优化

client/flutter/lib/models/message.dart

@@ -0,0 +1,81 @@
+class Message {
+  final String id;
+  final String content;
+  final String? author;
+  final String? groupId;
+  final String converseId;
+  final bool hasRecall;
+  final Map<String, dynamic>? meta;
+  final DateTime? createdAt;
+  final DateTime? updatedAt;
+
+  Message({
+    required this.id,
+    required this.content,
+    this.author,
+    this.groupId,
+    required this.converseId,
+    this.hasRecall = false,
+    this.meta,
+    this.createdAt,
+    this.updatedAt,
+  });
+
+  factory Message.fromJson(Map<String, dynamic> json) {
+    return Message(
+      id: (json['_id'] ?? json['id'] ?? '').toString(),
+      content: json['content'] ?? '',
+      author: json['author']?.toString(),
+      groupId: json['groupId']?.toString(),
+      converseId: (json['converseId'] ?? '').toString(),
+      hasRecall: json['hasRecall'] ?? false,
+      meta: json['meta'],
+      createdAt: json['createdAt'] != null
+          ? DateTime.parse(json['createdAt'].toString())
+          : null,
+      updatedAt: json['updatedAt'] != null
+          ? DateTime.parse(json['updatedAt'].toString())
+          : null,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      '_id': id,
+      'content': content,
+      'author': author,
+      'groupId': groupId,
+      'converseId': converseId,
+      'hasRecall': hasRecall,
+      'meta': meta,
+      'createdAt': createdAt?.toIso8601String(),
+      'updatedAt': updatedAt?.toIso8601String(),
+    };
+  }
+
+  /// Determine message type from meta
+  MessageType get type {
+    if (hasRecall) return MessageType.recalled;
+    final metaType = meta?['type'];
+    if (metaType == 'image' || metaType == 'file') {
+      return MessageType.file;
+    }
+    if (metaType == 'system') {
+      return MessageType.system;
+    }
+    return MessageType.text;
+  }
+
+  /// Convenience alias for author (sender ID)
+  String get senderId => author ?? '';
+
+  /// For display purposes - get sender name from meta if available
+  String get senderName => meta?['nickname']?.toString() ?? '';
+}
+
+enum MessageType {
+  text,
+  file,
+  system,
+  recalled,
+}