test(cron): crash-safety tests claim the fire before asserting not-due

advance_next_run alone no longer commits an occurrence — a restart before the
fire claim restores it (#107485). The at-most-once assertions model the real
tick sequence (advance → claim) so they keep guarding the mid-run crash case.

tests/cron/test_cron_timezone_migration_catchup.py

@@ -85,13 +85,15 @@ def test_legacy_utc_offset_next_run_still_fires(temp_home, monkeypatch):
 def test_legacy_offset_catchup_fires_at_most_once(temp_home, monkeypatch):
     """The catch-up run is a single fire: once the scheduler advances the
     job, the legacy instant is gone and a second scan finds nothing due."""
-    from cron.jobs import advance_next_run, get_due_jobs, get_job
+    from cron.jobs import advance_next_run, claim_job_for_fire, get_due_jobs, get_job
 
     monkeypatch.setattr("cron.jobs._hermes_now", lambda: _BRUSSELS_NOW)
     jid = _write_cron_job(_DAILY_0400, _LEGACY_UTC_NEXT_RUN)
 
     assert jid in [j["id"] for j in get_due_jobs()]
     assert advance_next_run(jid) is True
+    # The fire claim is what commits the occurrence; without it a restart restores the slot.
+    assert claim_job_for_fire(jid)
 
     # Re-anchored to tomorrow's occurrence, expressed in the configured zone.
     assert get_job(jid)["next_run_at"] == "2026-09-03T04:00:00+02:00"

tests/cron/test_jobs.py

@@ -860,12 +860,15 @@ class TestAdvanceNextRun:
         due_before = get_due_jobs()
         assert len(due_before) == 1
 
-        # Advance (simulating what tick() does before run_job)
+        # Advance + claim (what tick() does before run_job); the claim is the point after which
+        # side effects may exist, so a restart after it must not re-fire (#3396). A restart
+        # BEFORE the claim restores the occurrence instead (#107485, test_missed_window_catchup).
         advance_next_run(job["id"])
+        assert claim_job_for_fire(job["id"])
 
-        # Now the job should NOT be due (simulates restart after crash)
+        # Now the job should NOT be due (simulates restart after a mid-run crash)
         due_after = get_due_jobs()
-        assert len(due_after) == 0, "Job should not be due after advance_next_run"
+        assert len(due_after) == 0, "Job should not be due after advance + claim"
 
 
 class TestGetDueJobs: