feat(chat): Improve error handling and message versioning

lib/core/models/chat_message.dart

@@ -31,7 +31,8 @@ sealed class ChatMessage with _$ChatMessage {
     List<ChatSourceReference> sources,
     Map<String, dynamic>? usage,
     // Previous generated versions of this assistant message (OpenWebUI-style)
-    @JsonKey(includeFromJson: false, includeToJson: false)
+    // Parsed from sibling messages in OpenWebUI history
+    @JsonKey(fromJson: _versionsFromJson, toJson: _versionsToJson)
     @Default(<ChatMessageVersion>[])
     List<ChatMessageVersion> versions,
     // Error information from OpenWebUI (stored separately from content)
@@ -134,6 +135,9 @@ abstract class ChatMessageVersion with _$ChatMessageVersion {
     @Default(<String>[]) List<String> followUps,
     @Default(<ChatCodeExecution>[]) List<ChatCodeExecution> codeExecutions,
     Map<String, dynamic>? usage,
+    // Error information preserved from the original message
+    @JsonKey(fromJson: _chatMessageErrorFromJson, toJson: _chatMessageErrorToJson)
+    ChatMessageError? error,
   }) = _ChatMessageVersion;
 
   factory ChatMessageVersion.fromJson(Map<String, dynamic> json) =>
@@ -281,6 +285,35 @@ int? _safeInt(dynamic value) {
 List<String> _stringListToJson(List<String> value) =>
     List<String>.from(value, growable: false);
 
+/// Parse ChatMessageVersion list from JSON.
+List<ChatMessageVersion> _versionsFromJson(dynamic value) {
+  if (value is List) {
+    return value
+        .whereType<Map>()
+        .map((item) {
+          try {
+            final Map<String, dynamic> versionMap = {};
+            item.forEach((key, v) {
+              versionMap[key.toString()] = v;
+            });
+            return ChatMessageVersion.fromJson(versionMap);
+          } catch (e) {
+            // Skip invalid entries
+            return null;
+          }
+        })
+        .where((item) => item != null)
+        .cast<ChatMessageVersion>()
+        .toList(growable: false);
+  }
+  return const [];
+}
+
+/// Convert ChatMessageVersion list to JSON.
+List<Map<String, dynamic>> _versionsToJson(List<ChatMessageVersion> versions) {
+  return versions.map((v) => v.toJson()).toList(growable: false);
+}
+
 List<ChatStatusItem> _statusItemsFromJson(dynamic value) {
   if (value is List) {
     return value

lib/core/services/api_service.dart

@@ -1048,7 +1048,7 @@ class ApiService {
               'modelIdx': 0,
               'done': true,
               if (ver.files != null) 'files': _sanitizeFilesForWebUI(ver.files),
-              // Mirror follow-ups, code executions, and sources for versions
+              // Mirror follow-ups, code executions, sources, and errors for versions
               if (ver.followUps.isNotEmpty)
                 'followUps': List<String>.from(ver.followUps),
               if (ver.codeExecutions.isNotEmpty)
@@ -1057,6 +1057,8 @@ class ApiService {
                     .toList(),
               if (ver.sources.isNotEmpty)
                 'sources': ver.sources.map((s) => s.toJson()).toList(),
+              // Preserve error field for OpenWebUI compatibility
+              if (ver.error != null) 'error': ver.error!.toJson(),
             };
             // Link into parent (parentForVersions is always non-null here)
             if (messagesMap.containsKey(parentForVersions)) {

lib/core/services/conversation_parsing.dart

@@ -146,16 +146,24 @@ Map<String, dynamic> parseFullConversation(Map<String, dynamic> chatData) {
           merged['content'] = synthesized;
         }
 
-        messages.add(
+        final parsed = _parseOpenWebUIMessageToJson(
-          _parseOpenWebUIMessageToJson(merged, historyMsg: historyMsg),
+          merged,
+          historyMsg: historyMsg,
         );
+        // Add versions from siblings
+        _addVersionsFromSiblings(parsed, msgData, historyMessagesMap);
+        messages.add(parsed);
         index = j;
         continue;
       }
 
-      messages.add(
+      final parsed = _parseOpenWebUIMessageToJson(
-        _parseOpenWebUIMessageToJson(msgData, historyMsg: historyMsg),
+        msgData,
+        historyMsg: historyMsg,
       );
+      // Add versions from siblings
+      _addVersionsFromSiblings(parsed, msgData, historyMessagesMap);
+      messages.add(parsed);
       index++;
     }
   }
@@ -191,6 +199,120 @@ List<Map<String, dynamic>>? _extractToolCalls(
   return null;
 }
 
