feat: 添加 Agent 步骤事件与图片附件功能

- 新增 stepStarted/stepFinished 事件类型支持
- 前端实现图片附件上传和预览功能
- 后端增强工具结果存储和事件处理
- 完善相关单元测试和集成测试

apps/lib/features/chat/presentation/bloc/chat_bloc.dart

@@ -1,4 +1,5 @@
 import 'dart:convert';
+import 'dart:typed_data';
 
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:image_picker/image_picker.dart';
@@ -10,6 +11,8 @@ import '../../data/models/ag_ui_event.dart';
 import '../../data/models/chat_list_item.dart';
 import '../../data/services/ag_ui_service.dart';
 
+enum AgentStage { intent, execution, report }
+
 class ChatState {
   final List<ChatListItem> items;
   final bool isSending;
@@ -21,6 +24,7 @@ class ChatState {
   final String? error;
   final DateTime? oldestLoadedDate;
   final bool hasEarlierHistory;
+  final AgentStage? currentStage;
 
   const ChatState({
     this.items = const [],
@@ -33,6 +37,7 @@ class ChatState {
     this.error,
     this.oldestLoadedDate,
     this.hasEarlierHistory = false,
+    this.currentStage,
   });
 
   bool get isLoading =>
@@ -55,6 +60,7 @@ class ChatState {
     Object? error = _unset,
     Object? oldestLoadedDate = _unset,
     bool? hasEarlierHistory,
+    Object? currentStage = _unset,
   }) {
     return ChatState(
       items: items ?? this.items,
@@ -71,6 +77,9 @@ class ChatState {
           ? this.oldestLoadedDate
           : oldestLoadedDate as DateTime?,
       hasEarlierHistory: hasEarlierHistory ?? this.hasEarlierHistory,
+      currentStage: currentStage == _unset
+          ? this.currentStage
+          : currentStage as AgentStage?,
     );
   }
 }
@@ -78,6 +87,9 @@ class ChatState {
 class ChatBloc extends Cubit<ChatState> {
   final AgUiService _service;
   final Map<String, String> _toolCallArgsBuffer = {};
+  final Map<String, Uint8List> _attachmentPreviewCache = <String, Uint8List>{};
+  final Map<String, Future<Uint8List?>> _attachmentPreviewInflight =
+      <String, Future<Uint8List?>>{};
 
   ChatBloc({AgUiService? service, IApiClient? apiClient})
     : _service =
@@ -102,6 +114,7 @@ class ChatBloc extends Cubit<ChatState> {
             isWaitingFirstToken: true,
             isCancelling: false,
             error: null,
+            currentStage: null,
           ),
         );
       case AgUiEventType.runFinished:
@@ -112,6 +125,7 @@ class ChatBloc extends Cubit<ChatState> {
             isStreaming: false,
             isCancelling: false,
             currentMessageId: null,
+            currentStage: null,
           ),
         );
       case AgUiEventType.runError:
@@ -124,8 +138,13 @@ class ChatBloc extends Cubit<ChatState> {
             isCancelling: false,
             currentMessageId: null,
             error: errorEvent.message,
+            currentStage: null,
           ),
         );
+      case AgUiEventType.stepStarted:
+        _handleStepStarted(event as StepStartedEvent);
+      case AgUiEventType.stepFinished:
+        _handleStepFinished(event as StepFinishedEvent);
       case AgUiEventType.textMessageStart:
         _handleTextMessageStart(event as TextMessageStartEvent);
       case AgUiEventType.textMessageContent:
@@ -151,6 +170,16 @@ class ChatBloc extends Cubit<ChatState> {
     }
   }
 
+  void _handleStepStarted(StepStartedEvent event) {
+    emit(state.copyWith(currentStage: _stageFromName(event.stepName)));
+  }
+
+  void _handleStepFinished(StepFinishedEvent event) {
+    if (state.currentStage == _stageFromName(event.stepName)) {
+      emit(state.copyWith(currentStage: null));
+    }
+  }
+
   void _handleTextMessageStart(TextMessageStartEvent startEvent) {
     final newMessage = TextMessageItem(
       id: startEvent.messageId,
@@ -327,6 +356,7 @@ class ChatBloc extends Cubit<ChatState> {
             content: msg.content ?? '',
             timestamp: timestamp,
             sender: MessageSender.user,
+            attachments: msg.attachments ?? const [],
           );
         case 'assistant':
           return TextMessageItem(
@@ -369,11 +399,20 @@ class ChatBloc extends Cubit<ChatState> {
   }
 
   Future<void> sendMessage(String content, {List<XFile>? images}) async {
+    final attachments = (images ?? const <XFile>[])
+        .map(
+          (image) => <String, dynamic>{
+            "path": image.path,
+            "mimeType": "image/*",
+          },
+        )
+        .toList();
     final userMessage = TextMessageItem(
       id: 'user-${DateTime.now().millisecondsSinceEpoch}',
       content: content,
       timestamp: DateTime.now(),
       sender: MessageSender.user,
+      attachments: attachments,
     );
     emit(
       state.copyWith(
@@ -509,7 +548,43 @@ class ChatBloc extends Cubit<ChatState> {
     }
   }
 
+  Future<Uint8List?> loadAttachmentPreview(String previewPath) async {
+    final cached = _attachmentPreviewCache[previewPath];
+    if (cached != null) {
+      return cached;
+    }
+    final pending = _attachmentPreviewInflight[previewPath];
+    if (pending != null) {
+      return pending;
+    }
+    final future = _service
+        .fetchAttachmentPreview(previewPath)
+        .then((bytes) {
+          _attachmentPreviewCache[previewPath] = bytes;
+          return bytes;
+        })
+        .catchError((_) => null)
+        .whenComplete(() {
+          _attachmentPreviewInflight.remove(previewPath);
+        });
+    _attachmentPreviewInflight[previewPath] = future;
+    return future;
+  }
+
   void clearError() {
     emit(state.copyWith(error: null));
   }
 }
+
+AgentStage? _stageFromName(String value) {
+  switch (value) {
+    case 'intent':
+      return AgentStage.intent;
+    case 'execution':
+      return AgentStage.execution;
+    case 'report':
+      return AgentStage.report;
+    default:
+      return null;
+  }
+}