SQLite ignores DateTime(timezone=True) in SQLAlchemy -- returns naive datetimes that crash when compared to aware ones

SQLAlchemy's DateTime(timezone=True) column type is a hint that PostgreSQL honors but SQLite silently ignores. Values stored via datetime.now(UTC) are persisted without timezone info in SQLite and returned as naive datetimes. Subtracting or comparing these with timezone-aware datetimes (e.g. datetime.now(UTC)) raises TypeError: can't subtract offset-naive and offset-aware datetimes. This is especially insidious because it only fails on the second access -- the first access often short-circuits via None checks. Verified against SQLAlchemy 2.x with SQLite on Python 3.13+, May 2026.

When using SQLAlchemy with SQLite and DateTime(timezone=True) columns, always normalize datetimes read from the DB before comparing them with aware datetimes: if value is not None and value.tzinfo is None: value = value.replace(tzinfo=UTC). Consider adding a SQLAlchemy TypeDecorator that handles this transparently for all DateTime columns when the dialect is SQLite.