+/// Add versions from sibling messages (alternative responses with same parent).
+/// Siblings are stored in `_siblings` by `_buildMessagesListFromHistory`.
+void _addVersionsFromSiblings(
+  Map<String, dynamic> parsed,
+  Map<String, dynamic> msgData,
+  Map<String, dynamic>? historyMessagesMap,
+) {
+  final siblings = msgData['_siblings'];
+  if (siblings is! List || siblings.isEmpty) return;
+
+  final versions = <Map<String, dynamic>>[];
+  for (final siblingData in siblings) {
+    if (siblingData is! Map<String, dynamic>) continue;
+
+    final siblingId = siblingData['id']?.toString();
+    final historyMsg = historyMessagesMap != null && siblingId != null
+        ? (historyMessagesMap[siblingId] as Map<String, dynamic>?)
+        : null;
+
+    // Parse the sibling as a version
+    final version = _parseSiblingAsVersion(siblingData, historyMsg: historyMsg);
+    if (version != null) {
+      versions.add(version);
+    }
+  }
+
+  if (versions.isNotEmpty) {
+    parsed['versions'] = versions;
+  }
+}
+
+/// Parse a sibling message as a ChatMessageVersion JSON map.
+Map<String, dynamic>? _parseSiblingAsVersion(
+  Map<String, dynamic> msgData, {
+  Map<String, dynamic>? historyMsg,
+}) {
+  // Extract content (same logic as _parseOpenWebUIMessageToJson)
+  dynamic content = msgData['content'];
+  if ((content == null || (content is String && content.isEmpty)) &&
+      historyMsg != null &&
+      historyMsg['content'] != null) {
+    content = historyMsg['content'];
+  }
+
+  var contentString = '';
+  if (content is List) {
+    final buffer = StringBuffer();
+    for (final entry in content) {
+      if (entry is Map && entry['type'] == 'text') {
+        final text = entry['text']?.toString();
+        if (text != null && text.isNotEmpty) {
+          buffer.write(text);
+        }
+      }
+    }
+    contentString = buffer.toString();
+  } else {
+    contentString = content?.toString() ?? '';
+  }
+
+  if (historyMsg != null) {
+    final histContent = historyMsg['content'];
+    if (histContent is String && histContent.length > contentString.length) {
+      contentString = histContent;
+    }
+  }
+
+  // Extract files
+  final effectiveFiles = msgData['files'] ?? historyMsg?['files'];
+  List<Map<String, dynamic>>? files;
+  if (effectiveFiles is List) {
+    final allFiles = <Map<String, dynamic>>[];
+    for (final entry in effectiveFiles) {
+      if (entry is! Map) continue;
+      if (entry['type'] != null && entry['url'] != null) {
+        final fileMap = <String, dynamic>{
+          'type': entry['type'],
+          'url': entry['url'],
+        };
+        if (entry['name'] != null) fileMap['name'] = entry['name'];
+        if (entry['size'] != null) fileMap['size'] = entry['size'];
+        allFiles.add(fileMap);
+      }
+    }
+    files = allFiles.isNotEmpty ? allFiles : null;
+  }
+
+  // Extract other fields
+  final sourcesRaw = historyMsg != null
+      ? historyMsg['sources'] ?? historyMsg['citations']
+      : msgData['sources'] ?? msgData['citations'];
+  final followUpsRaw = historyMsg != null
+      ? historyMsg['followUps'] ?? historyMsg['follow_ups']
+      : msgData['followUps'] ?? msgData['follow_ups'];
+  final codeExecRaw = historyMsg != null
+      ? historyMsg['codeExecutions'] ?? historyMsg['code_executions']
+      : msgData['codeExecutions'] ?? msgData['code_executions'];
+  final rawUsage = _coerceJsonMap(historyMsg?['usage'] ?? msgData['usage']);
+  final errorData = _extractErrorData(msgData, historyMsg);
+
+  return <String, dynamic>{
+    'id': (msgData['id'] ?? _uuid.v4()).toString(),
+    'content': contentString,
+    'timestamp': _parseTimestamp(msgData['timestamp']).toIso8601String(),
+    if (msgData['model'] != null) 'model': msgData['model'].toString(),
+    if (files != null) 'files': files,
+    'sources': _parseSourcesField(sourcesRaw),
+    'followUps': _coerceStringList(followUpsRaw),
+    'codeExecutions': _parseCodeExecutionsField(codeExecRaw),
+    if (rawUsage.isNotEmpty) 'usage': rawUsage,
+    if (errorData != null) 'error': errorData,
+  };
+}
+
 /// Extract error data from OpenWebUI message format.
 /// OpenWebUI stores errors in a separate 'error' field with 'content' inside.
 /// Returns a map suitable for ChatMessageError.fromJson().
@@ -393,6 +515,8 @@ String _resolveRole(Map<String, dynamic> msgData) {
   return 'user';
 }
 
