fix: close bare open() in host.py and ResourceWarning in test_host_thread_cli

- host.py: 7 one-shot reads switched to with open (run_health_check
  pidfile, daemon-status pid/log, daemon-stop pid, daemon old pid,
  interrupt poll state, parallel jobs); read content, encoding args
  and error semantics unchanged.
- tests/test_host_thread_cli.py: test_old_archive_unchanged state
  read switched to with open; added a warnings-capture assertion
  scoped to the state read so a regression fails the test.
- Intentionally untouched: daemonize log handle (daemon-lifetime
  dup2 target) and the two _load_config_file / init sites owned
  by PR #266.

host.py

@@ -1120,7 +1120,8 @@ def run_health_check(state_path, cfg, codex_bin, codex_home, approval,
     checks["daemon_pidfile"] = pidfile
     if os.path.exists(pidfile):
         try:
-            pid = int(open(pidfile).read().strip())
+            with open(pidfile) as f:
+                pid = int(f.read().strip())
             os.kill(pid, 0)
             checks["daemon_alive"] = True
             checks["daemon_pid"] = pid
@@ -2707,7 +2708,8 @@ def main():
         pid = None
         if os.path.exists(pidfile):
             try:
-                pid = int(open(pidfile).read().strip())
+                with open(pidfile) as f:
+                    pid = int(f.read().strip())
                 os.kill(pid, 0)
                 alive = True
             except Exception:
@@ -2715,7 +2717,8 @@ def main():
         tail = ""
         if os.path.exists(logfile):
             try:
-                tail = "\n".join(open(logfile).read().splitlines()[-5:])
+                with open(logfile) as f:
+                    tail = "\n".join(f.read().splitlines()[-5:])
             except Exception:
                 pass
         print(json.dumps({"alive": alive, "pid": pid, "pidfile": pidfile,
@@ -2728,7 +2731,8 @@ def main():
             print("daemon 未运行（无 pidfile）")
             return
         try:
-            pid = int(open(pidfile).read().strip())
+            with open(pidfile) as f:
+                pid = int(f.read().strip())
         except Exception:
             print("pidfile 损坏，直接删除")
             os.remove(pidfile)
@@ -2758,7 +2762,8 @@ def main():
         if not args.foreground:
             if os.path.exists(pidfile):
                 try:
-                    old_pid = int(open(pidfile).read().strip())
+                    with open(pidfile) as f:
+                        old_pid = int(f.read().strip())
                     os.kill(old_pid, 0)
                     print(f"daemon 已在运行：pid {old_pid}，先 daemon-stop 再起")
                     return
@@ -3272,8 +3277,8 @@ def main():
                     for _ in range(10):
                         time.sleep(1)
                         try:
-                            cur = json.load(open(args.state,
-                                                 encoding="utf-8"))
+                            with open(args.state, encoding="utf-8") as f:
+                                cur = json.load(f)
                             if (cur.get("tasks", {}).get(args.task, {})
                                     .get("status") == "interrupted"):
                                 print(f"interrupt {args.task}: 属主已响应，"
@@ -3424,7 +3429,8 @@ def main():
                           last_turn_status=t.get("goal_last_turn_status"),
                           last_turn_text=last_result.get("text", "") or "")
         elif args.cmd == "parallel":
-            jobs = json.load(open(args.jobs))
+            with open(args.jobs) as f:
+                jobs = json.load(f)
             # 依赖 + 优先级：先拓扑排序，缺依赖/成环直接报错不跑；
             # 按波次派发 + 跑：依赖都 completed 的任务才进本波，
             # 依赖 failed/skipped 的任务标 skipped 不跑，避免在坏

tests/test_host_thread_cli.py

@@ -1,9 +1,11 @@
+import gc
 import io
 import json
 import os
 import sys
 import tempfile
 import unittest
+import warnings
 from contextlib import redirect_stdout
 from unittest import mock
 import host
@@ -246,7 +248,19 @@ class ThreadCliTest(unittest.TestCase):
                             code = e.code if isinstance(e.code, int) else 1
             self.assertEqual(code, 0)
             self.assertIn("archived t1", out.getvalue())
-            saved = json.loads(Path(state_path).read_text(encoding="utf-8"))
+            # 第 4 项回归：此处裸 open() 曾在 GC 时报 ResourceWarning；
+            # 只捕获本段读 state 的警告断言（_load_config_file 的
+            # 警告属 #266 轨，不在此断言范围内）。
+            with warnings.catch_warnings(record=True) as caught:
+                warnings.simplefilter("always", ResourceWarning)
+                with open(state_path, encoding="utf-8") as f:
+                    saved = json.load(f)
+                gc.collect()
+            self.assertEqual(
+                [w for w in caught
+                 if issubclass(w.category, ResourceWarning)
+                 and "host-state.json" in str(w.message)],
+                [])
             self.assertEqual(saved["tasks"]["t1"]["status"], "archived")
             calls = self._calls_before_close(fake)
             self.assertEqual(calls, [("archive", "th-1")])