Standardized Idempotency-Key documentation on idempotent endpoints

⚠️
Deprecation Warning
In the future, 128 character Idempotency-Key values will be deprecated in favor of 36 character UUIDs. Please preemptively migrate your keys to either UUIDv7 or UUIDv4, or any other <=36 character string.

The Idempotency-Key header is now described consistently across every idempotent operation in the Broker and Trading APIs. The accepted contract is unchanged: the header remains optional and still accepts keys up to 128 characters.

Each endpoint documents the same guidance: generate a unique UUIDv7 or UUIDv4 value (36 characters including hyphens) per logical operation, and do not reuse a key across operations.
Alpaca is moving toward a 36-character maximum for Idempotency-Key; new integrations should size keys accordingly.
Idempotent replay behavior is described on the operation itself: the same key with an identical request returns the original result, and the same key with a different request returns 422 Unprocessable Entity.

Broker API

POST /v1/journals
POST /v1/journals/batch
POST /v1/instant_funding
POST /v1/accounts/{account_id}/tokenization/mint
POST /v1/accounts/{account_id}/tokenization/callback/redeem

Trading API

POST /v1/locates
POST /v2/tokenization/mint