x402-stablecoin: x402 payment protocol enabling AI agents to autonomously pay for APIs on Arbitrum. Features Sperax USDs stablecoin with auto-yield, payment channels for streaming micropayments, on-chain subscriptions, and a tool registry marketplace. Includes TypeScript SDK, Express middleware, and upgradeable smart contracts.

If you discover a security issue, please report it responsibly:

1. Do NOT open a public issue
2. Email the maintainer or open a private security advisory on GitHub
3. Include steps to reproduce the vulnerability
4. Allow reasonable time for a fix before disclosure