Check an x402 endpoint's payment challenge shape (v1)

The per-check view: a check that never ran is not a check that passed. not_reached means an earlier check failed and blocked_by names it; not_exercised means the door refused every method the probe sends as a method (405/501), so nothing was asked — a wrong verb, never a defect — and refused_methods names them.

The legacy two-state list, unchanged, for consumers that read the old shape.

True and worth knowing, never folded into the verdict.

The SAME probe scored under the other battery, so a reader comparing verdicts never has to guess whether the doors differed or the rules did.

One unpaid response, with observed protocols, unverified advertised term summaries, existing structural findings and coverage gaps. The x402 verdict retains its meaning. No artifact signature verification, payment signing, payment submission, settlement or delivery check.

The additive mpp-core-v1 observable core reading under draft-01. Separates failed checks from unmeasured requirements; never changes the x402 verdict or historical MPP battery.

The MPP battery's reading of the same bytes (mpp-v1, draft-00): whether the door speaks it, its challenges summarised, its named checks when it does (none when it does not — a check against no challenge is not an observation), its advisories outside any verdict, and what one unpaid GET cannot tell you.

What to do about it, both sides: one row per failed check or raised advisory that a vocabulary class explains — the class, its definition URL, what the operator does, what the buyer does. Derived from /defects.json through the signal already reported; never part of the verdict; empty on a clean door.

Which question the door actually answered. The probe sends GET first (or the method a catalog declared for the resource) and, if that is refused AS a method with 405 or 501, sends exactly one more — the method named in Allow when the 405 carries one, POST otherwise. At most two requests per call, to the same URL, and only ever about the verb.

What a real wallet saw at this host, read off the latest sealed census round's crowd-walked rows (bounty claims this store paid after verifying the settlement on chain). The settlement is proven; house_probe_verdict is our own unpaid knock at the claim; walker_status, receipt and defect_classes are the walker's claim, never verified here. Its own tier, never folded into the verdict. Absent only when no round could be read.

The rungs this probe did not climb, and what climbs each one. Replaced next_steps 2026-09-16: the reading named the missing rungs in one place and the paid instruments in another, and a buyer had to join them. Each unclimbed rung carries the item, its price in USDC, the tool that calls it and the URL; a rung nothing can buy today says so rather than being sold a near-miss.