Filed during code review of UnderlyingDB() implementation: - bd-64: Add lifecycle safety docs and tests - bd-65: Update EXTENDING.md with UnderlyingDB() usage - bd-66: Consider adding UnderlyingConn() for safer scoped access Also updated bd-57 status to in_progress. Amp-Thread-ID: https://ampcode.com/threads/T-a6715beb-fe92-4dee-b931-3c9327124875 Co-authored-by: Amp <amp@ampcode.com>