React Router integration matches far more routes than the router on every navigation #25340

The React Router integration passes allRoutes (every nested route alongside its ancestors) to matchRoutes, which flattens each entry's children again, and then calls matchRoutes several times per navigation. On sentry.io's route tree this costs ~50ms per navigation (including query-only changes). It can also name a navigation after a nested route matched on its own instead of the route the router actually renders.

Fix: #25336