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>
Adds vector-based similar session discovery using the existing Voyage AI
embedding infrastructure and pgvector cosine similarity search.
- New AISessionEmbedding model with vector(1024) column
- session_embedding_service: generate + upsert embeddings, find similar sessions
- Embeddings generated on session create (from problem_summary/domain) and
updated on resolve (adds resolution_summary)
- GET /ai-sessions/{id}/similar endpoint returns top-N similar sessions
- Migration a7c9e3b1f402 creates ai_session_embeddings table
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
