Indeed this does look very useful. I had a quick glance over this, but for contexts which are defined as remote ssh hosts, I couldn't see where the images are

Indeed this does look very useful. I had a quick glance over this, but for contexts which are defined as remote ssh hosts, I couldn't see where the images are obtained. Are they being built remotely on the host, or are they being downloaded from your local machine over a tunnel or via a docker registry?