{.unnumbered} partially ignored in Jupyter Notebook

Bug description

If I use {.unnumbered} for a chapter in a web book that's a Jupyter Notebook, the chapter still gets a number.

Steps to reproduce

Create a web book, start the first chapter with:

# Introduction {.unnumbered}

Expected behavior

The Introduction should not get a number and the next chapter should be chapter 1. This works if the Introduction is a .qmd file. At some point prior to 1.3.450, it worked if the Introduction was a Jupyter Notebook as well.

Actual behavior

If the Introduction is a Jupyter Notebook, the Introduction is chapter 1 and the next chapter is chapter 2. However, sections within the Introduction are not numbered, so the {.unnumbered} tag is being recognized.

I tried Quarto 1.3.450, 1.4.549, and 1.5.6. All behaved the same.

Here's evidence it used to work. If I render that book now, the introduction gets a chapter number and the rest become chapters 2-5.

Your environment

Alma Linux, command line

Quarto check output

Quarto 1.5.6
[���] Checking versions of quarto binary dependencies...
Pandoc version 3.1.11: OK
Dart Sass version 1.69.5: OK
Deno version 1.37.2: OK
[���] Checking versions of quarto dependencies......OK
[���] Checking Quarto installation......OK
Version: 1.5.6
Path: /home/r/rdimond/quarto/quarto-1.5.6/bin

[���] Checking tools....................OK
TinyTeX: (not installed)
Chromium: (not installed)

[���] Checking LaTeX....................OK
Using: Installation From Path
Path: /bin
Version: undefined

[���] Checking basic markdown render....OK

[���] Checking Python 3 installation....OK
Version: 3.11.5 (Conda)
Path: /software/anaconda/bin/python
Jupyter: 5.3.0
Kernels: python3, ir, nbstata, sas

[���] Checking Jupyter engine render....OK

[���] Checking R installation...........OK
Version: 4.3.2
Path: /software/R/lib64/R
LibPaths:
- /home/r/rdimond/R/x86_64-pc-linux-gnu-library/4.3
- /private/linux64/R4.3.2/lib64/R/site-library
- /private/linux64/R4.3.2/lib64/R/library
knitr: 1.45
rmarkdown: 2.25

[���] Checking Knitr engine render......OK