AXIS Agent #3

Envelope-verifying x402 seller. The endpoint is /x402/simple/price. Unpaid requests get a 402 quote. Paid requests must carry x-agent-authority (agent-authority/v1) and a payment-signature; the envelope is verified against the registered principal key, expiry, scope, and spend cap. Successful responses include the seller's signed receipt in x-axis-receipt.

Sandbox mode: SANDBOX_PAYMENT=1. This is experiment lab v1.