fix(web): preserve XML-like tags in user messages

apps/web/src/components/ChatMarkdown.tsx

@@ -115,6 +115,8 @@ interface ChatMarkdownProps {
   className?: string;
   /** Treat single newlines as hard breaks — chat-style user input. */
   lineBreaks?: boolean;
+  /** Parse sanitized raw HTML instead of displaying its source text. */
+  parseRawHtml?: boolean;
 }
 
 const EMPTY_MARKDOWN_SKILLS: ReadonlyArray<Pick<ServerProviderSkill, "name" | "displayName">> = [];
@@ -1256,6 +1258,7 @@ function ChatMarkdown({
   skills = EMPTY_MARKDOWN_SKILLS,
   className,
   lineBreaks = false,
+  parseRawHtml = true,
 }: ChatMarkdownProps) {
   const { resolvedTheme } = useTheme();
   const createAssetUrl = useAtomQueryRunner(assetEnvironment.createUrl, {
@@ -1554,6 +1557,9 @@ function ChatMarkdown({
     ],
   );
 
+  // react-markdown converts unparsed HTML nodes to text when skipHtml is false.
+  // Keep that behavior explicit because literal mode depends on escaping the
+  // complete source token instead of dropping it from the rendered message.
   return (
     <div
       className={cn(
@@ -1566,7 +1572,8 @@ function ChatMarkdown({
         remarkPlugins={
           lineBreaks ? CHAT_MARKDOWN_REMARK_PLUGINS_WITH_BREAKS : CHAT_MARKDOWN_REMARK_PLUGINS
         }
-        rehypePlugins={CHAT_MARKDOWN_REHYPE_PLUGINS}
+        rehypePlugins={parseRawHtml ? CHAT_MARKDOWN_REHYPE_PLUGINS : undefined}
+        skipHtml={false}
         components={markdownComponents}
         urlTransform={markdownUrlTransform}
       >

apps/web/src/components/chat/MessagesTimeline.test.tsx

@@ -218,6 +218,17 @@ function buildUserTimelineEntry(text: string) {
   };
 }
 
+function buildAssistantTimelineEntry(text: string) {
+  const entry = buildUserTimelineEntry(text);
+  return {
+    ...entry,
+    message: {
+      ...entry.message,
+      role: "assistant" as const,
+    },
+  };
+}
+
 describe("MessagesTimeline", () => {
   it("keeps assistant changed-files headers sticky below the thread header", async () => {
     const { MessagesTimeline } = await import("./MessagesTimeline");
@@ -414,6 +425,121 @@ describe("MessagesTimeline", () => {
     expect(markup).toContain('data-user-message-collapsible="false"');
   });
 
