feat(notes): 阶段四 Markdown 往返（tiptap-markdown 导出/导入，导图降级大纲，wikiLink 转文本）

Author: Aparencia

client/package-lock.json

@@ -78,6 +78,7 @@
     "tailwind-merge": "^3.6.0",
     "tailwindcss-animate": "^1.0.7",
     "three": "^0.185.1",
+    "tiptap-markdown": "^0.9.0",
     "uuid": "^14.0.1",
     "zustand": "^5.0.14"
   },

client/package.json

@@ -7,7 +7,7 @@
  * 通过 onSummarize 提供。
  */
 import type { Ref } from 'react';
-import { ArrowLeft, Save, HelpCircle } from 'lucide-react';
+import { ArrowLeft, Save, HelpCircle, Download } from 'lucide-react';
 import { cn } from '@/lib/utils';
 import { AIButton } from '@/components/ui/AIButton';
 
@@ -57,6 +57,8 @@ export interface NoteEditHeaderProps {
   onManualSave: () => void;
   onOpenRescue: () => void;
   onSummarize: () => void;
+  /** 阶段四：导出当前笔记为 Markdown */
+  onExportMarkdown: () => void;
 }
 
 const SECONDARY_BTN = cn(
@@ -68,7 +70,7 @@ const SECONDARY_BTN = cn(
 
 export function NoteEditHeader({
   title, titleRef, saveStatus, aiLoading,
-  onBack, onTitleBlur, onTitleKeyDown, onManualSave, onOpenRescue, onSummarize,
+  onBack, onTitleBlur, onTitleKeyDown, onManualSave, onOpenRescue, onSummarize, onExportMarkdown,
 }: NoteEditHeaderProps) {
   return (
     <div className="relative z-10 flex items-center gap-kb-sm px-kb-md py-3 border-b border-border/50 flex-shrink-0">
@@ -110,6 +112,11 @@ export function NoteEditHeader({
         保存
       </button>
 
+      <button onClick={onExportMarkdown} className={SECONDARY_BTN} title="导出为 Markdown">
+        <Download className="w-icon-sm h-icon-sm" strokeWidth={1.5} />
+        导出 Md
+      </button>
+
       <button onClick={onOpenRescue} className={SECONDARY_BTN} title="卡壳了 (Ctrl+Shift+H)">
         <HelpCircle className="w-icon-sm h-icon-sm" strokeWidth={1.5} />
         卡壳了

client/src/features/notes/components/NoteEditHeader.tsx

@@ -0,0 +1,81 @@
+/**
+ * noteMarkdown 单测：Markdown 往返一致性
+ * Unit tests for Markdown round-trip
+ */
+import { describe, it, expect } from 'vitest';
+import { noteToMarkdown, markdownToNoteContent } from './noteMarkdown';
+
+/** 构造 TipTap doc JSON 字符串 */
+function tiptapDoc(...content: unknown[]): string {
+  return JSON.stringify({ type: 'doc', content });
+}
+
+describe('noteMarkdown', () => {
+  it('标题与段落转 Markdown', () => {
+    const md = noteToMarkdown(tiptapDoc(
+      { type: 'heading', attrs: { level: 1 }, content: [{ type: 'text', text: '标题' }] },
+      { type: 'paragraph', content: [{ type: 'text', text: '正文' }] },
+    ));
+    expect(md).toContain('# 标题');
+    expect(md).toContain('正文');
+  });
+
+  it('粗体/斜体/行内代码', () => {
+    const md = noteToMarkdown(tiptapDoc({
+      type: 'paragraph',
+      content: [
+        { type: 'text', text: '粗', marks: [{ type: 'bold' }] },
+        { type: 'text', text: '斜', marks: [{ type: 'italic' }] },
+        { type: 'text', text: '码', marks: [{ type: 'code' }] },
+      ],
+    }));
+    expect(md).toContain('**粗**');
+    expect(md).toContain('*斜*');
+    expect(md).toContain('`码`');
+  });
+
+  it('无序列表', () => {
+    const md = noteToMarkdown(tiptapDoc({
+      type: 'bulletList',
+      content: [
+        { type: 'listItem', content: [{ type: 'paragraph', content: [{ type: 'text', text: '项一' }] }] },
+      ],
+    }));
+    expect(md).toMatch(/[-*] 项一/);
+  });
+
+  it('wikiLink 降级为 [[label]] 文本（方括号被 markdown 转义）', () => {
+    const md = noteToMarkdown(tiptapDoc({
+      type: 'paragraph',
+      content: [{ type: 'wikiLink', attrs: { id: 'n1', label: '目标笔记' } }],
+    }));
+    // 标签保留；方括号可能被 markdown 转义为 \[\[
+    expect(md).toContain('目标笔记');
+    expect(md.replace(/\\/g, '')).toContain('[[目标笔记]]');
+  });
+
+  it('Markdown 转 TipTap JSON（标题+粗体）', () => {
+    const json = markdownToNoteContent('# 标题\n\n**粗体** 正文');
+    const doc = JSON.parse(json) as { type: string };
+    expect(doc.type).toBe('doc');
+    const str = JSON.stringify(doc);
+    expect(str).toContain('标题');
+    expect(str).toContain('heading');
+    expect(str).toContain('bold');
+  });
+
+  it('导图笔记降级为大纲纯文本', () => {
+    const mindmap = JSON.stringify({
+      type: 'mindmap',
+      version: 1,
+      root: { id: 'r', text: '中心', children: [{ id: 'a', text: '分支', children: [] }] },
+    });
+    const md = noteToMarkdown(mindmap);
+    expect(md).toContain('中心');
+    expect(md).toContain('分支');
+  });
+
+  it('损坏内容返回空字符串', () => {
+    expect(noteToMarkdown('not json')).toBe('');
+  });
+});