test(coding-agent): flushed coalesced observer sync before todo assertion

- Subagent lifecycle reconciliation now runs behind the 100ms observer UI
  coalescing timer; the test advances fake timers instead of asserting
  synchronously after emit.

packages/coding-agent/test/interactive-mode-todo-clear.test.ts

@@ -134,6 +134,9 @@ describe("InteractiveMode todo HUD persistence", () => {
 		mode.setTodos(session.getTodoPhases());
 
 		await mode.init();
+		// Subagent lifecycle changes coalesce behind a 100ms observer UI sync
+		// timer before todo reconciliation runs; flush it deterministically.
+		vi.useFakeTimers();
 		eventBus.emit(TASK_SUBAGENT_LIFECYCLE_CHANNEL, {
 			id: "ReviewFixer",
 			index: 0,
@@ -142,6 +145,7 @@ describe("InteractiveMode todo HUD persistence", () => {
 			status: "completed",
 			detached: true,
 		});
+		vi.advanceTimersByTime(100);
 
 		expect(session.getTodoPhases()[0]?.tasks[0]?.status).toBe("completed");
 	});