fix: prevent KaTeX from treating underscores as subscripts in plain text

[Abhijay007]

Closes: #6196

PR Summary

This PR fixes an issue with KaTeX math rendering where underscores (_) were incorrectly treated as subscripts. As a result, text such as $FOO_BAR or variable_name was rendered in math mode, making code snippets and shell examples unreadable.

The root cause was that remark-math plugin treats single-dollar expressions ($text$) as inline math by default. When users write shell variables like $FOO_BAR, it unintentionally enters math mode, and KaTeX interprets _ as a subscript operator.

Changes Made

Configuration Fix

• Set singleDollarTextMath: false in the remarkMath plugin.
• Single $ is now treated as plain text, preventing accidental math rendering.
• Users must use $$...$$ for display math.

Files Modified

• ui/desktop/src/components/MarkdownContent.tsx — added configuration and preprocessing logic.

Trade-off

Note: Users must now use $$...$$ for math instead of $...$.

Why this is acceptable:

• Goose is primarily a coding assistant, where code and shell commands are more common than math.
• This matches the behavior of platforms
• This approach aligns with recommendations from the remark-math maintainers and is adopted by other platforms (e.g., GitLab) facing similar issues.

Type of Change

• Bug fix

AI Assistance

• This PR was created or reviewed with AI assistance.

Testing

Tested in the desktop UI with:

• Plain text containing $...$
• Math expressions using $$...$$
• Shell commands and code snippets to ensure underscores render correctly.

Screenshots / Demos (UX)

Before:

After:

[DOsinga]

why does $FOO_BAR enter math mode? shouldn't there be a closing tag $

[Abhijay007]

why does $FOO_BAR enter math mode? shouldn't there be a closing tag $

The thing is with the default remark-math configuration, singleDollarTextMath is enabled (true) by default, which means a single $ is enough to trigger inline math mode. When the parser encounters a $, it starts looking for a closing $.

However, within math mode, the underscore character (_) is interpreted as a LaTeX subscript operator. As a result, a string like $FOO_BAR is parsed as the start of inline math, where FOO_BAR is interpreted as FOO with BAR as a subscript. Even if a closing $ is missing, KaTeX/remark-math still attempts to parse it as incomplete math, which leads to rendering issues.

[DOsinga]

yes, but my concern is that if you run this test:

describe('KaTeX Math Rendering - singleDollarTextMath: false', () => {
it('treats single dollar signs as plain text', async () => {
const content = 'The formula $x_i represents the i-th element.';

  const { container } = render(<MarkdownContent content={content} />);

  await waitFor(() => {
    const katexElements = container.querySelectorAll('.katex');
    expect(katexElements.length).toBe(0);
    expect(container).toHaveTextContent('$x_i');
  });
});
});

on main, it succeeds, so it is not that if it fails to find a closing $ it executes.

[Abhijay007]

yes, but my concern is that if you run this test:

describe('KaTeX Math Rendering - singleDollarTextMath: false', () => { it('treats single dollar signs as plain text', async () => { const content = 'The formula $x_i represents the i-th element.';

  const { container } = render(<MarkdownContent content={content} />);

  await waitFor(() => {
    const katexElements = container.querySelectorAll('.katex');
    expect(katexElements.length).toBe(0);
    expect(container).toHaveTextContent('$x_i');
  });
});
});

on main, it succeeds, so it is not that if it fails to find a closing $ it executes.

Um I tried this test on main, it's failing for me for the same reason that it counts it as a subscript