Everything a site has to publish for another program to find it lives under /.well-known/, and portal had no way to put a file there: the catch-all answered those paths 200 with the app shell, so a client probing for security.txt or matrix/server got HTML where it expected a document, and could not tell a missing file from a present one. The prefix is the one place this is safe to overlay. RFC 8615 reserves it, and a question's id comes from a file name under questions/, which cannot begin with a dot - so no file a repo ships can shadow a page. The path still goes through is_safe_site_path, so it cannot climb out of the repo either, and a miss is a real 404. Types: an extensionless file under the prefix is JSON, which is what matrix/server and nodeinfo are; .mobileconfig is the Apple profile type, without which iOS downloads a profile instead of offering to install it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015GeH3y8fwTaTudaD88P57o