fix(chat): align code block actions and restore horizontal scrolling across desktop and mobile (#564)

* fix(chat): use streamdown code controls for markdown blocks

* fix(chat): keep code block actions in header row and body scrollable

* fix(chat): allow horizontal scrolling in virtualized code output

* fix(chat): preserve mobile horizontal scrolling in code blocks

* fix: refine chat code block header and actions styling

* fix: restore themed code highlighting and polish chat code blocks

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/components/chat/MarkdownRenderer.tsx

@@ -1,6 +1,6 @@
 import React from 'react';
 import { Streamdown } from 'streamdown';
-import { code } from '@streamdown/code';
+import { createCodePlugin } from '@streamdown/code';
 import { renderMermaidASCII, renderMermaidSVG } from 'beautiful-mermaid';
 import 'streamdown/styles.css';
 import { FadeInOnReveal } from './message/FadeInOnReveal';
@@ -124,6 +124,20 @@ const useMarkdownShikiThemes = (): readonly [string | object, string | object] =
   return isVSCode ? themes : fallbackThemes;
 };
 
+type StreamdownCodeThemes = NonNullable<Parameters<typeof createCodePlugin>[0]>['themes'];
+
+const useStreamdownPlugins = (shikiThemes: readonly [string | object, string | object]) => {
+  return React.useMemo(
+    () => ({
+      code: createCodePlugin({
+        // Streamdown code plugin runtime accepts theme objects, but current type only models bundled theme names.
+        themes: shikiThemes as unknown as StreamdownCodeThemes,
+      }),
+    }),
+    [shikiThemes],
+  );
+};
+
 const useCurrentMermaidTheme = () => {
   const themeSystem = useOptionalThemeSystem();
   const fallbackLight = getDefaultTheme(false);
@@ -543,9 +557,6 @@ const MermaidBlock: React.FC<{ source: string; mode: 'svg' | 'ascii' }> = ({ sou
 };
 
 const CodeBlockWrapper: React.FC<CodeBlockWrapperProps> = ({ children, className, style, ...props }) => {
-  const [copied, setCopied] = React.useState(false);
-  const codeRef = React.useRef<HTMLDivElement>(null);
-  const { isMobile } = useDeviceInfo();
   const mermaidInfo = getMermaidInfo(children);
   const mermaidRenderingMode = useUIStore((state) => state.mermaidRenderingMode);
   const codeChild = React.useMemo(
@@ -583,7 +594,6 @@ const CodeBlockWrapper: React.FC<CodeBlockWrapperProps> = ({ children, className
     const bg = normalizeDeclarationString((style as React.CSSProperties).backgroundColor);
     if (bg.value) {
       next.backgroundColor = bg.value;
-      (next as Record<string, string>)['--shiki-light-bg'] = bg.value;
     }
     for (const [k, v] of Object.entries(bg.vars)) {
       (next as Record<string, string>)[k] = v;
@@ -592,7 +602,6 @@ const CodeBlockWrapper: React.FC<CodeBlockWrapperProps> = ({ children, className
     const fg = normalizeDeclarationString((style as React.CSSProperties).color);
     if (fg.value) {
       next.color = fg.value;
-      (next as Record<string, string>)['--shiki-light'] = fg.value;
     }
     for (const [k, v] of Object.entries(fg.vars)) {
       (next as Record<string, string>)[k] = v;
@@ -605,49 +614,14 @@ const CodeBlockWrapper: React.FC<CodeBlockWrapperProps> = ({ children, className
     return <MermaidBlock source={mermaidInfo.source} mode={mermaidRenderingMode} />;
   }
 
-  const getCodeContent = (): string => {
-    if (!codeRef.current) return '';
-    const codeEl = codeRef.current.querySelector('code');
-
-    return codeEl?.innerText || '';
-  };
-
-  const handleCopy = async () => {
-    const code = getCodeContent();
-    if (!code) return;
-    const result = await copyTextToClipboard(code);
-    if (result.ok) {
-      setCopied(true);
-      setTimeout(() => setCopied(false), 2000);
-    } else {
-      console.error('Failed to copy:', result.error);
-    }
-  };
-
   return (
-    <div className="group relative" ref={codeRef}>
+    <pre
-      <pre
+      {...props}
-        {...props}
+      className={cn(className, 'w-full min-w-full')}
-        className={cn(className)}
+      style={normalizedStyle}
-        style={normalizedStyle}
+    >
-      >
+      {codeChild}
-        {codeChild}
+    </pre>
-      </pre>
-      <div
-        className={cn(
-          'absolute top-1 right-2 transition-opacity',
-          isMobile ? 'opacity-100' : 'opacity-0 group-hover:opacity-100',
-        )}
-      >
-        <button
-          onClick={handleCopy}
-          className="p-1 rounded hover:bg-interactive-hover/60 text-muted-foreground hover:text-foreground transition-colors"
-          title="Copy"
-        >
-          {copied ? <RiCheckLine className="size-3.5" /> : <RiFileCopyLine className="size-3.5" />}
-        </button>
-      </div>
-    </div>
   );
 };
 
@@ -656,12 +630,8 @@ const streamdownComponents = {
   table: TableWrapper,
 };
 
