jupyterlab-myst does not render admonitions under nb7

[parmentelat]

Describe the bug

the jupyterlab-myst extension does not work as expected in nb7

To Reproduce

Steps to reproduce the behavior:

1. install jlab4 as released in pip
2. install nb7 with pip install -U --pre notebook
3. install jupyterlab-myst with
   pip install git+https://github.com/executablebooks/jupyterlab-myst.git@agoose77/feat-jupyterlab-v4
4. create a notebook with a simple admonition
5. open in jlab and check that the admonition renders properly
6. open the same notebook in nb7, the admonition is not rendered

Expected behavior
the extension should behave the same under both envs

Screenshots

the view under jlab

under nb7

Desktop (please complete the following information):

• OS: [e.g. iOS] MacOS & linux
• Browser [e.g. chrome, safari] - chrome
• Version [e.g. 22]

• jlab 4.0.2
• notebook 7.0.0b4
• as of this writing, https://github.com/executablebooks/jupyterlab-myst.git@agoose77/feat-jupyterlab-v4 is on commit b405903

Additional context

https://discourse.jupyter.org/t/generic-question-about-jlab4-and-nb7/19846

[jtpio]

Thanks @parmentelat for the detailed report.

Is there an error in the browser dev tools console?

[parmentelat]

yes indeed, and quite a few :)

like for the other issue #6914 I will try this again in a clean slate environment, and will then report the console errors

while doing so I will also be careful to not install any other extension, because I'm starting to believe I may have experienced unplanned interferences from others exts.

[jtpio]

3. install jupyterlab-myst with
pip install git+https://github.com/executablebooks/jupyterlab-myst.git@agoose77/feat-jupyterlab-v4

ok I just checked locally and this indeed works in lab:

But not in Notebook 7:

The error in Notebook 7 is the following:

Shared module @jupyterlab/markdownviewer doesn't exist in shared scope default

[jtpio]

This will likely be fixed #6921: