What

CustomAsyncSession existed for one reason: so the per-test rollback worked. Its close() became a no-op (expunge_all) when the session was bound to a connection — i.e. a test concern leaking into the production data-access module (app/resources/db.py).

This removes it. Test-transaction ownership now lives where it belongs (the db_session fixture), using SQLAlchemy 2.0's native join_transaction_mode="create_savepoint".

Ports modern-python/litestar-sqlalchemy-template#28 to this template.

How

With create_savepoint, each session owns its own savepoint. Advanced-alchemy's auto_commit releases that savepoint while the fixture's outer real transaction survives and is rolled back at the end of each test. This obsoletes both the close() override and the begin_nested() that the old conditional_savepoint default required.

The kwarg is inert in production: it only takes effect when the session is bound to a connection already in a transaction, which production never does (it binds to an engine).

Changes

• app/resources/db.py — delete CustomAsyncSession; create_session returns a plain AsyncSession(..., join_transaction_mode="create_savepoint") (commented to explain the prod-inert rationale).
• tests/conftest.py — drop connection.begin_nested(); the fixture's session takes the same mode.
• CLAUDE.md — update the Database-layer and Tests notes that documented CustomAsyncSession/expunge_all/the nested savepoint.

Verification

• just test → 19 passed, 100% coverage.
• just lint (ruff format / ruff check / ty check) clean.

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