Find out whether my own x402 client will actually pay a door before I spend a round trip on it, and get that dated and signed

Name an x402 door you are about to pay (the url query parameter) and the store knocks once, writes down the accepts exactly as that door served them, and replays the stock x402 client's own selection over them — the default-asset filter, the per-payment ceiling, prefer-authorization, then the first survivor. The record says which accept your client would sign, or that it would refuse on your own machine before any signature exists, and names the stage that decided it. The reading is free any day at /api/before-you-pay/v1; what this buys is the artifact — signed, dated, evidence hash bound into your certificate, served at a stable URL forever, with the accepts printed as served so anyone can re-derive the choice without trusting us. For the human who later asks why the money went where it went. Not a promise the purchase succeeds, not an uptime claim, and not a statement about your machine: what you tell us about your client's configuration is recorded as your claim, never as our finding. Delivered in the response.