So I got to this point:
Upgrading the Adapt authoring tool...please hold on!
I held on, but...
fatal: Not a git repository (or any parent up to mount point /vagrant)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
ERROR: 128
Any clues? Something to do with this being a vagrant install combined with the fact I originally downloaded the Authoring Tool folder rather than cloning from the repository?