+/// Build the message chain from history, following parent links from currentId.
+/// Also collects sibling messages (alternative versions) for each message.
 List<Map<String, dynamic>> _buildMessagesListFromHistory(
   Map<String, dynamic> history,
 ) {
@@ -402,6 +526,7 @@ List<Map<String, dynamic>> _buildMessagesListFromHistory(
     return const [];
   }
 
+  // Build the main chain from currentId back to root
   List<Map<String, dynamic>> buildChain(String? id) {
     if (id == null) return const [];
     final raw = messagesMap[id];
@@ -415,7 +540,48 @@ List<Map<String, dynamic>> _buildMessagesListFromHistory(
     return [msg];
   }
 
-  return buildChain(currentId);
+  final chain = buildChain(currentId);
+
+  // For each message in the chain, find sibling versions
+  // Siblings are other children of the same parent
+  for (final msg in chain) {
+    final parentId = msg['parentId']?.toString();
+    if (parentId == null || parentId.isEmpty) continue;
+
+    final parent = messagesMap[parentId];
+    if (parent is! Map) continue;
+
+    final childrenIds = parent['childrenIds'];
+    if (childrenIds is! List || childrenIds.length <= 1) continue;
+
+    // Collect sibling messages (same role, different id)
+    final msgId = msg['id']?.toString();
+    final msgRole = msg['role']?.toString();
+    final siblings = <Map<String, dynamic>>[];
+
+    for (final siblingId in childrenIds) {
+      final sibId = siblingId?.toString();
+      if (sibId == null || sibId == msgId) continue;
+
+      final siblingRaw = messagesMap[sibId];
+      if (siblingRaw is! Map) continue;
+
+      final sibling = _coerceJsonMap(siblingRaw);
+      final siblingRole = sibling['role']?.toString();
+
+      // Only include siblings with the same role (e.g., alternative assistant responses)
+      if (siblingRole == msgRole) {
+        sibling['id'] = sibId;
+        siblings.add(sibling);
+      }
+    }
+
+    if (siblings.isNotEmpty) {
+      msg['_siblings'] = siblings;
+    }
+  }
+
+  return chain;
 }
 
 DateTime _parseTimestamp(dynamic timestamp) {

lib/features/chat/providers/chat_providers.dart

@@ -644,6 +644,7 @@ class ChatMessagesNotifier extends Notifier<List<ChatMessage>> {
       followUps: List<String>.from(last.followUps),
       codeExecutions: List<ChatCodeExecution>.from(last.codeExecutions),
       usage: last.usage == null ? null : Map<String, dynamic>.from(last.usage!),
+      error: last.error, // Preserve error in version snapshot
     );
 
     final updated = last.copyWith(
@@ -655,6 +656,7 @@ class ChatMessagesNotifier extends Notifier<List<ChatMessage>> {
       codeExecutions: const [],
       sources: const [],
       usage: null,
+      error: null, // Clear error for new generation
       versions: [...last.versions, snapshot],
     );
 
