Function route_label 

pub fn route_label(req: &Request, routes: &RouteAllowList) -> String

Resolve the route-template label for a request.

Reads the MatchedPath extension that axum’s router inserts before invoking per-route layers; falls back to UNKNOWN_ROUTE if the extension is absent (no matching route) or if the matched template is not on the allow-list (cardinality guard).