diff --git a/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx b/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx
index b7275ee560..6996550c52 100644
--- a/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx
+++ b/client/src/components/Chat/Messages/Content/Parts/__tests__/TextAttachment.test.tsx
@@ -222,4 +222,40 @@ describe('AttachmentGroup', () => {
     expect(container.querySelector('pre')?.textContent).toBe('{"ok":true}');
     expect(screen.getByTestId('file-container')).toHaveTextContent('output.json');
   });
+
+  it('keeps long grouped text previews clamped until the nested preview is expanded', () => {
+    setScrollHeight(800);
+    const longJson = Array.from({ length: 1000 }, (_, index) => `{"line":${index}}`).join('\n');
+    const attachments = [
+      textAttachment({
+        file_id: 'archive',
+        filename: 'archive.zip',
+        type: 'application/zip',
+        text: undefined as unknown as string,
+      }),
+      textAttachment({
+        file_id: 'json',
+        filename: 'output.json',
+        filepath: '/files/output.json',
+        text: longJson,
+      }),
+    ] as TAttachment[];
+
+    const { container } = render(<AttachmentGroup attachments={attachments} />);
+    const groupToggle = screen.getByRole('button', { name: 'com_ui_show_n_files' });
+    fireEvent.click(groupToggle);
+
+    expect(screen.getByText('output.json')).toBeInTheDocument();
+    const pre = container.querySelector('pre');
+    expect(pre).not.toBeNull();
+    expect(pre).toHaveStyle({ maxHeight: '320px' });
+    const previewToggle = screen.getByRole('button', { name: 'Show all' });
+    expect(previewToggle).toHaveAttribute('aria-expanded', 'false');
+
+    fireEvent.click(previewToggle);
+    expect(screen.getByRole('button', { name: 'Collapse' })).toHaveAttribute(
+      'aria-expanded',
+      'true',
+    );
+  });
 });