Function make_backend_dispatcher 

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

Build a RoleDispatcher for a concrete BackendRuntime impl — the per-T dispatch_atomic closure plus the materialize_from_wire bridge the derive emits. Backend dispatchers are the only ones that wire a real materialize entry; every other role registers no_materialize.