so i'm still not 100% sure what i did, but if you're curious what happened:
- my old manjaro install is /dev/nvme0n1
- the 1TB hard drive that i broke is /dev/sda
- my new arch linux install (2 weeks old) is /dev/sdb
- sid meier's alpha centauri runs perfectly on arch, but with no sound
- boot into manjaro to try it on there, for comparison's sake
- manjaro prompts me to update and install a new kernel, which i do
(manjaro rolls its own linux kernels, for some reason) - the new kernel makes it so GRUB, which lives on the same drive as manjaro, can't boot into arch anymore!
- spend all morning trying to fix this with an arch linux install USB drive
- my lack of knowledge of how UEFI works leads me to try things like running
grub-installin the arch partition and reinstalling arch's linux kernel, to no avail
(but to the best of my knowledge i never touched /dev/sda???) - commenting out the /boot entry in arch's /etc/fstab as well as down-patching manjaro's kernel back to the old one finally let arch boot again
- collapse from relief and take a nap
- only when i wake up this evening do i discover the entirety of /dev/sda has been replaced with an empty FAT32 partition with a single EFI folder
- also, i can't seem to boot into manjaro anymore, but that's fine i wasn't really wanting to
EDIT: and if you're not following the tag, the current state of affairs is that the partition table of /dev/sda and the NTFS filesystem itself are toast, but almost all the actual files on the disk were recovered by photorec and are sitting in a folder in my home directory in an unnamed, unsorted pile. i still have to dig out all my art from this mess and put it somewhere.
ummmm the only advice i can give coming out of this is to avoid manjaro and its custom kernels if you're going to be dual booting with another linux system, and also to go for systemd-boot instead of grub whenever possible