[shandor]

It would be optimal if the team can have the discipline to never commit broken stuff, and we could live with "everything in master must be working all the time".

If that does not work in reality, or breaking it would simply cost too much (because mistakes will happen), I'd use release branch or use git tag to mark versions with "no really, this one really truly actually works in every way".

For your second point, see 'git revert'! It does exactly that, i.e. picks a commit and effectively removes it from a branch by making its "mirror commit". The other way is, of course, just deploying an actual fix asap, git revert is just for when fixing the problem is for some reason or other slow and master must be unbroken immediately.