Root cause: embedding generation could break the DB transaction via a failed
SQL statement. The except block caught the Python error but left the transaction
in a failed state. Subsequent queries (_record_usage → subscription lookup)
then failed with InFailedSQLTransactionError.
Fixes:
- session_embedding_service: use begin_nested() savepoint so failures don't
poison the parent transaction
- ai_sessions.py: add db.rollback() before _record_usage in all 3 error
handlers (create, respond, pickup) to recover from broken transactions
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
chihlasm
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