M0-M11 狩夜人笔记初始实现：11里程碑+86测试

tests/unit/frontmatter-codec.test.ts

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+import { describe, it, expect } from 'vitest';
+import { splitFrontmatter, joinFrontmatter } from '../../apps/desktop/src/main/safe/frontmatter-codec';
+import type { DocMeta } from '@hunter/shared';
+
+describe('splitFrontmatter', () => {
+  it('无 frontmatter 的纯 Markdown', () => {
+    const { meta, body } = splitFrontmatter('# 标题\n正文');
+    expect(meta).toEqual({});
+    expect(body).toBe('# 标题\n正文');
+  });
+  it('解析四字段', () => {
+    const raw = '---\ntitle: 我的标题\ntags: [a, b]\nstar: true\nlinks: [x/y.md]\n---\n# 正文';
+    const { meta, body } = splitFrontmatter(raw);
+    expect(meta).toEqual<DocMeta>({ title: '我的标题', tags: ['a','b'], star: true, links: ['x/y.md'] });
+    expect(body).toBe('# 正文');
+  });
+  it('带引号的值', () => {
+    const { meta } = splitFrontmatter('---\ntitle: "含: 冒号"\n---\n');
+    expect(meta.title).toBe('含: 冒号');
+  });
+  it('空数组与 false 不解析为有值', () => {
+    const { meta } = splitFrontmatter('---\ntags: []\nstar: false\n---\n');
+    expect(meta.tags).toEqual([]);
+    expect(meta.star).toBe(false);
+  });
+});
+
+describe('joinFrontmatter (FR-M2 精简)', () => {
+  it('空 meta 不写围栏', () => {
+    expect(joinFrontmatter({}, '# 正文')).toBe('# 正文');
+  });
+  it('默认值不落盘：star:false / 空数组', () => {
+    const out = joinFrontmatter({ star: false, tags: [], links: [] }, 'body');
+    expect(out).toBe('body');
+  });
+  it('star:true 落盘', () => {
+    const out = joinFrontmatter({ star: true }, 'body');
+    expect(out).toContain('star: true');
+  });
+  it('含特殊字符的标题加引号', () => {
+    const out = joinFrontmatter({ title: 'a:b#c' }, 'body');
+    expect(out).toContain('title: "a:b#c"');
+  });
+  it('往返：解析后再序列化保持等价', () => {
+    const raw = '---\ntitle: T\ntags: [x, y]\nstar: true\n---\n# H\n正文';
+    const { meta, body } = splitFrontmatter(raw);
+    const out = joinFrontmatter(meta, body);
+    const again = splitFrontmatter(out);
+    expect(again.meta).toEqual(meta);
+    expect(again.body).toBe(body);
+  });
+});