Hm. I trigger some systemd services by plugging in external drives. This used to work by WantedBy=dev-disk-by\x2duuid-<minus-escaped-UUID>.device. But setting up a new one, it seems not to ("added as a dependency to a non-existent unit")

another day wrestling systemd :( StopWhenUnneeded= seems really unreliable with cryptsetup units. It can work, but it isn't and I don't know why.