ContainerOpenListener

Pushes a block's despawn-target state to a client mod when the player opens that container.

This is the whole server-side footprint of the client interface: one read-only notification. It cancels nothing, changes nothing, and adds no items — so it cannot conflict with shops, protection plugins, storage mods or anything else that cares about container interaction. If the player's mod has not registered the channel (i.e. almost everyone), the send short-circuits and this listener costs a map lookup.

The reason it exists at all is latency: the mod's button should already show the right state the instant the screen appears, rather than flickering while a round trip completes.