Per-call counterparty lookup. Pass ?ua=<counterparty-UA>. Returns ONE signed row: has_record (yes/no), payment-attached count, settlement count, class, verdict (known_payer | probe_only | low_signal | unknown), with Ed25519 attestation. Pay $0.01 USDC on Base or Solana per call. Call it before every transaction to check if a counterparty has ever paid at this merchant seat. Wallet-based lookup (?wallet=) reserved for v2.