Running it remotely on a VM seems like a very sensible option. Just don't give it permission to nuke the remote repository hah (EG don't allow force-push, use protected branches, only allow write access to branches it created)

Same solution here - keep a base diskless image on the server, copy it to the diskless area, pxeboot the machine. Works for Windows too (iscsi).

Could do the same thing on EC2 of course.