || "Unavailable saved Scenario view".into(),
+            |view| format!("Saved view · {}", view.name),
+        ),
+        Representation::Derived { owner } => format!("Automatic view · {}", p.named(owner)),
+    };
+    let mut notice = column![text(title).size(14)].spacing(4);
+    match status {
+        PresentationStatus::Ready => {
+            for diagnostic in diagnostics.iter().take(3) {
+                let explanation = match diagnostic {
+                    Diagnostic::SourceOrderCrossing { before, after, .. } => format!(
+                        "Saved spacing places '{}' below '{}'. The Scenario order is unchanged.",
+                        p.named(*before),
+                        p.named(*after)
+                    ),
+                    Diagnostic::FrameExtendsPastFollowingAnchor { frame, following } => format!(
+                        "Saved spacing makes '{}' overlap '{}'. Both keep their saved positions.",
+                        p.named(*frame),
+                        p.named(*following)
+                    ),
+                };
+                notice = notice.push(text(explanation).size(12));
+            }
+            if diagnostics.len() > 3 {
+                notice = notice.push(
+                    text(format!(
+                        "{} additional spacing notices are retained.",
+                        diagnostics.len() - 3
+                    ))
+                    .size(12),
+                );
+            }
+        }
+        PresentationStatus::Fallback { requested_issues } => {
+            notice = notice.push(text("Showing the complete automatic arrangement because the saved positions cannot currently be displayed. Saved positions are preserved.").size(12));
+            if let Some(issue) = requested_issues.first() {
+                notice = notice.push(text(geometry_problem(p, issue)).size(12));
+            }
+            notice = notice.push(text("Selection, navigation and Fit remain available. Canvas insertion and reordering are unavailable until the saved positions are repaired.").size(12));
+        }
+        PresentationStatus::Unavailable { .. } => {
+            notice = notice.push(text("This view is unavailable. Its identity or automatic geometry cannot be resolved; the model and source remain available for inspection and repair.").size(12));
+        }
+    }
+    if !latent_messages.is_empty() {
+        notice = notice.push(text(format!("{} unfinished message position(s) are retained until their endpoints are complete.", latent_messages.len())).size(12));
+    }
+    notice = notice.push(button("Open selected source").on_press(Message::SourceForSelection));
+    container(notice)
+        .id("scenario-display-notice")
+        .padding(6)
+        .width(Fill)
+        .into()
+}
+
+fn spacing_feedback(
+    p: &Project,
+    refusal: Option<&spacing::Refusal>,
+    diagnostics: &[super::super::scenario_layout::Diagnostic],
+) -> String {
+    if let Some(refusal) = refusal {
+        let reason = match refusal {
+            spacing::Refusal::Geometry(issues) => issues
+                .first()
+                .map(|issue| geometry_problem(p, issue))
+                .unwrap_or_else(|| "This position cannot be displayed.".into()),
+            spacing::Refusal::Command(error) => error.clone(),
+            _ => "This position is unavailable in the current view.".into(),
+        };
+        return format!(
+            "Position unavailable · {reason} Move back to a supported position, or release to cancel."
+        );
+    }
+    let explanation = match diagnostics.first() {
+        Some(super::super::scenario_layout::Diagnostic::SourceOrderCrossing {
+            before,
+            after,
+            ..
+        }) => format!(
+            " '{}' is below '{}'; Scenario order stays unchanged.",
+            p.named(*before),
+            p.named(*after)
+        ),
+        Some(super::super::scenario_layout::Diagnostic::FrameExtendsPastFollowingAnchor {
+            frame,
+            following,
+        }) => format!(" '{}' overlaps '{}'.", p.named(*frame), p.named(*following)),
+        None => " Scenario order stays unchanged.".into(),
+    };
+    format!("Spacing preview · Release to finish; Escape cancels.{explanation}")
+}
+
+fn geometry_problem(p: &Project, issue: &super::super::scenario_layout::GeometryIssue) -> String {
+    use super::super::scenario_layout::GeometryIssue;
+    match issue {
+        GeometryIssue::TypedActivationCrossingNotSupported { call, event } => format!(
+            "The position of '{}' conflicts with the execution of '{}'.",
+            p.named(*event),
+            p.named(*call)
+        ),
+        GeometryIssue::CoincidentDistinctEndpoints(message) => format!(
+            "The distinct endpoints of '{}' have the same horizontal position.",
+            p.named(*message)
+        ),
+        GeometryIssue::TypedActivationOutsideLifetime { call, .. }
+        | GeometryIssue::TypedActivationOutsideScope { call, .. } => format!(
+            "The position of '{}' falls outside its supported execution interval.",
+            p.named(*call)
+        ),
+        GeometryIssue::FixedFrameHeaderWouldMove { frame } => format!(
+            "The saved spacing would move the fixed header of '{}'.",
+            p.named(*frame)
+        ),
+        GeometryIssue::OperandScopeOutsideEnclosingInterval { operand, .. } => format!(
+            "The spacing of '{}' extends outside its enclosing frame.",
+            p.named(*operand)
+        ),
+        GeometryIssue::LifecycleGeometryNotSupported { .. }
+        | GeometryIssue::LifecycleAnchorOutsideRenderScope { .. }
+        | GeometryIssue::LifetimeInversionNotSupported { .. } => {
+            "The saved spacing cannot preserve the participant lifetime geometry.".into()
+        }
+        _ => "These saved positions are outside the geometry currently supported by the canvas."
+            .into(),
+    }
+}
+
 fn sequence_action<'a>(
     title: &str,
     message: Message,
@@ -631,6 +923,12 @@ fn editor_panel<'a, R: iced::advanced::text::Renderer + 'a>(
 #[cfg(all(test, debug_assertions))]
 mod tests;
 
+#[cfg(all(test, debug_assertions))]
+mod spacing_tests;
+
+#[cfg(all(test, debug_assertions))]
+mod details_tests;
+
 fn sequence_rows<'a>(
     p: &'a Project,
     context: Context,

