@vagrantc Yup, and reprotest has shown that this can indeed be very useful!
My ideal, in the spirit of Nix/Guix, would be to have a way to keep those details under control. But VMs are more expensive than mere processes in separate namespaces: we wouldn’t want to run every build in a VM. Plus that creates a bootstrap problem: how do you provision the VM?
For now, this tool should at least let us rebuild old packages.