fix(cron): terminal-worker reaper lives in scheduler_detached_worker, not the scheduler facade

cron/scheduler.py is already past the facade line-count gate; the reap helper is a detached-worker teardown concern with an existing topical home. The waiter late-imports it so behaviour and the sync run_one_job contract are unchanged.

cron/scheduler.py

@@ -3096,23 +3096,6 @@ def _run_one_job_body(
             reset_terminal_scope(_terminal_scope_token)
 
 
-def _reap_terminal_worker_in_background(process: subprocess.Popen) -> None:
-    """Keep the reap contract when the waiter returns before the worker exits.
-
-    The ledger turning terminal lets the waiter return while the worker is
-    still in final teardown. The gateway remains the worker's parent, so if
-    nobody calls ``wait()`` afterwards the worker lingers as a zombie (STAT=Z)
-    under the gateway until it is restarted (#114509). A short-lived daemon
-    thread holds that single responsibility and ends with the process exit
-    it waits for.
-    """
-    threading.Thread(
-        target=process.wait,
-        name=f"cron-worker-reap-{getattr(process, 'pid', '?')}",
-        daemon=True,
-    ).start()
-
-
 def _wait_for_external_cron_worker_body(
     process: subprocess.Popen,
     *,
@@ -3139,7 +3122,9 @@ def _wait_for_external_cron_worker_body(
             returncode = process.wait(timeout=1.0)
         except subprocess.TimeoutExpired:
             if _is_terminal():
-                _reap_terminal_worker_in_background(process)
+                from cron.scheduler_detached_worker import reap_terminal_worker_in_background
+
+                reap_terminal_worker_in_background(process)
                 return True
             continue
         # The worker can commit its terminal row and exit between the first

cron/scheduler_detached_worker.py

@@ -9,6 +9,8 @@ overlap behind #102827. The worker's Future owns the teardown instead.
 from __future__ import annotations
 
 import concurrent.futures
+import subprocess
+import threading
 from typing import Optional
 
 
@@ -32,3 +34,20 @@ def defer_teardown_to_running_worker(
     # Runs inline if the worker finished between done() and here — still exactly once.
     future.add_done_callback(_finish)
     return True
+
+
+def reap_terminal_worker_in_background(process: subprocess.Popen) -> None:
+    """Keep the reap contract when the waiter returns before the worker exits.
+
+    The ledger turning terminal lets ``_wait_for_external_cron_worker_body``
+    return while the worker is still in final teardown. The gateway remains the
+    worker's parent, so if nobody calls ``wait()`` afterwards the worker lingers
+    as a zombie (STAT=Z) under the gateway until it is restarted (#114509). A
+    short-lived daemon thread holds that single responsibility and ends with
+    the process exit it waits for.
+    """
+    threading.Thread(
+        target=process.wait,
+        name=f"cron-worker-reap-{getattr(process, 'pid', '?')}",
+        daemon=True,
+    ).start()