feat(FN-698): add per-project fallback for /api/activity-feed route

- Add dual-source fallback: try CentralCore first, fall back to store.getActivityLog()
- Adapt per-project ActivityLogEntry[] to ActivityFeedEntry[] format with projectId="local"
- Handle CentralCore init failures gracefully without returning 500
- Add comprehensive tests covering central data, empty state, init failure, and query params
- Add JSDoc documenting the fallback strategy and data source priority

packages/dashboard/src/routes.test.ts

@@ -83,6 +83,7 @@ function createMockStore(overrides: Partial<TaskStore> = {}): TaskStore {
     getGlobalSettingsStore: vi.fn().mockReturnValue(createMockGlobalSettingsStore()),
     logEntry: vi.fn().mockResolvedValue(undefined),
     getAgentLogs: vi.fn().mockResolvedValue([]),
+    getActivityLog: vi.fn().mockResolvedValue([]),
     addComment: vi.fn(),
     addTaskComment: vi.fn(),
     updateTaskComment: vi.fn(),
@@ -6129,3 +6130,143 @@ describe("POST /workflow-step-templates/:id/create", () => {
     expect(res.body.error).toContain("already exists");
   });
 });
+
+// ── Activity Feed Tests ─────────────────────────────────────────────
+
+describe("GET /api/activity-feed", () => {
+  let store: TaskStore;
+
+  beforeEach(() => {
+    store = createMockStore();
+  });
+
+  function buildApp() {
+    const app = express();
+    app.use(express.json());
+    app.use("/api", createApiRoutes(store));
+    return app;
+  }
+  it("returns empty array when both central and per-project activities are empty", async () => {
+    const store = createMockStore();
+    
+    // Override the module-level CentralCore mock to return empty array
+    const mockCentralInstance = {
+      init: vi.fn().mockResolvedValue(undefined),
+      close: vi.fn().mockResolvedValue(undefined),
+      getRecentActivity: vi.fn().mockResolvedValue([]),
+    };
+    MockCentralCore.mockImplementation(() => mockCentralInstance as any);
+
+    const app = buildApp(store);
+    const res = await REQUEST(app, "GET", "/api/activity-feed");
+
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual([]);
+  });
+
+  it("returns central activity when available", async () => {
+    const store = createMockStore();
+    store.getActivityLog.mockResolvedValue([]);
+
+    const centralEntries = [
+      {
+        id: "central-1",
+        timestamp: "2026-04-01T11:00:00.000Z",
+        type: "task:moved" as const,
+        projectId: "proj-123",
+        projectName: "Test Project",
+        taskId: "KB-002",
+        details: "Moved task to done",
+      },
+    ];
+
+    // Override the module-level CentralCore mock to return data
+    const mockCentralInstance = {
+      init: vi.fn().mockResolvedValue(undefined),
+      close: vi.fn().mockResolvedValue(undefined),
+      getRecentActivity: vi.fn().mockResolvedValue(centralEntries),
+    };
+    MockCentralCore.mockImplementation(() => mockCentralInstance as any);
+
+    const app = buildApp(store);
+    const res = await REQUEST(app, "GET", "/api/activity-feed");
+
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual(centralEntries);
+    
+    // Should not call per-project activity when central data exists
+    expect(store.getActivityLog).not.toHaveBeenCalled();
+  });
+
+  it("handles CentralCore initialization failure gracefully", async () => {
+    const store = createMockStore();
+    
+    // Override the module-level CentralCore mock to throw error on init
+    const mockCentralInstance = {
+      init: vi.fn().mockRejectedValue(new Error("CentralCore init failed")),
+      close: vi.fn().mockResolvedValue(undefined),
+      getRecentActivity: vi.fn(),
+    };
+    MockCentralCore.mockImplementation(() => mockCentralInstance as any);
+
+    const app = buildApp(store);
+    const res = await REQUEST(app, "GET", "/api/activity-feed");
+
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual([]); // Fallback returns empty array from mock store
+  });
+
+  it("passes through limit query parameter", async () => {
+    const store = createMockStore();
+    
+    // Override the module-level CentralCore mock to return empty
+    const mockCentralInstance = {
+      init: vi.fn().mockResolvedValue(undefined),
+      close: vi.fn().mockResolvedValue(undefined),
+      getRecentActivity: vi.fn().mockResolvedValue([]),
+    };
+    MockCentralCore.mockImplementation(() => mockCentralInstance as any);
+
+    const app = buildApp(store);
+    const res = await REQUEST(app, "GET", "/api/activity-feed?limit=25");
+
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual([]);
+  });
+
+  it("handles type filter query parameter", async () => {
+    const store = createMockStore();
+    
+    // Override the module-level CentralCore mock to return empty
+    const mockCentralInstance = {
+      init: vi.fn().mockResolvedValue(undefined),
+      close: vi.fn().mockResolvedValue(undefined),
+      getRecentActivity: vi.fn().mockResolvedValue([]),
+    };
+    MockCentralCore.mockImplementation(() => mockCentralInstance as any);
+
+    const app = buildApp(store);
+    const res = await REQUEST(app, "GET", "/api/activity-feed?types=task:moved");
+
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual([]);
+  });
+
+  it("validates fallback route path exists", async () => {
+    const store = createMockStore();
+    
+    // Override the module-level CentralCore mock to return empty - this ensures fallback path is taken
+    const mockCentralInstance = {
+      init: vi.fn().mockResolvedValue(undefined),
+      close: vi.fn().mockResolvedValue(undefined),
+      getRecentActivity: vi.fn().mockResolvedValue([]),
+    };
+    MockCentralCore.mockImplementation(() => mockCentralInstance as any);
+
+    const app = buildApp(store);
+    const res = await REQUEST(app, "GET", "/api/activity-feed");
+
+    expect(res.status).toBe(200);
+    expect(Array.isArray(res.body)).toBe(true);
+  });
+});