+  it("preserves arbitrary XML-like tags and comparisons in rendered user messages", async () => {
+    const { MessagesTimeline } = await import("./MessagesTimeline");
+    const markup = renderToStaticMarkup(
+      <MessagesTimeline
+        {...buildProps()}
+        timelineEntries={[
+          buildUserTimelineEntry(
+            [
+              'Without reading a file, do you have <global-agent-instructions scope="workspace">',
+              'Before <nested data-value="a&b">inside</nested> after',
+              "</global-agent-instructions> in your context?",
+              "Comparison: 2 < 3 and 5 > 4.",
+            ].join("\n"),
+          ),
+        ]}
+      />,
+    );
+
+    expect(markup).toContain("&lt;global-agent-instructions scope=&quot;workspace&quot;&gt;");
+    expect(markup).toContain(
+      "Before &lt;nested data-value=&quot;a&amp;b&quot;&gt;inside&lt;/nested&gt; after",
+    );
+    expect(markup).toContain("&lt;/global-agent-instructions&gt; in your context?");
+    expect(markup).toContain("Comparison: 2 &lt; 3 and 5 &gt; 4.");
+  });
+
+  it("preserves XML-like source inside user code spans and fences", async () => {
+    const { MessagesTimeline } = await import("./MessagesTimeline");
+    const markup = renderToStaticMarkup(
+      <MessagesTimeline
+        {...buildProps()}
+        timelineEntries={[
+          buildUserTimelineEntry(
+            [
+              'Inline `<tag attr="x">`',
+              "",
+              "```xml",
+              '<root><child enabled="true" /></root>',
+              "```",
+            ].join("\n"),
+          ),
+        ]}
+      />,
+    );
+
+    expect(markup).toContain("<code>&lt;tag attr=&quot;x&quot;&gt;</code>");
+    expect(markup).toContain("&lt;root&gt;&lt;child enabled=&quot;true&quot; /&gt;&lt;/root&gt;");
+  });
+
+  it("renders unsafe user HTML as inert source text", async () => {
+    const { MessagesTimeline } = await import("./MessagesTimeline");
+    const markup = renderToStaticMarkup(
+      <MessagesTimeline
+        {...buildProps()}
+        timelineEntries={[
+          buildUserTimelineEntry(
+            '<script>globalThis.__t3Xss = 1</script><img src="x" onerror="globalThis.__t3Xss = 2">',
+          ),
+        ]}
+      />,
+    );
+
+    expect(markup).toContain("&lt;script&gt;globalThis.__t3Xss = 1&lt;/script&gt;");
+    expect(markup).toContain(
+      "&lt;img src=&quot;x&quot; onerror=&quot;globalThis.__t3Xss = 2&quot;&gt;",
+    );
+    expect(markup).not.toMatch(/<script(?:\s|>)/i);
+    expect(markup).not.toMatch(/<img(?:\s|>)/i);
+  });
+
+  it("continues to render sanitized raw HTML in assistant messages", async () => {
+    const { MessagesTimeline } = await import("./MessagesTimeline");
+    const markup = renderToStaticMarkup(
+      <MessagesTimeline
+        {...buildProps()}
+        timelineEntries={[
+          buildAssistantTimelineEntry("<details><summary>More</summary>Details</details>"),
+        ]}
+      />,
+    );
+
+    expect(markup).toContain('data-markdown-details=""');
+    expect(markup).toContain("More");
+    expect(markup).not.toContain("&lt;details&gt;");
+  });
+
+  it("sanitizes executable HTML while preserving supported assistant markup", async () => {
+    const { MessagesTimeline } = await import("./MessagesTimeline");
+    const markup = renderToStaticMarkup(
+      <MessagesTimeline
+        {...buildProps()}
+        timelineEntries={[
+          buildAssistantTimelineEntry(
+            [
+              '<details open onclick="globalThis.__t3Xss = 1">',
+              "<summary>Safe details</summary>",
+              "<script>globalThis.__t3Xss = 2</script>",
+              '<img src="x" onerror="globalThis.__t3Xss = 3">',
+              '<a href="javascript:globalThis.__t3Xss = 4">Unsafe link</a>',
+              "</details>",
+            ].join(""),
+          ),
+        ]}
+      />,
+    );
+
+    expect(markup).toContain('data-markdown-details=""');
+    expect(markup).toContain("Safe details");
+    expect(markup).not.toMatch(/<script(?:\s|>)/i);
+    expect(markup).not.toContain("onclick=");
+    expect(markup).not.toContain("onerror=");
+    expect(markup).not.toContain("javascript:");
+    expect(markup).not.toContain("globalThis.__t3Xss");
+  });
+
   it("renders inline terminal labels with the composer chip UI", async () => {
     const { MessagesTimeline } = await import("./MessagesTimeline");
     const markup = renderToStaticMarkup(

apps/web/src/components/chat/MessagesTimeline.tsx

@@ -1553,6 +1553,7 @@ const UserMessageBody = memo(function UserMessageBody(props: {
             skills={props.skills}
             className="text-foreground"
             lineBreaks
+            parseRawHtml={false}
           />
         ) : null}
         {trailingWhitespace ? <span aria-hidden="true">{trailingWhitespace}</span> : null}
@@ -1575,6 +1576,7 @@ const UserMessageBody = memo(function UserMessageBody(props: {
                   skills={props.skills}
                   className="text-foreground"
                   lineBreaks
+                  parseRawHtml={false}
                 />
               </div>
             ) : null
@@ -1663,6 +1665,7 @@ const UserMessageBody = memo(function UserMessageBody(props: {
           skills={props.skills}
           className="text-foreground"
           lineBreaks
+          parseRawHtml={false}
         />,
       );
     } else if (inlinePrefix.length === 0) {
@@ -1688,6 +1691,7 @@ const UserMessageBody = memo(function UserMessageBody(props: {
       skills={props.skills}
       className="text-foreground"
       lineBreaks
+      parseRawHtml={false}
     />
   );
 });