I'm struggling to find documentation on `IDLE_SERVER`, do you know of any? The only place I see it documented is on ArchWiki [0], but I don't know if that is an Arch distribution specific feature.
I do see `pause-when-empty-seconds` [1] when looking at the wiki, which seems the closest, although I can't find doc on what "paused" means (this is the closest [2]). Looks like a fairly new feature (2024), but it's neat they've thought about it.
Based on my read of the `minecraft-server` package [0], I think it is using a management script wrapper around the raw Minecraft JAR [1], which implements the aforementioned idle functionality [2].