-const streamdownPlugins = {
-  code,
-};
-
 const streamdownControls = {
-  code: false,
+  code: true,
   table: false,
 };
 
@@ -821,6 +791,7 @@ export const MarkdownRenderer: React.FC<MarkdownRendererProps> = ({
   useMermaidInlineInteractions({ containerRef: streamdownContainerRef, mermaidBlocks, onShowPopup });
 
   const shikiThemes = useMarkdownShikiThemes();
+  const streamdownPlugins = useStreamdownPlugins(shikiThemes);
   const currentMermaidTheme = useCurrentMermaidTheme();
   const componentKey = `markdown-${part?.id ? `part-${part.id}` : `message-${messageId}`}`;
 
@@ -829,7 +800,7 @@ export const MarkdownRenderer: React.FC<MarkdownRendererProps> = ({
     : 'streamdown-content';
 
   const markdownContent = (
-    <div className={cn('break-words', className)} ref={streamdownContainerRef}>
+    <div className={cn('break-words w-full min-w-0', className)} ref={streamdownContainerRef}>
       <Streamdown
          key={`streamdown-${componentKey}-${currentMermaidTheme.metadata.id}:${currentMermaidTheme.metadata.variant}`}
          mode={isStreaming ? 'streaming' : 'static'}
@@ -838,7 +809,7 @@ export const MarkdownRenderer: React.FC<MarkdownRendererProps> = ({
          controls={streamdownControls}
          plugins={streamdownPlugins}
          components={streamdownComponents}
-       >
+        >
         {content}
       </Streamdown>
     </div>
@@ -887,6 +858,7 @@ export const SimpleMarkdownRenderer: React.FC<{
   });
 
   const shikiThemes = useMarkdownShikiThemes();
+  const streamdownPlugins = useStreamdownPlugins(shikiThemes);
   const currentMermaidTheme = useCurrentMermaidTheme();
 
   const streamdownClassName = variant === 'tool'
@@ -894,7 +866,7 @@ export const SimpleMarkdownRenderer: React.FC<{
     : 'streamdown-content';
 
   return (
-    <div className={cn('break-words', className)} ref={streamdownContainerRef}>
+    <div className={cn('break-words w-full min-w-0', className)} ref={streamdownContainerRef}>
       <Streamdown
         key={`streamdown-simple-${currentMermaidTheme.metadata.id}:${currentMermaidTheme.metadata.variant}`}
         mode="static"

packages/ui/src/components/chat/message/parts/VirtualizedCodeBlock.tsx

@@ -194,7 +194,7 @@ export const VirtualizedCodeBlock: React.FC<VirtualizedCodeBlockProps> = React.m
     return (
       <div
         className="typography-code font-mono w-full min-w-0 oc-virtualized-prism"
-        style={{ maxHeight, overflowY: 'auto' }}
+        style={{ maxHeight, overflow: 'auto' }}
       >
         {prismThemeCss ? <style>{prismThemeCss}</style> : null}
         {lines.map((line, idx) => (
@@ -256,7 +256,7 @@ const VirtualizedRows: React.FC<VirtualizedRowsProps> = React.memo(({
     <div
       ref={parentRef}
       className="typography-code font-mono w-full min-w-0 oc-virtualized-prism"
-      style={{ maxHeight, overflowY: 'auto' }}
+      style={{ maxHeight, overflow: 'auto' }}
     >
       {prismThemeCss ? <style>{prismThemeCss}</style> : null}
       <div
@@ -327,8 +327,7 @@ const Row: React.FC<RowProps> = React.memo(({ line, language, showLineNumbers, s
           </div>
         ) : (
           <div
-            className="whitespace-pre-wrap break-all"
+            className="whitespace-pre"
-            style={{ overflowWrap: 'anywhere' }}
             dangerouslySetInnerHTML={{ __html: html }}
           />
         )}

packages/ui/src/index.css

@@ -825,12 +825,28 @@ html:not(.dark) .chat-scroll {
 /* Streamdown code blocks: ensure light/dark Shiki vars work even when Tailwind doesn't scan Streamdown's internal class names. */
 .streamdown-content [data-streamdown="code-block-body"] {
   font-size: var(--text-code);
-  background-color: var(--shiki-light-bg, transparent);
+  background-color: transparent;
   color: var(--shiki-light, inherit);
 }
 
+.streamdown-content [data-streamdown="code-block-body"] span[style*="--sdm-c"] {
+  color: var(--sdm-c) !important;
+}
+
+.streamdown-content [data-streamdown="code-block-body"] span[style*="--sdm-tbg"] {
+  background-color: var(--sdm-tbg) !important;
+}
+
+.streamdown-content [data-streamdown="code-block-body"] span[style*="--shiki-light"] {
+  color: var(--shiki-light) !important;
+}
+
+.streamdown-content [data-streamdown="code-block-body"] span[style*="--shiki-light-bg"] {
+  background-color: var(--shiki-light-bg) !important;
+}
+
 .dark .streamdown-content [data-streamdown="code-block-body"] {
-  background-color: var(--shiki-dark-bg, var(--shiki-light-bg, transparent));
+  background-color: transparent;
   color: var(--shiki-dark, var(--shiki-light, inherit));
 }
 
