fix: preserve CHFS shared redirect compatibility

chfs-ng/internal/api/server.go

@@ -76,7 +76,17 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("/chfs/shared/", s.shared)
 	mux.HandleFunc("/chfs/preview", s.preview)
 	mux.HandleFunc("/", s.fileHandler)
-	return s.ipFilter(mux)
+	h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Go's ServeMux canonicalizes a subtree route before dispatching.
+		// CHFS v4 deliberately returns a relative 301 from /chfs/shared, so
+		// intercept the exact path before ServeMux gets a chance to rewrite it.
+		if r.URL.Path == "/chfs/shared" {
+			s.shared(w, r)
+			return
+		}
+		mux.ServeHTTP(w, r)
+	})
+	return s.ipFilter(h)
 }
 func account(r *http.Request, s *Server) *auth.Account {
 	c, err := r.Cookie("JWT")
@@ -659,7 +669,9 @@ func (s *Server) shared(w http.ResponseWriter, r *http.Request) {
 		if r.URL.RawQuery != "" {
 			location += "?" + r.URL.RawQuery
 		}
-		http.Redirect(w, r, location, http.StatusMovedPermanently)
+		w.Header().Set("Content-Disposition", `attachment;filename="shared"`)
+		w.Header().Set("Location", location)
+		w.WriteHeader(http.StatusMovedPermanently)
 		return
 	}
 	p := strings.Trim(strings.TrimPrefix(r.URL.Path, "/chfs/shared/"), "/")
@@ -808,6 +820,7 @@ func (s *Server) downloadDir(w http.ResponseWriter, r *http.Request) {
 		name = "download"
 	}
 	w.Header().Set("Content-Type", "application/zip")
+	// CHFS v4 does not emit Content-Disposition for directory archives.
 	zw := zip.NewWriter(w)
 	defer zw.Close()
 	var walk func(string, string) error