OPDC API error code

REQUEST_ALREADY_COMPLETED

HTTP status 409

A cancel for a request that already has its outcome. 409. Nothing is undone: a posted document is reversed with a new document, never by a cancel. GET /api/v3/requests/{id} returns the outcome.

The API answers with a problem document (RFC 9457) whose type is https://twinn.engineering/errors/request-already-completed, and with X-Error-Code: REQUEST_ALREADY_COMPLETED. Branch on the code, never on the detail text.

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