feat: 流式展示设计 Agent 对话

需求：设计 Agent 对话与确认生成的回复需要实时展示。

实现：统一通过 Agent Gateway 提交 Turn，接收并去重 assistant delta，以 canonical Workspace 收口，并修复跨项目旧请求回写竞态。

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

@@ -6,6 +6,7 @@ import { ImageCanvas } from '@/pages/ImageCanvas';
 import { useAuthStore } from '@/stores/auth';
 import { useImageWorkspaceStore } from '@/stores/image-workspace';
 import type {
+  DesignAssistantDeltaEvent,
   DesignGenerationTask,
   DesignGenerationTaskUpdatedEvent,
   DesignWorkspace,
@@ -40,6 +41,14 @@ class MockEventSource {
   }
 }
 
+function deferred<T>(): { promise: Promise<T>; resolve(value: T): void } {
+  let resolve!: (value: T) => void;
+  const promise = new Promise<T>((accept) => {
+    resolve = accept;
+  });
+  return { promise, resolve };
+}
+
 vi.mock('@/lib/image-workspace', async (importOriginal) => {
   const actual = await importOriginal<typeof import('@/lib/image-workspace')>();
   return {
@@ -309,10 +318,57 @@ describe('ImageCanvas Workspace-first design experience', () => {
       'workspace-cloud',
       1,
       '把主角换成暖色轮廓光',
+      expect.stringMatching(/^turn-/),
     ));
     expect(confirmImageWorkspaceGenerationMock).not.toHaveBeenCalled();
   });
 
+  it('renders the pending user turn and assistant deltas while the command is running', async () => {
+    const response = deferred<DesignWorkspace>();
+    sendImageWorkspaceMessageMock.mockReturnValueOnce(response.promise);
+    render(<MemoryRouter><ImageCanvas /></MemoryRouter>);
+    await screen.findByText('云端角色设定');
+    await waitFor(() => expect(openImageWorkspaceTaskEventsMock).toHaveBeenCalledOnce());
+
+    fireEvent.change(screen.getByLabelText('设计需求'), {
+      target: { value: '让画面更有海洋呼吸感' },
+    });
+    fireEvent.click(screen.getByRole('button', { name: '发送给设计 Agent' }));
+
+    expect(await screen.findByText('让画面更有海洋呼吸感')).toBeInTheDocument();
+    expect(screen.getByRole('status', { name: '设计 Agent 正在回复' })).toBeInTheDocument();
+    const pending = useImageWorkspaceStore.getState().pendingTurn!;
+    act(() => {
+      taskEventSource.emit('design.assistant.delta', {
+        id: 'session-one:2',
+        type: 'design.assistant.delta',
+        workspaceId: 'workspace-cloud',
+        clientTurnId: pending.clientTurnId,
+        turnRevision: pending.turnRevision,
+        chunkIndex: 0,
+        delta: '可以先增加',
+      } satisfies DesignAssistantDeltaEvent);
+      taskEventSource.emit('design.assistant.delta', {
+        id: 'session-one:3',
+        type: 'design.assistant.delta',
+        workspaceId: 'workspace-cloud',
+        clientTurnId: pending.clientTurnId,
+        turnRevision: pending.turnRevision,
+        chunkIndex: 1,
+        delta: '留白和水流节奏。',
+      } satisfies DesignAssistantDeltaEvent);
+    });
+
+    expect(screen.getByTestId('image-workspace-conversation'))
+      .toHaveTextContent('可以先增加留白和水流节奏。');
+    act(() => response.resolve({
+      ...workspaceFixture(),
+      turnRevision: 2,
+      viewRevision: 2,
+    }));
+    await waitFor(() => expect(useImageWorkspaceStore.getState().pendingTurn).toBeNull());
+  });
+
   it('refreshes tasks after an Agent turn creates a generation task', async () => {
     const queuedTask = {
       ...taskFixture,
@@ -337,6 +393,7 @@ describe('ImageCanvas Workspace-first design experience', () => {
       'workspace-cloud',
       1,
       confirmationReply,
+      expect.stringMatching(/^turn-/),
     ));
     await waitFor(() => expect(fetchImageWorkspaceTasksMock).toHaveBeenCalledTimes(2));
     expect(await screen.findByTestId('design-task-task-two')).toBeInTheDocument();
@@ -357,7 +414,12 @@ describe('ImageCanvas Workspace-first design experience', () => {
     fireEvent.click(screen.getByRole('button', { name: '确认并开始生成' }));
 
     await waitFor(() => expect(confirmImageWorkspaceGenerationMock)
-      .toHaveBeenCalledWith('workspace-cloud', 1, 'quote-one'));
+      .toHaveBeenCalledWith(
+        'workspace-cloud',
+        1,
+        'quote-one',
+        expect.stringMatching(/^turn-/),
+      ));
     await waitFor(() => expect(fetchImageWorkspaceTasksMock).toHaveBeenCalledTimes(2));
   });