Signals: mod to mod

signal::subscribe("core:buttons/pressed")?;           // usually in init
signal::emit("core:buttons/pressed", payload)?;       // any time after

A subscriber receives server-api::on-signal(channel, source, payload). Server realm only.

What a signal is, and is not

A signal is a fact that already happened. There is no consuming it, no vetoing it, no reply, and no defined order between two different subscribers. If you find yourself wanting to decide something with a signal — approve a press, block a spawn — that is a different mechanism the engine does not have yet.

There is no replay either: a late subscriber misses history. Subscribe in init.

source is trustworthy; the channel name is convention

The host stamps source with the emitting mod’s id — a mod cannot forge it. So “only obey the gamemode” is one comparison:

async fn on_signal(channel: String, source: String, payload: Vec<u8>) {
    if source != "core:freeroam" { return; }
    ...
}

Channel names are pure convention (addon:name in the owner’s namespace) and are never enforced, because commands legitimately cross namespaces: a gamemode emitting on another mod’s command channel is the intended shape.

⚠ Channels are matched as exact strings, so renaming a mod or a channel breaks every partner silently. There is no compile-time link between two mods.

Put the data in the payload

A signal does not synchronise with anything else the emitter did. “Hear a signal, then read the world” is an anti-pattern — the world may not have caught up, and the receiver cannot see the emitter’s entities anyway.

Carry everything the handler needs in the payload.

Why not just share entities?

Because a handle is permission to mutate. find is scoped to your own mod and a ray that hits a foreign entity withholds its handle, so bytes over a channel is the only cross-mod reach — by design. The receiver decides what to do to its own content.

The plates → freeroam → balloons chain in the reference mods is the worked example: a pressure plate announces, the gamemode interprets, a content mod reacts, and none of them can touch another’s entities.