fix(cron): don't silently disable recurring cron jobs when croniter is missing (#16368)

If the gateway's Python env loses access to 'croniter' between when a
cron job was created and when mark_job_run() fires, compute_next_run()
returns None for cron schedules. mark_job_run() treated that as terminal
completion and wrote enabled=false, state=completed — turning a missing
runtime dep into a silent, permanent job-off.

That behaviour is safe for one-shot jobs but wrong for recurring ones. A
missing dep should surface as an error the user can see, not as successful
completion of a job that is about to stop firing.

mark_job_run() now only disables the job on next_run_at=None when the
schedule is one-shot. For recurring (cron/interval) schedules it keeps
enabled=true, sets state=error, and records last_error so the user can
see why the job isn't advancing. compute_next_run() also logs a warning
the first time cron+no-croniter hits, so the underlying cause is visible
in the gateway log.

Tests cover:
- recurring cron job stays enabled with state=error when HAS_CRONITER=False
- recurring interval stays enabled when compute_next_run returns None
- one-shot jobs still flip to enabled=false, state=completed (no regression)

Fixes #16265

cron/jobs.py

@@ -311,6 +311,12 @@ def compute_next_run(schedule: Dict[str, Any], last_run_at: Optional[str] = None
 
     elif schedule["kind"] == "cron":
         if not HAS_CRONITER:
+            logger.warning(
+                "Cannot compute next run for cron schedule %r: 'croniter' "
+                "is not installed. Install the 'cron' extra (pip install "
+                "'hermes-agent[cron]') to re-enable recurring cron jobs.",
+                schedule.get("expr"),
+            )
             return None
         cron = croniter(schedule["expr"], now)
         next_run = cron.get_next(datetime)
@@ -698,10 +704,32 @@ def mark_job_run(job_id: str, success: bool, error: Optional[str] = None,
                 # Compute next run
                 job["next_run_at"] = compute_next_run(job["schedule"], now)
 
-                # If no next run (one-shot completed), disable
+                # If no next run, decide whether this is terminal completion
+                # (one-shot) or a transient failure (recurring schedule couldn't
+                # compute — e.g. 'croniter' missing from the runtime env).
+                # Recurring jobs must NEVER be silently disabled: that turns a
+                # missing runtime dep into "job completed" and the user's
+                # schedule quietly goes off. See issue #16265.
                 if job["next_run_at"] is None:
-                    job["enabled"] = False
-                    job["state"] = "completed"
+                    kind = job.get("schedule", {}).get("kind")
+                    if kind in ("cron", "interval"):
+                        job["state"] = "error"
+                        if not job.get("last_error"):
+                            job["last_error"] = (
+                                "Failed to compute next run for recurring "
+                                "schedule (is the 'croniter' package "
+                                "installed in the gateway's Python env?)"
+                            )
+                        logger.error(
+                            "Job '%s' (%s) could not compute next_run_at; "
+                            "leaving enabled and marking state=error so the "
+                            "job is not silently disabled.",
+                            job.get("name", job["id"]),
+                            kind,
+                        )
+                    else:
+                        job["enabled"] = False
+                        job["state"] = "completed"
                 elif job.get("state") != "paused":
                     job["state"] = "scheduled"