feat(renderer): markdown lib (marked + DOMPurify + mermaid placeholders)

tests/unit/lib/markdown.test.ts

@@ -0,0 +1,30 @@
+import { describe, it, expect } from 'vitest';
+import { renderMarkdown } from '@/lib/markdown';
+
+describe('renderMarkdown', () => {
+  it('renders headings', () => {
+    const html = renderMarkdown('# Hello');
+    expect(html).toContain('<h1>Hello</h1>');
+  });
+
+  it('renders bold and italic', () => {
+    const html = renderMarkdown('**bold** and *italic*');
+    expect(html).toContain('<strong>bold</strong>');
+    expect(html).toContain('<em>italic</em>');
+  });
+
+  it('renders code blocks with language class', () => {
+    const html = renderMarkdown('```js\nconst x = 1;\n```');
+    expect(html).toContain('language-js');
+  });
+
+  it('renders mermaid blocks with a placeholder', () => {
+    const html = renderMarkdown('```mermaid\ngraph TD\nA-->B\n```');
+    expect(html).toContain('data-mermaid-source=');
+  });
+
+  it('sanitizes dangerous HTML', () => {
+    const html = renderMarkdown('<script>alert(1)</script>');
+    expect(html).not.toContain('<script>');
+  });
+});