@@ -838,6 +854,10 @@ html:not(.dark) .chat-scroll {
   color: var(--shiki-dark) !important;
 }
 
+.dark .streamdown-content [data-streamdown="code-block-body"] span[style*="--shiki-dark-bg"] {
+  background-color: var(--shiki-dark-bg) !important;
+}
+
 /* Fix list styling - override Tailwind reset */
 .streamdown-content ul {
   list-style-type: disc;
@@ -857,13 +877,125 @@ html:not(.dark) .chat-scroll {
 
 /* Reduce code block header height */
 [data-streamdown="code-block-header"] {
+  margin: 0;
   padding: 0.375rem 0.75rem;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  width: 100%;
+  padding-right: 5.25rem;
+  border: 0;
+  border-bottom: 1px solid var(--interactive-border);
+  border-radius: 0;
+  background: var(--surface-muted);
 }
 
-/* Disable Streamdown's code block virtualization (content-visibility) to avoid late height changes that break scroll-to-bottom. */
+/* Disable Streamdown's code block virtualization and keep block chrome fixed */
 .streamdown-content [data-streamdown="code-block"] {
   content-visibility: visible !important;
   contain-intrinsic-size: none !important;
+  position: relative;
+  display: flex;
+  flex-direction: column;
+  padding: 0 !important;
+  box-sizing: border-box;
+  inline-size: 100%;
+  max-inline-size: 100%;
+  min-inline-size: 0;
+  overflow: hidden;
+  background: var(--surface-background);
+  border: 1px solid var(--interactive-border);
+  border-radius: 0.75rem;
+}
+
+.streamdown-content [data-streamdown="code-block"] > div:not([data-streamdown]) {
+  position: absolute;
+  top: 0;
+  right: 0;
+  margin-top: 0;
+  height: 2rem;
+  z-index: 6;
+  pointer-events: none;
+}
+
+/* Streamdown code block body: scroll text content within the card body */
+.streamdown-content [data-streamdown="code-block-body"] {
+  display: block;
+  inline-size: 100%;
+  min-width: 0;
+  max-width: 100%;
+  margin: 0;
+  padding: 0;
+  overflow-x: auto;
+  overflow-y: hidden;
+  box-sizing: border-box;
+  scrollbar-gutter: stable;
+  background: transparent;
+  border: 0;
+  border-radius: 0;
+}
+
+.streamdown-content [data-streamdown="code-block-body"] pre {
+  display: block;
+  width: 100%;
+  min-width: 100%;
+  max-width: 100%;
+  margin: 0 !important;
+  padding: 0.75rem !important;
+  border: 0 !important;
+  border-radius: 0 !important;
+  box-shadow: none !important;
+  background: transparent !important;
+}
+
+.streamdown-content [data-streamdown="code-block-body"] > * {
+  border: 0 !important;
+  border-radius: 0 !important;
+  box-shadow: none !important;
+  background: transparent !important;
+}
+
+.streamdown-content [data-streamdown="code-block-body"] code {
+  white-space: pre;
+  overflow-wrap: normal;
+  word-break: normal;
+  background: transparent !important;
+}
+
+.streamdown-content [data-streamdown="code-block-actions"] {
+  pointer-events: auto;
+  transition: opacity 0.15s ease;
+  border: 0 !important;
+  background: transparent !important;
+  box-shadow: none !important;
+  gap: 0.125rem;
+}
+
+.streamdown-content [data-streamdown="code-block-actions"] button {
+  border: 0 !important;
+  background: transparent !important;
+  box-shadow: none !important;
+  padding: 0.25rem !important;
+  min-width: 1.5rem;
+  min-height: 1.5rem;
+}
+
+.streamdown-content [data-streamdown="code-block-actions"] button svg {
+  width: 0.875rem;
+  height: 0.875rem;
+}
+
+@media (hover: hover) and (pointer: fine) {
+  .streamdown-content [data-streamdown="code-block"] [data-streamdown="code-block-actions"] {
+    opacity: 0;
+    pointer-events: none;
+  }
+
+  .streamdown-content [data-streamdown="code-block"]:hover [data-streamdown="code-block-actions"],
+  .streamdown-content [data-streamdown="code-block"]:focus-within [data-streamdown="code-block-actions"] {
+    opacity: 1;
+    pointer-events: auto;
+  }
 }
 
 /* Mermaid block: position context for controls wrapper. */

packages/ui/src/styles/mobile.css

@@ -150,6 +150,13 @@
     -webkit-overflow-scrolling: touch;
   }
 
+  /* Keep Streamdown code blocks horizontally scrollable on mobile. */
+  :root.mobile-pointer:not(.desktop-runtime) .streamdown-content [data-streamdown="code-block-body"] {
+    overflow-x: auto !important;
+    overflow-y: hidden !important;
+    -webkit-overflow-scrolling: touch;
+  }
+
   /* Fix mobile viewport height */
   :root.mobile-pointer:not(.desktop-runtime),
   :root.mobile-pointer:not(.desktop-runtime) body {