fix: 修复设计 Agent 慢响应超时

问题：客户端每 250ms 轮询 Run，并在 120 秒固定超时，导致服务端日志刷屏且慢响应被提前判定失败。

修复：将轮询改为 1 秒起步、最高 5 秒的指数退避，并将等待窗口调整为 10 分钟；新增 150 秒慢 Run 回归测试。

tests/unit/works-square-design-workspace.test.ts

@@ -210,6 +210,59 @@ describe('Works Square AI design adapter', () => {
     );
   });
 
+  it('waits for a slow design run without flooding the run endpoint', async () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(new Date('2026-08-03T02:00:00Z'));
+    const startedAt = Date.now();
+    let runPolls = 0;
+    const fetchMock = vi.fn<typeof fetch>(async (input, init) => {
+      const url = String(input);
+      if (url.endsWith('/api/agents/sessions')) {
+        return jsonResponse({ session_id: 'session-slow', status: 'active' }, 201);
+      }
+      if (url.endsWith('/api/agents/sessions/session-slow/commands')) {
+        return jsonResponse({ run_id: 'run-slow', status: 'queued', error: null }, 202);
+      }
+      if (url.endsWith('/api/agents/sessions/session-slow/runs/run-slow')) {
+        runPolls += 1;
+        return jsonResponse({
+          run_id: 'run-slow',
+          status: Date.now() - startedAt >= 150_000 ? 'succeeded' : 'running',
+          error: null,
+        });
+      }
+      if (url.endsWith('/api/design/workspaces/workspace-one')) {
+        return jsonResponse(serverWorkspace);
+      }
+      throw new Error(`Unexpected request: ${url} ${init?.method ?? 'GET'}`);
+    });
+    const adapter = new WorksSquareDesignWorkspace({
+      apiBaseUrl: 'https://square.example',
+      fetchImpl: fetchMock,
+    });
+
+    try {
+      const outcomePromise = adapter.submitMessage({
+        workspaceId: 'workspace-one',
+        clientTurnId: 'turn-slow',
+        expectedTurnRevision: 1,
+        message: '整理一个复杂的品牌设计方向',
+      }).then(
+        (value) => ({ value, error: null }),
+        (error: unknown) => ({ value: null, error }),
+      );
+
+      await vi.advanceTimersByTimeAsync(160_000);
+      const outcome = await outcomePromise;
+
+      expect(outcome.error).toBeNull();
+      expect(outcome.value).toMatchObject({ workspaceId: 'workspace-one' });
+      expect(runPolls).toBeLessThanOrEqual(40);
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
   it('maps an invalid Runtime command to a user input error', async () => {
     const fetchMock = vi.fn<typeof fetch>()
       .mockResolvedValueOnce(jsonResponse({