Fix: an unknown method on the modern lane returns -32601

Web-audit fix skill for the mcp-modern-unknown-method check (MCP, SHOULD).

Goal

Reject unknown header-routed methods with -32601 on the 2026-07-28 lane.

Fix

Reject a modern request (MCP-Protocol-Version: 2026-07-28, Mcp-Method naming a method you do not implement) with error.code: -32601 (Method not found). Delivering the envelope at HTTP 404 conforms; a bare 404 with no envelope does not (it is indistinguishable from a dead endpoint).

Resources

• JSON-RPC 2.0
• MCP lifecycle (2026-07-28)

Copy-paste prompt

Paste this into your coding agent. Your audit adds what it observed for this check:

Verify

Re-run the audit at https://anc.dev/audit or call the audit_website MCP tool; the mcp-modern-unknown-method check should report pass.