Implements 100% exactly-once semantics for CDC events from 1.0 databases
(identity-service, planting-service, referral-service) to contribution-service.
Key changes:
- Add ProcessedCdcEvent model with (sourceTopic, offset) unique constraint
- Add withIdempotency() wrapper using Serializable transaction isolation
- Add registerTransactionalHandler() for handlers requiring idempotency
- Modify CDC handlers to accept external transaction client
- All database operations now use the passed transaction client
This ensures that:
1. Each CDC event is processed exactly once
2. Idempotency record and business logic are in the same transaction
3. Any failure causes complete rollback
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
hailin
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