\boldsymbol rendered incorrectly to PDF default (using Lualatex) because unicode-math takes precedence

Bug description

I was rendering a .qmd file into a PDF document when I found that \boldsymbol didn't work: the letters inside them are just ordinary, not bold.

However, rendering it to HTML would work perfectly; the \boldsymbols are rendered as bold characters.

I was using a separate install of TinyTeX (directly, without Quarto), whose path was manually added to Path.

A test of TinyTeX itself was done as follows: I write a separate .tex file:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$$
\boldsymbol{r} r
$$

\end{document}

and used xelatex test.tex AND lualatex test.tex to render it; the result is perfect, the first r is bold while the second is ordinary.

Also, directly using pandoc to convert to PDF file works perfect.

Steps to reproduce

---
title: "quarto boldsymbol test"
format:
    pdf:
        toc: false

latex-tinytex: true
---

# Title

$\boldsymbol{r} r$

$$
\boldsymbol{r} r
$$

I also tried using xelatex as PDF engine, which didn't work either.

I also tried latex-tinytex: false, which didn't work either.

I also tried manually adding amsmath by:

header-includes:
    - \usepackage{amsmath}

which didn't work.

Actual behavior

For example, in the .qmd file above, the rendered PDF file displays every r as ordinary letters, no bold.

Expected behavior

rs inside \boldsymbol should be bold.

Your environment

• OS: Windows 11
• Quarto: 1.9.37
• TinyTeX:
  • tlmgr: tlmgr revision 78616 (2026-04-06 15:48:59 +0200)
  • xelatex: XeTeX 3.141592653-2.6-0.999998 (TeX Live 2026)
  • lualatex: This is LuaHBTeX, Version 1.24.0 (TeX Live 2026) Development id: 7724

Reproduce the issue with the provided .qmd example and compare it with the standalone test.tex using lualatex and xelatex. Trace the PDF rendering path and how unicode-math is included; done when \boldsymbol renders bold in Quarto PDFs without breaking the existing engines.