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

@@ -0,0 +1,443 @@
+//! Mounted Scenario Details → inspector regression and retained-intent guards.
+use super::*;
+use crate::behavior::canvas_workspace::tests::Mounted;
+use crate::behavior::scenario_layout::resolve;
+use iced::advanced::widget;
+use iced::{Vector, keyboard};
+use std::sync::Arc;
+
+const FIXTURE: &str = include_str!("../../../app/diagram_usages/tests/saved_scenario.arcadia");
+
+fn id(app: &App, alias: &str) -> Id {
+    app.project()
+        .identities()
+        .into_iter()
+        .find(|(_, name)| *name == alias)
+        .unwrap()
+        .0
+}
+fn send(app: &mut App, event: impl FnOnce(Context) -> CanvasEvent) {
+    let context = app.scenario_context().unwrap();
+    let _ = app.update(Message::ScenarioCanvas(event(context)));
+}
+fn setup() -> (App, Id, Id) {
+    let mut app = App::with_project(oa_core::language::parse(FIXTURE).unwrap());
+    let owner = id(&app, "incident_response");
+    let diagram = id(&app, "incident_readable");
+    let message = id(&app, "initial_report");
+    let _ = app.update(Message::Select(owner));
+    let _ = app.update(Message::Diagram(crate::app::Choice {
+        id: diagram,
+        label: "A".into(),
+    }));
+    send(&mut app, |c| CanvasEvent::Select(c, message));
+    app.window_size = Size::new(1440., 1000.);
+    (app, diagram, message)
+}
+fn open_focused_details(app: &mut App) {
+    if !app.behavior.scenario.focused() {
+        send(app, CanvasEvent::Focus);
+    }
+    if app.behavior.scenario.presentation.shelf.is_none() {
+        send(app, |c| CanvasEvent::Shelf(c, Shelf::Selection));
+    }
+}
+fn stored_camera(app: &App) -> (Vector, Option<f32>, bool) {
+    let p = &app.behavior.scenario.presentation;
+    (p.pan, p.zoom, p.fit)
+}
+
+#[tokio::test]
+async fn focused_saved_details_opens_real_editable_inspector_and_returns_to_same_view() {
+    let (mut app, diagram, message) = setup();
+    let _ = app.update(Message::InspectorTab(
+        crate::navigation::InspectorTab::Connections,
+    ));
+    let mut mounted = Mounted::new(&mut app).await;
+    open_focused_details(&mut app);
+    mounted.settle(&mut app).await;
+    let before = mounted.geometry(&app);
+    assert!(!before.scrolls.contains_key(&widget::Id::new("inspector")));
+    let (details, offset) = before.scrolls[&widget::Id::new("scenario-details")];
+    let button = before.bounds("scenario-properties").center() - offset;
+    assert!(
+        details.contains(button),
+        "Properties must be actually visible"
+    );
+    let context = app.scenario_context().unwrap();
+    let camera = stored_camera(&app);
+    let original = app.document.snapshot();
+    let bundle = app.document.bundle().clone();
+    let messages = mounted.click(&mut app, button).await;
+    assert!(messages.iter().any(|event| matches!(event,
+        Message::ScenarioCanvas(CanvasEvent::Properties(c, selected))
+        if *c == context && *selected == message)));
+    mounted.settle(&mut app).await;
+    assert!(!app.behavior.scenario.focused());
+    assert!(app.behavior.scenario.presentation.shelf.is_none());
+    assert_eq!(
+        app.inspector_tab,
+        crate::navigation::InspectorTab::Properties
+    );
+    assert_eq!(app.selected, message);
+    assert_eq!(app.active_diagram, Some(diagram));
+    assert_eq!(app.page, crate::app::Page::Behavior);
+    let current = app.scenario_context().unwrap();
+    assert_eq!(current.representation, context.representation);
+    assert_eq!(current.visit, context.visit);
+    assert_eq!(
+        stored_camera(&app),
+        camera,
+        "restoring panels retains camera intent"
+    );
+    assert!(Arc::ptr_eq(&original, &app.document.snapshot()));
+    assert_eq!(app.document.bundle(), &bundle);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+
+    let shown = mounted.geometry(&app);
+    assert!(
+        !shown
+            .scrolls
+            .contains_key(&widget::Id::new("scenario-details"))
+    );
+    let (inspector, offset) = shown.scrolls[&widget::Id::new("inspector")];
+    assert!(inspector.width > 250. && inspector.height > 500.);
+    // Production Properties places Name before the other scalar text inputs.
+    // Account for the retained inspector scroll, rather than clicking content coordinates.
+    let input = shown
+        .text_inputs
+        .iter()
+        .map(|bounds| bounds.center() - offset)
+        .filter(|point| inspector.contains(*point))
+        .min_by(|a, b| a.y.total_cmp(&b.y))
+        .expect("visible editable property");
+    mounted.click(&mut app, input).await;
+    let typed = mounted
+        .batch(
+            &mut app,
+            &[iced::Event::Keyboard(keyboard::Event::KeyPressed {
+                key: keyboard::Key::Character("x".into()),
+                modified_key: keyboard::Key::Character("x".into()),
+                physical_key: keyboard::key::Physical::Unidentified(
+                    keyboard::key::NativeCode::Unidentified,
+                ),
+                location: keyboard::Location::Standard,
+                modifiers: keyboard::Modifiers::empty(),
+                text: Some("x".into()),
+                repeat: false,
+            })],
+            mouse::Cursor::Available(input),
+        )
+        .await;
+    assert!(
+        typed
+            .iter()
+            .any(|message| matches!(message, Message::Field(path, _) if path == "/name")),
+        "real Name editor must publish its edit: {typed:?}"
+    );
+    assert!(app.draft_dirty());
+    assert!(
+        Arc::ptr_eq(&original, &app.document.snapshot()),
+        "typing is only a draft"
+    );
+    let _ = app.update(Message::RevertProperties);
+    assert!(!app.draft_dirty());
+    send(&mut app, CanvasEvent::Focus);
+    mounted.settle(&mut app).await;
+    let returned = mounted.geometry(&app);
+    assert!(!returned.scrolls.contains_key(&widget::Id::new("inspector")));
+    let viewport = returned.bounds("scenario-viewport");
+    assert_eq!(app.selected, message);
+    assert_eq!(app.scenario_context().unwrap().visit, context.visit);
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        context.representation
+    );
+    assert_eq!(stored_camera(&app), camera);
+    let geometry = resolve(app.project(), context.representation, message).unwrap();
+    let line = geometry
+        .scene
+        .lines
+        .iter()
+        .find(|line| line.id == message)
+        .unwrap();
+    let effective = app.behavior.scenario.presentation.camera(geometry.bounds);
+    let point = viewport.position()
+        + effective.pan
+        + Vector::new(line.points[0].x, line.points[0].y) * effective.scale;
+    assert!(
+        viewport.contains(point),
+        "the same selected message remains in fitted view"
+    );
+    assert!(Arc::ptr_eq(&original, &app.document.snapshot()));
+    assert_eq!(app.document.bundle(), &bundle);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+}
+
+#[test]
+fn details_properties_refuses_pending_property_source_and_behavior_drafts_without_apply() {
+    for kind in 0..3 {
+        let (mut app, _, message) = setup();
+        open_focused_details(&mut app);
+        match kind {
+            0 => {
+                let _ = app.update(Message::Field(
+                    "/name".into(),
+                    "Retained property draft".into(),
+                ));
+                assert!(app.draft_dirty());
+            }
+            1 => {
+                let _ = app.update(Message::SourceEdit(
+                    iced::widget::text_editor::Action::Edit(
+                        iced::widget::text_editor::Edit::Insert('x'),
+                    ),
+                ));
+                assert!(app.source_dirty());
+            }
+            _ => {
+                let owner = app.scenario_context().unwrap().scenario;
+                let _ = app.update(Message::Behavior(super::super::super::Event::Scenario(
+                    Event::Start(owner, Tool::Lifeline),
+                )));
+                assert!(app.behavior.has_pending());
+            }
+        }
+        let snapshot = app.document.snapshot();
+        let bundle = app.document.bundle().clone();
+        let property = app.draft.as_ref().unwrap().materialize();
+        let source = app.source_editor.text();
+        let behavior = app.behavior.recovery_snapshot();
+        let camera = app.behavior.scenario.camera_boundary();
+        let context = app.scenario_context().unwrap();
+        let epochs = (app.canvas_epoch, app.camera_epoch);
+        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Properties(
+            context, message,
+        )));
+        assert!(app.behavior.scenario.camera_boundary() == camera);
+        assert_eq!(app.scenario_context(), Some(context));
+        assert_eq!((app.canvas_epoch, app.camera_epoch), epochs);
+        assert_eq!(app.draft.as_ref().unwrap().materialize(), property);
+        assert_eq!(app.source_editor.text(), source);
+        assert_eq!(app.behavior.recovery_snapshot(), behavior);
+        assert_eq!(app.selected, message);
+        assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+        assert_eq!(app.document.bundle(), &bundle);
+        assert!(!app.document.can_undo() && !app.document.can_redo());
+    }
+}
+
+#[tokio::test]
+async fn focused_details_opens_current_saved_view_properties_after_following_diagram_picker() {
+    let (mut app, a, _) = setup();
+    let b = id(&app, "incident_wide");
+    // Selecting the current view record makes the real picker follow that
+    // record selection to B. Do not seed selected=B or its property draft.
+    let _ = app.update(Message::Select(a));
+    assert_eq!(app.selected, a);
+    let _ = app.update(Message::Diagram(crate::app::Choice {
+        id: b,
+        label: "B".into(),
+    }));
+    assert_eq!(app.selected, b);
+    assert_eq!(app.draft.as_ref().unwrap().original, b);
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        Representation::Saved { diagram: b }
+    );
+    let _ = app.update(Message::InspectorTab(
+        crate::navigation::InspectorTab::Connections,
+    ));
+    let mut mounted = Mounted::new(&mut app).await;
+    open_focused_details(&mut app);
+    mounted.settle(&mut app).await;
+    let context = app.scenario_context().unwrap();
+    let camera = stored_camera(&app);
+    let snapshot = app.document.snapshot();
+    let bundle = app.document.bundle().clone();
+    let before = mounted.geometry(&app);
+    assert!(!before.scrolls.contains_key(&widget::Id::new("inspector")));
+    let (details, offset) = before.scrolls[&widget::Id::new("scenario-details")];
+    let point = before.bounds("scenario-properties").center() - offset;
+    assert!(details.contains(point));
+    let events = mounted.click(&mut app, point).await;
+    assert!(events.iter().any(|event| matches!(event,
+        Message::ScenarioCanvas(CanvasEvent::Properties(c, selected))
+        if *c == context && *selected == b)));
+    mounted.settle(&mut app).await;
+    let shown = mounted.geometry(&app);
+    assert!(
+        !shown
+            .scrolls
+            .contains_key(&widget::Id::new("scenario-details"))
+    );
+    let (inspector, offset) = shown.scrolls[&widget::Id::new("inspector")];
+    assert!(
+        shown
+            .text_inputs
+            .iter()
+            .any(|bounds| inspector.contains(bounds.center() - offset)),
+        "current Saved diagram has a visible editable inspector"
+    );
+    assert!(!app.behavior.scenario.focused());
+    assert_eq!(
+        app.inspector_tab,
+        crate::navigation::InspectorTab::Properties
+    );
+    assert_eq!(app.selected, b);
+    assert_eq!(app.draft.as_ref().unwrap().original, b);
+    assert_eq!(app.active_diagram, Some(b));
+    assert_eq!(app.page, crate::app::Page::Behavior);
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        context.representation
+    );
+    assert_eq!(app.scenario_context().unwrap().visit, context.visit);
+    assert_eq!(stored_camera(&app), camera);
+    assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+    assert_eq!(app.document.bundle(), &bundle);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+}
+
+#[test]
+fn details_properties_refuses_another_saved_view_even_with_the_same_scenario_owner() {
+    let (mut app, a, _) = setup();
+    let b = id(&app, "incident_wide");
+    let _ = app.update(Message::Diagram(crate::app::Choice {
+        id: b,
+        label: "B".into(),
+    }));
+    let _ = app.update(Message::Select(a));
+    assert_eq!(app.selected, a);
+    open_focused_details(&mut app);
+    let context = app.scenario_context().unwrap();
+    assert_eq!(context.representation, Representation::Saved { diagram: b });
+    assert_eq!(
+        presentation::checked_owner(app.project(), Representation::Saved { diagram: a }),
+        Some(context.scenario)
+    );
+    assert!(!properties_target(app.project(), context, a));
+    let camera = app.behavior.scenario.camera_boundary();
+    let epochs = (app.canvas_epoch, app.camera_epoch);
+    let snapshot = app.document.snapshot();
+    let bundle = app.document.bundle().clone();
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Properties(context, a)));
+    assert!(app.behavior.scenario.camera_boundary() == camera);
+    assert_eq!((app.canvas_epoch, app.camera_epoch), epochs);
+    assert_eq!(app.scenario_context(), Some(context));
+    assert_eq!(app.selected, a);
+    assert_eq!(app.draft.as_ref().unwrap().original, a);
+    assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+    assert_eq!(app.document.bundle(), &bundle);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+}
+
+#[test]
+fn details_properties_rejects_retired_view_selection_and_epoch_without_changing_panels() {
+    for kind in 0..3 {
+        let (mut app, diagram, message) = setup();
+        open_focused_details(&mut app);
+        let captured = app.scenario_context().unwrap();
+        match kind {
+            0 => {
+                let other = id(&app, "incident_wide");
+                for view in [other, diagram] {
+                    let _ = app.update(Message::Diagram(crate::app::Choice {
+                        id: view,
+                        label: "view".into(),
+                    }));
+                }
+                open_focused_details(&mut app);
+                assert_ne!(app.scenario_context().unwrap().visit, captured.visit);
+            }
+            1 => {
+                let other = id(&app, "updated_report");
+                send(&mut app, |c| CanvasEvent::Select(c, other));
+            }
+            _ => {
+                send(&mut app, |c| CanvasEvent::Zoom(c, Some(0.5)));
+            }
+        }
+        let camera = app.behavior.scenario.camera_boundary();
+        let context = app.scenario_context();
+        let selected = app.selected;
+        let tab = app.inspector_tab;
+        let epochs = (app.canvas_epoch, app.camera_epoch);
+        let snapshot = app.document.snapshot();
+        let bundle = app.document.bundle().clone();
+        let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Properties(
+            captured, message,
+        )));
+        assert!(app.behavior.scenario.camera_boundary() == camera);
+        assert_eq!(app.scenario_context(), context);
+        assert_eq!(app.selected, selected);
+        assert_eq!(app.inspector_tab, tab);
+        assert_eq!((app.canvas_epoch, app.camera_epoch), epochs);
+        assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+        assert_eq!(app.document.bundle(), &bundle);
+    }
+}
+
+#[test]
+fn opening_scenario_properties_cancels_held_spacing_and_rejects_its_late_finish() {
+    use super::super::spacing::{Event as Spacing, Target, controller::tests::packet};
+    let (mut app, _, message) = setup();
+    send(&mut app, |c| {
+        CanvasEvent::Viewport(c, Size::new(900., 600.))
+    });
+    open_focused_details(&mut app);
+    let begin = packet(
+        app.project(),
+        &app.behavior.scenario,
+        app.scenario_context().unwrap(),
+        app.camera_epoch,
+        Target::Message(message),
+    );
+    let Spacing::Begin { press_screen, .. } = begin else {
+        panic!()
+    };
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Spacing(begin)));
+    assert_eq!(app.behavior.scenario.spacing_token(), Some(begin.token()));
+    let snapshot = app.document.snapshot();
+    let end = press_screen + Vector::new(0., 12.);
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Spacing(
+        Spacing::Move {
+            stamp: begin.stamp(),
+            token: begin.token(),
+            screen: end,
+        },
+    )));
+    let paint = app
+        .behavior
+        .scenario
+        .spacing_paint(begin.stamp().context, begin.stamp().camera_epoch)
+        .unwrap();
+    assert!(paint.refusal.is_none());
+    let line = paint
+        .scene
+        .lines
+        .iter()
+        .find(|line| line.id == message)
+        .unwrap();
+    assert!(
+        line.points[0].y > 160.,
+        "a real proposed scene moved the first message"
+    );
+    assert!(
+        Arc::ptr_eq(&snapshot, &app.document.snapshot()),
+        "preview is not authored"
+    );
+    let camera = stored_camera(&app);
+    send(&mut app, |c| CanvasEvent::Properties(c, message));
+    assert!(app.behavior.scenario.spacing_token().is_none());
+    assert_eq!(stored_camera(&app), camera);
+    let _ = app.update(Message::ScenarioCanvas(CanvasEvent::Spacing(
+        Spacing::Finish {
+            stamp: begin.stamp(),
+            token: begin.token(),
+            screen: end,
+        },
+    )));
+    assert!(Arc::ptr_eq(&snapshot, &app.document.snapshot()));
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+}

