fix(cron): a due slot skipped as already completed is logged, not silent

The completed-occurrence dedup gate (due scan in _evaluate_due_job and the
fire claim in claim_job_for_fire) consumes the due slot and advances
next_run_at without a run and without a ledger row, so before this change
a skip left zero trace: no log line, no execution, last_status untouched
(#111414 reported exactly that silhouette). The gate now logs a WARNING
naming the job, the skipped instant and the completed execution that
already covers it, from the one seam both gates share.

The reporter's root mechanism — an off-tick run stamping the NEXT
occurrence's identity onto its row, which the dedup later honoured — is
already closed on main (ac10770894, a73b750391, cd685a22e6; 82ae78cc11
ignores such backdated rows), so a stale-stamped row fires normally; only
a genuinely completed slot is skipped, and now says so.

Co-authored-by: holny <holny@foxmail.com>

cron/occurrences.py

@@ -31,7 +31,7 @@ def completed_occurrence(job, instant):
     try:
         with _transaction() as conn:
             rows = conn.execute(
-                "SELECT finished_at, claimed_at FROM executions "
+                "SELECT id, finished_at, claimed_at FROM executions "
                 "WHERE job_id=? AND scheduled_instant=? "
                 "AND status='completed'", (str(job['id']), instant)
             ).fetchall()
@@ -40,6 +40,13 @@ def completed_occurrence(job, instant):
             # Legacy or malformed timestamps remain proof; only positively identified poison
             # rows — completions recorded before their claimed occurrence — are ignored.
             if completed_at is None or datetime.fromisoformat(completed_at) >= earliest_real:
+                # Both dedup gates (due scan and fire claim) consume the slot on True without a
+                # run or a ledger row, so this line is the only trace the skip leaves (#111414).
+                logger.warning(
+                    "Job '%s' (%s): scheduled occurrence %s was already completed by execution "
+                    "%s (finished %s); skipping the due slot without a new run",
+                    job.get("name", job.get("id")), job.get("id"), instant, row["id"],
+                    row["finished_at"] or row["claimed_at"])
                 return True
         return False
     except Exception:

tests/cron/test_scheduled_occurrence.py

@@ -178,3 +178,34 @@ def test_completion_before_occurrence_does_not_prove_slot_completed(tmp_path, mo
     executions.finish_execution(legitimate['id'], success=True)
 
     assert completed_occurrence({'id': 'job'}, slot)
+
+
+def test_completed_occurrence_skip_names_job_slot_and_row(tmp_path, monkeypatch, caplog):
+    """A due slot the dedup gate consumes (already completed, e.g. after a jobs.json rollback)
+    leaves no run and no ledger row, so the skip itself must be logged with the job, the
+    instant and the completed execution (#111414: a consumed slot left zero trace)."""
+    import logging
+    from datetime import timedelta
+
+    from cron import executions, jobs
+    from hermes_time import now
+
+    monkeypatch.setattr(executions, 'EXECUTIONS_FILE', tmp_path / 'executions.db')
+    slot = (now() - timedelta(minutes=2)).isoformat()
+    with jobs.use_cron_store(tmp_path / 'cron'):
+        stored = jobs.create_job(prompt='test', schedule='every 4h')
+        rows = jobs.load_jobs()
+        rows[0]['next_run_at'] = slot
+        jobs.save_jobs(rows)
+        completed = executions.create_execution(stored['id'], source='builtin', scheduled_instant=slot)
+        executions.finish_execution(completed['id'], success=True)
+
+        with caplog.at_level(logging.WARNING, logger='cron.occurrences'):
+            assert jobs.get_due_jobs() == []
+
+        assert jobs.load_jobs()[0]['next_run_at'] != slot
+    skip = [r.getMessage() for r in caplog.records if completed['id'] in r.getMessage()]
+    assert len(skip) == 1, caplog.text
+    assert stored['id'] in skip[0]
+    from cron.occurrences import scheduled_instant
+    assert scheduled_instant(slot) in skip[0]