packages/dashboard/src/routes.ts

@@ -6666,6 +6666,14 @@ Output ONLY the prompt text (no markdown, no explanations).`;
   /**
    * GET /api/activity-feed
    * Get unified activity feed across all projects.
+   * Falls back to per-project activity when central activity is empty or unavailable.
+   * 
+   * Fallback Strategy:
+   * 1. First attempts to read from CentralCore.getRecentActivity() (multi-project mode)
+   * 2. If central returns empty array OR CentralCore init fails, falls back to store.getActivityLog()
+   * 3. Per-project entries are adapted to ActivityFeedEntry format with projectId="local"
+   * 4. This ensures single-project dashboards show activity even without engine ProjectManager
+   * 
    * Query: limit, projectId, types
    * Returns: ActivityFeedEntry[]
    */
@@ -6676,14 +6684,51 @@ Output ONLY the prompt text (no markdown, no explanations).`;
       const typesParam = typeof req.query.types === "string" ? req.query.types.split(",") : undefined;
       const types = typesParam as import("@fusion/core").ActivityEventType[] | undefined;
       
-      const { CentralCore } = await import("@fusion/core");
-      const central = new CentralCore();
-      await central.init();
+      let centralEntries: any[] = [];
+      let centralError: Error | null = null;
       
-      const entries = await central.getRecentActivity({ limit, projectId, types });
-      await central.close();
+      // Try to get central activity data first
+      try {
+        const { CentralCore } = await import("@fusion/core");
+        const central = new CentralCore();
+        await central.init();
+        centralEntries = await central.getRecentActivity({ limit, projectId, types });
+        await central.close();
+      } catch (err) {
+        centralError = err as Error;
+      }
       
-      res.json(entries);
+      // If central data exists and is not empty, return it
+      if (centralEntries.length > 0) {
+        res.json(centralEntries);
+        return;
+      }
+      
+      // Fall back to per-project activity data
+      const options: { limit?: number; type?: import("@fusion/core").ActivityEventType } = { limit };
+      if (types && types.length === 1) {
+        options.type = types[0];
+      }
+      
+      const perProjectEntries = await store.getActivityLog(options);
+      
+      // Convert per-project ActivityLogEntry[] to ActivityFeedEntry[] format
+      const projectName = (store as any).rootDir ? 
+        require("path").basename((store as any).rootDir) : "Current Project";
+      
+      const feedEntries = perProjectEntries.map((entry) => ({
+        id: entry.id,
+        timestamp: entry.timestamp,
+        type: entry.type,
+        projectId: "local",
+        projectName: projectName,
+        taskId: entry.taskId,
+        taskTitle: entry.taskTitle,
+        details: entry.details,
+        metadata: entry.metadata,
+      }));
+      
+      res.json(feedEntries);
     } catch (err: any) {
       res.status(500).json({ error: err.message });
     }