feat: code blocks with language label, line numbers, and copy button

frontend/src/components/MarkdownPreview.tsx

@@ -1,7 +1,40 @@
-import { useMemo } from 'react';
-import { marked } from 'marked';
+import { useCallback, useMemo } from 'react';
+import { marked, Renderer } from 'marked';
 import DOMPurify from 'dompurify';
 
+function esc(text: string): string {
+  return text
+    .replace(/&/g, '&')
+    .replace(/</g, '&lt;')
+    .replace(/>/g, '&gt;')
+    .replace(/"/g, '&quot;');
+}
+
+const renderer = new Renderer();
+(renderer as unknown as Record<string, unknown>).code = function ({
+  text,
+  lang,
+}: {
+  text: string;
+  lang?: string;
+}) {
+  const language = (lang ?? '').split(/\s+/)[0];
+  const lines = text.replace(/\n$/, '').split('\n');
+  const linesHtml = lines
+    .map((line) => `<span class="code-line">${esc(line) || '​'}</span>`)
+    .join('\n');
+  const langLabel = language
+    ? `<span class="code-lang">${esc(language)}</span>`
+    : '';
+  return (
+    `<div class="code-block">` +
+    `<div class="code-header">${langLabel}` +
+    `<button class="copy-btn" type="button">复制</button></div>` +
+    `<pre><code class="${language ? `language-${esc(language)}` : ''}">${linesHtml}</code></pre>` +
+    `</div>`
+  );
+};
+
 interface MarkdownPreviewProps {
   content: string;
   isMarkdown: boolean;
@@ -9,15 +42,34 @@ interface MarkdownPreviewProps {
 
 export default function MarkdownPreview({ content, isMarkdown }: MarkdownPreviewProps) {
   const html = useMemo(() => {
-    const rawHtml = isMarkdown ? (marked.parse(content, { async: false }) as string) : content;
-    return DOMPurify.sanitize(rawHtml);
+    const rawHtml = isMarkdown
+      ? (marked.parse(content, { async: false, renderer }) as string)
+      : content;
+    return DOMPurify.sanitize(rawHtml, { ADD_TAGS: ['button'] });
   }, [content, isMarkdown]);
 
+  const handleClick = useCallback((e: React.MouseEvent<HTMLDivElement>) => {
+    const btn = (e.target as HTMLElement).closest<HTMLElement>('.copy-btn');
+    if (!btn) return;
+    const code = btn.closest('.code-block')?.querySelector('code');
+    if (!code) return;
+    navigator.clipboard.writeText(code.textContent ?? '').then(() => {
+      const prev = btn.textContent;
+      btn.textContent = '已复制';
+      btn.classList.add('copied');
+      setTimeout(() => {
+        btn.textContent = prev;
+        btn.classList.remove('copied');
+      }, 1500);
+    });
+  }, []);
+
   return (
     <div
       className="markdown-preview"
       data-testid="markdown-preview"
       dangerouslySetInnerHTML={{ __html: html }}
+      onClick={handleClick}
     />
   );
 }

frontend/src/styles.css

@@ -571,6 +571,85 @@ body {
   padding: 0;
 }
 
+/* ---------- Code block with header ---------- */
+.code-block {
+  margin: 0.8em 0;
+  border: 1px solid var(--rule);
+  border-radius: var(--radius);
+  overflow: hidden;
+}
+
+.code-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  background: var(--paper-alt);
+  border-bottom: 1px solid var(--rule);
+  padding: 5px 12px;
+}
+
+.code-lang {
+  font-family: 'IBM Plex Mono', monospace;
+  font-size: 11px;
+  color: var(--pine);
+  background: var(--pine-soft);
+  border: 1px solid rgba(47, 93, 80, 0.18);
+  border-radius: 4px;
+  padding: 1px 7px;
+  letter-spacing: 0.03em;
+}
+
+.copy-btn {
+  font-family: 'IBM Plex Mono', monospace;
+  font-size: 11px;
+  color: var(--ash);
+  background: none;
+  border: 1px solid var(--rule);
+  border-radius: 4px;
+  padding: 2px 9px;
+  cursor: pointer;
+  transition: color 0.1s, border-color 0.1s;
+}
+
+.copy-btn:hover { color: var(--ink); border-color: var(--ash); }
+.copy-btn.copied { color: var(--pine); border-color: var(--pine); }
+
+.code-block pre {
+  margin: 0;
+  background: var(--paper-alt);
+  border: none;
+  border-radius: 0;
+  padding: 14px 0;
+  overflow-x: auto;
+  counter-reset: line;
+}
+
+.code-block pre code {
+  display: block;
+  padding: 0;
+  background: none;
+}
+
+.code-line {
+  display: block;
+  padding: 0 16px 0 0;
+  counter-increment: line;
+  line-height: 1.6;
+}
+
+.code-line::before {
+  content: counter(line);
+  display: inline-block;
+  width: 36px;
+  padding-right: 16px;
+  text-align: right;
+  color: var(--ash-faint);
+  font-size: 12px;
+  user-select: none;
+  border-right: 1px solid var(--rule);
+  margin-right: 16px;
+}
+
 .markdown-preview ul,
 .markdown-preview ol {
   padding-left: 1.6em;