fix(cron): treat empty agent response as error in last_status (fixes #8585)

When a cron job's agent run completes but produces an empty final_response
(e.g. API 404 from invalid model name), the scheduler now marks last_status
as "error" instead of "ok", so the failure is visible in job listings.

Previously, any run that didn't raise an exception was marked "ok" regardless
of whether the agent actually produced output.

cron/scheduler.py

@@ -979,6 +979,13 @@ def tick(verbose: bool = True, adapters=None, loop=None) -> int:
                         delivery_error = str(de)
                         logger.error("Delivery failed for job %s: %s", job["id"], de)
 
+                # Treat empty final_response as a soft failure so last_status
+                # is not "ok" — the agent ran but produced nothing useful.
+                # (issue #8585)
+                if success and not final_response:
+                    success = False
+                    error = "Agent completed but produced empty response (model error, timeout, or misconfiguration)"
+
                 mark_job_run(job["id"], success, error, delivery_error=delivery_error)
                 executed += 1