fix(s11): support background cleanup on Windows

s11_background_tasks/README.ja.md

@@ -78,7 +78,7 @@ class BackgroundManager:
             self._ready.append(task_id)
 ```
 
-command が非ゼロで終了した場合や worker で例外が起きた場合は `failed` となる。Shell は独立した process group で起動し、command の完了、timeout、または Agent が通常経路や `SIGTERM` で終了する時に元の group を停止する。これは lifecycle cleanup であって sandbox ではなく、別の session を作った process は group から離れられる。
+command が非ゼロで終了した場合や worker で例外が起きた場合は `failed` となる。POSIX では Shell を独立した process group で起動し、command の完了、timeout、または Agent が通常経路や `SIGTERM` で終了する時に元の group を停止する。Windows には POSIX の process-group signal がないため、実行中の Shell process に `Popen.terminate()` と `Popen.kill()` を使う。これは lifecycle cleanup であって sandbox ではなく、管理対象の Shell から離れたり別の session を作ったりした process は残る場合がある。
 
 ### collect_background_results: 通知収集
 
@@ -160,9 +160,9 @@ python s11_background_tasks/code.py
 
 以下のプロンプトを試してください：
 
-1. `Run pip list in the background and find all Python files in this directory`
-2. `Run npm install (use run_in_background) and while waiting, read package.json`
-3. `Run a short sleep in the background, then list all Markdown files`
+1. `Run python -m pip list in the background and find all Python files in this directory`
+2. `Run npm --prefix web install (use run_in_background) and while waiting, read web/package.json`
+3. `Run python -c "import time; time.sleep(3); print('done')" in the background, then list all Markdown files`
 
 観察ポイント：`run_in_background` を明示的に設定すると、コマンドがバックグラウンドに送られるか？`bg_id` は返されるか？後続のターンで完了結果が `<task_notification>` 形式で収集されるか？
 

s11_background_tasks/README.md

@@ -78,7 +78,7 @@ class BackgroundManager:
             self._ready.append(task_id)
 ```
 
-A non-zero exit code or worker exception becomes `failed`. The shell starts in its own process group. When the command finishes, times out, or the Agent exits through the normal or `SIGTERM` path, the runtime stops that original group. This is lifecycle cleanup, not a sandbox: a process that creates another session can leave the group.
+A non-zero exit code or worker exception becomes `failed`. On POSIX, the shell starts in its own process group, which the runtime stops when the command finishes, times out, or the Agent exits through the normal or `SIGTERM` path. Windows has no POSIX process-group signals, so the runtime uses `Popen.terminate()` and `Popen.kill()` for a still-running shell process. This is lifecycle cleanup, not a sandbox: a process that escapes the managed shell or creates another session may survive it.
 
 ### collect_background_results: Notification Collection
 
@@ -160,9 +160,9 @@ python s11_background_tasks/code.py
 
 Try these prompts:
 
-1. `Run pip list in the background and find all Python files in this directory`
-2. `Run npm install (use run_in_background) and while waiting, read package.json`
-3. `Run a short sleep in the background, then list all Markdown files`
+1. `Run python -m pip list in the background and find all Python files in this directory`
+2. `Run npm --prefix web install (use run_in_background) and while waiting, read web/package.json`
+3. `Run python -c "import time; time.sleep(3); print('done')" in the background, then list all Markdown files`
 
 What to observe: After explicitly setting `run_in_background`, is the command dispatched to the background? Is a `bg_id` returned? Are completed results collected in `<task_notification>` format on a later turn?
 

