Verify a signed refusal receipt

When a payment provider says no, the AGENT carries the blame: its principal sees an incomplete task and has only the agent’s account of why. "The relay refused me" is indistinguishable from "I got it wrong" or "I never tried". Send x-anygas-receipt: 1 on any request and, IF we refuse it, the error response carries a signed refusalReceipt recording what was asked, when, and the reason we actually returned. Hand it to your principal; they verify it against our published signer address. Rewrite the reason or the error code and verification fails — the digest is recomputed from the submitted fields, never taken from the digest field, so blame cannot be shifted in either direction. A receipt proves the refusal HAPPENED. It is explicitly not a claim that the refusal was correct — use it to evidence that you were blocked, or to contest the decision with us. Receipts are opt-in and error-only: successful requests never mint one.