added cache folder sweep check before file actions, preventing errors

lib/widget/downloads/download_tray.dart

@@ -7,6 +7,7 @@ import '../../utils/downloads/download_job.dart';
 import '../../utils/downloads/download_manager.dart';
 import '../../utils/haptics.dart';
 import 'downloads_sheet.dart';
+import 'stale_download_guard.dart';
 
 /// Decides whether a just-finished download should open straight in the viewer.
 ///
@@ -198,9 +199,13 @@ class _DownloadTrayHostState extends State<DownloadTrayHost>
 
   void _openJob(DownloadJob job) {
     final path = job.localPath;
-    _manager.markOpened(job);
     final ctx = AppRoutes.overlayContext;
-    if (path == null || ctx == null) return;
+    if (path == null || ctx == null) {
+      _manager.markOpened(job);
+      return;
+    }
+    if (!ensureDownloadStillExists(ctx, job)) return;
+    _manager.markOpened(job);
     Haptics.success();
     AppRoutes.openFileViewer(ctx, path, remoteFile: job.remoteFile);
   }

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,

lib/widget/downloads/stale_download_guard.dart

@@ -0,0 +1,40 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:flutter/material.dart';
+
+import '../../utils/downloads/download_job.dart';
+import '../../utils/downloads/download_manager.dart';
+import '../confirm_dialog.dart';
+import '../info_dialog.dart';
+
+/// Verifies a finished download's cache file is still on disk before opening.
+///
+/// Downloads live in the app's temp dir, which Android may clear at any time
+/// (storage pressure, "Cache leeren") — while completion notifications and
+/// tray entries stay tappable indefinitely. Returns true when the file exists;
+/// otherwise drops the stale job (incl. its notification) and offers a
+/// re-download when the remote path is known (it isn't for notification taps
+/// whose task metadata got lost).
+bool ensureDownloadStillExists(BuildContext context, DownloadJob job) {
+  final path = job.localPath;
+  if (path == null || File(path).existsSync()) return true;
+
+  DownloadManager.instance.markOpened(job);
+  if (job.remotePath.isNotEmpty) {
+    ConfirmDialog(
+      title: 'Datei nicht mehr verfügbar',
+      content:
+          'Die heruntergeladene Datei wurde vom System aus dem Zwischenspeicher entfernt.\nErneut herunterladen?',
+      confirmButton: 'Herunterladen',
+      onConfirm: () => unawaited(DownloadManager.instance.retry(job)),
+    ).asDialog(context);
+  } else {
+    InfoDialog.show(
+      context,
+      'Die heruntergeladene Datei wurde vom System aus dem Zwischenspeicher entfernt. Bitte lade sie erneut herunter.',
+      title: 'Datei nicht mehr verfügbar',
+    );
+  }
+  return false;
+}