feat: 浏览器二期后端：远控服务 + ref 快照 + server 代理

- playwright_remote.py（新）：MCP 进程内 Unix socket HTTP 服务，
  监听 worktree/.browser-remote.sock；GET /state、GET /stream
  （SSE 画面流）、POST /input、POST /control（接管/交还）。
  线程契约（实测）：Playwright 同步调用只能在创建页面的线程，
  所以 HTTP 线程只读属性/读最新帧/入队，MCP 主循环用
  select 轮询（50ms） draining 输入并 pump screencast 帧
  （无 ack 则 CDP 首帧后停流）。
- 画面流走 CDP screencast 帧（学 chrome-devtools-mcp），不用
  定时截图；ffmpeg 录像暂不做。
- snapshot_refs/click_ref（学 playwright-mcp 的 ref 机制）+
  mouse_move/key_press/type_text；agent 工具在 holder=user 时
  直接报错，等用户交还。
- server.py：/tasks/{id}/browser/{state,stream,input,control}
  代理到 worktree socket，复用任务鉴权与 worktree 解析；
  会话不存在时 503（轮次结束即消失是设计）。
- 播种器：MCP 脚本是系统文件，版本变化时刷新老租户旧脚本
  （script_refreshed 打日志），否则远控只对新项目生效；
  新增 playwright_remote.py 进播种清单。
- 队列遮蔽修复：cloud/queue.py 会遮蔽 stdlib queue，改用
  SimpleQueue（deque+锁），仓库模式与 flat-copy 两路都通。
- 测试：新 20 项（remote 服务、server 代理、ref/输入/
  screencast fake），全量 1354 项通过（skipped 4）。

cloud/tests/test_server_browser_proxy.py

@@ -0,0 +1,140 @@
+"""Browser proxy endpoints: /tasks/{id}/browser/{state,input,control}.
+
+The control plane forwards to the MCP remote service over the Unix
+socket in the task worktree. Here the socket server is the real
+playwright_remote module with a stub browser; no Chromium, no
+worker, no model.
+"""
+
+import http.client
+import json
+import os
+import sqlite3
+import sys
+import tempfile
+import threading
+import unittest
+from pathlib import Path
+
+try:
+    from cloud.auth import AuthStore
+    from cloud.playwright_remote import RemoteState, start_remote_server
+    from cloud.server import create_server
+except ImportError:
+    sys.path.insert(0, str(Path(__file__).resolve().parents[2]))
+    from cloud.auth import AuthStore
+    from cloud.playwright_remote import RemoteState, start_remote_server
+    from cloud.server import create_server
+
+
+class _StubBrowser:
+    def cached_info(self):
+        return {"url": "https://example.com", "title": "T",
+                "started": True}
+
+
+class BrowserProxyTestCase(unittest.TestCase):
+    def setUp(self):
+        self.tmp = tempfile.TemporaryDirectory()
+        self.db_path = os.path.join(self.tmp.name, "control.db")
+        self.auth = AuthStore(self.db_path)
+        self.owner_id, self.owner_key = self.auth.create_user("owner")
+        self.outsider_id, self.outsider_key = self.auth.create_user("o")
+        self.server = create_server(self.db_path, "127.0.0.1", 0)
+        self.worktrees = os.path.join(self.tmp.name, "host-worktrees")
+        os.makedirs(self.worktrees)
+        self.server.host_worktrees_dir = self.worktrees
+        self.port = self.server.server_address[1]
+        self.thread = threading.Thread(
+            target=self.server.serve_forever, daemon=True)
+        self.thread.start()
+        status, self.project = self._req(
+            "POST", "/projects", {"name": "demo"}, self.owner_key)
+        self.assertEqual(status, 201)
+        self._task("task-b1")
+        wt = os.path.join(self.worktrees, "task-b1")
+        os.makedirs(wt)
+        self.remote = RemoteState(_StubBrowser())
+        self.sock_server = start_remote_server(
+            self.remote, os.path.join(wt, ".browser-remote.sock"))
+        self._task("task-nosock")
+        os.makedirs(os.path.join(self.worktrees, "task-nosock"))
+
+    def tearDown(self):
+        self.sock_server.shutdown()
+        self.sock_server.server_close()
+        self.server.shutdown()
+        self.server.server_close()
+        self.thread.join(timeout=5)
+        try:
+            self.auth.conn.close()
+        except Exception:
+            pass
+        self.tmp.cleanup()
+
+    def _task(self, task_id):
+        conn = sqlite3.connect(self.db_path)
+        try:
+            conn.execute(
+                "INSERT INTO tasks(id, project_id, prompt, status)"
+                " VALUES(?, ?, ?, ?)",
+                (task_id, self.project["id"], "do it", "running"))
+            conn.commit()
+        finally:
+            conn.close()
+
+    def _req(self, method, path, body=None, key=None):
+        conn = http.client.HTTPConnection("127.0.0.1", self.port, timeout=10)
+        hdrs = {}
+        payload = None
+        if body is not None:
+            payload = json.dumps(body).encode("utf-8")
+            hdrs["Content-Type"] = "application/json"
+        if key is not None:
+            hdrs["X-API-Key"] = key
+        try:
+            conn.request(method, path, body=payload, headers=hdrs)
+            resp = conn.getresponse()
+            data = resp.read()
+        finally:
+            conn.close()
+        try:
+            parsed = json.loads(data.decode("utf-8")) if data else None
+        except ValueError:
+            parsed = None
+        return resp.status, parsed
+
+    def test_state_input_control_flow(self):
+        status, body = self._req(
+            "GET", "/tasks/task-b1/browser/state", key=self.owner_key)
+        self.assertEqual(status, 200, body)
+        self.assertEqual(body["holder"], "agent")
+        self.assertEqual(body["url"], "https://example.com")
+        status, body = self._req(
+            "POST", "/tasks/task-b1/browser/input",
+            {"type": "mouse_click", "x": 1, "y": 2}, self.owner_key)
+        self.assertEqual(status, 409, body)
+        status, body = self._req(
+            "POST", "/tasks/task-b1/browser/control",
+            {"holder": "user"}, self.owner_key)
+        self.assertEqual((status, body["holder"]), (200, "user"))
+        status, body = self._req(
+            "POST", "/tasks/task-b1/browser/input",
+            {"type": "key", "key": "Enter"}, self.owner_key)
+        self.assertEqual((status, body["queued"]), (200, True))
+        status, body = self._req(
+            "POST", "/tasks/task-b1/browser/control",
+            {"holder": "agent"}, self.owner_key)
+        self.assertEqual(body["holder"], "agent")
+
+    def test_forbidden_and_no_session(self):
+        status, _ = self._req(
+            "GET", "/tasks/task-b1/browser/state", key=self.outsider_key)
+        self.assertEqual(status, 403)
+        status, body = self._req(
+            "GET", "/tasks/task-nosock/browser/state", key=self.owner_key)
+        self.assertEqual(status, 503, body)
+
+
+if __name__ == "__main__":
+    unittest.main()