Polling / status endpoint: returns the current state of a reserve funding request by its externalRequestId — status (Pending / Approved / Rejected) plus, for a completed decision, the processingResult (Approved) or the rejection comment (Rejected). This is the authoritative reconciliation path complementing the best-effort decision callback. Unknown externalRequestId returns HTTP 404. Requires the same module / role option as the submit endpoint (otherwise HTTP 403).