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

@@ -0,0 +1,438 @@
+//! Real mounted widgets dispatch the gesture; expectations name authored fields
+//! and actual displayed anchors independently of controller command results.
+use super::*;
+use crate::behavior::canvas_workspace::tests::{Mounted, key};
+use crate::behavior::scenario_layout::{ResolvedScenarioPlan, resolve};
+use crate::document::Document;
+use iced::Vector;
+use std::sync::Arc;
+
+const FIXTURE: &str = include_str!("../../../app/diagram_usages/tests/saved_scenario.arcadia");
+
+fn id(app: &App, alias: &str) -> Id {
+    app.project()
+        .identities()
+        .into_iter()
+        .find(|(_, name)| *name == alias)
+        .unwrap()
+        .0
+}
+
+async fn setup(fit: bool) -> (App, Mounted, Id) {
+    let mut app = App::with_project(oa_core::language::parse(FIXTURE).unwrap());
+    let owner = id(&app, "incident_response");
+    let diagram = id(&app, "incident_readable");
+    let _ = app.update(Message::Select(owner));
+    let _ = app.update(Message::Diagram(crate::app::Choice {
+        id: diagram,
+        label: "A - Incident review readable".into(),
+    }));
+    app.window_size = Size::new(1440., 900.);
+    let mut mounted = Mounted::new(&mut app).await;
+    if !fit {
+        let context = app.scenario_context().unwrap();
+        let task = app.update(Message::ScenarioCanvas(CanvasEvent::Zoom(
+            context,
+            Some(0.5),
+        )));
+        mounted.perform(&mut app, task).await;
+        mounted.settle(&mut app).await;
+    }
+    assert_eq!(
+        app.scenario_context().unwrap().representation,
+        Representation::Saved { diagram }
+    );
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+    (app, mounted, diagram)
+}
+
+fn resolved(app: &App) -> ResolvedScenarioPlan {
+    resolve(
+        app.project(),
+        app.scenario_context().unwrap().representation,
+        app.selected,
+    )
+    .unwrap()
+}
+
+fn stored_camera(app: &App) -> (Vector, Option<f32>, bool) {
+    let p = &app.behavior.scenario.presentation;
+    (p.pan, p.zoom, p.fit)
+}
+
+fn screen(mounted: &mut Mounted, app: &App, world: Point) -> Point {
+    let bounds = mounted.geometry(app).bounds("scenario-viewport");
+    let geometry = resolved(app);
+    let camera = app.behavior.scenario.presentation.camera(geometry.bounds);
+    let point = bounds.position() + camera.pan + Vector::new(world.x, world.y) * camera.scale;
+    assert!(
+        bounds.contains(point),
+        "actual visible world {world:?}: {point:?} in {bounds:?}"
+    );
+    point
+}
+
+fn mouse_event(event: mouse::Event) -> iced::Event {
+    iced::Event::Mouse(event)
+}
+
+async fn press(mounted: &mut Mounted, app: &mut App, point: Point) -> Vec<Message> {
+    mounted
+        .batch(
+            app,
+            &[
+                mouse_event(mouse::Event::CursorMoved { position: point }),
+                mouse_event(mouse::Event::ButtonPressed(mouse::Button::Left)),
+            ],
+            mouse::Cursor::Available(point),
+        )
+        .await
+}
+
+async fn move_to(mounted: &mut Mounted, app: &mut App, point: Point) -> Vec<Message> {
+    mounted
+        .batch(
+            app,
+            &[mouse_event(mouse::Event::CursorMoved { position: point })],
+            mouse::Cursor::Available(point),
+        )
+        .await
+}
+
+async fn release(mounted: &mut Mounted, app: &mut App, point: Point) -> Vec<Message> {
+    mounted
+        .batch(
+            app,
+            &[mouse_event(mouse::Event::ButtonReleased(
+                mouse::Button::Left,
+            ))],
+            mouse::Cursor::Available(point),
+        )
+        .await
+}
+
+fn set_expected_message(project: &mut oa_core::Project, diagram: Id, occurrence: Id, y: f32) {
+    let Some(oa_core::DiagramLayout::Scenario(layout)) =
+        &mut project.diagrams.get_mut(&diagram).unwrap().layout
+    else {
+        panic!()
+    };
+    layout
+        .messages
+        .iter_mut()
+        .find(|m| m.address.occurrence == occurrence)
+        .unwrap()
+        .send_y = y;
+}
+
+fn set_expected_lane(project: &mut oa_core::Project, diagram: Id, lifeline: Id, x: f32) {
+    let Some(oa_core::DiagramLayout::Scenario(layout)) =
+        &mut project.diagrams.get_mut(&diagram).unwrap().layout
+    else {
+        panic!()
+    };
+    layout
+        .lanes
+        .iter_mut()
+        .find(|lane| lane.lifeline == lifeline)
+        .unwrap()
+        .x = x;
+}
+
+fn assert_reopens_exactly(app: &App) {
+    let reopened = Document::from_bundle(
+        app.document.bundle().clone(),
+        oa_core::source_project::ProjectLimits::default(),
+    )
+    .unwrap();
+    assert_eq!(reopened.project(), app.project());
+    assert_eq!(reopened.bundle(), app.document.bundle());
+}
+
+#[tokio::test]
+async fn saved_message_same_batch_pointer_events_commit_once_and_one_undo_redo_restores_exact_source()
+ {
+    let (mut app, mut mounted, diagram) = setup(false).await;
+    let target = id(&app, "updated_report");
+    let before = app.document.snapshot();
+    let revision = app.document.revision();
+    let projected = screen(&mut mounted, &app, Point::new(400., 252.));
+    // This fixture asks for exactly +20 world units. A fractional start near a
+    // screen-coordinate exponent boundary need not retain an exact +10 delta.
+    let start = Point::new(projected.x.round(), projected.y.round());
+    let mut geometry = resolved(&app);
+    let camera = app.behavior.scenario.presentation.camera(geometry.bounds);
+    assert_eq!(camera.scale, 0.5);
+    let bounds = mounted.geometry(&app).bounds("scenario-viewport");
+    let world = Point::new(
+        (start.x - bounds.x - camera.pan.x) / camera.scale,
+        (start.y - bounds.y - camera.pan.y) / camera.scale,
+    );
+    geometry.scene.scale = camera.scale;
+    geometry.scene.camera_pan = camera.pan;
+    let hit = geometry.scene.hit_item(world).unwrap();
+    assert_eq!(hit.id, target);
+    assert_eq!(hit.role, crate::behavior::SceneHitRole::MessageBody);
+    let end = start + Vector::new(0., 10.); // .5 display scale: +20 authored y.
+    assert_eq!(end.y - start.y, 10.);
+    assert!(bounds.contains(start) && bounds.contains(end));
+    let messages = mounted
+        .batch(
+            &mut app,
+            &[
+                mouse_event(mouse::Event::CursorMoved { position: start }),
+                mouse_event(mouse::Event::ButtonPressed(mouse::Button::Left)),
+                mouse_event(mouse::Event::CursorMoved { position: end }),
+                mouse_event(mouse::Event::ButtonReleased(mouse::Button::Left)),
+            ],
+            mouse::Cursor::Available(end),
+        )
+        .await;
+    assert_eq!(
+        messages
+            .iter()
+            .filter(|m| matches!(
+                m,
+                Message::ScenarioCanvas(CanvasEvent::Spacing(spacing::Event::Begin { .. }))
+            ))
+            .count(),
+        1
+    );
+    assert_eq!(
+        messages
+            .iter()
+            .filter(|m| matches!(
+                m,
+                Message::ScenarioCanvas(CanvasEvent::Spacing(spacing::Event::Finish { .. }))
+            ))
+            .count(),
+        1
+    );
+    let mut expected = before.decoded.project.clone();
+    set_expected_message(&mut expected, diagram, target, 272.);
+    assert_eq!(
+        app.project(),
+        &expected,
+        "Only Saved A's addressed y changes; steps, other occurrences and B/C are exact"
+    );
+    assert_eq!(app.document.revision(), revision + 1);
+    assert_eq!(app.selected, target);
+    assert!(app.behavior.scenario.spacing_token().is_none());
+    assert_reopens_exactly(&app);
+    let after = app.document.snapshot();
+    let task = app.update(Message::Undo);
+    mounted.perform(&mut app, task).await;
+    assert_eq!(app.project(), &before.decoded.project);
+    assert_eq!(app.document.bundle(), &before.bundle);
+    assert!(!app.document.can_undo() && app.document.can_redo());
+    let task = app.update(Message::Redo);
+    mounted.perform(&mut app, task).await;
+    assert_eq!(app.project(), &after.decoded.project);
+    assert_eq!(app.document.bundle(), &after.bundle);
+}
+
+#[tokio::test]
+async fn saved_header_preview_survives_frames_and_freezes_fit_while_actual_bounds_expand() {
+    let (mut app, mut mounted, diagram) = setup(true).await;
+    let assessor = id(&app, "assessor");
+    let before = app.document.snapshot();
+    let original = resolved(&app);
+    let original_camera = app.behavior.scenario.presentation.camera(original.bounds);
+    let stored = stored_camera(&app);
+    assert!(stored.2, "test must exercise original Fit");
+    let start = screen(&mut mounted, &app, Point::new(640., 45.));
+    press(&mut mounted, &mut app, start).await;
+    let token = app
+        .behavior
+        .scenario
+        .spacing_token()
+        .expect("actual header press begins");
+    for x in [670., 700.] {
+        let end = start + Vector::new((x - 640.) * original_camera.scale, 0.);
+        move_to(&mut mounted, &mut app, end).await;
+        mounted.settle(&mut app).await; // Actual borrowed Scene/Stack tree is rebuilt.
+        assert_eq!(app.behavior.scenario.spacing_token(), Some(token));
+        assert!(Arc::ptr_eq(&before, &app.document.snapshot()));
+        assert_eq!(stored_camera(&app), stored);
+        let paint = app
+            .behavior
+            .scenario
+            .spacing_paint(app.scenario_context().unwrap(), app.camera_epoch)
+            .unwrap();
+        assert!(paint.refusal.is_none());
+        assert!((paint.scene.render_lanes[&assessor] - x).abs() < 0.001);
+        assert!(paint.bounds.width > original.bounds.width);
+        assert_eq!(paint.scene.scale, original_camera.scale);
+        assert_eq!(paint.scene.camera_pan, original_camera.pan);
+        let header = paint.scene.boxes.iter().find(|b| b.id == assessor).unwrap();
+        let displayed = Vector::new(header.rect.center().x, header.rect.center().y)
+            * paint.scene.scale
+            + paint.scene.camera_pan;
+        let baseline = Vector::new(640., 50.) * original_camera.scale + original_camera.pan;
+        assert!((displayed.x - baseline.x - (x - 640.) * original_camera.scale).abs() < 0.001);
+        assert_eq!(displayed.y, baseline.y);
+    }
+    let end = start + Vector::new(60. * original_camera.scale, 0.);
+    release(&mut mounted, &mut app, end).await;
+    let final_geometry = resolved(&app);
+    let actual_x = final_geometry.scene.render_lanes[&assessor];
+    assert!((actual_x - 700.).abs() < 0.001);
+    let mut expected = before.decoded.project.clone();
+    set_expected_lane(&mut expected, diagram, assessor, actual_x);
+    assert_eq!(app.project(), &expected);
+    let final_camera = app
+        .behavior
+        .scenario
+        .presentation
+        .camera(final_geometry.bounds);
+    assert_eq!(
+        final_camera, original_camera,
+        "commit must not refit underneath pointer"
+    );
+    assert!(!app.behavior.scenario.presentation.fit);
+    assert_eq!(app.selected, assessor);
+    assert_reopens_exactly(&app);
+}
+
+#[tokio::test]
+async fn saved_body_and_header_clicks_select_without_materializing_spacing() {
+    let (mut app, mut mounted, _) = setup(false).await;
+    let before = app.document.snapshot();
+    let original_camera = stored_camera(&app);
+    for (alias, world) in [
+        ("updated_report", Point::new(400., 252.)),
+        ("assessor", Point::new(640., 45.)),
+    ] {
+        let target = id(&app, alias);
+        let point = screen(&mut mounted, &app, world);
+        mounted.click(&mut app, point).await;
+        assert_eq!(app.selected, target);
+        assert!(app.behavior.scenario.spacing_token().is_none());
+        assert!(Arc::ptr_eq(&before, &app.document.snapshot()));
+        assert_eq!(stored_camera(&app), original_camera);
+    }
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+}
+
+#[tokio::test]
+async fn saved_valid_preview_then_refused_self_call_never_commits_last_valid_candidate() {
+    let (mut app, mut mounted, _) = setup(false).await;
+    let target = id(&app, "assess_call");
+    let before = app.document.snapshot();
+    let camera = stored_camera(&app);
+    let start = screen(&mut mounted, &app, Point::new(680., 344.));
+    press(&mut mounted, &mut app, start).await;
+    let valid = start + Vector::new(0., -10.); // send324, receive348, reply436 unchanged.
+    move_to(&mut mounted, &mut app, valid).await;
+    mounted.settle(&mut app).await;
+    let paint = app
+        .behavior
+        .scenario
+        .spacing_paint(app.scenario_context().unwrap(), app.camera_epoch)
+        .unwrap();
+    assert!(paint.refusal.is_none());
+    let line = paint.scene.lines.iter().find(|l| l.id == target).unwrap();
+    assert_eq!(line.points[0].y, 324.);
+    assert_eq!(line.points.last().unwrap().y, 348.);
+    let refused = start + Vector::new(0., 53.); // send450, receive474 would follow reply436.
+    move_to(&mut mounted, &mut app, refused).await;
+    mounted.settle(&mut app).await;
+    let paint = app
+        .behavior
+        .scenario
+        .spacing_paint(app.scenario_context().unwrap(), app.camera_epoch)
+        .unwrap();
+    assert!(paint.refusal.is_some());
+    assert_eq!(
+        paint
+            .scene
+            .lines
+            .iter()
+            .find(|l| l.id == target)
+            .unwrap()
+            .points[0]
+            .y,
+        344.
+    );
+    assert!(Arc::ptr_eq(&before, &app.document.snapshot()));
+    release(&mut mounted, &mut app, refused).await;
+    assert!(app.behavior.scenario.spacing_token().is_none());
+    assert!(Arc::ptr_eq(&before, &app.document.snapshot()));
+    assert_eq!(stored_camera(&app), camera);
+    assert!(!app.document.can_undo() && !app.document.can_redo());
+}
+
+#[tokio::test]
+async fn saved_escape_and_outside_pointer_cancel_actual_held_preview() {
+    for escape in [true, false] {
+        let (mut app, mut mounted, _) = setup(false).await;
+        let before = app.document.snapshot();
+        let camera = stored_camera(&app);
+        let start = screen(&mut mounted, &app, Point::new(400., 252.));
+        let end = start + Vector::new(0., 10.);
+        press(&mut mounted, &mut app, start).await;
+        move_to(&mut mounted, &mut app, end).await;
+        mounted.settle(&mut app).await;
+        assert!(app.behavior.scenario.spacing_token().is_some());
+        let release_at = if escape {
+            mounted
+                .batch(
+                    &mut app,
+                    &[key(iced::keyboard::key::Named::Escape)],
+                    mouse::Cursor::Available(end),
+                )
+                .await;
+            end
+        } else {
+            let bounds = mounted.geometry(&app).bounds("scenario-viewport");
+            let outside = Point::new(bounds.x - 5., bounds.y + 100.);
+            move_to(&mut mounted, &mut app, outside).await;
+            outside
+        };
+        assert!(app.behavior.scenario.spacing_token().is_none());
+        release(&mut mounted, &mut app, release_at).await;
+        assert!(Arc::ptr_eq(&before, &app.document.snapshot()));
+        assert_eq!(stored_camera(&app), camera);
+        assert!(!app.document.can_undo() && !app.document.can_redo());
+    }
+}
+
+#[tokio::test]
+async fn saved_drag_return_to_origin_preserves_redo_selection_and_original_fit_camera() {
+    let (mut app, mut mounted, _) = setup(true).await;
+    let owner = id(&app, "incident_response");
+    app.document
+        .execute(oa_core::Command::Rename(
+            owner,
+            "Previously edited owner".into(),
+        ))
+        .unwrap();
+    let redo = app.document.snapshot();
+    let task = app.update(Message::Undo);
+    mounted.perform(&mut app, task).await;
+    mounted.settle(&mut app).await;
+    assert!(app.document.can_redo());
+    let before = app.document.snapshot();
+    let camera = stored_camera(&app);
+    let selected = app.selected;
+    let revision = app.document.revision();
+    let start = screen(&mut mounted, &app, Point::new(400., 252.));
+    press(&mut mounted, &mut app, start).await;
+    move_to(&mut mounted, &mut app, start + Vector::new(0., 12.)).await;
+    mounted.settle(&mut app).await;
+    assert!(app.behavior.scenario.spacing_token().is_some());
+    move_to(&mut mounted, &mut app, start).await;
+    mounted.settle(&mut app).await;
+    release(&mut mounted, &mut app, start).await;
+    assert!(app.behavior.scenario.spacing_token().is_none());
+    assert!(Arc::ptr_eq(&before, &app.document.snapshot()));
+    assert_eq!(app.document.bundle(), &before.bundle);
+    assert_eq!(app.document.revision(), revision);
+    assert_eq!(stored_camera(&app), camera);
+    assert_eq!(app.selected, selected);
+    assert!(app.document.can_redo());
+    let task = app.update(Message::Redo);
+    mounted.perform(&mut app, task).await;
+    assert_eq!(app.project(), &redo.decoded.project);
+    assert_eq!(app.document.bundle(), &redo.bundle);
+}

