TUI: option to keep TeX math verbatim in the final render, for terminals that typeset it

Summary

Please add a way to keep TeX math verbatim in the TUI's final render — an option, or a rule that leaves $…$ / $$…$$ / \(…\) / \[…\] untouched when the terminal says it can typeset them — so that a terminal which renders LaTeX in command output receives the bytes the model wrote.

Background

Until #45501 and #45612 (0.155 alphas) the TUI's final redraw ran assistant text through CommonMark with no math protection. On 0.153.4 the effect on a display block is:

• \\ → \ (every matrix / aligned / cases row separator loses a backslash),
• \, → ,, \! → !, \[ / \] → [ / ],
• a line holding only = — an A x = b written across three lines of matrices — is taken as a setext underline: the paragraph above becomes an H1, shown as # $$ …, and the = is deleted.

Reproduction (0.153.4, Windows 11): ask for exactly

矩阵乘法

$$
\begin{pmatrix} a & b \\ c & d \end{pmatrix}
\begin{pmatrix} x \\ y \end{pmatrix}
=
\begin{pmatrix} ax + by \\ cx + dy \end{pmatrix}
$$

Streamed text is intact; the final redraw is # $$, rows ending in a single \, and no = line.

#45501 / #45612 mask math before the CommonMark pass, which fixes the corruption — thank you. But they then replace supported expressions with Unicode (α² + β₁₀, stacked fractions), and only unsupported ones fall back to source. For a terminal that typesets LaTeX itself (I maintain one, Folio, which typesets $…$ and $$…$$ where a program prints them), the Unicode form is a step down: the delimiters and the TeX are gone, so nothing can be typeset, and what is copied is no longer TeX.

Request

One of:

1. A config key (e.g. tui.math = "unicode" | "source") that keeps the masked spans verbatim instead of converting them;
2. or honouring an environment hint (a TERM_PROGRAM allow-list, or a capability the terminal advertises) to pick source automatically.

The masking already exists after #45501, so source is the conversion step switched off — the delimiters and bytes are restored exactly as written, the way unsupported expressions already are.

Environment

• codex-cli 0.153.4, Windows 11, model gpt-6-astra
• Terminal: Folio 0.4.2 (typesets LaTeX in command output)

Start by tracing the TUI math masking and conversion introduced by #45501 and #45612. Review the existing configuration or capability-detection entry points before choosing between an explicit source mode and terminal-based selection. Done means supported math can preserve its original delimiters and TeX bytes for capable terminals without regressing the current Unicode rendering.