fix(gateway): probe Windows clients safely

nanobot/gateway/runtime.py

@@ -26,6 +26,7 @@ from nanobot.process_runtime import (
     ProcessRuntimePaths,
     ProcessStartOptions,
     ProcessStatus,
+    process_is_running,
 )
 
 GatewayStartOptions = ProcessStartOptions
@@ -374,7 +375,7 @@ class GatewayClientLease:
 
     def _process_is_running(self, pid: int) -> bool:
         checker = getattr(self.runtime, "process_is_running", None)
-        return bool(checker(pid)) if callable(checker) else _pid_is_running(pid)
+        return bool(checker(pid)) if callable(checker) else process_is_running(pid)
 
     @staticmethod
     def _clients(state: dict[str, object]) -> dict[str, object]:
@@ -442,17 +443,3 @@ def _instance_suffix(*, workspace: str | None, config_path: str | None) -> str |
     if not raw:
         return None
     return hashlib.sha1(raw.encode("utf-8")).hexdigest()[:16]
-
-
-def _pid_is_running(pid: int) -> bool:
-    if pid <= 0:
-        return False
-    try:
-        os.kill(pid, 0)
-    except ProcessLookupError:
-        return False
-    except PermissionError:
-        return True
-    except OSError:
-        return False
-    return True

nanobot/process_runtime.py

@@ -356,17 +356,7 @@ class ManagedProcessRuntime(Generic[_StartOptionsT]):
                     return poll() is None
                 except OSError:
                     pass
-        if self.platform_name == "Windows":
-            return _windows_process_identity(pid) is not None
-        try:
-            os.kill(pid, 0)
-        except ProcessLookupError:
-            return False
-        except PermissionError:
-            return True
-        except OSError:
-            return False
-        return True
+        return process_is_running(pid, platform_name=self.platform_name)
 
     def _process_identity(self, pid: int) -> str | int | None:
         if self.platform_name == "Windows":
@@ -455,6 +445,25 @@ def _platform_name() -> str:
     return "Linux"
 
 
+def process_is_running(pid: int, *, platform_name: str | None = None) -> bool:
+    """Probe a PID without delivering a control event on Windows."""
+    if pid <= 0:
+        return False
+    if (platform_name or _platform_name()) == "Windows":
+        # On Windows ``os.kill(pid, 0)`` sends CTRL_C_EVENT (whose value is 0)
+        # instead of performing the harmless POSIX existence probe.
+        return _windows_process_identity(pid) is not None
+    try:
+        os.kill(pid, 0)
+    except ProcessLookupError:
+        return False
+    except PermissionError:
+        return True
+    except OSError:
+        return False
+    return True
+
+
 def _utc_now() -> str:
     return datetime.now(UTC).isoformat().replace("+00:00", "Z")
 

tests/gateway/test_runtime.py

@@ -18,6 +18,7 @@ from nanobot.gateway import (
     GatewayStatus,
 )
 from nanobot.gateway.runtime import monitor_gateway_clients
+from nanobot.process_runtime import process_is_running
 
 
 class FakeProcess:
@@ -436,6 +437,20 @@ def test_start_background_uses_windows_process_group_flags(tmp_path, monkeypatch
     assert "start_new_session" not in calls[0]["kwargs"]
 
 
+def test_windows_process_probe_never_sends_ctrl_c(monkeypatch):
+    monkeypatch.setattr(
+        "nanobot.process_runtime._windows_process_identity",
+        lambda pid: "created-at" if pid == 12345 else None,
+    )
+    monkeypatch.setattr(
+        "nanobot.process_runtime.os.kill",
+        lambda *_args: pytest.fail("Windows process probes must not call os.kill(pid, 0)"),
+    )
+
+    assert process_is_running(12345, platform_name="Windows") is True
+    assert process_is_running(54321, platform_name="Windows") is False
+
+
 def test_status_clears_stale_state(tmp_path, monkeypatch):
     runtime = GatewayRuntime(paths=_paths(tmp_path), platform_name="Linux")
     runtime.paths.run_dir.mkdir(parents=True)