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

@@ -48,8 +48,28 @@ async fn production_scenario_canvas_keeps_bounds_draft_identity_and_camera_throu
             mounted.pan(&mut app, start, start + delta).await;
             let diff = app.behavior.scenario.presentation.pan - next_pan;
             assert!(diff.x.hypot(diff.y) < 0.01);
-            let tool = mounted.geometry(&app).bounds("behavior-tool:A").center();
-            mounted.click(&mut app, tool).await;
+            // Iced operations report palette children in content coordinates.
+            // The preceding Action focus may have scrolled this retained palette.
+            let geometry = mounted.geometry(&app);
+            let scope = canvas_workspace::Scope::current(&app).unwrap();
+            let (palette, offset) = geometry.scrolls[&scope.control_id("palette-scroll")];
+            let tool = geometry.bounds("behavior-tool:A").center() - offset;
+            assert!(
+                palette.contains(tool),
+                "visible Action at {tool:?}: {palette:?}"
+            );
+            let chosen = mounted.click(&mut app, tool).await;
+            assert!(
+                chosen.iter().any(|message| matches!(
+                    canvas_workspace::tests::intent_action(message),
+                    Message::ScenarioCanvas(CanvasEvent::Choose(_, CanvasTool::Add(Tool::Action)))
+                )),
+                "Action palette click at scale {scale}, offset {offset:?}: {chosen:?}"
+            );
+            assert_eq!(
+                app.behavior.scenario.canvas_tool(f.owner),
+                CanvasTool::Add(Tool::Action)
+            );
             let messages = mounted.click(&mut app, bounds.position() + desired).await;
             assert!(
                 messages.iter().any(
@@ -57,7 +77,7 @@ async fn production_scenario_canvas_keeps_bounds_draft_identity_and_camera_throu
                 tool: Tool::Action, slot, lifeline: Some(line), ..
             }) if *slot == expected && *line == f.sender)
                 ),
-                "scale {scale}: {messages:?}"
+                "scale {scale}, expected slot {expected:?}: {messages:?}"
             );
             let session = app.behavior.scenario.form_session().unwrap();
             let invocation = app.behavior.scenario.draft.as_ref().unwrap().invocation;
@@ -1337,7 +1357,18 @@ async fn production_scenario_camera_external_controls_bounds_and_retained_deltas
         let bounds = mounted.geometry(&app).bounds("scenario-viewport");
         let point = bounds.position() + iced::Vector::new(95., 90.);
         let lifetime = app.camera_epoch;
-        let pan = app.behavior.scenario.presentation.pan;
+        // Fit stores no pan offset. A real drag starts from the displayed fitted
+        // camera, then materializes it before applying its ordered screen deltas.
+        let shown = app
+            .behavior
+            .scenario
+            .display(app.project(), f.owner, app.selected)
+            .unwrap();
+        let before_camera = app
+            .behavior
+            .scenario
+            .presentation
+            .camera(shown.bounds().unwrap());
         let first = point + iced::Vector::new(13., 9.);
         let last = first + iced::Vector::new(17., -3.);
         let emitted = mounted
@@ -1352,7 +1383,21 @@ async fn production_scenario_camera_external_controls_bounds_and_retained_deltas
                 mouse::Cursor::Available(last),
             )
             .await;
-        assert_eq!(app.behavior.scenario.presentation.pan, pan + (last - point));
+        let expected_pan = before_camera.pan + (last - point);
+        let actual_pan = app.behavior.scenario.presentation.pan;
+        let difference = actual_pan - expected_pan;
+        assert!(
+            difference.x.hypot(difference.y) < 0.001,
+            "{boundary}: displayed pan {actual_pan:?} must follow {expected_pan:?}"
+        );
+        assert_eq!(
+            app.behavior.scenario.presentation.zoom,
+            Some(before_camera.scale)
+        );
+        assert!(
+            !app.behavior.scenario.presentation.fit,
+            "drag materializes the visible Fit camera"
+        );
         assert_eq!(
             app.camera_epoch, lifetime,
             "own ordered deltas retain their lifetime"
@@ -1760,14 +1805,19 @@ fn scenario_workspace_fit_uses_measured_inner_viewport_and_rejects_nonfinite_inp
     assert!(!presentation.viewport(Size::new(484., 204.)));
     let scale = presentation.scale(graph);
     assert!(graph.width * scale <= 468. && graph.height * scale <= 188.);
-    assert!(scale > MIN_SCALE);
+    assert!(scale > camera::MIN_SCALE);
     for bad in [f32::NAN, f32::INFINITY, 0., -1.] {
         assert!(!presentation.zoom(Some(bad)));
         assert!(!presentation.viewport(Size::new(bad, 100.)));
         assert!(!presentation.viewport(Size::new(100., bad)));
         assert_eq!(presentation.scale(graph), scale);
     }
-    assert_eq!(presentation.scale(Size::new(900., 10000.)), MIN_SCALE);
+    let tall = Rectangle::with_size(Size::new(900., 10000.));
+    let camera = presentation.camera(tall);
+    assert!(camera.scale < 0.05 && camera.scale > 0.);
+    assert!((camera.scale - 188. / 10000.).abs() < 1e-8);
+    assert!((tall.height * camera.scale + camera.pan.y - 196.).abs() < 1e-4);
+    assert!((camera.pan.y - 8.).abs() < 1e-4);
     assert!(presentation.zoom(Some(1.25)));
     presentation.viewport(Size::new(200., 100.));
     assert_eq!(

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

@@ -0,0 +1,386 @@
+//! Actual Scene primitives, with independently chosen points and semantic IDs.
+//! These preserve the existing label hit band; they do not establish ink bounds
+//! or authoring eligibility, and do not dispatch a spacing gesture.
+use super::*;
+use crate::document::Document;
+
+struct Fixture {
+    project: Project,
+    owner: Id,
+    sender: Id,
+    receiver: Id,
+    call: Id,
+    reply: Id,
+    exchange: Id,
+}
+
+fn fixture() -> Fixture {
+    let project = language::parse(r#"arcadia 7;
+project hits "Hit roles" {
+ oa_activity source "Source" {}
+ oa_activity target "Target" {}
+ interaction exchange "Contract" { source @source; target @target; }
+ oa_scenario conversation "Conversation" { viewpoint OperationalActivity; steps [@call, @reply]; }
+ oa_lifeline left "Left" { parent @conversation; represented @source; }
+ oa_lifeline right "Right" { parent @conversation; represented @target; }
+ oa_occurrence call "Call" { parent @conversation; body { Exchange { exchange @exchange; sender @left; receiver @right; message_kind Call; }; }; }
+ oa_occurrence reply "Reply" { parent @conversation; body { Exchange { exchange @exchange; sender @right; receiver @left; message_kind Reply; reply_to @call; }; }; }
+}
+"#).unwrap();
+    let id = |alias: &str| {
+        project
+            .identities()
+            .into_iter()
+            .find(|(_, name)| *name == alias)
+            .unwrap()
+            .0
+    };
+    Fixture {
+        owner: id("conversation"),
+        sender: id("left"),
+        receiver: id("right"),
+        call: id("call"),
+        reply: id("reply"),
+        exchange: id("exchange"),
+        project,
+    }
+}
+
+fn scene(f: &Fixture) -> Scene {
+    let document =
+        Document::from_project(f.project.clone(), source_project::ProjectLimits::default())
+            .unwrap();
+    let before = document.snapshot();
+    let result = Scene::sequence_geometry(
+        document.project(),
+        f.owner,
+        f.call,
+        Some(&BTreeMap::from([(f.sender, 160.), (f.receiver, 400.)])),
+        None,
+    );
+    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());
+    result
+}
+
+fn hit(scene: &Scene, point: Point, id: Id, role: SceneHitRole) {
+    assert_eq!(scene.hit_item(point), Some(SceneHit { id, role }));
+    assert_eq!(scene.hit(point), Some(id));
+}
+
+fn occurrence(p: &mut Project, parent: Id, body: OccurrenceBody) -> Id {
+    let mut element = p
+        .make_element(Kind::Occurrence, Layer::Oa, "Hit target", Some(parent))
+        .unwrap();
+    let id = element.id;
+    *element.shared_mut().unwrap() = SharedBody::Occurrence {
+        body,
+        precondition: String::new(),
+        postcondition: String::new(),
+    };
+    p.elements.insert(id, element);
+    p.elements
+        .get_mut(&parent)
+        .unwrap()
+        .steps_mut()
+        .unwrap()
+        .push(id);
+    id
+}
+
+fn exchange_mut(p: &mut Project, id: Id) -> &mut OccurrenceBody {
+    let SharedBody::Occurrence { body, .. } =
+        p.elements.get_mut(&id).unwrap().shared_mut().unwrap()
+    else {
+        panic!("expected occurrence")
+    };
