I like to have a message bus to send messages to queues and have systems consuming those queues. The shared mutable reference to this message bus would be prov

I like to have a message bus to send messages to queues and have systems consuming those queues. The shared mutable reference to this message bus would be provided to each system requiring it. It's easily achievable in Rust with Bevy, or with Unity DOTS. When I don't use Unity DOTS and simply good old MonoBehaviours, I call the message handlers as soon as the message is published instead.