Just found this out the hard way...
It looks like the attachment of /KVMROOT/guest-dev-app.img on guest-dev did not persist when the KVM host rebooted for patching.
As it appears the virsh attach-disk command works a lot like the mount command.
In order to have a disk attachment persist after a reboot, I think we still need to do a virsh edit.
the virsh attach-disk command is useful because it allows us to attach disk images to guests without restarting.