added cache folder sweep check before file actions, preventing errors

lib/widget/file_viewer.dart

@@ -14,8 +14,11 @@ import 'package:share_plus/share_plus.dart';
 import '../routing/app_routes.dart';
 import '../share_intent/remote_file_ref.dart';
 import '../state/app/modules/settings/bloc/settings_cubit.dart';
+import '../utils/downloads/download_manager.dart';
 import 'app_progress_indicator.dart';
+import 'async_action_button.dart';
 import 'centered_leading.dart';
+import 'confirm_dialog.dart';
 import 'file_viewer/code_line.dart';
 import 'file_viewer/deferred_pdf_viewer.dart';
 import 'file_viewer/file_kind.dart';
@@ -82,9 +85,43 @@ class _FileViewerState extends State<FileViewer> {
     super.dispose();
   }
 
+  /// Android may clear the cache dir behind an open viewer at any time —
+  /// verify the file is still there before handing its path to an action.
+  bool _ensureLocalFile() {
+    if (File(widget.path).existsSync()) return true;
+    final remote = widget.remoteFile;
+    if (remote == null) {
+      InfoDialog.show(
+        context,
+        'Die Datei wurde vom System aus dem Zwischenspeicher entfernt. Bitte lade sie erneut herunter.',
+        title: 'Datei nicht mehr verfügbar',
+      );
+      return false;
+    }
+    ConfirmDialog(
+      title: 'Datei nicht mehr verfügbar',
+      content:
+          'Die Datei wurde vom System aus dem Zwischenspeicher entfernt.\nErneut herunterladen?',
+      confirmButton: 'Herunterladen',
+      onConfirm: () {
+        // Pop the viewer before starting so the fresh download auto-opens.
+        Navigator.of(context).pop();
+        unawaited(
+          DownloadManager.instance.start(
+            remotePath: remote.path,
+            name: remote.name,
+            remoteFile: remote,
+          ),
+        );
+      },
+    ).asDialog(context);
+    return false;
+  }
+
   Future<void> _handleAction(FileViewingActions value) async {
     switch (value) {
       case FileViewingActions.openExternal:
+        if (!_ensureLocalFile()) return;
         AppRoutes.openFileViewer(
           context,
           widget.path,
@@ -99,16 +136,21 @@ class _FileViewerState extends State<FileViewer> {
         AppRoutes.openInternalSaveToFolder(context, widget.remoteFile!);
         break;
       case FileViewingActions.share:
+        if (!_ensureLocalFile()) return;
         unawaited(
-          SharePlus.instance.share(
-            ShareParams(
-              files: [XFile(widget.path)],
-              sharePositionOrigin: SharePositionOrigin.get(context),
+          runWithErrorDialog(
+            context,
+            () => SharePlus.instance.share(
+              ShareParams(
+                files: [XFile(widget.path)],
+                sharePositionOrigin: SharePositionOrigin.get(context),
+              ),
             ),
           ),
         );
         break;
       case FileViewingActions.save:
+        if (!_ensureLocalFile()) return;
         try {
           final source = File(widget.path);
           final size = await source.length();