s11_background_tasks/README.zh.md

@@ -78,7 +78,7 @@ class BackgroundManager:
             self._ready.append(task_id)
 ```
 
-命令以非零状态退出或 worker 抛出异常时，任务会进入 `failed`。Shell 会在独立的进程组中启动；命令完成、超时，或 Agent 经正常路径、`SIGTERM` 退出时，运行时会停止原进程组。这只是生命周期清理，并不是沙箱；另建 session 的进程仍可能离开该进程组。
+命令以非零状态退出或 worker 抛出异常时，任务会进入 `failed`。在 POSIX 上，Shell 会在独立的进程组中启动；命令完成、超时，或 Agent 经正常路径、`SIGTERM` 退出时，运行时会停止原进程组。Windows 没有 POSIX 进程组信号，因此运行时会对仍在运行的 Shell 进程调用 `Popen.terminate()` 和 `Popen.kill()`。这只是生命周期清理，并不是沙箱；脱离受管 Shell 或另建 session 的进程仍可能存活。
 
 ### collect_background_results: 通知收集
 
@@ -160,9 +160,9 @@ python s11_background_tasks/code.py
 
 试试这些 prompt：
 
-1. `Run pip list in the background and find all Python files in this directory`
-2. `Run npm install (use run_in_background) and while waiting, read package.json`
-3. `Run a short sleep in the background, then list all Markdown files`
+1. `Run python -m pip list in the background and find all Python files in this directory`
+2. `Run npm --prefix web install (use run_in_background) and while waiting, read web/package.json`
+3. `Run python -c "import time; time.sleep(3); print('done')" in the background, then list all Markdown files`
 
 观察重点：显式设置 `run_in_background` 后，命令有没有被送到后台？`bg_id` 是否返回？后续轮次有没有以 `<task_notification>` 格式收集完成结果？
 

s11_background_tasks/code.py

@@ -44,7 +44,13 @@
 
 SYSTEM = (
     f"You are a coding agent at {WORKDIR}. Use tools to solve tasks. "
-    "Set run_in_background to true only for independent Bash commands."
+    "Set run_in_background to true only for independent shell commands."
+    + (
+        " On Windows, the bash tool uses cmd.exe; use cmd-compatible or "
+        "cross-platform commands."
+        if os.name == "nt"
+        else ""
+    )
 )
 
 
@@ -56,6 +62,23 @@
 
 def _stop_process_group(process: subprocess.Popen):
     """Stop processes that remain in the command's original process group."""
+    if os.name == "nt":
+        # Windows has no os.killpg or SIGKILL. Use Popen's native methods
+        # without changing the background-task protocol demonstrated here.
+        if process.poll() is not None:
+            return
+        try:
+            process.terminate()
+            process.wait(timeout=0.2)
+        except subprocess.TimeoutExpired:
+            try:
+                process.kill()
+            except OSError:
+                pass
+        except OSError:
+            pass
+        return
+
     for sig in (signal.SIGTERM, signal.SIGKILL):
         try:
             os.killpg(process.pid, sig)
@@ -383,15 +406,19 @@ def collect(self) -> list[str]:
 
         notifications = []
         for task_id, task, result in ready:
-            notifications.append(
+            notification = (
                 f"<task_notification>\n"
                 f"  <task_id>{task_id}</task_id>\n"
                 f"  <status>{task['status']}</status>\n"
                 f"  <command>{task['command']}</command>\n"
                 f"  <summary>{result[:500]}</summary>\n"
                 f"</task_notification>"
             )
-            print(f"  [background] collected {task_id}: {task['status']}")
+            notifications.append(notification)
+            print(
+                f"  [background] collected {task_id} "
+                f"as <task_notification>: {task['status']}"
+            )
         return notifications
 
 

tests/test_background_tasks.py

@@ -1,8 +1,10 @@
 import copy
 import importlib.util
 import os
+import subprocess
 import sys
 import tempfile
+import threading
 import time
 import types
 from pathlib import Path
@@ -63,6 +65,50 @@ def wait_until(predicate, timeout: float = 2.0) -> bool:
     return False
 
 
+def test_windows_process_cleanup_avoids_posix_only_signals():
+    with tempfile.TemporaryDirectory() as tmp:
+        lesson = load_lesson(Path(tmp))
+        calls = []
+
+        class RunningProcess:
+            def poll(self):
+                return None
+
+            def terminate(self):
+                calls.append("terminate")
+
+            def wait(self, timeout):
+                calls.append(("wait", timeout))
+                return 0
+
+            def kill(self):
+                calls.append("kill")
+
+        original_os_name = lesson.os.name
+        try:
+            lesson.os.name = "nt"
+            lesson._stop_process_group(RunningProcess())
+        finally:
+            lesson.os.name = original_os_name
+
+        assert calls == ["terminate", ("wait", 0.2)]
+
+        calls.clear()
+
+        class StubbornProcess(RunningProcess):
+            def wait(self, timeout):
+                calls.append(("wait", timeout))
+                raise subprocess.TimeoutExpired("test", timeout)
+
+        try:
+            lesson.os.name = "nt"
+            lesson._stop_process_group(StubbornProcess())
+        finally:
+            lesson.os.name = original_os_name
+
+        assert calls == ["terminate", ("wait", 0.2), "kill"]
+
+
 def test_s11_keeps_the_s04_kernel_and_adds_one_bash_option():
     with tempfile.TemporaryDirectory() as tmp:
         lesson = load_lesson(Path(tmp))
@@ -122,12 +168,30 @@ def test_background_bash_passes_permission_before_dispatch():
 def test_completed_result_is_collected_once_before_a_later_llm_call():
     with tempfile.TemporaryDirectory() as tmp:
         lesson = load_lesson(Path(tmp))
+        worker_started = threading.Event()
+        release_worker = threading.Event()
+
+        def controlled_command(command):
+            assert command == "controlled command"
+            worker_started.set()
+            assert release_worker.wait(timeout=2)
+            return "ready", 0
+
+        lesson._run_bash_process = controlled_command
         block = types.SimpleNamespace(
             id="tool_ready",
             name="bash",
-            input={"command": "printf ready", "run_in_background": True},
+            input={"command": "controlled command", "run_in_background": True},
         )
-        task_id = lesson.start_background_task(block)
+        start_result = lesson.execute_tool(block)
+        task_id = next(iter(lesson.background_tasks))
+
+        assert worker_started.wait(timeout=2)
+        assert task_id == "bg_0001"
+        assert task_id in start_result
+        assert lesson.background_tasks[task_id]["status"] == "running"
+
+        release_worker.set()
         assert wait_until(
             lambda: lesson.background_tasks[task_id]["status"] == "completed"
         )