Marks the nonce spent without naming what spent it — x402 defect class nonce-unbound-from-settlement

Asserts: A till that refuses an already-settled payment can name the settlement transaction that spent the authorization's nonce.

What a buyer loses when it is present: A buyer who paid and lost the response cannot be told apart from one who never paid. The seller can say 'spent' but not prove WHAT spent it, so honest recovery and fraud look identical — and any paid-retry lane (deliver again for the SAME settlement, charge nothing) has nothing to stand on. The money moved once; the proof of which movement is gone.

Detectable: only by a paid probe — a settled payment reveals it.

Falsified by: The door's replay refusal, or an equivalent receipt surface, producing the settlement transaction hash for the spent nonce at the stated moment.

How an operator clears it: Store the settlement transaction hash beside the nonce when you mark it spent, and return it on the replay refusal — one extra column, and a buyer's honest recovery becomes distinguishable from fraud.

Our signal: this store's own replay refusals return the original settlement transaction (HTTP door since the paid-retry lane; MCP door since 2026-08-27 — it exhibited this class until that day's fix, found live by an outside reproduction, and that is recorded here rather than smoothed over)..

Named by SolomonisBlack (github.com/SolomonisBlack), who named the class during the response-provenance collaboration. Registered at his request — source, not author, as agreed., registered 2026-08-27 — this store is the registrar, not the author.

Vocabulary v9, CC BY 4.0. Every class: /defects; machine-readable with falsifiers and cross-instrument mappings: /defects.json. A class describes a property of one endpoint at one moment and never accumulates into a judgment on an operator.