[lesnik512]

The README's CreateChatUseCase holds one Transaction and one Inbox per request, as modern-di wires them, so every postgres_retry attempt reuses the same session. The existing db-retry tests open a new session per attempt, so this shape wasn't covered.

Two tests run a copy of the example against PostgreSQL:

• Retry on the same session. The first attempt claims, writes, then hits a real SerializationError (SQLSTATE 40001, raised with RAISE ... USING ERRCODE). The retry goes through the same Transaction and commits one marker and one business row. With DB_RETRY_RETRIES_NUMBER=1 the test fails, so it passes only because of the retry.
• Duplicate early return. The same use case processes m-1, then m-1 again (it returns from inside the transaction without committing), then m-2. The duplicate does nothing, the session ends outside a transaction, and m-2 commits normally.

Both passed on the first run, so the README stays as it is.