added support for simultan downloads in files and talk, support for background downloads, enhanced loading in files with retry

lib/api/marianumcloud/webdav/queries/list_files/list_files.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 
 import 'package:nextcloud/nextcloud.dart';
 
+import '../../../../retry.dart';
 import '../../webdav_api.dart';
 import 'cacheable_file.dart';
 import 'list_files_params.dart';
@@ -10,7 +11,11 @@ import 'list_files_response.dart';
 class ListFiles extends WebdavApi<ListFilesParams> {
   ListFilesParams params;
 
-  ListFiles(this.params) : super(params);
+  /// Forwarded to [retryOnTransientError] so the UI can surface "Erneuter
+  /// Versuch (2 von 3)" while a 5xx-plagued listing self-heals.
+  final void Function(int nextAttempt, int maxAttempts)? onRetry;
+
+  ListFiles(this.params, {this.onRetry}) : super(params);
 
   // The Nextcloud root listing is significantly slower than subdirectories on
   // our instance, so it gets a much longer ceiling. Subfolders fall back to a
@@ -44,15 +49,25 @@ class ListFiles extends WebdavApi<ListFilesParams> {
       ncmounttype: true,
     );
 
-    var files = await _fetch(webdav, prop, timeout);
+    // Our instance intermittently answers the (slow) root PROPFIND with a
+    // quick empty 500 — retry those transparently before surfacing an error.
+    var files = await retryOnTransientError(
+      () => _fetch(webdav, prop, timeout),
+      onRetry: onRetry,
+    );
     // A freshly-entered incoming share sometimes answers its first PROPFIND
     // without the OC/NC props (no fileid / has-preview / mount-type) while the
     // share mount warms up server-side — which drops thumbnails AND share
     // badges together. Retry a couple of times so the folder self-heals
-    // instead of needing manual re-entry.
+    // instead of needing manual re-entry. Best-effort: a failure here must
+    // not discard the listing that was already fetched successfully.
     for (var attempt = 0; attempt < 2 && _looksIncomplete(files); attempt++) {
       await Future<void>.delayed(const Duration(milliseconds: 700));
-      files = await _fetch(webdav, prop, timeout);
+      try {
+        files = await _fetch(webdav, prop, timeout);
+      } on Exception {
+        break;
+      }
     }
 
     return ListFilesResponse(files);
@@ -65,7 +80,11 @@ class ListFiles extends WebdavApi<ListFilesParams> {
   ) async {
     final davFiles =
         (await webdav
-                .propfind(PathUri.parse(params.path), prop: prop)
+                .propfind(
+                  PathUri.parse(params.path),
+                  prop: prop,
+                  depth: WebDavDepth.one,
+                )
                 .timeout(timeout))
             .toWebDavFiles();
     final files = davFiles.map(CacheableFile.fromDavFile).toSet();

lib/api/marianumcloud/webdav/queries/list_files/list_files_cache.dart

@@ -17,9 +17,10 @@ class ListFilesCache extends SimpleCache<ListFilesResponse> {
     super.onError,
     required String path,
     super.renew = false,
+    void Function(int nextAttempt, int maxAttempts)? onRetry,
   }) : super(
          cacheTime: _cacheTimeFor(path),
-         loader: () => ListFiles(ListFilesParams(path)).run(),
+         loader: () => ListFiles(ListFilesParams(path), onRetry: onRetry).run(),
          fromJson: ListFilesResponse.fromJson,
          onUpdate: onUpdate,
        ) {