fix(cron): missing field init, unnecessary save, and shutdown cleanup

1. Add missing `last_delivery_error` field initialization in `create_job()`.
   `mark_job_run()` sets this field on line 596 but it was never initialized,
   causing inconsistent job schemas between new and executed jobs.

2. Replace unnecessary `save_jobs()` call with a warning log when
   `mark_job_run()` is called with a non-existent job_id. Previously the
   function would silently write unchanged data to disk.

3. Add `cancel_futures=True` to the `finally` block in cron scheduler's
   thread pool shutdown. The `except` path already passes this flag but
   the normal exit path did not, leaving futures running after inactivity
   timeout detection.

cron/jobs.py

@@ -452,6 +452,7 @@ def create_job(
         "last_run_at": None,
         "last_status": None,
         "last_error": None,
+        "last_delivery_error": None,
         # Delivery configuration
         "deliver": deliver,
         "origin": origin,  # Tracks where job was created for "origin" delivery
@@ -620,8 +621,8 @@ def mark_job_run(job_id: str, success: bool, error: Optional[str] = None,
 
             save_jobs(jobs)
             return
-    
-    save_jobs(jobs)
+
+    logger.warning("mark_job_run: job_id %s not found, skipping save", job_id)
 
 
 def advance_next_run(job_id: str) -> bool:

cron/scheduler.py

@@ -769,7 +769,7 @@ def run_job(job: dict) -> tuple[bool, str, str, Optional[str]]:
             _cron_pool.shutdown(wait=False, cancel_futures=True)
             raise
         finally:
-            _cron_pool.shutdown(wait=False)
+            _cron_pool.shutdown(wait=False, cancel_futures=True)
 
         if _inactivity_timeout:
             # Build diagnostic summary from the agent's activity tracker.