Function lumen_on 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn lumen_on(
    node: LumenNode,
    event_type: *const c_char,
    capture: c_int,
    callback: Option<LumenEventFn>,
    user_data: *mut c_void,
) -> LumenEventToken

Bind callback to node for event_type. capture (non-zero) makes it a capture-phase listener. Returns an off token (0 on a bad argument); unbind with lumen_off. Thread-safe.