[codex] Add GateCheck MCP server

[LarryLemonBot]

Summary

• add GateCheck to the Security category
• include the public GateCheck metadata repository in both README.md and the category doc

Validation

• ran git diff --check
• confirmed the GateCheck metadata repository is public: https://github.com/LarryLemonBot/gatecheck
• confirmed the remote GateCheck MCP endpoint returns HTTP 200: https://x402-resource-scanner.vercel.app/gatecheck/mcp

Claim boundary

This submission describes GateCheck as preflight checks and receipts for paid x402 and MCP marketplace readiness. It does not claim marketplace endorsement, security certification, payment settlement, or downstream execution.

[wilsonccccc]

Thanks for the contribution. The entry is mirrored in README.md and docs/security.md, and the linked repository is public.

P.S. a ⭐ on the repo helps more folks find your project too!

[egoriklok]

Useful addition. For a paid MCP/x402 listing, I would add one buyer-agent readiness check before treating this as agent-safe commerce.

Free public snapshot:

• Strong signal: MCP + payment + x402 is the right surface for autonomous buyers.
• Missing proof an agent will look for: preflight schema, charge/receipt evidence, spend-cap semantics, policy version/hash, and a clear allow/caution/block failure mode.
• If this registry accepts metadata, a small readiness block with payment_required, preflight_url, receipt_ref, policy_hash, and trust_check_ref would make the listing much easier for agents to evaluate.

No invoice, no payment link, no delivery link; just a public readiness note.

[wilsonccccc]

Closing this because the entry has been migrated into the current docs-first MCP Index flow and merged via #748, with structured metadata sidecars where available. Thanks for the submission.