+    body
+}
+
+#[test]
+fn exact_headers_include_unassigned_lifelines_but_guides_are_not_headers() {
+    let mut f = fixture();
+    *f.project
+        .elements
+        .get_mut(&f.receiver)
+        .unwrap()
+        .shared_mut()
+        .unwrap() = SharedBody::Lifeline { represented: None };
+    let s = scene(&f);
+    assert!(!s.lanes.contains_key(&f.receiver));
+    assert_eq!(s.render_lanes[&f.receiver], 400.);
+    for (id, x) in [(f.sender, 160.), (f.receiver, 400.)] {
+        // The actual header is x-102..x+102, y15..85, including its padding.
+        for point in [Point::new(x - 101., 16.), Point::new(x + 101., 84.)] {
+            hit(&s, point, id, SceneHitRole::LifelineHeader);
+        }
+        hit(&s, Point::new(x, 95.), id, SceneHitRole::LifelineGuide);
+    }
+}
+
+#[test]
+fn repeated_exchange_occurrences_keep_distinct_message_body_and_label_hits() {
+    let f = fixture();
+    let s = scene(&f);
+    assert_eq!(s.rows[&f.call].1, 148.);
+    assert_eq!(s.rows[&f.reply].1, 240.);
+    for (id, y) in [(f.call, 148.), (f.reply, 240.)] {
+        hit(&s, Point::new(280., y), id, SceneHitRole::MessageBody);
+        hit(
+            &s,
+            Point::new(180., y - 16.),
+            id,
+            SceneHitRole::MessageLabel,
+        );
+        assert_ne!(id, f.exchange);
+    }
+}
+
+#[test]
+fn self_call_elbow_and_receive_endpoint_are_messages_not_execution_hits() {
+    let mut f = fixture();
+    for id in [f.call, f.reply] {
+        let OccurrenceBody::Exchange {
+            sender,
+            receiver,
+            exchange,
+            ..
+        } = exchange_mut(&mut f.project, id)
+        else {
+            unreachable!()
+        };
+        *sender = Some(f.sender);
+        *receiver = Some(f.sender);
+        *exchange = None;
+    }
+    let s = scene(&f);
+    let call = s.lines.iter().find(|l| l.id == f.call).unwrap();
+    assert_eq!(call.points.len(), 4);
+    assert_eq!(call.points[0].y, 148.);
+    assert_eq!(call.points[3].y, 172.);
+    hit(
+        &s,
+        Point::new(call.points[1].x, 160.),
+        f.call,
+        SceneHitRole::MessageBody,
+    );
+    hit(&s, call.points[3], f.call, SceneHitRole::MessageBody);
+    hit(
+        &s,
+        Point::new(180., 132.),
+        f.call,
+        SceneHitRole::MessageLabel,
+    );
+    let bar = s.activations.iter().find(|a| a.call == f.call).unwrap();
+    hit(
+        &s,
+        Point::new(bar.rect.x + 2., 190.),
+        f.call,
+        SceneHitRole::Activation,
+    );
+}
+
+#[test]
+fn activation_shoulder_beats_another_calls_label_and_broad_message_tolerance() {
+    let mut f = fixture();
+    let mut inner = f.project.elements[&f.call].clone();
+    inner.id = Id::new_v4();
+    inner.alias = "inner_call_hit".into();
+    inner.name = "Pressure verification with a descriptive operation label".into();
+    let inner_id = inner.id;
+    f.project.elements.insert(inner_id, inner);
+    let mut inner_reply = f.project.elements[&f.reply].clone();
+    inner_reply.id = Id::new_v4();
+    inner_reply.alias = "inner_reply_hit".into();
+    let reply_id = inner_reply.id;
+    f.project.elements.insert(reply_id, inner_reply);
+    let OccurrenceBody::Exchange { reply_to, .. } = exchange_mut(&mut f.project, reply_id) else {
+        unreachable!()
+    };
+    *reply_to = Some(inner_id);
+    *f.project
+        .elements
+        .get_mut(&f.owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap() = vec![f.call, inner_id, reply_id, f.reply];
+    let mut s = scene(&f);
+    let inner = s.lines.iter().find(|l| l.id == inner_id).unwrap();
+    let outer = s.activations.iter().find(|a| a.call == f.call).unwrap();
+    let shoulder = Point::new(outer.rect.x + 1., 225.);
+    assert!(outer.rect.contains(shoulder));
+    assert!(inner.label_bounds().contains(shoulder));
+    let endpoint = *inner.points.last().unwrap();
+    for scale in [1., 0.05, 0.0003] {
+        s.scale = scale;
+        hit(&s, shoulder, f.call, SceneHitRole::Activation);
+        hit(&s, endpoint, inner_id, SceneHitRole::MessageBody);
+        hit(
+            &s,
+            Point::new(180., 225.),
+            inner_id,
+            SceneHitRole::MessageLabel,
+        );
+    }
+}
+
+#[test]
+fn create_delete_markers_are_distinct_from_their_own_message_body_and_label() {
+    let mut f = fixture();
+    for (id, kind) in [
+        (f.call, MessageKind::Create),
+        (f.reply, MessageKind::Delete),
+    ] {
+        let OccurrenceBody::Exchange {
+            sender,
+            receiver,
+            message_kind,
+            reply_to,
+            ..
+        } = exchange_mut(&mut f.project, id)
+        else {
+            unreachable!()
+        };
+        *sender = Some(f.sender);
+        *receiver = Some(f.receiver);
+        *message_kind = kind;
+        *reply_to = None;
+    }
+    let s = scene(&f);
+    for (id, y, label_y) in [(f.call, 148., 118.), (f.reply, 240., 224.)] {
+        hit(&s, Point::new(400., y), id, SceneHitRole::LifecycleMarker);
+        hit(&s, Point::new(280., y), id, SceneHitRole::MessageBody);
+        hit(
+            &s,
+            Point::new(180., label_y),
+            id,
+            SceneHitRole::MessageLabel,
+        );
+    }
+    // Capsule boundary owns its contact with the incoming Create arrow.
+    hit(
+        &s,
+        Point::new(330., 148.),
+        f.call,
+        SceneHitRole::LifecycleMarker,
+    );
+}
+
+#[test]
+fn tiny_scale_nearest_hit_retains_the_winning_marker_or_message_role() {
+    let mut f = fixture();
+    let OccurrenceBody::Exchange {
+        sender,
+        receiver,
+        message_kind,
+        reply_to,
+        ..
+    } = exchange_mut(&mut f.project, f.reply)
+    else {
+        unreachable!()
+    };
+    *sender = Some(f.sender);
+    *receiver = Some(f.receiver);
+    *message_kind = MessageKind::Delete;
+    *reply_to = None;
+    let mut s = scene(&f);
+    s.scale = 0.0003;
+    // Both are outside exact strokes/labels. Comparing all broad candidates
+    // chooses the actual nearer shape, even when their UUID is identical.
+    hit(
+        &s,
+        Point::new(280., 246.),
+        f.reply,
+        SceneHitRole::MessageBody,
+    );
+    hit(
+        &s,
+        Point::new(400., 265.),
+        f.reply,
+        SceneHitRole::LifecycleMarker,
+    );
+    hit(
+        &s,
+        Point::new(280., 154.),
+        f.call,
+        SceneHitRole::MessageBody,
+    );
+}
+
+#[test]
+fn action_frame_and_use_boxes_do_not_advertise_message_or_header_roles() {
+    for body in [
+        OccurrenceBody::Action {
+            action: None,
+            lifeline: None,
+        },
+        OccurrenceBody::Fragment {
+            operator: FragmentOperator::Alternative,
+            branches: vec![],
+        },
+        OccurrenceBody::ScenarioUse {
+            scenario: None,
+            bindings: vec![],
+        },
+        OccurrenceBody::Exchange {
+            exchange: None,
+            sender: None,
+            receiver: None,
+            message_kind: MessageKind::Asynchronous,
+            operation: None,
+            reply_to: None,
+            values: vec![],
+        },
+    ] {
+        let mut f = fixture();
+        let id = occurrence(&mut f.project, f.owner, body);
+        let s = scene(&f);
+        let item = s.boxes.iter().find(|b| b.id == id).unwrap();
+        hit(
+            &s,
+            item.rect.position() + iced::Vector::new(15., 15.),
+            id,
+            SceneHitRole::Box,
+        );
+    }
+}
+
+#[test]
+fn winning_primitive_role_does_not_come_from_its_shared_uuid() {
+    let f = fixture();
+    let mut s = scene(&f);
+    // A controlled overlapping primitive verifies reverse box order without
+    // inventing a core alias. Its ID intentionally equals a real header's ID.
+    s.boxes.push(BoxItem {
+        id: f.sender,
+        role: SceneHitRole::Box,
+        rect: Rectangle::new(Point::new(150., 20.), Size::new(20., 20.)),
+        title: "Overlay control".into(),
+        detail: String::new(),
+        marker: None,
+    });
+    hit(&s, Point::new(160., 30.), f.sender, SceneHitRole::Box);
+    hit(
+        &s,
+        Point::new(180., 30.),
+        f.sender,
+        SceneHitRole::LifelineHeader,
+    );
+}
+
+#[test]
+fn invalid_points_never_produce_a_semantic_or_spacing_hit() {
+    let f = fixture();
+    let s = scene(&f);
+    for point in [
+        Point::new(f32::NAN, 148.),
+        Point::new(280., f32::NAN),
+        Point::new(f32::INFINITY, 148.),
+        Point::new(280., f32::NEG_INFINITY),
+    ] {
+        assert_eq!(s.hit_item(point), None);
+        assert_eq!(s.hit(point), None);
+    }
+}

