Improve Idempotency & Concurrency

Goal

Correct the selected duplicate or concurrent operation so final state and effects satisfy the intended contract.

Domain rules

• Enforce uniqueness/versioning at the authoritative boundary and return the prior result or stable terminal status for duplicates.
• Use fencing/version checks for leased work and reject stale completion.
• Keep critical sections small and avoid lock-based coordination when a store-level atomic operation fits existing architecture.
• Synchronize retries, acknowledgements, status, cleanup, metrics, and tests with the concurrency contract.

Validation

• Run deterministic concurrent/duplicate/crash/timeout/stale-worker tests and repository race detectors where available.
• Verify side-effect count, final state/version, lock/lease cleanup, and duplicate response.
• List distributed timing or multi-node gates not exercised.

Use controlled barriers to reproduce the conflicting read/write or ambiguous effect before changing the owning constraint, transaction, version or operation key. Replay the same interleaving with a normal control and inspect final state, effect count and duplicate result separately. Recheck failed ownership/effect criteria after correction and finish Patch Checking. Local fencing must not be presented as an external atomicity guarantee it cannot enforce.