Idempotency

All financial write operations require idempotency protection.

Components

Component	Description
Idempotency-Key	Client-provided unique key (UUID)
Request Hash	SHA-256 of request body
Idempotency Record	Stored mapping of key → response
Original Response	Cached response for duplicate requests
Request Status	IN_PROGRESS, COMPLETED, FAILED

Flow

Concurrent Duplicates

Database unique constraint on idempotency_key prevents race conditions. Second request waits or receives IN_PROGRESS status.