### Bug description

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

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
    ```
1. Create `slides/index.qmd` with `format: 'revealjs'` in front-matter
1. Add link from `index.qmd` to `slides/index.qmd`
1. `quarto preview index.qmd`
1. Click the link to view the slides, and it will display as an HTML page, not a RevealJS presentation
1. CTRL+C on the `preview` process, and run it again.
1. Click the link to view the slides, and it will display as a RevealJS presentation
1. 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

- [X] 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.
- [X] Please [format your issue](https://quarto.org/bug-reports.html#formatting-make-githubs-markdown-work-for-us) so it is easier for us to read the bug report.
- [X] Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
- [X] Please document the operating system you're running. If on Linux, please provide the specific distribution.
cscheid
2023-02-22T23:46:37Z
MattF-NSIDC
bug
v1.4
open
`quarto preview` unexpected non-idempotent behavior
https://github.com/quarto-dev/quarto-cli/issues/4469