Function sum_has_open_member 

pub fn sum_has_open_member(
    by: &ByClause,
    actors: &HashMap<String, ActorDecl>,
) -> bool

#2155: whether an actor sum has an open member — Visitor, or a declared actor with no auth scheme. The sum’s seam resolves a request with a missing or bad credential as that member, so it never answers 401: by Nobody, by Forged and by Stale have nothing to drive there.