refactor(cron): decompose run_job and _run_one_job_body into phase helpers

run_job 307 -> ~75: _prepare_job_prompt (pre-agent gates, wake gate, injection block),
_CronRunScope (ContextVar/tool-cwd scope with paired enter/exit), _reload_dotenv_and_publish_
delivery_target, _resolve_cron_agent_setup -> _CronAgentSetup (same gate order), _construct_cron_
agent, _FireAudit. _run_one_job_body 338 -> 170: _FireOwnership (fence + ownership check),
_RunDelivery + _save_compose_deliver, _finish_interrupted_run, _finish_completed_run,
_deliver_crash_failure. Source-inspection test repointed to _finish_interrupted_run.

tests/gateway/test_cron_interrupt_notification.py

@@ -251,10 +251,12 @@ class TestDeliveryErrorIsRecordedWhenTheNoticeCannotBeSent:
 
         import cron.scheduler as sched
 
-        src = inspect.getsource(sched._run_one_job_body)
+        body_src = inspect.getsource(sched._run_one_job_body)
+        src = inspect.getsource(sched._finish_interrupted_run)
         assert 'update_job(job["id"], {"last_delivery_error": delivery_error})' in src, (
             "interrupted runs must still persist the delivery failure"
         )
         # The recovery branch hangs off the interrupted-flag short-circuit,
         # not off a second mark_job_run call.
-        assert "if interrupted:" in src and "if delivery_error:" in src
+        assert "_consume_interrupted_flag(" in body_src and "_finish_interrupted_run(" in body_src
+        assert "if delivery_error:" in src and "mark_job_run(" not in src