diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 571ce3430..0c16b353b 100644
--- a/.github/workflows/ci.yml
+++ b/.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
diff --git a/tests/tools/test_exec_platform.py b/tests/tools/test_exec_platform.py
index 637a3ec60..3162453d3 100644
--- a/tests/tools/test_exec_platform.py
+++ b/tests/tools/test_exec_platform.py
@@ -896,30 +896,33 @@ class TestWindowsRealExec:
     @pytest.mark.asyncio
     async def test_windows_powershell_session_output_is_utf8(self):
         manager = ExecSessionManager()
-        result = await ExecTool(timeout=180, session_manager=manager).execute(
-            command="Start-Sleep -Milliseconds 1500; Write-Output 'café λ 你好'",
-            shell="powershell",
-            yield_time_ms=1000,
-        )
-
-        if "session_id:" in result:
-            session_id = result.split("session_id:", 1)[1].splitlines()[0].strip()
-            poll_result = await WriteStdinTool(manager=manager).execute(
-                session_id=session_id,
-                chars="",
-                wait_for="café λ 你好",
-                wait_timeout_ms=120_000,
+        try:
+            result = await ExecTool(timeout=180, session_manager=manager).execute(
+                command="Start-Sleep -Milliseconds 1500; Write-Output 'café λ 你好'",
+                shell="powershell",
+                yield_time_ms=1000,
             )
-            result += "\n" + poll_result
-            if "Process running." in poll_result:
-                final_result = await WriteStdinTool(manager=manager).execute(
+
+            if "session_id:" in result:
+                session_id = result.split("session_id:", 1)[1].splitlines()[0].strip()
+                poll_result = await WriteStdinTool(manager=manager).execute(
                     session_id=session_id,
                     chars="",
-                    yield_time_ms=30_000,
+                    wait_for="café λ 你好",
+                    wait_timeout_ms=120_000,
                 )
-                result += "\n" + final_result
-                assert "Process running." not in final_result
+                result += "\n" + poll_result
+                if "Process running." in poll_result:
+                    final_result = await WriteStdinTool(manager=manager).execute(
+                        session_id=session_id,
+                        chars="",
+                        yield_time_ms=30_000,
+                    )
+                    result += "\n" + final_result
+                    assert "Process running." not in final_result
 
-        assert "café λ 你好" in result
-        assert "Exit code: 0" in result
-        assert "\x00" not in result
+            assert "café λ 你好" in result
+            assert "Exit code: 0" in result
+            assert "\x00" not in result
+        finally:
+            await manager.close_all()