Good gods I forgot @Ylfingr wrote this

https://git.brightfur.net/ylfingr/btrfs-unreachable-dependency-tracker

The whole thing is cursed. The whole SITUATION is cursed. I bet this is the issue I'm seeing again tonight.

*snootdesks.*

(btrfs can wind up in a state where you have to defrag _very specific files_ to free up the black-hole unreachable space, and defragging everything either does nothing or makes it WORSE.)

#btrfs