refactor(ai): remove Windows patch alias — gate calls apply_thread_isolation() directly

_patch_conductor_use_threads_on_windows was a private, single-caller
delegating alias after the shim moved to worker_isolation; Windows and
CONDUCTOR_WORKER_ISOLATION=thread now share one visible entry point.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: Kowser

CHANGELOG.md

@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Worker isolation mode: `CONDUCTOR_WORKER_ISOLATION=thread` runs every worker as a thread instead of a `multiprocessing.Process` (default `process` is unchanged — `spawn` remains the start method). For environments where multiprocessing's fork+exec bootstraps (spawn children, `resource_tracker`) fail, e.g. Firecracker microVM guests. Thread-mode tradeoffs: no per-worker force-kill (shutdown is cooperative), CPU-bound workers share the GIL, and `signal.signal` becomes a no-op off the main thread. Implementation: the Windows-only Process→Thread shim moved to `conductor.client.automator.worker_isolation` (the old `worker_manager._patch_conductor_use_threads_on_windows` remains as a delegating alias) and now also swaps the logging-relay `Queue` for a plain `queue.Queue`
+- Worker isolation mode: `CONDUCTOR_WORKER_ISOLATION=thread` runs every worker as a thread instead of a `multiprocessing.Process` (default `process` is unchanged — `spawn` remains the start method). For environments where multiprocessing's fork+exec bootstraps (spawn children, `resource_tracker`) fail, e.g. Firecracker microVM guests. Thread-mode tradeoffs: no per-worker force-kill (shutdown is cooperative), CPU-bound workers share the GIL, and `signal.signal` becomes a no-op off the main thread. Implementation: the Windows-only Process→Thread shim moved to `conductor.client.automator.worker_isolation` (the private `worker_manager._patch_conductor_use_threads_on_windows` helper is removed — the Windows gate calls `apply_thread_isolation()` directly) and now also swaps the logging-relay `Queue` for a plain `queue.Queue`
 
 - Canonical metrics mode: opt-in harmonized metric surface via `WORKER_CANONICAL_METRICS=true` -- [details](METRICS.md#detailed-technical-notes--unreleased)
 - `MetricsSettings` gains `clean_directory` and `clean_dead_pids` for opt-in stale `.db` file cleanup (both default to `False`)

src/conductor/ai/agents/runtime/worker_manager.py

@@ -21,17 +21,6 @@
 logger = logging.getLogger("conductor.ai.agents.worker_manager")
 
 
-def _patch_conductor_use_threads_on_windows() -> None:
-    """Deprecated alias — kept for existing callers.
-
-    The Process->Thread shim (plus the Queue->queue.Queue half it was
-    missing) now lives in :mod:`conductor.client.automator.worker_isolation`
-    and is also activated by ``CONDUCTOR_WORKER_ISOLATION=thread``, read by
-    :class:`TaskHandler` itself. See :func:`apply_thread_isolation`.
-    """
-    apply_thread_isolation()
-
-
 if TYPE_CHECKING:
     from conductor.client.automator.task_handler import TaskHandler
     from conductor.client.configuration.configuration import Configuration
@@ -89,8 +78,11 @@ def start(self) -> None:
         """
         from conductor.client.automator.task_handler import TaskHandler
 
+        # Windows always needs thread isolation (spawn-pickling of worker
+        # closures fails there); other environments opt in via
+        # CONDUCTOR_WORKER_ISOLATION=thread, read by TaskHandler itself.
         if platform.system() == "Windows":
-            _patch_conductor_use_threads_on_windows()
+            apply_thread_isolation()
 
         with self._lock:
             if self._task_handler is None:

tests/unit/ai/test_worker_manager.py

@@ -358,32 +358,37 @@ def test_filter_installed_on_conductor_logger(self):
             conductor_logger.removeFilter(f)
 
 
-class TestThreadPatchAlias:
-    """The Windows patch entry point now delegates to worker_isolation."""
-
-    def test_alias_delegates_to_apply_thread_isolation(self):
-        import conductor.ai.agents.runtime.worker_manager as wm
+class TestWindowsThreadIsolation:
+    """On Windows the gate applies thread isolation via worker_isolation directly."""
 
+    def test_windows_gate_applies_thread_isolation(self):
+        config = MagicMock()
+        manager = WorkerManager(configuration=config)
         with patch(
+            "conductor.ai.agents.runtime.worker_manager.platform.system",
+            return_value="Windows",
+        ), patch(
             "conductor.ai.agents.runtime.worker_manager.apply_thread_isolation"
-        ) as mock_apply:
-            wm._patch_conductor_use_threads_on_windows()
+        ) as mock_apply, patch(
+            "conductor.client.automator.task_handler.TaskHandler"
+        ) as mock_th:
+            mock_th.return_value.task_runner_processes = []
+            mock_th.return_value.metrics_provider_process = None
+            manager.start()
         mock_apply.assert_called_once_with()
 
-    def test_windows_gate_calls_the_alias(self):
-        import conductor.ai.agents.runtime.worker_manager as wm
-
+    def test_non_windows_gate_does_not_apply(self):
         config = MagicMock()
         manager = WorkerManager(configuration=config)
         with patch(
             "conductor.ai.agents.runtime.worker_manager.platform.system",
-            return_value="Windows",
+            return_value="Linux",
         ), patch(
-            "conductor.ai.agents.runtime.worker_manager._patch_conductor_use_threads_on_windows"
-        ) as mock_patch, patch(
+            "conductor.ai.agents.runtime.worker_manager.apply_thread_isolation"
+        ) as mock_apply, patch(
             "conductor.client.automator.task_handler.TaskHandler"
         ) as mock_th:
             mock_th.return_value.task_runner_processes = []
             mock_th.return_value.metrics_provider_process = None
             manager.start()
-        mock_patch.assert_called_once_with()
+        mock_apply.assert_not_called()