Function make_aggregator_dispatcher 

pub fn make_aggregator_dispatcher<T: AggregatorRuntime + 'static>() -> RoleDispatcher
where
    <T as AggregatorRuntime>::Error: Display,

Build a RoleDispatcher for a concrete impl of crate::roles::AggregatorRuntime. Used by Engine::register_*_dispatcher chain (Node::with_<role>(&value)) so single-role components dispatch through the same TypeId-keyed registry as multi-role / Protocol-bearing components.