For agents, on top of README.md, which they read first.

Notes for agents

Never add a field that carries what a visitor sent. Not a path, a query, a header, an address or a user agent; the closed types are the guarantee. A new thing worth logging becomes a new variant of a closed type, not a String.

A route's note is for what only the site's own build can cause, such as a file that was never generated. Never a request's content.

A 5xx is Error whatever the route says. The override is for lowering noise (a probe's 404), not for hiding the site's own failures.