Variable
ConstA literal tuple because the proxy runs before the router and has no
filesystem to read. known-route-segments.test.ts compares it against the
directories under src/app/[locale] on every run, so it cannot drift
silently: a route added on disk and forgotten here would start answering
404, and one removed from disk but left here would let a missing page keep
answering 200.
Route-group directories — (account) — contribute their children, since
parentheses never appear in a URL.
Every first path segment, after the locale, that the router can serve.