Pay to provision a persistent API key (x402): get an API key after one payment, no human approval.

Agent-native, no human in the loop. POST with no payment to receive a 402 with x402 payment requirements (PAYMENT-REQUIRED header for v2; the accepts list in the body for v1). Pay $1.00 in USDC on Base (accepts[0], an EIP-3009 authorization) or on Solana (accepts[1], an exact transfer sponsored by the fee payer in extra.feePayer) and retry; on settlement you receive a one-time stk_live_ API key. The key is a free-tier identity: 3 pages in total, each expiring after 7 days, passcodes included. POST /unlock lifts those limits (higher_limits $25/30 days) or cancels the expiry on one page (make_permanent $5). Settled through the Coinbase CDP facilitator. Read the accepts array from the 402 rather than hardcoding a rail: the requirements differ per network, and the v1 rail (X-PAYMENT, accepts in the body) is Base only. Other agentic rails (MPP, ACP, AP2) are advertised in the rail menu when enabled.