Re: `git-rev-parse master` not referred to by any ref?

Junio C Hamano [off-list ref] wrote:

Also, I *think* objects that are only reachable via ORIG_HEAD
are not considered as reachable by fsck/prune --- we probably
would want to fix this.

Probably.  But most users also have reflog enabled on HEAD in the
repository if they were to also have ORIG_HEAD there.  In such a
case ORIG_HEAD is usually HEAD@{1}, which is considered reachable
by fsck/prune/repack.

-- 
Shawn.