test(ci): isolate Windows process checks

.github/workflows/ci.yml

@@ -96,10 +96,11 @@ jobs:
             os: windows-latest
             python-version: "3.14"
             coverage: false
-            # Keep each test file in one worker while using both hosted-runner cores.
-            # Keep test names visible until a Windows-only control-event
-            # interruption can be attributed to its active worker/file.
-            pytest_args: "-n 2 --dist loadfile -vv"
+            # Real PowerShell/process-tree tests share the hosted runner's
+            # Windows console. Separate xdist workers can therefore deliver a
+            # control event across worker boundaries; run this compatibility
+            # matrix serially, as nanobot itself does in one client process.
+            pytest_args: "--full-trace"
 
     steps:
       - uses: actions/checkout@v4

tests/tools/test_exec_platform.py

@@ -896,6 +896,7 @@ class TestWindowsRealExec:
     @pytest.mark.asyncio
     async def test_windows_powershell_session_output_is_utf8(self):
         manager = ExecSessionManager()
+        try:
             result = await ExecTool(timeout=180, session_manager=manager).execute(
                 command="Start-Sleep -Milliseconds 1500; Write-Output 'café λ 你好'",
                 shell="powershell",
@@ -923,3 +924,5 @@ class TestWindowsRealExec:
             assert "café λ 你好" in result
             assert "Exit code: 0" in result
             assert "\x00" not in result
+        finally:
+            await manager.close_all()