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-workspace-api.test.ts

@@ -1,6 +1,7 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 import { AppError } from '@/lib/error-model';
 import {
+  createHostEventSource,
   ensureHostApiToken,
   getHostApiBase,
   hostApiFetch,
@@ -10,17 +11,20 @@ import {
   createImageWorkspaceProject,
   fetchImageWorkspace,
   ImageWorkspaceApiError,
+  openImageWorkspaceTaskEvents,
   resolveImageWorkspaceAssetUrl,
   sendImageWorkspaceMessage,
 } from '@/lib/image-workspace';
 
 vi.mock('@/lib/host-api', () => ({
   hostApiFetch: vi.fn(),
+  createHostEventSource: vi.fn(),
   ensureHostApiToken: vi.fn(),
   getHostApiBase: vi.fn(),
 }));
 
 const hostApiFetchMock = vi.mocked(hostApiFetch);
+const createHostEventSourceMock = vi.mocked(createHostEventSource);
 const ensureHostApiTokenMock = vi.mocked(ensureHostApiToken);
 const getHostApiBaseMock = vi.mocked(getHostApiBase);
 
@@ -40,6 +44,8 @@ describe('AI design renderer API boundary', () => {
     hostApiFetchMock.mockResolvedValue({ success: true, status: 200, data: bootstrap });
     ensureHostApiTokenMock.mockReset();
     ensureHostApiTokenMock.mockResolvedValue('host-token');
+    createHostEventSourceMock.mockReset();
+    createHostEventSourceMock.mockReturnValue({ close: vi.fn() } as unknown as EventSource);
     getHostApiBaseMock.mockReset();
     getHostApiBaseMock.mockReturnValue('http://127.0.0.1:13210');
   });
@@ -50,6 +56,17 @@ describe('AI design renderer API boundary', () => {
     expect(hostApiFetchMock).toHaveBeenCalledWith('/api/works/image-workspace', {});
   });
 
+  it('opens task events only after the local Host API token is ready', async () => {
+    const source = await openImageWorkspaceTaskEvents('workspace/one');
+
+    expect(source).toBe(createHostEventSourceMock.mock.results[0].value);
+    expect(createHostEventSourceMock).toHaveBeenCalledWith(
+      '/api/works/image-workspace/workspaces/workspace%2Fone/events',
+    );
+    expect(ensureHostApiTokenMock.mock.invocationCallOrder[0])
+      .toBeLessThan(createHostEventSourceMock.mock.invocationCallOrder[0]);
+  });
+
   it('creates an idempotent Workspace with a trimmed user-visible title', async () => {
     await createImageWorkspaceProject('  角色设计  ', 'workspace-client-1');