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

@@ -6,6 +6,8 @@ use oa_core::{DiagramLayout, ScenarioLayout};
 #[cfg(test)]
 mod tests;
 
+pub(crate) mod presentation;
+
 type Candidate = BTreeMap<Id, f32>;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -30,13 +32,13 @@ struct MessageAnchors {
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
-enum Diagnostic {
+pub(crate) enum Diagnostic {
     SourceOrderCrossing { scope: Id, before: Id, after: Id },
     FrameExtendsPastFollowingAnchor { frame: Id, following: Id },
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub(super) enum GeometryIssue {
+pub(crate) enum GeometryIssue {
     UnknownAnchor(Id),
     LifecycleGeometryNotSupported { lifeline: Id, scope: Id },
     InvalidRepresentation(Id),
@@ -62,7 +64,7 @@ pub(super) struct Plan {
     pub(super) frames: BTreeMap<Id, Rectangle>,
     pub(super) scopes: BTreeMap<Id, (f32, f32)>,
     pub(super) height: f32,
-    diagnostics: Vec<Diagnostic>,
+    pub(super) diagnostics: Vec<Diagnostic>,
 }
 
 pub(super) fn occurrence(p: &Project, id: Id) -> Option<&OccurrenceBody> {
@@ -473,7 +475,7 @@ impl Plan {
 
 /// An appearance identity, never inferred from selection or from the owner alone.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub(super) enum Representation {
+pub(crate) enum Representation {
     Derived { owner: Id },
     Saved { diagram: Id },
 }

