feat(14.2.1-01): add optional surf LocaleResolver seam

Look up a backpack-published resolver so a compiled translate plugin can
strip an enabled URL prefix and write a validated locale onto context.

Co-authored-by: Cursor <cursoragent@cursor.com>

modules/surf/router.go

@@ -59,6 +59,7 @@ type Router struct {
 	defaultBytes int64
 	uploadBytes  int64
 	built        map[string]pact.Middleware
+	app          *backpack.App
 }
 
 var (
@@ -375,7 +376,7 @@ func (r *Router) compile() (http.Handler, error) {
 	if err := registerOverlapFamilies(mux, r.routes, handlers, families); err != nil {
 		return nil, err
 	}
-	return pathScopedCORS(r.corsCfg, mux), nil
+	return r.stripLocalePrefix(pathScopedCORS(r.corsCfg, mux)), nil
 }
 
 // handleRoute registers a route, converting a ServeMux conflict panic into an error.
@@ -436,7 +437,7 @@ func (r *Router) wrap(rt route) (http.Handler, error) {
 	if limit > 0 {
 		h = bodyLimit(limit)(h)
 	}
-	h = locale(h)
+	h = r.locale(h)
 	if rt.raw {
 		h = recoverBare(h)
 	} else {
@@ -458,6 +459,7 @@ func Assemble(app *backpack.App, plugins []party.Plugin) (http.Handler, error) {
 // so callers (route:list) can inspect Routes() after a successful boot.
 func BuildRouter(app *backpack.App, plugins []party.Plugin) (*Router, error) {
 	r := New(corsOrigins(app))
+	r.app = app
 	trusted := TrustedProxies(nil)
 	if app != nil {
 		trusted = TrustedProxies(app.Config)
@@ -704,9 +706,27 @@ func (w *bufferedResponse) commit(dst http.ResponseWriter) {
 	_, _ = dst.Write(w.body.Bytes())
 }
 
-func locale(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		next.ServeHTTP(w, r.WithContext(towel.WithLocale(r.Context(), r.Header.Get("Accept-Language"))))
+func (r *Router) locale(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		if r != nil && r.app != nil {
+			if resolver, ok := r.app.Lookup[LocaleResolver](); ok && resolver != nil {
+				code := resolver.Resolve(w, req)
+				next.ServeHTTP(w, req.WithContext(towel.WithLocale(req.Context(), code)))
+				return
+			}
+		}
+		next.ServeHTTP(w, req.WithContext(towel.WithLocale(req.Context(), req.Header.Get("Accept-Language"))))
+	})
+}
+
+func (r *Router) stripLocalePrefix(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		if r != nil && r.app != nil {
+			if resolver, ok := r.app.Lookup[LocaleResolver](); ok && resolver != nil {
+				req = resolver.Rewrite(req)
+			}
+		}
+		next.ServeHTTP(w, req)
 	})
 }