Function make_index_dispatcher 

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

Build a RoleDispatcher for a concrete impl of crate::roles::IndexRuntime. 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.