added cache folder sweep check before file actions, preventing errors

lib/widget/downloads/downloads_sheet.dart

@@ -10,6 +10,7 @@ import '../../view/pages/files/data/file_type_icon.dart';
 import '../centered_leading.dart';
 import '../details_bottom_sheet.dart';
 import '../info_dialog.dart';
+import 'stale_download_guard.dart';
 
 /// Overview of all active and finished-but-unopened downloads. Lets the user
 /// open/switch between finished files, cancel running ones and retry failures.
@@ -86,8 +87,11 @@ class _DownloadsListState extends State<_DownloadsList> {
   void _open(DownloadJob job) {
     final path = job.localPath;
     if (path == null) return;
-    Haptics.success();
+    // Pop the sheet first so a stale-file dialog lands on the underlying
+    // screen instead of an emptied sheet.
     Navigator.of(widget.sheetContext).pop();
+    if (!ensureDownloadStillExists(widget.rootContext, job)) return;
+    Haptics.success();
     DownloadManager.instance.markOpened(job);
     AppRoutes.openFileViewer(
       widget.rootContext,