fix(cron): prevent recurring job re-fire on gateway crash/restart loop (#3396)

When a gateway crashes mid-job execution (before mark_job_run can persist
the updated next_run_at), the job would fire again on every restart attempt
within the grace window. For a daily 6:15 AM job with a 2-hour grace,
rapidly restarting the gateway could trigger dozens of duplicate runs.

Fix: call advance_next_run() BEFORE run_job() in tick(). For recurring
jobs (cron/interval), this preemptively advances next_run_at to the next
future occurrence and persists it to disk. If the process then crashes
during execution, the job won't be considered due on restart.

One-shot jobs are left unchanged — they still retry on restart since
there's no future occurrence to advance to.

This changes the scheduler from at-least-once to at-most-once semantics
for recurring jobs, which is the correct tradeoff: missing one daily
message is far better than sending it dozens of times.

cron/scheduler.py

@@ -35,7 +35,7 @@ logger = logging.getLogger(__name__)
 # Add parent directory to path for imports
 sys.path.insert(0, str(Path(__file__).parent.parent))
 
-from cron.jobs import get_due_jobs, mark_job_run, save_job_output
+from cron.jobs import get_due_jobs, mark_job_run, save_job_output, advance_next_run
 
 # Sentinel: when a cron agent has nothing new to report, it can start its
 # response with this marker to suppress delivery.  Output is still saved
@@ -524,6 +524,12 @@ def tick(verbose: bool = True) -> int:
         executed = 0
         for job in due_jobs:
             try:
+                # For recurring jobs (cron/interval), advance next_run_at to the
+                # next future occurrence BEFORE execution.  This way, if the
+                # process crashes mid-run, the job won't re-fire on restart.
+                # One-shot jobs are left alone so they can retry on restart.
+                advance_next_run(job["id"])
+
                 success, output, final_response, error = run_job(job)
 
                 output_file = save_job_output(job["id"], output)