optimized avatar and linkify performance, refined navigation to preserve popups, implemented read marker caching, and added file size limits for saving, minor timetable details changes

lib/widget/file_viewer.dart

@@ -254,7 +254,26 @@ class _FileViewerState extends State<FileViewer> {
         break;
       case FileViewingActions.save:
         try {
-          final bytes = await File(widget.path).readAsBytes();
+          final source = File(widget.path);
+          final size = await source.length();
+          // Hard-cap to avoid loading the entire file into memory just to
+          // hand it back to the platform's saveFile dialog. The package
+          // currently has no streaming/path-based save path, so for big
+          // media the user has to fall back to "Teilen" → save-to-files.
+          // 200 MB peak is comfortable on modern mid-range devices and big
+          // enough for typical school videos.
+          const maxBytes = 200 * 1024 * 1024; // 200 MB
+          if (size > maxBytes) {
+            if (!mounted) return;
+            InfoDialog.show(
+              context,
+              'Diese Datei ist zu groß (${(size / (1024 * 1024)).toStringAsFixed(0)} MB), '
+              'um direkt gespeichert zu werden. Nutze stattdessen die Teilen-Funktion.',
+              title: 'Speichern nicht möglich',
+            );
+            return;
+          }
+          final bytes = await source.readAsBytes();
           final saved = await FilePicker.saveFile(
             fileName: widget.path.split('/').last,
             bytes: bytes,

lib/widget/user_avatar.dart

@@ -1,3 +1,4 @@
+import 'dart:collection';
 import 'dart:convert';
 import 'dart:typed_data';
 
@@ -29,11 +30,44 @@ class _AvatarPayload {
   _AvatarPayload(this.bytes, this.isSvg);
 }
 
+class _AvatarCacheEntry {
+  final _AvatarPayload? payload;
+  final DateTime fetchedAt;
+  _AvatarCacheEntry(this.payload, this.fetchedAt);
+}
+
+// Cap keeps the heap bounded for power-users in Talk; TTL ensures
+// server-side avatar updates become visible within a session without
+// requiring an app restart. LinkedHashMap insertion-order plus a remove
+// on hit gives us LRU eviction.
+const int _kAvatarCacheMax = 256;
+const Duration _kAvatarCacheTtl = Duration(minutes: 30);
+
 // Resolved payloads are cached so re-mounts render synchronously; in-flight
 // requests are deduped so concurrent mounts share one HTTP call.
-final Map<String, _AvatarPayload?> _resolvedAvatars = {};
+final LinkedHashMap<String, _AvatarCacheEntry> _resolvedAvatars =
+    LinkedHashMap<String, _AvatarCacheEntry>();
 final Map<String, Future<_AvatarPayload?>> _pendingAvatars = {};
 
+_AvatarCacheEntry? _readAvatarCache(String url) {
+  final entry = _resolvedAvatars.remove(url);
+  if (entry == null) return null;
+  if (DateTime.now().difference(entry.fetchedAt) > _kAvatarCacheTtl) {
+    return null;
+  }
+  // Re-insert at the tail so it counts as most-recently-used.
+  _resolvedAvatars[url] = entry;
+  return entry;
+}
+
+void _writeAvatarCache(String url, _AvatarPayload? payload) {
+  _resolvedAvatars.remove(url);
+  _resolvedAvatars[url] = _AvatarCacheEntry(payload, DateTime.now());
+  while (_resolvedAvatars.length > _kAvatarCacheMax) {
+    _resolvedAvatars.remove(_resolvedAvatars.keys.first);
+  }
+}
+
 class _UserAvatarState extends State<UserAvatar> {
   _AvatarPayload? _payload;
 
@@ -63,14 +97,15 @@ class _UserAvatarState extends State<UserAvatar> {
 
   void _attach() {
     final url = _url();
-    if (_resolvedAvatars.containsKey(url)) {
-      _payload = _resolvedAvatars[url];
+    final cached = _readAvatarCache(url);
+    if (cached != null) {
+      _payload = cached.payload;
       return;
     }
     _payload = null;
     final pending = _pendingAvatars.putIfAbsent(url, () => _fetch(url));
     pending.then((p) {
-      _resolvedAvatars[url] = p;
+      _writeAvatarCache(url, p);
       _pendingAvatars.remove(url);
       if (!mounted || _url() != url) return;
       setState(() => _payload = p);