Lovely... I somehow managed to bork the #Manjaro install on a machine by unplugging the drive, using the machine to install Manjaro on a laptop drive to try to get around the installer crashing on the laptop itself, and swapping the drives around again. The drive works, is plugged into the same SATA port it was in before, and it has partitions but it won't boot from it even though everything appears to be correct.

For bonus points, the laptop still isn't working either.