Root cause: calculateForAdoption uses separate DB connections, which
cannot see uncommitted data in Serializable isolation level, causing
"Adoption not found" errors.
Solution (following Kafka Idempotent Consumer best practice):
- Add TransactionalCDCHandlerWithResult<T> type for handlers with return
- Add withIdempotencyAndCallback() wrapper for post-commit callbacks
- Add registerTransactionalHandlerWithCallback() registration method
- AdoptionSyncedHandler.handle() now returns AdoptionSyncResult
- Contribution calculation runs AFTER transaction commits via callback
Reference: Lydtech Consulting - Kafka Idempotent Consumer Pattern
https://www.lydtechconsulting.com/blog/kafka-idempotent-consumer-transactional-outbox
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
