refactor: route WebDAV through storage backend

chfs-ng/internal/api/webdav_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"chfs-ng/internal/auth"
+	"chfs-ng/internal/storage"
 	"github.com/emersion/go-webdav"
 )
 
@@ -35,3 +36,22 @@ func TestWebDAVAuthFSCheckTree(t *testing.T) {
 		t.Fatalf("public file should be deletable: %v", err)
 	}
 }
+
+func TestWebDAVStorageFSCopyAndMove(t *testing.T) {
+	root1 := t.TempDir()
+	root2 := t.TempDir()
+	if err := os.WriteFile(filepath.Join(root1, "a.txt"), []byte("one"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	m := storage.NewMulti([]string{root1, root2})
+	fs := &webdavStorageFS{store: m}
+	if _, err := fs.Copy(context.Background(), "/"+m.Names[0]+"/a.txt", "/"+m.Names[0]+"/b.txt", &webdav.CopyOptions{}); err != nil {
+		t.Fatalf("copy: %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(root1, "b.txt")); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := fs.Move(context.Background(), "/"+m.Names[0]+"/b.txt", "/"+m.Names[1]+"/b.txt", &webdav.MoveOptions{}); err == nil {
+		t.Fatal("expected cross-root move rejection")
+	}
+}