perf: optimize app startup and background lifecycles

tests/unit/image-canvas-page.test.tsx

@@ -1411,8 +1411,8 @@ describe('ImageCanvas Workspace-first design experience', () => {
       } satisfies DesignAssistantDeltaEvent);
     });
 
-    expect(screen.getByTestId('image-workspace-conversation'))
-      .toHaveTextContent('可以先增加');
+    await waitFor(() => expect(screen.getByTestId('image-workspace-conversation'))
+      .toHaveTextContent('可以先增加'));
     expect(screen.getByTestId('image-workspace-conversation'))
       .not.toHaveTextContent('留白和水流节奏');
 
@@ -1429,8 +1429,8 @@ describe('ImageCanvas Workspace-first design experience', () => {
       } satisfies DesignAssistantDeltaEvent);
     });
 
-    expect(screen.getByTestId('image-workspace-conversation'))
-      .toHaveTextContent('可以先增加留白和水流节奏。');
+    await waitFor(() => expect(screen.getByTestId('image-workspace-conversation'))
+      .toHaveTextContent('可以先增加留白和水流节奏。'));
     act(() => response.resolve({
       ...conversationFixture(),
       turnRevision: 2,
@@ -1475,8 +1475,8 @@ describe('ImageCanvas Workspace-first design experience', () => {
 
     expect(await screen.findByText('继续优化海报')).toBeInTheDocument();
     expect(await screen.findByText('已完成最新方向整理。')).toBeInTheDocument();
-    expect(openImageWorkspaceTaskEventsMock).toHaveBeenCalledOnce();
-    expect(taskEventSource.close).not.toHaveBeenCalled();
+    expect(openImageWorkspaceTaskEventsMock).toHaveBeenCalledTimes(2);
+    expect(taskEventSource.close).toHaveBeenCalledOnce();
 
     await act(async () => {
       response.resolve(canonical);