Switching kernel breaks the extensions

[dpinte]

The jupyterlab extension is registering the comm target at notebook creation time (see

jupyter-dash/extensions/jupyterlab/src/index.ts

Line 78 in 351cb7c

notebooks.widgetAdded.connect((sender, nbPanel: NotebookPanel) => {

). This means that changing the kernel will not work. In practice all calls to JupyterDash.infer_jupyter_proxy_config() will fail after the kernel is changed (for a good reason).

A potential solution would be to listen to the ISessionContext.kernelChanged signal and register the comm target against the updated kernel.

I have only tested it with Jupyterlab but I suspect the nbextension has the same problem.