refactor(canvas): review fixes for the busy flag, the comparison note and the bundle size check

- busyReason had no reader: the chat engine sets isBusy through the store's
  generic set, like every other flag.
- The isSameDocument comment says the two "same document" rules disagree
  in both directions, so neither is a subset of the other.
- The import boundary test bundles minified with one pako (the MCP core
  resolves its own copy) and caps the canvas core at 160 KB (134 KB now).

components/chat/chat-engine.tsx

@@ -729,7 +729,7 @@ export function ChatEngineProvider({
     // Canvas components (version cards, the compare dialog, "ask AI") read
     // the busy flag from the canvas store
     useEffect(() => {
-        useCanvasStore.getState().setBusy(isBusy ? "chat" : null)
+        useCanvasStore.getState().set({ isBusy })
     }, [isBusy])
     // The page goes (another language mounts a new one): the answer stops,
     // so it cannot reach the next page's canvas

lib/diagram-diff.ts

@@ -288,7 +288,10 @@ export function sameFileVars(a: string | null, b: string | null): boolean {
  * page settings and file variables. This is the web app's one rule for "is
  * this version on the canvas" (versions, compare, one-step commits). The
  * MCP server's edit gate has its own (contentFingerprint): it compares the
- * cells as written, and leaves page settings and file variables out.
+ * cells as written, and leaves page settings and file variables out. The
+ * two disagree both ways (a background change is a difference only here;
+ * a geometry written "40.0" and "40" is one only there), so neither is a
+ * subset of the other.
  */
 export function isSameDocument(a: string, b: string): boolean {
     const pagesOf = (doc: Document) => {

stores/canvas-store.ts

@@ -33,10 +33,7 @@ interface CanvasState {
     /** Something is changing the canvas (an answer streams in, a sync
      * runs): version actions and "ask AI" wait */
     isBusy: boolean
-    /** Who set the busy flag ("chat", "sync"); null when not busy */
-    busyReason: string | null
-    set: (partial: Partial<Omit<CanvasState, "set" | "setBusy">>) => void
-    setBusy: (reason: string | null) => void
+    set: (partial: Partial<Omit<CanvasState, "set">>) => void
 }
 
 export const useCanvasStore = create<CanvasState>((set) => ({
@@ -48,7 +45,5 @@ export const useCanvasStore = create<CanvasState>((set) => ({
     isFreehand: false,
     isDrawioPopupOpen: false,
     isBusy: false,
-    busyReason: null,
     set: (partial) => set(partial),
-    setBusy: (reason) => set({ isBusy: reason !== null, busyReason: reason }),
 }))

tests/unit/canvas-import-boundary.test.ts

@@ -122,8 +122,11 @@ describe("canvas import boundary", () => {
             platform: "browser",
             format: "esm",
             jsx: "automatic",
-            alias: { "@": root },
+            // The MCP core (packages/mcp-server/src) resolves pako from its
+            // own node_modules; one copy, as the shell build must do
+            alias: { "@": root, pako: path.join(root, "node_modules/pako") },
             external: ["react", "react-dom", "next/*"],
+            minify: true,
             logLevel: "silent",
         })
         const inputs = result.metafile.inputs
@@ -145,5 +148,12 @@ describe("canvas import boundary", () => {
                 .map((specifier) => `${file} -> ${specifier}`),
         )
         expect(nextImports).toEqual([])
+        // The canvas core stays small enough for the MCP's browser shell
+        // (134 KB minified, pako once)
+        const stage = Object.values(result.metafile.outputs).find(
+            (output) =>
+                output.entryPoint === "components/canvas/canvas-stage.tsx",
+        )
+        expect(stage?.bytes).toBeLessThan(160 * 1024)
     })
 })