SPT-Txn × x402 — Demo

x402 moves the money. SPT-Txn proves the agent was allowed to.

SPT-Txn is the per-transaction authorization layer x402 is missing. It authorizes any actor initiating a payment — a person acting through an interface, a non-human workload, or an AI agent (including agents acting over MCP) — with the autonomous-agent case the most urgent. Authority lives only inside a short-lived token bound to one exact payment — one asset, one amount, one recipient — verified offline with no call home, so a hijacked or prompt-injected agent holds a token that's useless for any other payment. A pre-sign guard refuses any transaction that doesn't match; a real USDC transfer settles on Solana devnet; and every decision emits a signed receipt whose log's Merkle root is anchored on-chain. Drop-in middleware adds it to any x402 server in one line.