Function bearer_seam_for 

pub fn bearer_seam_for(
    handler: &Handler,
    actors: &HashMap<String, ActorDecl>,
) -> Option<BearerSeam>

Resolve a handler’s Bearer seam, if its by clause names a local Bearer actor — or a refinement of one (v0.53), following the refinement to its base for the scheme/secret/identity and carrying the authorisation predicate. Returns None for non-Bearer handlers (prelude actors are never Bearer) — those emit unchanged.