diff --git a/apps/ai-game-creator-shell/src/components/ChatMarkdownMessage/index.tsx b/apps/ai-game-creator-shell/src/components/ChatMarkdownMessage/index.tsx
index d8acce153..543351e25 100644
--- a/apps/ai-game-creator-shell/src/components/ChatMarkdownMessage/index.tsx
+++ b/apps/ai-game-creator-shell/src/components/ChatMarkdownMessage/index.tsx
@@ -6,6 +6,7 @@ import {
   Component,
   createContext,
   isValidElement,
+  memo,
   useContext,
 } from 'react';
 import ReactMarkdown, { type Components } from 'react-markdown';
@@ -302,7 +303,15 @@ const streamingMarkdownComponents: Components = {
   p: StreamingMarkdownParagraph,
 };
 
-export function ChatMarkdownMessage({
+/**
+ * 解析器的输入只有 `text` / `role` / `streaming` / `preserveBlankLines` 这几个标量，所以
+ * 内容没变的旧消息在父级重渲染时可以直接跳过：Markdown 解析与语法高亮是这个组件里最贵的
+ * 两件事（`react-markdown` 每次渲染都会重建 `unified()` 处理器并重跑全部插件），而旧消息
+ * 的文本永远不会再改。
+ */
+export const ChatMarkdownMessage = memo(ChatMarkdownMessageImpl);
+
+function ChatMarkdownMessageImpl({
   text,
   role,
   streaming = false,
@@ -317,8 +326,13 @@ export function ChatMarkdownMessage({
       <ReactMarkdown
         skipHtml
         remarkPlugins={[remarkGfm]}
+        // 流式中不高亮：高亮要跑一遍完整 AST + highlight.js，而流式增量会让同一段代码
+        // 每来一个 chunk 就重新高亮一次（文本还在长，结果立刻作废）。文本定稿时
+        // `streaming` 变回 false，这一笔高亮自然补上。
         rehypePlugins={
-          text.length <= MAX_HIGHLIGHT_CHARACTERS ? [rehypeHighlight] : []
+          streaming || text.length > MAX_HIGHLIGHT_CHARACTERS
+            ? []
+            : [rehypeHighlight]
         }
         components={
           streaming ? streamingMarkdownComponents : markdownComponents
diff --git a/apps/ai-game-creator-shell/src/view/project-development/chat/components/AgentReasoning/AgentReasoning.tsx b/apps/ai-game-creator-shell/src/view/project-development/chat/components/AgentReasoning/AgentReasoning.tsx
index f2d836663..c3d7da397 100644
--- a/apps/ai-game-creator-shell/src/view/project-development/chat/components/AgentReasoning/AgentReasoning.tsx
+++ b/apps/ai-game-creator-shell/src/view/project-development/chat/components/AgentReasoning/AgentReasoning.tsx
@@ -1,5 +1,5 @@
 import { ChevronDown, Lightbulb } from 'lucide-react';
-import { useState } from 'react';
+import { memo, useMemo, useState } from 'react';
 
 import { AgentMessageContent } from '../../../../../../../../packages/shared/src/components/AgentMessageContent';
 import { AgentProcessSummary } from '../../../../../../../../packages/shared/src/components/AgentProcessSummary';
@@ -12,7 +12,9 @@ import { agentProcessPreview } from '../../../../../features/project-workspace/a
  * 折叠态是单行纯文本预览（Markdown 只取可见文字，符号不进预览）；展开态复用助手正文的
  * 安全 Markdown 链路。这里只有表现与展开态，思考内容本身由两条产品路径各自的事实源提供。
  */
-export function AgentReasoning({
+export const AgentReasoning = memo(AgentReasoningImpl);
+
+function AgentReasoningImpl({
   text,
   label = '思考过程',
   testId,
@@ -22,7 +24,12 @@ export function AgentReasoning({
   testId?: string;
 }) {
   const [expanded, setExpanded] = useState(false);
-  const preview = agentProcessPreview(text);
+  /*
+    折叠态那一行预览是**完整 Markdown AST 解析**（`remark-parse` + `unified`），和展开态
+    `react-markdown` 那次解析是两笔开销；上面那层 `memo` 让内容没变的思考块整个跳过，
+    这里的 `useMemo` 再兜一层，避免同一文本在真正重渲染时被重算。
+  */
+  const preview = useMemo(() => agentProcessPreview(text), [text]);
   return (
     <AgentMessageContent
       as="details"