feat(FN-3053): consolidate mock helpers across CLI, dashboard, and engine p

The merge consolidates mock helpers across packages by creating a new shared `mockCoreEngine.ts` in the CLI package and strengthening the core/engine helpers, then migrating both CLI command tests and the dashboard's `AgentsView` tests to use the canonical helpers. It also publishes SSE architecture

Fusion-Task-Id: FN-3053

packages/dashboard/app/test/mockApi.ts

@@ -3,6 +3,12 @@
  *
  * Add new `app/api.ts` or `app/api/legacy.ts` exports here first before
  * introducing ad-hoc per-test `vi.mock("../../api", …)` export lists.
+ *
+ * Behavior contract:
+ * - preserve real exports by default
+ * - apply canonical/common test mocks
+ * - allow per-suite overrides
+ * - auto-synthesize stable fallback fns for missing callable exports
  */
 import { vi, type Mock } from "vitest";
 

packages/dashboard/app/test/mockHelpers.test.ts

@@ -27,6 +27,16 @@ describe("dashboard test mock helpers", () => {
     expect(rendered.props.className).toBe("x");
   });
 
+  it("preserves real non-function exports and respects overrides", async () => {
+    const module = await createDashboardApiMock(
+      async () => ({ API_VERSION: "v1", fetchTasks: async () => ["real"] }),
+      { fetchTasks: vi.fn().mockResolvedValue(["mocked"]) },
+    );
+
+    expect(module.API_VERSION).toBe("v1");
+    await expect((module.fetchTasks as () => Promise<string[]>)()).resolves.toEqual(["mocked"]);
+  });
+
   it("keeps canonical dashboard api mocks resettable", () => {
     dashboardApiMocks.fetchSettings.mockResolvedValueOnce({ hello: "world" });
     resetDashboardApiMockState();