$ git clone -n https://src.fedoraproject.org/rpms/capnproto.git /var/lib/mock/f40-build-1992273-43579/root/chroot_tmpdir/scmroot/capnproto
Cloning into '/var/lib/mock/f40-build-1992273-43579/root/chroot_tmpdir/scmroot/capnproto'...
$ git fetch origin de40beefba213631b0fbb0d672482cd2737b1f9a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/capnproto
 * [new ref]         de40beefba213631b0fbb0d672482cd2737b1f9a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at de40bee Rebase to 1.0.1