How do we install extensions when lab is in dev-mode?

I installed JupyterLab with pip install -e . (starting it with jupyter-lab --dev-mode).
How should we install extension then?
I created minimal extension example from tutorial.
Then installed it with pip install -e .. But seems like it only works with standard JupyterLab installation.

jupyter lab --dev-mode --extensions-in-dev-mode (Develop Extensions — JupyterLab 4.1.0a1 documentation)

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