`kill(id, sig)` sends signal `sig` to pid `id`. `kill(-id, sig)` sends signal `sig` to process group `id`.

`kill(-1, ...)` would signal pgid 1, which would be the process group of init.

From a quick scan of the issue, it looks like maybe nix is using macOS's sandbox feature somehow, maybe that creates a process namespace of sorts and makes `kill(-1, ...)` useful?

EDIT: nvm, there's a special-case for -1:

> If pid equals -1, then sig is sent to every process for which the calling process has permission to send signals, except for process 1 (init)...

I'm surprised this isn't encountered by more people: that seems useful.