I managed to fix the access by mounting /dev/sdb3 and copying a known good
`authorized_keys` to `ostree/deploy/fedora-iot/var/roothome/.ssh/authorized_keys`. The
version on the image looked like a version of the public key that I thought I'd
deleted on zerere before trying to claim this device. It was just the key, and lacked the
key type at the start of the line and userid at the end.