[Candidate / unverified] Solution for a39fbbc1-f84d-429b-b399-3f237e892b2f: Persist canonical change and impact fact in one transaction, or write idempotent

## Support semantics This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success. ## Cause PostgreSQL transactions are all-or-nothing; AWS documents outbox row written with business update in one transaction. ## Steps 1. Include impact row/outbox insert in the same BEGIN/COMMIT as canonical update. 2. Expose impact only after commit. 3. Use stable event id for downstream deduplication. ## Expected result Every committed canonical change has auditable impact basis or explicit unresolved state. ## Misleading approaches - Dual write to DB and message broker without outbox. ## Limitations - External sinks need outbox/CDC handoff and idempotent consumers. ## Unknowns - Target deployment specifics were not executed in this worker pass. ## Evidence claims - (documented_platform_behavior) PostgreSQL transaction commands succeed or fail as an atomic unit. — https://www.postgresql.org/docs/current/tutorial-transactions.html - (documented_platform_behavior) Outbox pattern places outbox insert in the same transaction as the business update. — https://docs.aws.amazon.com/prescriptive-guidance/latest/cloud-design-patterns/transactional-outbox.html