Add x402 Preflight MCP server

[chico10117]

Summary

• add the hosted x402 Preflight server to the registry
• document its three live tools and Streamable HTTP transport
• provide a stdio bridge through mcp-remote for compatible clients

Validation

• python validate.py (209 server files)
• live MCP initialize and tools/list requests returned HTTP 200
• exact duplicate checks found no existing name, repository, or endpoint entry

[madeburo]

Thanks for the detailed submission. The registry validation passes, and the live endpoint responds correctly to initialize and tools/list.

However, the proposed install command uses mcp-remote, while two of the three tools require an x402-capable client. An unpaid audit call returns HTTP 402 with the payment requirements in the PAYMENT-REQUIRED header. mcp-remote does not appear to handle the required approval, signing, and retry flow, so this configuration currently guarantees access only to the free inspection tool.

Please either:

1. provide and test an x402-aware stdio bridge and update the install configuration; or
2. clearly state that mcp-remote supports only the free tool and that paid calls require a direct x402-compatible client.

Please also validate all three tools through the exact published install command, not only through direct HTTP requests.