- upsert re-checks 'today' after acquiring the connection lock (call
date can go stale while queued across midnight); delete cutoff
clamps to the lock-time date too
- mutation regex now matches INSERT [OR x] INTO completion_events;
test_schema.py's raw-SQL CHECK-constraint helper exempted narrowly
via INSERT-strip, guard file self-scanned
- NOW replaced by _now_stamp() (today 08:00 UTC, computed at call
time); occurred-at test derives its query date from the stamp so it
is midnight-safe
- new rollover-contention test: a lock holder delays A's upsert across
a shifted clock; the in-lock re-check rejects the now-past date