Incorrect comments for YAML multiline strings

Bug description

Hello, and apologies if this should be reported elsewhere.

When commenting out a .qmd line that's part of a YAML multiline string, I get # in Positron (which leads to an error when rendering). In RStudio, I get <!-- (which renders fine).

Many thanks in advance!

Steps to reproduce

Open the following .qmd in Positron, and then do "Add line comment" on either \setlength... or \usepackage....

---
title: "Hello"
format: 
  pdf:
    include-in-header: 
      text: |
        \setlength\parindent{.2in}
        \usepackage{indentfirst}
---

## Hello

Hello

Hello

The line gets prefixed by #. Finally, render and get and error:

ERROR: compilation failed- error You can't use `macro parameter character #' in vertical mode.

Expected behavior

In RStudio, the lines get commented out in HTML style, e.g.: <!-- \usepackage{indentfirst} -->. This renders without errors.

Your environment

Positron Version: 2026.08.1 build 2
Code - OSS Version: 1.124.0
Commit: 48dc4cee686939f35fe4a714d34375f67fd62082
Date: 2026-08-09T13:35:16-06:00
Electron: 42.2.0
Chromium: 148.0.7778.97
Node.js: 24.15.0
V8: 14.8.178.14-electron.0
OS: Linux x64 7.1.8-200.fc44.x86_64

Reproduce the issue in Positron using the supplied .qmd example, applying “Add line comment” to either LaTeX line inside the YAML multiline string. Compare the generated comment with the expected HTML-style comment and verify that rendering completes without the reported LaTeX error.