Idempotency and retries

Distinguish requests, provider tasks and internal money actions.

Persist keys for interfaces that support media/compliance/order idempotency. The same key and canonical payload repeat the same operation; changes in identity, model/profile, quantity, amount, rate contract or operation must conflict.

Initial ordinary text support does not promise response replay or exactly-once execution. SDK POST must not blindly retry. X-Request-ID is transport correlation, X-Acosmi-Request-Id is consumption correlation, and the provider task ID is a separate domain.

Settlement, release and reversal have separate internal financial idempotency domains. Late usage and authorized refunds append under their original mode contracts; cancelled/settled states do not erase real measurement. Query an unknown result before repeating execution.