A signed offer promises terms the challenge does not carry — x402 defect class offer-contradicts-challenge

Asserts: Every signed offer a door serves commits to a network, asset, payTo and amount that appear together on one entry of the same response's accepts.

What a buyer loses when it is present: A buyer holding the offer as a pre-payment commitment and the challenge as the terms to sign has two prices from one door in one breath, and whichever it pays, the other document says it paid wrong. In a dispute the door's own signature argues against its own challenge.

Detectable: by an unpaid probe — a GET nobody paid for can see it.

Falsified by: The offer's decoded payload matching an accepts entry of the same response on network, asset, payTo and amount; the spec tells verifiers to match on those fields, never on array position.

How an operator clears it: Sign offers from the accepts entries themselves at the moment the challenge is built, one offer per entry, so the two cannot drift; never sign a cached offer beside a freshly priced challenge.

Our signal: offer-contradicts-challenge (advisory).

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.