feat(FN-3584): add memory file markdown preview to agent detail and log vie

This merge introduces a memory file markdown preview feature (FN-3584) with corresponding documentation, refines the AgentDetailView and AgentLogViewer components in the dashboard, and adds defensive collision handling for worktree operations during manual task moves (FN-3583).

Fusion-Task-Id: FN-3584

packages/engine/src/__tests__/notification-service.test.ts

@@ -128,4 +128,36 @@ describe("NotificationService", () => {
     expect(initSpy).not.toHaveBeenCalled();
     initSpy.mockRestore();
   });
+
+  it("duplicates merged dispatch when multiple NotificationService instances subscribe to the same store", async () => {
+    const store = createStore({ ntfyEnabled: true, ntfyTopic: "topic" });
+    const sendNotification = vi.fn(async () => ({ success: true, providerId: "mock" }));
+    const provider: NotificationProvider = {
+      getProviderId: () => "mock",
+      isEventSupported: () => true,
+      sendNotification,
+    };
+
+    const first = new NotificationService(store as any);
+    const second = new NotificationService(store as any);
+    first.registerProvider(provider);
+    second.registerProvider(provider);
+    await first.start();
+    await second.start();
+
+    // Confirms duplication is from duplicate listener graphs, not duplicate task:merged payloads.
+    store.emit("task:merged", {
+      task: task(),
+      branch: "fusion/fn-1",
+      merged: true,
+      worktreeRemoved: true,
+      branchDeleted: true,
+    });
+    await Promise.resolve();
+
+    expect(sendNotification).toHaveBeenCalledTimes(2);
+
+    await first.stop();
+    await second.stop();
+  });
 });

packages/engine/src/__tests__/notifier.test.ts

@@ -1093,7 +1093,7 @@ describe("NtfyNotifier", () => {
       expect(fetchMock).toHaveBeenCalledTimes(1);
     });
 
-    it("emits a single merged notification when notifier shares an already-started NotificationService", async () => {
+    it("emits a single merged notification when notifier shares the same already-started NotificationService (ProjectEngine wiring)", async () => {
       const sharedService = new NotificationService(store, { projectId: "proj-1" });
       await sharedService.start();
 

packages/engine/src/__tests__/project-engine.test.ts

@@ -288,6 +288,22 @@ describe("ProjectEngine notification ownership wiring", () => {
     expect(mocks.notificationServiceStop).toHaveBeenCalledTimes(1);
     expect(mocks.notifierStop).toHaveBeenCalledTimes(1);
   });
+
+  it("does not recreate notification listeners on repeated start calls, preventing duplicate merged delivery", async () => {
+    const engine = createEngine({ skipNotifier: false, projectId: "proj_for_notifier" });
+
+    await engine.start();
+    await engine.start();
+
+    // Root cause guard: if ProjectEngine.start is called more than once, it should not
+    // wire a second NotificationService/NtfyNotifier pair for the same store.
+    expect(NotificationService).toHaveBeenCalledTimes(1);
+    expect(NtfyNotifier).toHaveBeenCalledTimes(1);
+    expect(mocks.notificationServiceStart).toHaveBeenCalledTimes(1);
+    expect(mocks.notifierStart).toHaveBeenCalledTimes(1);
+
+    await engine.stop();
+  });
 });
 
 describe("ProjectEngine PR monitoring wiring", () => {

packages/engine/src/project-engine.ts

@@ -139,6 +139,7 @@ export interface ProjectEngineOptions {
  */
 export class ProjectEngine {
   private runtime: InProcessRuntime;
+  private started = false;
   private prMonitor?: PrMonitor;
   private prCommentHandler?: PrCommentHandler;
   private notifier?: NtfyNotifier;
@@ -243,6 +244,10 @@ export class ProjectEngine {
    * Start the engine: initialize the runtime and all auxiliary subsystems.
    */
   async start(): Promise<void> {
+    if (this.started) {
+      return;
+    }
+
     // 1. Start the core runtime (TaskStore, Scheduler, Executor, Triage, etc.)
     await this.runtime.start();
 
@@ -422,6 +427,7 @@ export class ProjectEngine {
     // 8. Start periodic merge retry sweep
     this.scheduleMergeRetry(store);
 
+    this.started = true;
     runtimeLog.log(`ProjectEngine started for ${this.config.projectId}`);
   }
 
@@ -433,6 +439,10 @@ export class ProjectEngine {
    * promptly without continuing git/verification work after shutdown starts.
    */
   async stop(): Promise<void> {
+    if (!this.started) {
+      return;
+    }
+
     this.shuttingDown = true;
 
     // Stop merge retry timer
@@ -518,6 +528,8 @@ export class ProjectEngine {
     // Stop the core runtime (Triage, Scheduler, Executor, etc.)
     await this.runtime.stop();
 
+    this.started = false;
+    this.shuttingDown = false;
     runtimeLog.log(`ProjectEngine stopped for ${this.config.projectId}`);
   }