Arvados

The "Subprocesses" panel takes up a lot of space when there are no subprocesses (e.g. when viewing individual workflow steps), so it should be hidden until we know there is at least one subprocess.

If the currently displayed process is in "running" state and there are no subprocesses yet, it should poll periodically for subprocesses (it is probably already be doing something like this to keep the process list up to date) as well as refresh in response to websocket events which indicate a subprocess has appeared.