refactor(agent): 优化 architectPlan 解析兼容无 steps 的直接回答

- 移除旧的 tryParsePlan 函数，统一使用 parsePlanOutput 解析内容
- 解析 architectChat.content 时兼容没有 steps 的直接回答场景
- 改进错误处理逻辑，直接使用 parsePlanOutput 返回的错误信息
- 新增测试覆盖无 steps 的直接回答恢复场景，确保行为正确

packages/designer/src/components/widgets/agent/composables/useReplayChat.ts

@@ -35,15 +35,6 @@ function extractIntent(content: string): string {
   return content.trim();
 }
 
-/** 尝试从 content 中解析 JSON 计划 */
-function tryParsePlan(content: string): PlanResult | null {
-  const parsed = parseJsonObject<PlanResult>(content);
-  if (parsed?.intent && Array.isArray(parsed.steps)) {
-    return parsed;
-  }
-  return null;
-}
-
 /**
  * 从 editor chat 中解析步骤元数据
  * 优先读取持久化的 stepMeta 快照（新记录）；旧记录回退到正则解析 prompt
@@ -372,8 +363,9 @@ function buildRound(chats: ChatRecord[]): ConversationRound | null {
     round.attachments = architectChat.files || undefined;
     round.promptSent = architectChat.prompt || '';
 
-    // 尝试解析 plan
-    round.architectPlan = tryParsePlan(architectChat.content || '');
+    // 与运行时使用相同的解析规则，兼容没有 steps 的直接回答
+    const parsedPlan = parsePlanOutput(architectChat.content || '');
+    round.architectPlan = parsedPlan.plan;
 
     // 若 plan 解析失败，从 editor chats 重建最小 plan
     if (!round.architectPlan && editorChats.length > 0) {
@@ -408,9 +400,8 @@ function buildRound(chats: ChatRecord[]): ConversationRound | null {
     } else if (editorChats.length === 0 && !round.architectPlan) {
       const content = architectChat.content || '';
       // 模型自报错误（{"error": "..."}）→ 还原为具体规划失败原因
-      const parsed = parsePlanOutput(content);
-      if (parsed.error) {
-        round.architectError = parsed.error;
+      if (parsedPlan.error) {
+        round.architectError = parsedPlan.error;
       } else if (content.trim()) {
         // 无法解析 plan 且无 steps，content 作为直接回答
         round.architectAnswer = content;

packages/designer/tests/useReplayChat.test.ts

@@ -4,6 +4,37 @@ import { useReplayChat } from '../src/components/widgets/agent/composables/useRe
 import type { ConversationRound } from '../src/components/widgets/agent/types/agent';
 
 describe('useReplayChat', () => {
+  it('restores a direct answer without steps', async () => {
+    const rounds = ref<ConversationRound[]>([]);
+    const answer = 'VTJ 可视化设计器的主要使用流程';
+    const content = JSON.stringify({
+      intent: '介绍设计器的使用方法',
+      contextKeys: [],
+      safety: 'readonly',
+      answer
+    });
+    const { loadChatHistory } = useReplayChat(
+      {
+        getChats: vi.fn(async () => [
+          {
+            id: 'architect',
+            agentRole: 'architect',
+            prompt: '设计器如何使用',
+            content,
+            status: 'Success'
+          }
+        ]) as any,
+        setStatus: vi.fn()
+      },
+      rounds
+    );
+
+    await loadChatHistory('topic');
+
+    expect(rounds.value[0].architectAnswer).toBe(answer);
+    expect(rounds.value[0].architectPlan?.steps).toEqual([]);
+  });
+
   it('clears the previous conversation before loading an empty topic', async () => {
     const rounds = ref([{ id: 'old' }] as ConversationRound[]);
     const statusText = ref('');