Function dispatch_empty_event 

pub fn dispatch_empty_event(snapshot: &RegistrySnapshot, tag: EventTag) -> bool

Build + dispatch a no-payload event (e.g. session_start, session_shutdown, the rpi-specific before_tui_start) to the tag’s handlers. Returns whether any handler was invoked. Mirrors dispatch_data_event for events whose payload is EventEmpty; a handler that subscribes to a no-payload tag receives the event with an empty payload.