@@ -1414,6 +1416,7 @@ Future<void> regenerateMessage(
             followUps: prev.followUps,
             codeExecutions: prev.codeExecutions,
             usage: prev.usage,
+            error: prev.error, // Preserve error in version snapshot
           );
           ref
               .read(chatMessagesProvider.notifier)
@@ -2483,16 +2486,16 @@ Future<void> _sendMessageInternal(
       final errorMessage = ChatMessage(
         id: const Uuid().v4(),
         role: 'assistant',
-        content:
+        content: '',
-            '''⚠️ There was an issue with the message format. This might be because:
-
-• The image attachment couldn't be processed
-• The request format is incompatible with the selected model
-• The message contains unsupported content
-
-Please try sending the message again, or try without attachments.''',
         timestamp: DateTime.now(),
         isStreaming: false,
+        error: const ChatMessageError(
+          content: 'There was an issue with the message format. This might be '
+              'because the image attachment couldn\'t be processed, the request '
+              'format is incompatible with the selected model, or the message '
+              'contains unsupported content. Please try sending the message '
+              'again, or try without attachments.',
+        ),
       );
       ref.read(chatMessagesProvider.notifier).addMessage(errorMessage);
     } else if (e.toString().contains('401') || e.toString().contains('403')) {
@@ -2502,11 +2505,14 @@ Please try sending the message again, or try without attachments.''',
       final errorMessage = ChatMessage(
         id: const Uuid().v4(),
         role: 'assistant',
-        content:
+        content: '',
-            '⚠️ Unable to connect to the AI model. The server returned an error (500).\n\n'
-            'This is typically a server-side issue. Please try again or contact your administrator.',
         timestamp: DateTime.now(),
         isStreaming: false,
+        error: const ChatMessageError(
+          content: 'Unable to connect to the AI model. The server returned an '
+              'error (500). This is typically a server-side issue. Please try '
+              'again or contact your administrator.',
+        ),
       );
       ref.read(chatMessagesProvider.notifier).addMessage(errorMessage);
     } else if (e.toString().contains('404')) {
@@ -2517,11 +2523,14 @@ Please try sending the message again, or try without attachments.''',
       final errorMessage = ChatMessage(
         id: const Uuid().v4(),
         role: 'assistant',
-        content:
+        content: '',
-            '🤖 The selected AI model doesn\'t seem to be available.\n\n'
-            'Please try selecting a different model or check with your administrator.',
         timestamp: DateTime.now(),
         isStreaming: false,
+        error: const ChatMessageError(
+          content: 'The selected AI model doesn\'t seem to be available. '
+              'Please try selecting a different model or check with your '
+              'administrator.',
+        ),
       );
       ref.read(chatMessagesProvider.notifier).addMessage(errorMessage);
     } else {
@@ -2529,11 +2538,13 @@ Please try sending the message again, or try without attachments.''',
       final errorMessage = ChatMessage(
         id: const Uuid().v4(),
         role: 'assistant',
-        content:
+        content: '',
-            '❌ An unexpected error occurred while processing your request.\n\n'
-            'Please try again or check your connection.',
         timestamp: DateTime.now(),
         isStreaming: false,
+        error: const ChatMessageError(
+          content: 'An unexpected error occurred while processing your request. '
+              'Please try again or check your connection.',
+        ),
       );
       ref.read(chatMessagesProvider.notifier).addMessage(errorMessage);
     }

lib/features/chat/widgets/assistant_message_widget.dart

@@ -878,13 +878,10 @@ class _AssistantMessageWidgetState extends ConsumerState<AssistantMessageWidget>
                             ),
                     ),
 
-                    // Display error banner if message has an error
+                    // Display error banner if message or active version has an error
-                    if (widget.message is ChatMessage &&
+                    if (_getActiveError() != null) ...[
-                        (widget.message as ChatMessage).error != null) ...[
                       const SizedBox(height: Spacing.sm),
-                      _buildErrorBanner(
+                      _buildErrorBanner(_getActiveError()!),
-                        (widget.message as ChatMessage).error!,
-                      ),
                     ],
 
                     if (hasCodeExecutions) ...[
@@ -933,6 +930,21 @@ class _AssistantMessageWidgetState extends ConsumerState<AssistantMessageWidget>
         );
   }
 
+  /// Get the error for the currently active message or version.
+  ChatMessageError? _getActiveError() {
+    if (widget.message is! ChatMessage) return null;
+    final msg = widget.message as ChatMessage;
+
+    // If viewing a version, return the version's error
+    if (_activeVersionIndex >= 0 &&
+        _activeVersionIndex < msg.versions.length) {
+      return msg.versions[_activeVersionIndex].error;
+    }
+
+    // Otherwise return the main message's error
+    return msg.error;
+  }
+
   /// Build an error banner matching OpenWebUI's error display style.
   /// Shows error content in a red-tinted container with an info icon.
   Widget _buildErrorBanner(ChatMessageError error) {
@@ -1303,8 +1315,9 @@ class _AssistantMessageWidgetState extends ConsumerState<AssistantMessageWidget>
     final messageId = _messageId;
     final hasSpeechText = _ttsPlainText.trim().isNotEmpty;
     // Check for error using the error field (preferred) or legacy content detection
-    final hasErrorField = widget.message is ChatMessage &&
+    // Also check the active version's error if viewing a version
-        (widget.message as ChatMessage).error != null;
+    final activeError = _getActiveError();
+    final hasErrorField = activeError != null;
     final isErrorMessage = hasErrorField ||
         widget.message.content.contains('⚠️') ||
         widget.message.content.contains('Error') ||