Use json_serializable and const to improve AI data model

scribe/lib/scribe/ai/data/model/ai_api_request.dart

@@ -1,6 +1,8 @@
 import 'ai_message.dart';
 
 class AIAPIRequest {
+  static const String _defaultModel = 'gpt-oss-120b';
+
   final List<AIMessage> messages;
 
   const AIAPIRequest({
@@ -9,7 +11,7 @@ class AIAPIRequest {
 
   Map<String, dynamic> toJson() {
     return {
-      'model': 'gpt-oss-120b',
+      'model': _defaultModel,
       'messages': messages.map((m) => m.toJson()).toList(),
     };
   }

scribe/lib/scribe/ai/data/model/ai_api_response.dart

@@ -1,31 +1,44 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'ai_api_response.g.dart';
+
+@JsonSerializable()
 class AIApiResponse {
-  final String content;
+  final List<Choice> choices;
 
   const AIApiResponse({
+    required this.choices
+  });
+
+  factory AIApiResponse.fromJson(Map<String, dynamic> json) => _$AIApiResponseFromJson(json);
+
+  Map<String, dynamic> toJson() => _$AIApiResponseToJson(this);
+
+  String? get content => choices.isNotEmpty ? choices[0].message.content : null;
+}
+
+@JsonSerializable()
+class Choice {
+  final Message message;
+
+  const Choice({
+    required this.message
+  });
+
+  factory Choice.fromJson(Map<String, dynamic> json) => _$ChoiceFromJson(json);
+
+  Map<String, dynamic> toJson() => _$ChoiceToJson(this);
+}
+
+@JsonSerializable()
+class Message {
+  final String content;
+
+  const Message({
     required this.content
   });
 
-  static AIApiResponse? parse(Map<String, dynamic> json) {
-    final choices = json['choices'] as List<dynamic>?;
-    if (choices == null || choices.isEmpty) {
-      return null;
-    }
+  factory Message.fromJson(Map<String, dynamic> json) => _$MessageFromJson(json);
 
-    final firstChoice = choices[0] as Map<String, dynamic>?;
-    if (firstChoice == null) {
-      return null;
-    }
-
-    final message = firstChoice['message'] as Map<String, dynamic>?;
-    if (message == null) {
-      return null;
-    }
-
-    final content = message['content'] as String?;
-    if (content == null || content.isEmpty) {
-      return null;
-    }
-
-    return AIApiResponse(content: content);
-  }
+  Map<String, dynamic> toJson() => _$MessageToJson(this);
 }

scribe/lib/scribe/ai/data/model/ai_message.dart

@@ -1,3 +1,8 @@
+import 'package:json_annotation/json_annotation.dart';
+
+part 'ai_message.g.dart';
+
+@JsonSerializable()
 class AIMessage {
   final String role;
   final String content;
@@ -7,10 +12,7 @@ class AIMessage {
     required this.content,
   });
 
-  Map<String, dynamic> toJson() {
-    return {
-      'role': role,
-      'content': content,
-    };
-  }
+  factory AIMessage.fromJson(Map<String, dynamic> json) => _$AIMessageFromJson(json);
+
+  Map<String, dynamic> toJson() => _$AIMessageToJson(this);
 }

scribe/lib/scribe/ai/data/network/ai_api.dart

@@ -28,12 +28,7 @@ class AIApi {
     );
 
     if (response.statusCode == 200) {
-      final parsedResponse = AIApiResponse.parse(response.data);
-      if (parsedResponse != null) {
-        return parsedResponse;
-      } else {
-        throw Exception('Empty response from AI service');
-      }
+      return AIApiResponse.fromJson(response.data);
     } else {
       throw Exception('AI API returned status code: ${response.statusCode}');
     }

scribe/lib/scribe/ai/domain/model/ai_response.dart

@@ -1,5 +1,5 @@
 class AIResponse {
-  final String result;
+  final String? result;
 
   const AIResponse({required this.result});