fix(frontend): 修复 Markdown 代码块折叠空白，收起滚回块顶

避免客户端覆盖 SSR 高亮；空行撑高；收起后 scrollIntoView 到代码块头部。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/globals.css

@@ -1723,6 +1723,14 @@ a.j13-mention-token:hover {
   border-radius: 0;
   font-size: inherit;
   color: inherit;
+  min-width: 100%;
+}
+/* rehype-pretty-code grid 行：保证每行有高度，避免折叠/展开后大片空白 */
+.prose-content pre code[style*="grid"] > [data-line],
+.prose-content .md-code-shiki-host code > .line,
+.prose-content .md-code-shiki-host code > [data-line] {
+  min-height: 1.65em;
+  line-height: 1.65;
 }
 .prose-content blockquote {
   border-left: 3px solid var(--accent);
@@ -1807,6 +1815,8 @@ a.j13-mention-token:hover {
   border-radius: var(--r-sm);
   background: var(--panel-2);
   overflow: hidden;
+  /* 收起后 scrollIntoView(start) 时避开 sticky 顶栏 */
+  scroll-margin-top: 5.5rem;
 }
 .prose-content .md-code-toolbar {
   display: flex;
@@ -1881,10 +1891,10 @@ a.j13-mention-token:hover {
   background: var(--accent-soft);
 }
 
-/* Shiki 双主题：跟随 html.dark */
+/* Shiki 双主题：跟随 html.dark；变量缺省时回退到正文色，避免整块「隐形」 */
 .prose-content .shiki,
 .prose-content .shiki span {
-  color: var(--shiki-light);
+  color: var(--shiki-light, var(--ink));
   background-color: transparent !important;
 }
 .prose-content .shiki {
@@ -1892,7 +1902,7 @@ a.j13-mention-token:hover {
 }
 html.dark .prose-content .shiki,
 html.dark .prose-content .shiki span {
-  color: var(--shiki-dark) !important;
+  color: var(--shiki-dark, var(--ink)) !important;
   font-style: var(--shiki-dark-font-style) !important;
   font-weight: var(--shiki-dark-font-weight) !important;
   text-decoration: var(--shiki-dark-text-decoration) !important;

frontend/components/markdown/MdCodeBlock.tsx

@@ -7,6 +7,7 @@ import {
   useEffect,
   type HTMLAttributes,
   type ReactNode,
+  type ReactElement,
 } from "react";
 import { Check, Copy, ChevronDown, ChevronUp } from "lucide-react";
 import { toast } from "@/lib/toast";
@@ -19,21 +20,51 @@ type MdCodeBlockProps = HTMLAttributes<HTMLPreElement> & {
   children?: ReactNode;
 };
 
+function isReactElement(
+  node: ReactNode
+): node is ReactElement<{ children?: ReactNode; className?: string }> {
+  return !!node && typeof node === "object" && "props" in node;
+}
+
+/** 按 data-line / 块级结构补换行，避免行间文本被拼成一行 */
 function extractText(node: ReactNode): string {
   if (node == null || typeof node === "boolean") return "";
   if (typeof node === "string" || typeof node === "number") return String(node);
-  if (Array.isArray(node)) return node.map(extractText).join("");
-  if (typeof node === "object" && "props" in node) {
-    const el = node as { props?: { children?: ReactNode } };
-    return extractText(el.props?.children);
+  if (Array.isArray(node)) {
+    return node
+      .map((child, i) => {
+        const text = extractText(child);
+        if (
+          i < node.length - 1 &&
+          isReactElement(child) &&
+          hasLineMarker(child)
+        ) {
+          return text.endsWith("\n") ? text : `${text}\n`;
+        }
+        return text;
+      })
+      .join("");
+  }
+  if (isReactElement(node)) {
+    return extractText(node.props.children);
   }
   return "";
 }
 
+function hasLineMarker(node: ReactElement): boolean {
+  const props = node.props as Record<string, unknown>;
+  return (
+    props["data-line"] != null ||
+    (typeof props.className === "string" &&
+      /\bline\b/.test(props.className))
+  );
+}
+
 function countLines(pre: HTMLElement | null, fallbackText: string): number {
   if (pre) {
-    const lineEls = pre.querySelectorAll(".line, [data-line]");
-    if (lineEls.length > 0) return lineEls.length;
+    // pretty-code / shiki：一行一个 [data-line] 或 .line，挂在 code 直下
+    const direct = pre.querySelectorAll(":scope > code > [data-line], :scope > code > .line");
+    if (direct.length > 0) return direct.length;
   }
   const text = fallbackText.replace(/\n$/, "");
   if (!text) return 0;
@@ -49,22 +80,39 @@ function readLanguage(
   if (fromData) return fromData;
   const cls = [className, el?.className].filter(Boolean).join(" ");
   const m = cls.match(/language-([\w+-]+)/);
-  return m?.[1] || "";
+  if (m?.[1]) return m[1];
+  // react-markdown：语言在子 code 上
+  const childCode = el?.querySelector(":scope > code");
+  const childCls = childCode?.className || "";
+  const m2 = childCls.match(/language-([\w+-]+)/);
+  return m2?.[1] || "";
 }
 
