fix(tui): render LaTeX math in messages as Unicode - #53418

Issue for this PR

Closes #53648

#40508 tracks LaTeX rendering for the v2 TUI.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Models often write math as \( … \), \[ … \] or $$ … $$ in prose. The TUI passes message text straight to the opentui <markdown> component, which has no math support, so formulas show as raw LaTeX (e.g. \text{saved} = (\text{units …}) \times \text{rate} or \(0.5^5 \approx 3\%\)).

This adds renderMath (packages/tui/src/util/math.ts), a small LaTeX-to-Unicode pass applied to assistant text and reasoning before markdown rendering. The two examples above become saved = (units …) × rate and 0.5⁵ ≈ 3%. It handles \text{}, fractions, square roots, superscripts and subscripts (falling back to _(…) when Unicode has no subscript for a letter), Greek letters, common operators and arrows, \left/\right, \mathbb, and multi-line environments.

What it leaves alone:

• Code spans and fenced code blocks are left untouched.
• A single $ is not treated as math, so amounts like "$900M" stay as written.
• Math that is still open while a reply streams stays raw until the closing delimiter arrives.
• Unknown commands are kept as written.

#45339 added fenced ```latex rendering to v2. This covers prose math on the current TUI.

How did you verify your code works?

• Unit tests in packages/tui/test/util/math.test.ts (7 tests), and bun run typecheck in packages/tui.
• Ran renderMath over every assistant message containing math delimiters in my local session database (16 parts). 3 changed, all correctly, and nothing inside code was modified.

Screenshots / recordings

Rendered with the TUI's <markdown> component and default opencode theme.

Before: the delimiters and commands show raw.

After: the same text after renderMath. Inline code is unchanged.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR