`quarto preview` unexpected non-idempotent behavior

Bug description

Hello all, I'm a new Quarto user and have been having a great time. Thank you ❤️

I'm using Quarto 1.2.335 via conda-forge on Ubuntu 20 LTS. I'm not using the RStudio IDE, just editing with vi.

I've been building a presentation which consists of several revealjs slide decks, and I want those to render to GH Pages, and that's working great. However, since I have multiple slide decks, I also want to render an HTML index page which includes links to all the slide decks. This seems to render correctly, but does not preview as expected; on the first run the slides appear as an HTML page using the "cosmo" theme instead of a revealJS presentation. Only after a hot-reload or re-run of the preview command do the slides appear as slides.

I was not able to make a reproducible example in a single QMD file, but my process to reproduce this issue was:

1. Create project template

   quarto create-project sscce-quarto-slides-in-website --type website
   

2. Create slides/index.qmd with format: 'revealjs' in front-matter
3. Add link from index.qmd to slides/index.qmd
4. quarto preview index.qmd
5. Click the link to view the slides, and it will display as an HTML page, not a RevealJS presentation
6. CTRL+C on the preview process, and run it again.
7. Click the link to view the slides, and it will display as a RevealJS presentation
8. Delete the .quarto and _site directories, do a preview, and the slides will again display as a HTML page, not a RevealJS presentation

I've created a repository with the project state that reproduces the issue, and the details of the issue in README.md: https://github.com/MattF-NSIDC/sscce-quarto-slides-in-website

Checklist

• Please include a minimal, fully reproducible example in a single .qmd file? Please provide the whole file rather than the snippet you believe is causing the issue.
• Please format your issue so it is easier for us to read the bug report.
• Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
• Please document the operating system you're running. If on Linux, please provide the specific distribution.