Cached sphinx builds and file content

[benbovy]

Description

Contents seem to be removed when re-building the documentation (with the cache).

Reproduce

1. Run sphinx

$ python -m sphinx -b html -d build/doctrees . build/html
...
[LiteBuildApp] [lite] [contents] All Contents ['/Path/to/notebook.ipynb']
...
LiteBuildApp] creating folder /Users/bbovy/Git/github/benbovy/ipytone/docs/build/html/lite/files
[jupyterlite-sphinx] JupyterLite build done

The directory build/html/lite/files exists and contains the notebook.

2. Re-run sphinx

$ python -m sphinx -b html -d build/doctrees . build/html
...
[LiteBuildApp] [lite] [contents] All Contents []
...
[jupyterlite-sphinx] JupyterLite build done

No build/html/lite/files directory

Expected behavior

Contents are copied into the JupyterLite build when re-running sphinx.

Context

• JupyterLite version: 0.1.0b7
• Sphinx version: 4.3.2
• Jupyterlite-sphinx version: 0.4.7