test(gateway): isolate lifecycle lock behavior

.github/workflows/ci.yml

@@ -96,9 +96,9 @@ jobs:
             os: windows-latest
             python-version: "3.14"
             coverage: false
-            # Process lifecycle tests run serially below. Keep them out of
-            # xdist so workers never share Windows console or process state.
-            pytest_args: "-n 2 --dist loadfile --ignore=tests/gateway/test_runtime.py --ignore=tests/tools/test_exec_platform.py"
+            # Real PowerShell/process-tree tests run serially below. Keep
+            # them out of xdist so workers never share a Windows console.
+            pytest_args: "-n 2 --dist loadfile --ignore=tests/tools/test_exec_platform.py"
 
     steps:
       - uses: actions/checkout@v4
@@ -148,11 +148,10 @@ jobs:
           ${{ matrix.pytest_args }}
           --durations=25 --durations-min=1.0
 
-      - name: Run Windows lifecycle compatibility tests
+      - name: Run Windows process compatibility tests
         if: runner.os == 'Windows'
         run: >-
           uv run --no-sync python -m pytest
-          tests/gateway/test_runtime.py
           tests/tools/test_exec_platform.py
           --durations=25 --durations-min=1.0
 

tests/gateway/test_runtime.py

@@ -206,6 +206,7 @@ def test_stop_reaps_an_owned_child_without_consuming_the_shutdown_timeout(
 def test_concurrent_background_starts_create_only_one_process(tmp_path, monkeypatch):
     first_spawned = threading.Event()
     release_first = threading.Event()
+    lifecycle_lock = threading.Lock()
     calls: list[list[str]] = []
 
     def fake_popen(command, **_kwargs):
@@ -231,6 +232,10 @@ def test_concurrent_background_starts_create_only_one_process(tmp_path, monkeypa
     for runtime in (first, second):
         monkeypatch.setattr(runtime, "_is_pid_running", lambda _pid: True)
         monkeypatch.setattr(runtime, "_process_identity", lambda _pid: 12345)
+        # Exercise the runtime's critical section without mixing an OS-level
+        # file lock into a same-process thread scheduling test. FileLock is
+        # independently responsible for cross-process portability.
+        monkeypatch.setattr(runtime, "_lifecycle_lock", lambda: lifecycle_lock)
 
     results = []
     first_thread = threading.Thread(