I have an altair chart and would like to make it interactive in the following way. When I click on a data point, I want an application to be started via its CLI, with attributes from the data point provided as arguments to the startup command. My understanding is that this should be possible using the new JupyterChart class introduced in Altair 5.3.0 – see an example here. However, following the example, when I try to run my application by making a call to subprocess.Popen in my observer callback, nothing happens. What am I doing wrong?