REG-011 — before (no integration coverage existed; premise: race guard was written but never executed against a real server)
The mocked suite already passed (proves nothing about real server behaviour):
.....................................................................    [100%]
69 passed in 0.52s

Real integration tests did not exist prior to this commit. git status of the new files:
?? tests/test_dynamodb_concurrent_append_race.py
?? tests/test_postgres_concurrent_append_race.py
