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-workspace-store.test.ts

@@ -1,6 +1,7 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { useImageWorkspaceStore } from '@/stores/image-workspace';
 import type {
+  DesignAssistantDeltaEvent,
   DesignGenerationTask,
   DesignGenerationTasksSnapshotEvent,
   DesignGenerationTaskUpdatedEvent,
@@ -12,6 +13,7 @@ const fetchImageWorkspaceMock = vi.hoisted(() => vi.fn());
 const fetchImageWorkspaceProjectMock = vi.hoisted(() => vi.fn());
 const fetchImageWorkspaceTasksMock = vi.hoisted(() => vi.fn());
 const openImageWorkspaceTaskEventsMock = vi.hoisted(() => vi.fn());
+const sendImageWorkspaceMessageMock = vi.hoisted(() => vi.fn());
 
 vi.mock('@/lib/image-workspace', async (importOriginal) => {
   const actual = await importOriginal<typeof import('@/lib/image-workspace')>();
@@ -21,6 +23,7 @@ vi.mock('@/lib/image-workspace', async (importOriginal) => {
     fetchImageWorkspaceProject: (...args: unknown[]) => fetchImageWorkspaceProjectMock(...args),
     fetchImageWorkspaceTasks: (...args: unknown[]) => fetchImageWorkspaceTasksMock(...args),
     openImageWorkspaceTaskEvents: (...args: unknown[]) => openImageWorkspaceTaskEventsMock(...args),
+    sendImageWorkspaceMessage: (...args: unknown[]) => sendImageWorkspaceMessageMock(...args),
   };
 });
 
@@ -123,6 +126,7 @@ function taskSnapshotEvent(
     type: 'design.generation_tasks.snapshot',
     workspaceId: 'workspace-one',
     workspaceViewRevision,
+    workspace: workspace('workspace-one', workspaceViewRevision),
     generationTasks: [{
       ...task,
       status,
@@ -139,6 +143,7 @@ describe('AI design task event store', () => {
     fetchImageWorkspaceMock.mockResolvedValue(bootstrap());
     fetchImageWorkspaceProjectMock.mockResolvedValue(workspace());
     fetchImageWorkspaceTasksMock.mockResolvedValue([task]);
+    sendImageWorkspaceMessageMock.mockResolvedValue(workspace());
   });
 
   afterEach(() => {
@@ -167,6 +172,70 @@ describe('AI design task event store', () => {
     });
   });
 
+  it('assembles assistant deltas once and replaces them with the canonical snapshot', async () => {
+    const source = new MockEventSource();
+    const response = deferred<DesignWorkspace>();
+    openImageWorkspaceTaskEventsMock.mockResolvedValue(source as unknown as EventSource);
+    sendImageWorkspaceMessageMock.mockReturnValueOnce(response.promise);
+
+    await useImageWorkspaceStore.getState().load();
+    await vi.waitFor(() => expect(openImageWorkspaceTaskEventsMock).toHaveBeenCalledOnce());
+    const sending = useImageWorkspaceStore.getState().sendMessage('把主视觉改成鲸鱼');
+    const pending = useImageWorkspaceStore.getState().pendingTurn;
+    expect(pending).toMatchObject({
+      userText: '把主视觉改成鲸鱼',
+      assistantText: '',
+      turnRevision: 2,
+    });
+
+    const firstDelta = {
+      id: 'session-one:2',
+      type: 'design.assistant.delta',
+      workspaceId: 'workspace-one',
+      clientTurnId: pending!.clientTurnId,
+      turnRevision: 2,
+      chunkIndex: 0,
+      delta: '可以，先强化',
+    } satisfies DesignAssistantDeltaEvent;
+    source.emit('design.assistant.delta', firstDelta);
+    source.emit('design.assistant.delta', firstDelta);
+    source.emit('design.assistant.delta', {
+      ...firstDelta,
+      id: 'session-one:3',
+      chunkIndex: 1,
+      delta: '鲸鱼的轮廓。',
+    } satisfies DesignAssistantDeltaEvent);
+
+    expect(useImageWorkspaceStore.getState().pendingTurn?.assistantText)
+      .toBe('可以，先强化鲸鱼的轮廓。');
+
+    const canonical = {
+      ...workspace('workspace-one', 2),
+      turnRevision: 2,
+      messages: [{
+        id: 'workspace-one:2:assistant:0',
+        role: 'assistant' as const,
+        kind: 'reply' as const,
+        text: '可以，先强化鲸鱼的轮廓。',
+        quickReplies: [],
+        generationQuote: null,
+        turnRevision: 2,
+        createdAt: '2026-08-02T10:01:00Z',
+      }],
+    };
+    source.emit('design.generation_tasks.snapshot', {
+      ...taskSnapshotEvent(2, 'queued'),
+      id: 'session-one:4',
+      workspace: canonical,
+    } satisfies DesignGenerationTasksSnapshotEvent);
+
+    expect(useImageWorkspaceStore.getState().pendingTurn).toBeNull();
+    expect(useImageWorkspaceStore.getState().workspace?.messages[0].text)
+      .toBe('可以，先强化鲸鱼的轮廓。');
+    response.resolve(canonical);
+    await sending;
+  });
+
   it('closes the previous stream when switching workspaces and on reset', async () => {
     const first = new MockEventSource();
     const second = new MockEventSource();
@@ -189,6 +258,35 @@ describe('AI design task event store', () => {
     expect(useImageWorkspaceStore.getState().taskStreamState).toBe('idle');
   });
 
+  it('does not switch back when an Agent turn finishes after selecting another Workspace', async () => {
+    const first = new MockEventSource();
+    const second = new MockEventSource();
+    const response = deferred<DesignWorkspace>();
+    openImageWorkspaceTaskEventsMock
+      .mockResolvedValueOnce(first as unknown as EventSource)
+      .mockResolvedValueOnce(second as unknown as EventSource);
+    fetchImageWorkspaceMock.mockResolvedValue(bootstrap(['workspace-one', 'workspace-two']));
+    fetchImageWorkspaceProjectMock.mockImplementation((workspaceId: string) => (
+      Promise.resolve(workspace(workspaceId))
+    ));
+    sendImageWorkspaceMessageMock.mockReturnValueOnce(response.promise);
+
+    await useImageWorkspaceStore.getState().load();
+    const sending = useImageWorkspaceStore.getState().sendMessage('继续优化海报');
+    await useImageWorkspaceStore.getState().selectProject('workspace-two');
+    response.resolve({
+      ...workspace('workspace-one', 2),
+      turnRevision: 2,
+    });
+    await sending;
+
+    expect(useImageWorkspaceStore.getState()).toMatchObject({
+      activeWorkspaceId: 'workspace-two',
+      workspace: { workspaceId: 'workspace-two' },
+      pendingTurn: null,
+    });
+  });
+
   it('does not let a slow previous Workspace selection overwrite the latest one', async () => {
     const rootSource = new MockEventSource();
     const latestSource = new MockEventSource();