Have I paid this address before?

Address substitution is the most common theft in this space and it is silent — one hex string looks exactly like another. Signed payment requests solve it when the payee cooperates; this covers the other half: an agent about to pay an address it has never paid, with nothing telling it so. Returns YOUR OWN history with the address: times paid, how recently, typical amount, and whether this amount is unusual for that counterparty. IT IS NOT A REPUTATION SCORE. It says nothing about whether the address is honest, and a FAMILIAR ADDRESS IS NOT A SAFE ADDRESS — keys get compromised. A first-time-recipient result is not a warning about the recipient either; every legitimate relationship has a first payment. It is the moment to confirm the address by a second channel. READ coverage: the float-lane ledger does not retain recipient addresses, so float-lane payouts are excluded and "first time" can be wrong. Surfaced automatically as a WARNING (never a blocker) in /api/preflight/full.