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/locale_resolver_test.go

@@ -0,0 +1,81 @@
+package surf
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"git.golem15.com/golem15/summercms/modules/towel"
+)
+
+type stubLocaleResolver struct {
+	code      string
+	rewriteTo string
+}
+
+func (s stubLocaleResolver) Resolve(http.ResponseWriter, *http.Request) string {
+	return s.code
+}
+
+func (s stubLocaleResolver) Rewrite(r *http.Request) *http.Request {
+	if s.rewriteTo == "" {
+		return r
+	}
+	clone := r.Clone(r.Context())
+	clone.URL.Path = s.rewriteTo
+	return clone
+}
+
+func TestLocaleResolverWritesValidatedCodeAndStripsPrefix(t *testing.T) {
+	cfg := writeHTTPConfig(t, "body_limits:\n  default_bytes: 1024\n  upload_bytes: 1024\n")
+	app := backpack.New(cfg)
+	if err := app.Publish[LocaleResolver](stubLocaleResolver{code: "pl", rewriteTo: "/posts"}); err != nil {
+		t.Fatal(err)
+	}
+	r := New(nil)
+	r.app = app
+	r.defaultBytes = 1024
+	r.BindPlugin("acme.blog")
+	var gotPath, gotLoc string
+	var ok bool
+	r.Get("/posts", func(w http.ResponseWriter, req *http.Request) {
+		gotPath = req.URL.Path
+		gotLoc, ok = towel.Locale(req.Context())
+		w.WriteHeader(http.StatusNoContent)
+	})
+	h, err := r.compile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	req := httptest.NewRequest(http.MethodGet, "/pl/posts", nil)
+	req.Header.Set("Accept-Language", "de")
+	h.ServeHTTP(httptest.NewRecorder(), req)
+	if gotPath != "/posts" {
+		t.Fatalf("path = %q, want /posts", gotPath)
+	}
+	if !ok || gotLoc != "pl" {
+		t.Fatalf("locale = %q ok=%t, want pl from resolver", gotLoc, ok)
+	}
+}
+
+func TestLocaleAbsentResolverKeepsAcceptLanguage(t *testing.T) {
+	r := New(nil)
+	r.BindPlugin("acme.blog")
+	var gotLoc string
+	var ok bool
+	r.Get("/posts", func(w http.ResponseWriter, req *http.Request) {
+		gotLoc, ok = towel.Locale(req.Context())
+		w.WriteHeader(http.StatusNoContent)
+	})
+	h, err := r.compile()
+	if err != nil {
+		t.Fatal(err)
+	}
+	req := httptest.NewRequest(http.MethodGet, "/posts", nil)
+	req.Header.Set("Accept-Language", "pl")
+	h.ServeHTTP(httptest.NewRecorder(), req)
+	if !ok || gotLoc != "pl" {
+		t.Fatalf("locale = %q ok=%t, want pl from Accept-Language", gotLoc, ok)
+	}
+}