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Fix: 404 body is markdown with a recovery link

Web-audit fix skill for the agent-friendly-404-md check (Discoverability, SHOULD).

Goal

Serve a short markdown 404 that links at least one agent recovery surface.

Fix

When Accept: text/markdown hits an unknown path, return 404 or 410 with a short markdown body that includes at least one recovery link: sitemap, llms.txt, a docs index, or an equivalent same-origin href. Linking both sitemap and llms.txt as absolute URLs is the stronger pattern. Zero links is a miss even when the status is correct.

Resources

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 agent-friendly-404-md check should report pass.