-/** Markdown 代码块：语言标签、复制、>5 行默认折叠；客户端可补 Shiki 双主题 */
+function readProp(
+  rest: Record<string, unknown>,
+  key: string
+): string | undefined {
+  const v = rest[key];
+  return typeof v === "string" ? v : undefined;
+}
+
+/** Markdown 代码块：语言标签、复制、>5 行默认折叠；客户端仅在未 SSR 高亮时补色 */
 export default function MdCodeBlock({ children, className, ...rest }: MdCodeBlockProps) {
+  const rootRef = useRef<HTMLDivElement>(null);
   const hostRef = useRef<HTMLDivElement>(null);
 
-  const plainText = useMemo(() => extractText(children), [children]);
-  const dataLanguage =
-    typeof (rest as Record<string, unknown>)["data-language"] === "string"
-      ? String((rest as Record<string, unknown>)["data-language"])
-      : undefined;
+  const restMap = rest as Record<string, unknown>;
+  const dataLanguage = readProp(restMap, "data-language");
+  const dataTheme = readProp(restMap, "data-theme");
 
+  const plainText = useMemo(() => extractText(children), [children]);
   const approxLines = useMemo(() => countLines(null, plainText), [plainText]);
-  const alreadyShiki =
-    typeof className === "string" && className.includes("shiki");
+
+  // rehype-pretty-code 会去掉 pre 上的 shiki class，但会保留 data-theme / data-language
+  const serverHighlighted =
+    (typeof className === "string" && className.includes("shiki")) ||
+    !!dataTheme ||
+    !!dataLanguage;
 
   const [copied, setCopied] = useState(false);
   const [expanded, setExpanded] = useState(false);
@@ -81,9 +129,9 @@ export default function MdCodeBlock({ children, className, ...rest }: MdCodeBloc
     setLanguage(readLanguage(pre, className, dataLanguage));
   }, [plainText, className, dataLanguage, clientHtml]);
 
-  // 服务端已着色时跳过；客户端预览动态补双主题
+  // 仅客户端预览（无 SSR 高亮）时动态补双主题；切勿覆盖服务端已渲染内容
   useEffect(() => {
-    if (alreadyShiki || !plainText.trim()) return;
+    if (serverHighlighted || !plainText.trim()) return;
     const lang = readLanguage(null, className, dataLanguage) || "plaintext";
     let cancelled = false;
     (async () => {
@@ -105,7 +153,7 @@ export default function MdCodeBlock({ children, className, ...rest }: MdCodeBloc
     return () => {
       cancelled = true;
     };
-  }, [plainText, className, dataLanguage, alreadyShiki]);
+  }, [plainText, className, dataLanguage, serverHighlighted]);
 
   const effectiveLines = lineCount > 0 ? lineCount : approxLines;
   const canCollapse = effectiveLines > COLLAPSE_LINE_THRESHOLD;
@@ -125,10 +173,22 @@ export default function MdCodeBlock({ children, className, ...rest }: MdCodeBloc
     }
   };
 
+  const toggleFold = () => {
+    if (expanded) {
+      setExpanded(false);
+      // 收起后滚到该代码块顶部（含工具栏），便于继续往下读
+      requestAnimationFrame(() => {
+        rootRef.current?.scrollIntoView({ block: "start", behavior: "smooth" });
+      });
+    } else {
+      setExpanded(true);
+    }
+  };
+
   const preClass = ["md-code-pre", className].filter(Boolean).join(" ");
 
   return (
-    <div className="md-code-block">
+    <div className="md-code-block" ref={rootRef}>
       <div className="md-code-toolbar">
         <span className="md-code-lang">{language || "text"}</span>
         <button
@@ -159,11 +219,7 @@ export default function MdCodeBlock({ children, className, ...rest }: MdCodeBloc
         {collapsed && <div className="md-code-fade" aria-hidden="true" />}
       </div>
       {canCollapse && (
-        <button
-          type="button"
-          className="md-code-fold"
-          onClick={() => setExpanded((v) => !v)}
-        >
+        <button type="button" className="md-code-fold" onClick={toggleFold}>
           {expanded ? (
             <>
               <ChevronUp size={14} />

frontend/components/markdown/renderMarkdown.tsx

@@ -17,6 +17,12 @@ export const prettyCodeOptions = {
   },
   keepBackground: false,
   defaultLang: "plaintext",
+  // 空行在 display:grid 下会塌缩成 0 高，补一个空格撑住行高
+  onVisitLine(element: { children: unknown[] }) {
+    if (element.children.length === 0) {
+      element.children = [{ type: "text", value: " " }];
+    }
+  },
 } as const;
 
 /** 服务端异步管线：GFM + Shiki 双主题高亮 → React 树 */