Combine source navigation and alias rename with canvas ownership guards

crates/oa-desktop/src/document.rs

@@ -10,6 +10,10 @@ use std::{fmt, sync::Arc};
 const HISTORY_LIMIT: usize = 100;
 const HISTORY_BYTES: usize = 32 * 1024 * 1024;
 
+#[path = "document_alias_rename.rs"]
+mod alias_rename;
+pub use alias_rename::PreparedAliasRename;
+
 struct HistoryEntry {
     snapshot: Arc<CompiledSourceProject>,
     bytes: usize,
@@ -91,6 +95,8 @@ impl From<Vec<SourceDiagnostic>> for DocumentError {
 }
 
 pub struct Document {
+    // Distinguishes equal accepted snapshots belonging to different documents.
+    alias_owner: Arc<()>,
     current: Arc<CompiledSourceProject>,
     past: Vec<HistoryEntry>,
     future: Vec<HistoryEntry>,
@@ -121,6 +127,7 @@ impl Document {
         let current = Arc::new(source_project::compile_bundle(&bundle, limits)?);
         let current_bytes = estimated_bytes(&current);
         Ok(Self {
+            alias_owner: Arc::new(()),
             current,
             current_bytes,
             past: Vec::new(),
@@ -394,8 +401,17 @@ impl Document {
             return false;
         }
         let bytes = estimated_bytes(&compiled);
+        self.commit_snapshot(Arc::new(compiled), bytes)
+    }
+
+    // Only validated internal paths supply a changed snapshot and its exact
+    // estimate. The ordinary commit wrapper checks bundle inequality; the alias
+    // path checks its private changed flag and exact accepted-snapshot authority.
+    // Alias preparation shares this algorithm while retaining the live save and
+    // history state, and does not clone/recompile the candidate on adoption.
+    fn commit_snapshot(&mut self, compiled: Arc<CompiledSourceProject>, bytes: usize) -> bool {
         self.past.push(HistoryEntry {
-            snapshot: std::mem::replace(&mut self.current, Arc::new(compiled)),
+            snapshot: std::mem::replace(&mut self.current, compiled),
             bytes: std::mem::replace(&mut self.current_bytes, bytes),
         });
         self.future.clear();