crates/oa-desktop/src/behavior/scenario_layout/presentation.rs

@@ -0,0 +1,234 @@
+//! Display policy for one requested Scenario representation, without authoring.
+//! The resolver remains the sole renderer. Freshness and editor admission belong
+//! to the caller; a capability here never bypasses those guards.
+use super::{Diagnostic, GeometryIssue, Representation, ResolvedScenarioPlan, resolve};
+use crate::behavior::Scene;
+use iced::Rectangle;
+use oa_core::{DiagramLayout, Id, Kind, OccurrenceBody, Project, SharedBody};
+use std::collections::BTreeSet;
+
+#[cfg(test)]
+mod tests;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) enum PresentationStatus {
+    Ready,
+    Fallback {
+        requested_issues: Vec<GeometryIssue>,
+    },
+    Unavailable {
+        requested_issues: Vec<GeometryIssue>,
+        automatic_issues: Vec<GeometryIssue>,
+    },
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) struct PresentationCapabilities {
+    /// Actual geometry exists for inspection, Fit and geometry-based navigation.
+    pub(crate) geometry_navigation: bool,
+    /// Still subject to document, gesture, editor and view-visit admission.
+    pub(crate) coordinate_input: bool,
+}
+
+pub(crate) struct ScenarioPresentation {
+    requested: Representation,
+    owner: Option<Id>,
+    status: PresentationStatus,
+    geometry: Option<ResolvedScenarioPlan>,
+    // Saved metadata must survive a complete automatic fallback.
+    latent_messages: Vec<Id>,
+}
+
+impl ScenarioPresentation {
+    pub(crate) fn requested(&self) -> Representation {
+        self.requested
+    }
+    pub(crate) fn owner(&self) -> Option<Id> {
+        self.owner
+    }
+    pub(crate) fn status(&self) -> &PresentationStatus {
+        &self.status
+    }
+    pub(crate) fn geometry_representation(&self) -> Option<Representation> {
+        self.geometry
+            .as_ref()
+            .map(|geometry| geometry.representation)
+    }
+    pub(crate) fn bounds(&self) -> Option<Rectangle> {
+        self.geometry.as_ref().map(|geometry| geometry.bounds)
+    }
+    /// Diagnostics describe the actual displayed geometry. Requested hard failures
+    /// are retained separately in status(), never presented as automatic warnings.
+    pub(crate) fn diagnostics(&self) -> &[Diagnostic] {
+        self.geometry
+            .as_ref()
+            .map_or(&[], |geometry| &geometry.plan.diagnostics)
+    }
+    pub(crate) fn latent_messages(&self) -> &[Id] {
+        &self.latent_messages
+    }
+    pub(crate) fn capabilities(&self) -> PresentationCapabilities {
+        PresentationCapabilities {
+            geometry_navigation: self.geometry.is_some(),
+            coordinate_input: matches!(self.status, PresentationStatus::Ready),
+        }
+    }
+    pub(in crate::behavior) fn scene(&self) -> Option<&Scene> {
+        self.geometry.as_ref().map(|geometry| &geometry.scene)
+    }
+    pub(in crate::behavior) fn into_scene(self) -> Option<Scene> {
+        self.geometry.map(|geometry| geometry.scene)
+    }
+}
+
+/// Resolve a structurally accepted Project for passive display. This is not a
+/// second model validator: identity and resolver-reported structural failures
+/// cannot be converted into a more permissive automatic representation.
+pub(crate) fn present(
+    project: &Project,
+    requested: Representation,
+    selected: Id,
+) -> ScenarioPresentation {
+    let owner = checked_owner(project, requested);
+    let Some(owner_id) = owner else {
+        let id = match requested {
+            Representation::Derived { owner } => owner,
+            Representation::Saved { diagram } => diagram,
+        };
+        return ScenarioPresentation {
+            requested,
+            owner: None,
+            geometry: None,
+            latent_messages: vec![],
+            status: PresentationStatus::Unavailable {
+                requested_issues: vec![GeometryIssue::InvalidRepresentation(id)],
+                automatic_issues: vec![],
+            },
+        };
+    };
+    match resolve(project, requested, selected) {
+        Ok(geometry) => ScenarioPresentation {
+            requested,
+            owner,
+            status: PresentationStatus::Ready,
+            latent_messages: geometry.latent_messages.clone(),
+            geometry: Some(geometry),
+        },
+        Err(requested_issues) => {
+            if matches!(requested, Representation::Derived { .. })
+                || requested_issues.iter().any(structural_failure)
+            {
+                return ScenarioPresentation {
+                    requested,
+                    owner,
+                    geometry: None,
+                    latent_messages: vec![],
+                    status: PresentationStatus::Unavailable {
+                        requested_issues,
+                        automatic_issues: vec![],
+                    },
+                };
+            }
+            match resolve(
+                project,
+                Representation::Derived { owner: owner_id },
+                selected,
+            ) {
+                Ok(geometry) => {
+                    let latent_messages =
+                        saved_latent_messages(project, requested, &geometry.scene);
+                    ScenarioPresentation {
+                        requested,
+                        owner,
+                        status: PresentationStatus::Fallback { requested_issues },
+                        geometry: Some(geometry),
+                        latent_messages,
+                    }
+                }
+                Err(automatic_issues) => ScenarioPresentation {
+                    requested,
+                    owner,
+                    geometry: None,
+                    latent_messages: vec![],
+                    status: PresentationStatus::Unavailable {
+                        requested_issues,
+                        automatic_issues,
+                    },
+                },
+            }
+        }
+    }
+}
+
+pub(crate) fn checked_owner(project: &Project, requested: Representation) -> Option<Id> {
+    let owner = match requested {
+        Representation::Derived { owner } => owner,
+        Representation::Saved { diagram } => {
+            let view = project.diagrams.get(&diagram)?;
+            let owner = view.projection.scenario()?;
+            if view.id != diagram || project.elements.get(&owner)?.layer() != view.layer {
+                return None;
+            }
+            owner
+        }
+    };
+    project
+        .elements
+        .get(&owner)
+        .is_some_and(|element| element.kind() == Kind::Scenario)
+        .then_some(owner)
+}
+
+fn structural_failure(issue: &GeometryIssue) -> bool {
+    // These violate the existing identity/address/finite-coordinate admission
+    // contract. Geometry support failures below do not invalidate stored intent.
+    match issue {
+        GeometryIssue::InvalidRepresentation(_)
+        | GeometryIssue::UnknownAnchor(_)
+        | GeometryIssue::InvalidCoordinate(_)
+        | GeometryIssue::DuplicateCoordinate(_)
+        | GeometryIssue::ExpandedAddressNotSupported(_)
+        | GeometryIssue::NonFinite(_) => true,
+        GeometryIssue::LifecycleGeometryNotSupported { .. }
+        | GeometryIssue::CoincidentDistinctEndpoints(_)
+        | GeometryIssue::TypedActivationOutsideScope { .. }
+        | GeometryIssue::TypedActivationOutsideLifetime { .. }
+        | GeometryIssue::TypedActivationCrossingNotSupported { .. }
+        | GeometryIssue::CompoundMoveNotImplemented(_)
+        | GeometryIssue::FixedFrameHeaderWouldMove { .. }
+        | GeometryIssue::OperandScopeOutsideEnclosingInterval { .. }
+        | GeometryIssue::LifecycleAnchorOutsideRenderScope { .. }
+        | GeometryIssue::LifetimeInversionNotSupported { .. } => false,
+    }
+}
+
+fn saved_latent_messages(project: &Project, requested: Representation, scene: &Scene) -> Vec<Id> {
+    let Representation::Saved { diagram } = requested else {
+        return vec![];
+    };
+    let Some(DiagramLayout::Scenario(layout)) = project.diagrams[&diagram].layout.as_ref() else {
+        return vec![];
+    };
+    let lines: BTreeSet<_> = scene.lines.iter().map(|line| line.id).collect();
+    layout
+        .messages
+        .iter()
+        .filter_map(|message| {
+            let id = message.address.occurrence;
+            (message.address.references.is_empty()
+                && scene.rows.contains_key(&id)
+                && !lines.contains(&id)
+                && matches!(
+                    project
+                        .elements
+                        .get(&id)
+                        .and_then(|element| element.shared()),
+                    Some(SharedBody::Occurrence {
+                        body: OccurrenceBody::Exchange { .. },
+                        ..
+                    })
+                ))
+            .then_some(id)
+        })
+        .collect()
+}

