feat(folders): Improve folder management and parsing logic

lib/core/services/api_service.dart

@@ -3003,23 +3003,23 @@ class ApiService {
     );
     final data = response.data;
     // The endpoint can return a List[ChatTitleIdResponse] or a map.
-    // Normalize to a List<Conversation> using our safe parser.
+    // Normalize to a List<Conversation> using our isolate parser.
     if (data is List) {
-      return data
-          .whereType<Map<String, dynamic>>()
-          .map((e) => Conversation.fromJson(parseConversationSummary(e)))
-          .toList();
+      return _parseConversationSummaryList(
+        data,
+        debugLabel: 'parse_search_direct',
+      );
     }
     if (data is Map<String, dynamic>) {
       final list = (data['conversations'] ?? data['items'] ?? data['results']);
       if (list is List) {
-        return list
-            .whereType<Map<String, dynamic>>()
-            .map((e) => Conversation.fromJson(parseConversationSummary(e)))
-            .toList();
+        return _parseConversationSummaryList(
+          list,
+          debugLabel: 'parse_search_wrapped',
+        );
       }
     }
-    return <Conversation>[];
+    return const <Conversation>[];
   }
 
   /// Search within messages content (capability-safe)

lib/core/services/optimized_storage_service.dart

@@ -322,9 +322,13 @@ class OptimizedStorageService {
 
   Future<void> saveLocalConversations(List<Conversation> conversations) async {
     try {
-      final serialized = conversations
+      final jsonReady = conversations
           .map((conversation) => conversation.toJson())
           .toList();
+      final serialized = await _workerManager
+          .schedule<Map<String, dynamic>, String>(_encodeConversationsWorker, {
+            'conversations': jsonReady,
+          }, debugLabel: 'encode_local_conversations');
       await _cachesBox.put(_localConversationsKey, serialized);
       DebugLogger.log(
         'Saved ${conversations.length} local conversations',
@@ -478,3 +482,15 @@ List<Map<String, dynamic>> _decodeStoredConversationsWorker(
 
   return <Map<String, dynamic>>[];
 }
+
+String _encodeConversationsWorker(Map<String, dynamic> payload) {
+  final raw = payload['conversations'];
+  if (raw is List) {
+    return jsonEncode(raw);
+  }
+  if (raw is String) {
+    // Already encoded.
+    return raw;
+  }
+  return jsonEncode([]);
+}