TimestampMixin was setting default=datetime.now(UTC) — calling the
function once at module import time. Every INSERT (and every UPDATE
via onupdate) since the app last restarted got stamped with the same
process-start timestamp, silently breaking created_at / updated_at on
every table that uses the mixin (customers, stores, cards, users,
orders, etc.).
Pass the _utc_now callable instead so SQLAlchemy invokes it per row.
Forward fix only — historical rows on prod since the most recent app
restart all read as the start-time microsecond and will need a
separate decision on whether to backfill.
Found while debugging why a customer + their loyalty card had
microsecond-identical created_at timestamps despite being created
through separate service calls.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Samir Boulahtit
bdb613581c