How to rebuild Lab in docker

Hi, what is the right way to rebuild jupyter lab with new changed source code?
I have changed package (notebook-extension)


// install node

// copy changed source code for Lab UI
COPY submodule/changedLab /tmp/lab
RUN cd /tmp/lab && pip install -e . && jlpm install

// change in notebook-extension source code is what we need
RUN cd /tmp/lab/packages/notebook-extension && jlpm build && jupyter labextension install
RUN cd /tmp/lab && jupyter lab build

It builds nicely but loose jupyterlab extension after that. When container runs, it doesn’t log out any sign of jupyter lab, nor do I find jupyterlab in …/python3.6/site-packages

And that’s were I’m lost… Any idea why did it happen?