feat: 对接设计 Agent Gateway WebSocket

需求：服务端统一 Agent Gateway 将设计任务状态流切换为 WebSocket，客户端需要实时展示生成任务并支持断线恢复。

实现：Electron Main 管理 Session、一次性 Ticket、WebSocket 心跳与游标续传，按关闭码回收会话；Renderer 继续通过本机 Host API 的 SSE 投影接收任务事件，并保留 REST 降级同步。

验证：typecheck、变更文件 ESLint、37 个聚焦测试及 build:vite 通过。

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

@@ -1,4 +1,4 @@
-import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { act, fireEvent, render, screen, waitFor } from '@testing-library/react';
 import { MemoryRouter } from 'react-router-dom';
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { ImageWorkspaceApiError } from '@/lib/image-workspace';
@@ -7,6 +7,7 @@ import { useAuthStore } from '@/stores/auth';
 import { useImageWorkspaceStore } from '@/stores/image-workspace';
 import type {
   DesignGenerationTask,
+  DesignGenerationTaskUpdatedEvent,
   DesignWorkspace,
   DesignWorkspaceBootstrap,
 } from '../../shared/image-workspace';
@@ -16,8 +17,29 @@ const fetchImageWorkspaceProjectMock = vi.hoisted(() => vi.fn());
 const fetchImageWorkspaceTasksMock = vi.hoisted(() => vi.fn());
 const sendImageWorkspaceMessageMock = vi.hoisted(() => vi.fn());
 const confirmImageWorkspaceGenerationMock = vi.hoisted(() => vi.fn());
+const openImageWorkspaceTaskEventsMock = vi.hoisted(() => vi.fn());
 const resolveImageWorkspaceAssetUrlMock = vi.hoisted(() => vi.fn());
 
+type EventListener = (event: MessageEvent<string>) => void;
+
+class MockEventSource {
+  onopen: ((event: Event) => void) | null = null;
+  onerror: ((event: Event) => void) | null = null;
+  readonly close = vi.fn();
+  private readonly listeners = new Map<string, Set<EventListener>>();
+
+  addEventListener(type: string, listener: EventListener): void {
+    const listeners = this.listeners.get(type) ?? new Set<EventListener>();
+    listeners.add(listener);
+    this.listeners.set(type, listeners);
+  }
+
+  emit(type: string, payload: unknown): void {
+    const event = { data: JSON.stringify(payload) } as MessageEvent<string>;
+    for (const listener of this.listeners.get(type) ?? []) listener(event);
+  }
+}
+
 vi.mock('@/lib/image-workspace', async (importOriginal) => {
   const actual = await importOriginal<typeof import('@/lib/image-workspace')>();
   return {
@@ -29,6 +51,9 @@ vi.mock('@/lib/image-workspace', async (importOriginal) => {
     confirmImageWorkspaceGeneration: (...args: unknown[]) => (
       confirmImageWorkspaceGenerationMock(...args)
     ),
+    openImageWorkspaceTaskEvents: (...args: unknown[]) => (
+      openImageWorkspaceTaskEventsMock(...args)
+    ),
     resolveImageWorkspaceAssetUrl: (...args: unknown[]) => (
       resolveImageWorkspaceAssetUrlMock(...args)
     ),
@@ -122,6 +147,8 @@ const taskFixture: DesignGenerationTask = {
 };
 
 describe('ImageCanvas Workspace-first design experience', () => {
+  let taskEventSource: MockEventSource;
+
   beforeEach(() => {
     vi.clearAllMocks();
     useImageWorkspaceStore.getState().reset();
@@ -134,6 +161,10 @@ describe('ImageCanvas Workspace-first design experience', () => {
       turnRevision: 2,
       phase: 'shaping',
     });
+    taskEventSource = new MockEventSource();
+    openImageWorkspaceTaskEventsMock.mockResolvedValue(
+      taskEventSource as unknown as EventSource,
+    );
     resolveImageWorkspaceAssetUrlMock.mockResolvedValue(
       'http://127.0.0.1:13210/content?token=host',
     );
@@ -330,27 +361,33 @@ describe('ImageCanvas Workspace-first design experience', () => {
     await waitFor(() => expect(fetchImageWorkspaceTasksMock).toHaveBeenCalledTimes(2));
   });
 
-  it('keeps checking after Quote confirmation until the new task becomes visible', async () => {
+  it('renders a new task pushed by the design event stream without repeated polling', async () => {
     const queuedTask = {
       ...taskFixture,
       taskId: 'task-delayed',
       status: 'queued' as const,
       resultAssets: [],
     };
-    fetchImageWorkspaceTasksMock
-      .mockResolvedValueOnce([])
-      .mockResolvedValueOnce([])
-      .mockResolvedValueOnce([queuedTask]);
+    fetchImageWorkspaceTasksMock.mockResolvedValue([]);
 
     render(<MemoryRouter><ImageCanvas /></MemoryRouter>);
     await screen.findByTestId('design-quote-quote-one');
+    await waitFor(() => expect(openImageWorkspaceTaskEventsMock)
+      .toHaveBeenCalledWith('workspace-cloud'));
+    await waitFor(() => expect(taskEventSource.onopen).not.toBeNull());
+    act(() => {
+      taskEventSource.onopen?.(new Event('open'));
+      taskEventSource.emit('design.generation_task.updated', {
+        id: 'session-one:2',
+        type: 'design.generation_task.updated',
+        workspaceId: 'workspace-cloud',
+        workspaceViewRevision: 2,
+        generationTask: queuedTask,
+      } satisfies DesignGenerationTaskUpdatedEvent);
+    });
 
-    fireEvent.click(screen.getByRole('button', { name: '确认并开始生成' }));
-
-    await waitFor(() => expect(confirmImageWorkspaceGenerationMock)
-      .toHaveBeenCalledWith('workspace-cloud', 1, 'quote-one'));
-    await waitFor(() => expect(fetchImageWorkspaceTasksMock).toHaveBeenCalledTimes(3));
     expect(await screen.findByTestId('design-task-task-delayed'))
       .toBeInTheDocument();
+    expect(fetchImageWorkspaceTasksMock).toHaveBeenCalledOnce();
   });
 });