chunkedhtml: top-level chunk ignores --mathjax

[jeffgerickson]

Explain the problem.
pandoc -t chunkedhtml --mathjax does not enable MathJax on the top-level chunk. MathJax is correctly enabled in later chunks, but any latex math in section titles appears as plain text in the top-level table of contents. See the screen shots below.

Pandoc version:
pandoc 3.1.3, MacOS, freshly installed from .dmg

Exact command:
pandoc -t chunkedhtml --split-level=1 --toc --toc-depth=2 --mathjax -o Test test.md

Contents of test.md:

---
title: This is a Test
author: Testy McTestface
---
# This is $\alpha$ test.

## This is only a test: $e^{\pi i} + 1 = 0$.

Lorem ipsum dolor sit amet, consectetur adipiscing elit $e^{\pi i} + 1 = 0$. Maecenas at risus eu ligula tincidunt consectetur. Vestibulum nulla leo, vulputate ut arcu laoreet, maximus tempor ipsum. Duis tempor convallis diam, a hendrerit ante finibus et.

## Only this is a $\textsf{test}$.

Vivamus tempus est vitae erat ullamcorper rutrum. Integer porttitor dolor et augue pretium tempus. Donec nec lacinia enim. Integer at nisi porta, feugiat turpis id, venenatis enim. Suspendisse sit amet tristique risus, ac pharetra quam.

# This only is $\mathbb{A}$ test.

Etiam id fringilla $\textsf{lectus}$, nec hendrerit nulla. $\textbf{Pellentesque}$ fermentum eget massa vel consectetur. Morbi a enim $\textit{scelerisque}$, fringilla nunc a, volutpat ex. Praesent ac tincidunt purus. Nullam commodo dapibus nunc, vulputate convallis mi semper vitae. 

## Thi$\int$ i$\int$ a te$\int$t only.

Quisque non lobortis mi. Pellentesque eleifend libero ullamcorper eleifend rutrum. Donec rutrum, tortor vehicula bibendum facilisis, massa sapien posuere sapien, et congue quam purus at lorem.

# This is also a $\tau$esτ.

Sed maximus mattis nisi vel rutrum. Ut tempor, neque et tincidunt volutpat, justo eros egestas quam, mattis malesuada sapien nunc eget eros. Aliquam at malesuada libero, sit amet maximus sem. Nullam lobortis eros non ex sollicitudin, ac porttitor tortor gravida.

Screenshot of top-level chunk:

Screenshot of typical later chunk:

[jeffgerickson]

This is potentially (at least tangentially) related to #8620. (I also experienced this bug with pandoc 3.0, but upgrading to pandoc 3.1.3 fixed it.)