Issue timeout warning in UI

Maybe this doesn't belong into batchspawner, but I'll ask here anyways:

We're using batchspawner for having JupyterHub start notebook instances as SLURM jobs. Naturally, these have a limited runtime, and SLURM will just terminate the process after the requested runtime is over. This can be confusing (and frustrating) to users.

Obviously, users need to be properly educated.

But, maybe there could be a mechanism to warn users (via a browser notification) about an approaching batch job timeout? How should this be done?

One could implement it as an extension to Jupyter Notebook / JupyterLab, but then how would the extension know about the batch job?

Any help is greatly appreciated :)