feat: AG-UI 协议对齐与路由导航功能

- 前端: 添加 SSE 流式支持、stateSnapshot 事件、路由导航工具
- 前端: 实现工具调用审批流程，支持 pending 状态展示
- 后端: Agent 状态管理与会话持久化相关重构
- 文档: 新增 agent-agui-full-alignance 设计文档
- 测试: 补充相关单元测试和集成测试

apps/test/features/chat/ag_ui_event_test.dart

@@ -68,6 +68,13 @@ void main() {
       );
     });
 
+    test('maps STATE_SNAPSHOT correctly', () {
+      expect(
+        agUiEventTypeFromWire('STATE_SNAPSHOT'),
+        AgUiEventType.stateSnapshot,
+      );
+    });
+
     test('returns unknown for unknown type', () {
       expect(agUiEventTypeFromWire('UNKNOWN_TYPE'), AgUiEventType.unknown);
     });
@@ -228,7 +235,7 @@ void main() {
         'type': 'TOOL_CALL_RESULT',
         'messageId': 'msg_123',
         'toolCallId': 'tc_123',
-        'result': {'ok': true, 'eventId': 'evt_001'},
+        'content': '{"result":{"ok":true,"eventId":"evt_001"}}',
       };
 
       final event = AgUiEvent.fromJson(json);
@@ -240,6 +247,24 @@ void main() {
       expect(toolResult.result['ok'], true);
     });
 
+    test('parses ToolCallResultEvent content payload', () {
+      final json = {
+        'type': 'TOOL_CALL_RESULT',
+        'messageId': 'msg_123',
+        'toolCallId': 'tc_123',
+        'content': '{"result":{"ok":true,"eventId":"evt_001"}}',
+      };
+
+      final event = AgUiEvent.fromJson(json);
+
+      expect(event, isA<ToolCallResultEvent>());
+      final toolResult = event as ToolCallResultEvent;
+      expect(toolResult.messageId, 'msg_123');
+      expect(toolResult.toolCallId, 'tc_123');
+      expect(toolResult.result['ok'], true);
+      expect(toolResult.result['eventId'], 'evt_001');
+    });
+
     test('parses ToolCallErrorEvent', () {
       final json = {
         'type': 'TOOL_CALL_ERROR',
@@ -257,6 +282,19 @@ void main() {
       expect(toolError.code, 'EXEC_ERROR');
     });
 
+    test('parses StateSnapshotEvent', () {
+      final json = {
+        'type': 'STATE_SNAPSHOT',
+        'snapshot': {'scope': 'history_day', 'hasMore': false, 'messages': []},
+      };
+
+      final event = AgUiEvent.fromJson(json);
+
+      expect(event, isA<StateSnapshotEvent>());
+      final stateSnapshot = event as StateSnapshotEvent;
+      expect(stateSnapshot.snapshot['scope'], 'history_day');
+    });
+
     test('returns UnknownAgUiEvent for unknown type', () {
       final json = {'type': 'UNKNOWN_TYPE', 'someField': 'someValue'};