fix(gateway): handle Windows stop fallback

tests/gateway/test_runtime.py

@@ -1,4 +1,6 @@
 import json
+import signal
+import subprocess
 from pathlib import Path
 
 from nanobot.gateway import GatewayRuntime, GatewayRuntimePaths, GatewayStartOptions
@@ -168,3 +170,42 @@ def test_stop_keeps_state_when_process_survives_timeout(tmp_path, monkeypatch):
     assert result.status.running is True
     assert result.status.reason == "stop_timeout"
     assert runtime.paths.state_path.exists()
+
+
+def test_terminate_windows_falls_back_when_ctrl_break_is_rejected(tmp_path, monkeypatch):
+    taskkill_calls: list[dict] = []
+
+    def fake_run(command, **kwargs):
+        taskkill_calls.append({"command": command, "kwargs": kwargs})
+
+    runtime = GatewayRuntime(
+        paths=_paths(tmp_path),
+        platform_name="Windows",
+        subprocess_run=fake_run,
+        sleep=lambda _seconds: None,
+    )
+
+    monkeypatch.setattr(signal, "CTRL_BREAK_EVENT", 1, raising=False)
+
+    def fake_kill(_pid, _signal):
+        raise OSError(87, "The parameter is incorrect")
+
+    monkeypatch.setattr("nanobot.gateway.runtime.os.kill", fake_kill)
+
+    def fake_wait_for_exit(_pid, _timeout_s):
+        # Simulate a process that only exits after the taskkill fallback runs.
+        return bool(taskkill_calls)
+
+    monkeypatch.setattr(runtime, "_wait_for_exit", fake_wait_for_exit)
+
+    assert runtime._terminate_windows(12345, timeout_s=20) is True
+    assert taskkill_calls == [
+        {
+            "command": ["taskkill", "/PID", "12345", "/T"],
+            "kwargs": {
+                "check": False,
+                "stdout": subprocess.DEVNULL,
+                "stderr": subprocess.DEVNULL,
+            },
+        }
+    ]