crates/oa-desktop/src/behavior/scenario_layout/presentation/tests.rs

@@ -0,0 +1,351 @@
+use super::*;
+use crate::document::Document;
+use oa_core::{
+    Command, Diagram, OccurrenceEndpoint, ProjectionKind, ScenarioLanePosition, ScenarioLayout,
+    ScenarioMessagePosition, language, validation,
+};
+
+fn fixture() -> (Project, Id) {
+    let project = language::parse(FIXTURE).unwrap();
+    assert_admitted(&project);
+    let owner = named(&project, "conversation");
+    (project, owner)
+}
+fn named(project: &Project, alias: &str) -> Id {
+    project
+        .identities()
+        .into_iter()
+        .find(|(_, name)| *name == alias)
+        .unwrap()
+        .0
+}
+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 save(project: &mut Project, owner: Id, layout: Option<ScenarioLayout>) -> Id {
+    let id = Id::new_v4();
+    project.diagrams.insert(
+        id,
+        Diagram {
+            id,
+            alias: format!("view_{}", project.diagrams.len()),
+            name: "Saved conversation".into(),
+            description: String::new(),
+            layer: project.elements[&owner].layer(),
+            projection: ProjectionKind::Scenario { scenario: owner },
+            view_options: Default::default(),
+            nodes: Default::default(),
+            routes: vec![],
+            layout: layout.map(DiagramLayout::Scenario),
+        },
+    );
+    id
+}
+fn layout(messages: &[(Id, f32)], lanes: &[(Id, f32)]) -> ScenarioLayout {
+    ScenarioLayout {
+        lanes: lanes
+            .iter()
+            .map(|&(lifeline, x)| ScenarioLanePosition { lifeline, x })
+            .collect(),
+        messages: messages
+            .iter()
+            .map(|&(occurrence, send_y)| ScenarioMessagePosition {
+                address: OccurrenceEndpoint {
+                    occurrence,
+                    references: vec![],
+                },
+                send_y,
+            })
+            .collect(),
+    }
+}
+fn same_geometry(a: &Scene, b: &Scene) {
+    assert!(
+        !a.activations.is_empty(),
+        "fallback must include real typed executions"
+    );
+    assert_eq!(a.activations, b.activations);
+    assert_eq!(a.lifecycle, b.lifecycle);
+    assert_eq!(a.rows, b.rows);
+    assert_eq!(a.sequence_bounds, b.sequence_bounds);
+    assert_eq!(a.render_lanes, b.render_lanes);
+    assert_eq!(a.lanes, b.lanes);
+    assert_eq!(a.open_calls, b.open_calls);
+    assert_eq!((a.size, a.layout_origin), (b.size, b.layout_origin));
+    let boxes = |scene: &Scene| {
+        scene
+            .boxes
+            .iter()
+            .map(|item| {
+                (
+                    item.id,
+                    item.rect,
+                    item.title.clone(),
+                    item.detail.clone(),
+                    item.marker,
+                )
+            })
+            .collect::<Vec<_>>()
+    };
+    let lines = |scene: &Scene| {
+        scene
+            .lines
+            .iter()
+            .map(|line| {
+                (
+                    line.id,
+                    line.points.clone(),
+                    line.label.clone(),
+                    line.label_at,
+                    line.dashed,
+                )
+            })
+            .collect::<Vec<_>>()
+    };
+    let slots = |scene: &Scene| {
+        scene
+            .slots
+            .iter()
+            .map(|slot| {
+                (
+                    slot.slot.parent,
+                    slot.slot.before,
+                    slot.y,
+                    slot.label.clone(),
+                )
+            })
+            .collect::<Vec<_>>()
+    };
+    assert_eq!(boxes(a), boxes(b));
+    assert_eq!(lines(a), lines(b));
+    assert_eq!(slots(a), slots(b));
+}
+
+#[test]
+fn absent_and_empty_saved_layouts_remain_saved_ready_representations() {
+    let (mut project, owner) = fixture();
+    let absent = save(&mut project, owner, None);
+    let empty = save(&mut project, owner, Some(ScenarioLayout::default()));
+    assert_admitted(&project);
+    let automatic = present(&project, Representation::Derived { owner }, owner);
+    assert_eq!(automatic.status(), &PresentationStatus::Ready);
+    for diagram in [absent, empty] {
+        let requested = Representation::Saved { diagram };
+        let displayed = present(&project, requested, owner);
+        assert_eq!(displayed.requested(), requested);
+        assert_eq!(displayed.geometry_representation(), Some(requested));
+        assert_eq!(displayed.owner(), Some(owner));
+        assert_eq!(displayed.status(), &PresentationStatus::Ready);
+        assert!(displayed.capabilities().coordinate_input);
+        assert_eq!(displayed.bounds(), automatic.bounds());
+        same_geometry(displayed.scene().unwrap(), automatic.scene().unwrap());
+    }
+}
+
+#[test]
+fn successful_crossing_diagnostic_keeps_authored_geometry_and_latent_identity() {
+    let (mut project, owner) = fixture();
+    let first = named(&project, "first");
+    let second = named(&project, "second");
+    let left = named(&project, "left");
+    let unfinished = named(&project, "unfinished");
+    let diagram = save(
+        &mut project,
+        owner,
+        Some(layout(
+            &[(first, 1000.), (unfinished, 2000.)],
+            &[(left, 900.)],
+        )),
+    );
+    assert_admitted(&project);
+    let shown = present(&project, Representation::Saved { diagram }, first);
+    assert_eq!(shown.status(), &PresentationStatus::Ready);
+    assert_eq!(shown.scene().unwrap().rows[&first].1, 1000.);
+    assert_eq!(shown.scene().unwrap().rows[&second].1, 240.);
+    assert_eq!(shown.scene().unwrap().render_lanes[&left], 900.);
+    assert!(
+        shown
+            .diagnostics()
+            .contains(&Diagnostic::SourceOrderCrossing {
+                scope: owner,
+                before: first,
+                after: second
+            })
+    );
+    assert_eq!(shown.latent_messages(), &[unfinished]);
+    assert_eq!(shown.scene().unwrap().rows[&unfinished].1, 516.);
+}
+
+#[test]
+fn hard_failure_uses_complete_automatic_geometry_but_retains_each_saved_request_and_latent_notice()
+{
+    let (mut project, owner) = fixture();
+    let call = named(&project, "call");
+    let reply = named(&project, "reply");
+    let unfinished = named(&project, "unfinished");
+    let left = named(&project, "left");
+    let right = named(&project, "right");
+    let authored = layout(
+        &[(reply, 300.), (unfinished, 2000.)],
+        &[(left, 900.), (right, -500.)],
+    );
+    let a = save(&mut project, owner, Some(authored.clone()));
+    let b = save(&mut project, owner, Some(authored));
+    assert_admitted(&project);
+    let before = project.clone();
+    let automatic = present(&project, Representation::Derived { owner }, call);
+    let control = automatic.scene().unwrap();
+    assert_eq!(control.render_lanes[&left], 160.);
+    assert_eq!(control.render_lanes[&right], 400.);
+    assert_eq!(control.rows[&reply].1, 424.);
+    assert_eq!(control.activations.len(), 1);
+    assert_eq!(
+        (
+            control.activations[0].rect.y,
+            control.activations[0].rect.height
+        ),
+        (356., 68.)
+    );
+    for diagram in [a, b] {
+        let request = Representation::Saved { diagram };
+        let shown = present(&project, request, call);
+        assert_eq!(shown.requested(), request);
+        assert_eq!(
+            shown.geometry_representation(),
+            Some(Representation::Derived { owner })
+        );
+        assert_eq!(
+            shown.status(),
+            &PresentationStatus::Fallback {
+                requested_issues: vec![GeometryIssue::TypedActivationCrossingNotSupported {
+                    call,
+                    event: reply
+                }],
+            }
+        );
+        assert_eq!(
+            shown.capabilities(),
+            PresentationCapabilities {
+                geometry_navigation: true,
+                coordinate_input: false
+            }
+        );
+        assert_eq!(shown.latent_messages(), &[unfinished]);
+        assert!(shown.diagnostics().is_empty());
+        assert_eq!(shown.bounds(), automatic.bounds());
+        same_geometry(shown.scene().unwrap(), control);
+    }
+    assert_eq!(project, before);
+}
+
+#[test]
+fn missing_or_incompatible_identity_and_structural_coordinate_errors_are_unavailable() {
+    let (mut project, owner) = fixture();
+    let left = named(&project, "left");
+    let diagram = save(&mut project, owner, None);
+    let missing = Id::new_v4();
+    for request in [
+        Representation::Saved { diagram: missing },
+        Representation::Derived { owner: left },
+    ] {
+        let shown = present(&project, request, owner);
+        assert_eq!(shown.requested(), request);
+        assert_eq!(shown.owner(), None);
+        assert!(
+            matches!(shown.status(), PresentationStatus::Unavailable { automatic_issues, .. } if automatic_issues.is_empty())
+        );
+        assert!(shown.scene().is_none() && shown.bounds().is_none());
+        assert_eq!(
+            shown.capabilities(),
+            PresentationCapabilities {
+                geometry_navigation: false,
+                coordinate_input: false
+            }
+        );
+    }
+    project.diagrams.get_mut(&diagram).unwrap().projection =
+        ProjectionKind::Scenario { scenario: missing };
+    assert!(matches!(
+        present(&project, Representation::Saved { diagram }, owner).status(),
+        PresentationStatus::Unavailable { .. }
+    ));
+    // Deliberately invalid-model control, not a warning-admitted geometry failure.
+    project.diagrams.get_mut(&diagram).unwrap().projection =
+        ProjectionKind::Scenario { scenario: owner };
+    project.diagrams.get_mut(&diagram).unwrap().layout = Some(DiagramLayout::Scenario(layout(
+        &[],
+        &[(left, oa_core::MAX_COORDINATE + 1.)],
+    )));
+    assert!(
+        validation::validate(&project)
+            .iter()
+            .any(|issue| issue.severity == validation::Severity::Error)
+    );
+    let before = project.clone();
+    let shown = present(&project, Representation::Saved { diagram }, owner);
+    assert!(
+        matches!(shown.status(), PresentationStatus::Unavailable { requested_issues, automatic_issues }
+        if requested_issues == &[GeometryIssue::InvalidCoordinate(left)] && automatic_issues.is_empty())
+    );
+    assert!(shown.scene().is_none());
+    assert_eq!(project, before);
+}
+
+#[test]
+fn passive_fallback_preserves_exact_document_source_and_one_step_undo_redo() {
+    let (mut project, owner) = fixture();
+    let first = named(&project, "first");
+    let reply = named(&project, "reply");
+    let view = save(&mut project, owner, Some(layout(&[(reply, 300.)], &[])));
+    assert_admitted(&project);
+    let mut document = Document::from_project(project, Default::default()).unwrap();
+    let initial_project = document.project().clone();
+    let initial_source = document.bundle().clone();
+    document
+        .execute(Command::Rename(first, "An intentional prior edit".into()))
+        .unwrap();
+    let accepted_project = document.project().clone();
+    let accepted_source = document.bundle().clone();
+    let revision = document.revision();
+    {
+        let shown = present(
+            document.project(),
+            Representation::Saved { diagram: view },
+            first,
+        );
+        assert!(matches!(
+            shown.status(),
+            PresentationStatus::Fallback { .. }
+        ));
+        assert!(shown.scene().is_some());
+    }
+    assert_eq!(document.project(), &accepted_project);
+    assert_eq!(document.bundle(), &accepted_source);
+    assert_eq!(document.revision(), revision);
+    assert!(document.undo());
+    assert_eq!(document.project(), &initial_project);
+    assert_eq!(document.bundle(), &initial_source);
+    assert!(document.redo());
+    assert_eq!(document.project(), &accepted_project);
+    assert_eq!(document.bundle(), &accepted_source);
+}
+
+const FIXTURE: &str = r#"arcadia 7;
+project display_probe "Scenario display probe" id "70000000-0000-4000-8000-000000000001" {
+ oa_activity source "Source" id "70000000-0000-4000-8000-000000000002" {}
+ oa_activity target "Target" id "70000000-0000-4000-8000-000000000003" {}
+ interaction exchange "Repeated exchange" id "70000000-0000-4000-8000-000000000004" { source @source; target @target; }
+ oa_scenario conversation "Conversation" id "70000000-0000-4000-8000-000000000005" { viewpoint OperationalActivity; steps [@first, @second, @call, @reply, @unfinished]; }
+ oa_lifeline left "Left" id "70000000-0000-4000-8000-000000000006" { parent @conversation; represented @source; }
+ oa_lifeline right "Right" id "70000000-0000-4000-8000-000000000007" { parent @conversation; represented @target; }
+ oa_occurrence first "First" id "70000000-0000-4000-8000-000000000008" { parent @conversation; body { Exchange { exchange @exchange; sender @left; receiver @right; message_kind Asynchronous; }; }; }
+ oa_occurrence second "Second" id "70000000-0000-4000-8000-000000000009" { parent @conversation; body { Exchange { exchange @exchange; sender @left; receiver @right; message_kind Asynchronous; }; }; }
+ oa_occurrence call "Call" id "70000000-0000-4000-8000-00000000000a" { parent @conversation; body { Exchange { exchange none; sender @right; receiver @right; message_kind Call; }; }; }
+ oa_occurrence reply "Reply" id "70000000-0000-4000-8000-00000000000b" { parent @conversation; body { Exchange { exchange none; sender @right; receiver @right; message_kind Reply; reply_to @call; }; }; }
+ oa_occurrence unfinished "Unfinished" id "70000000-0000-4000-8000-00000000000c" { parent @conversation; body { Exchange { exchange @exchange; sender @left; receiver none; message_kind Asynchronous; }; }; }
+}
+"#;

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

@@ -219,6 +219,7 @@ pub(super) fn view<'a>(app: &'a App, owner: Id, out: Column<'a, Message>) -> Ele
     graph.interaction = Some((context, state.tool, clean));
     let scale = graph.scale;
     let scope = super::super::canvas_workspace::Scope {
+        scenario_view: None,
         document: context.document,
         owner,
         revision: context.revision,

crates/oa-desktop/src/diagram_usage.rs

@@ -170,6 +170,13 @@ impl Surface {
             {
                 "State views"
             }
+            Self::Saved(id)
+                if p.diagrams
+                    .get(&id)
+                    .is_some_and(|d| d.projection.scenario().is_some()) =>
+            {
+                "Scenarios"
+            }
             Self::Saved(_) => "Architecture",
             Self::Process(_) => "Processes and chains",
             Self::Scenario(_) => "Scenarios",
@@ -276,6 +283,18 @@ pub(crate) fn saved_usages_for(p: &Project, subject: Id, only_diagram: Option<Id
     if only_diagram.is_some_and(|id| !p.diagrams.contains_key(&id)) {
         return Vec::new();
     }
+    if let Some(diagram) = only_diagram
+        .and_then(|id| p.diagrams.get(&id))
+        .filter(|d| d.projection.scenario().is_some())
+    {
+        return crate::behavior::scenario::State::default().representation_usages(
+            p,
+            crate::behavior::scenario_layout::Representation::Saved {
+                diagram: diagram.id,
+            },
+            subject,
+        );
+    }
     let index = ViewIndex::new(p);
     let mut usages = Vec::new();
     for diagram in p
@@ -283,6 +302,18 @@ pub(crate) fn saved_usages_for(p: &Project, subject: Id, only_diagram: Option<Id
         .values()
         .filter(|diagram| only_diagram.is_none_or(|id| diagram.id == id))
     {
+        if diagram.projection.scenario().is_some() {
+            usages.extend(
+                crate::behavior::scenario::State::default().representation_usages(
+                    p,
+                    crate::behavior::scenario_layout::Representation::Saved {
+                        diagram: diagram.id,
+                    },
+                    subject,
+                ),
+            );
+            continue;
+        }
         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) {