Function oidc_seam_for 

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

Resolve a handler’s OIDC seam, if its by clause names a single local Oidc actor. Returns None for non-Oidc handlers, for a multi-actor by clause (Oidc is single-actor this slice), and for a refinement (refinement over Oidc is a later slice) — those follow the existing seam paths. The checker guarantees issuer/audience/jwks are present and the identity is a string-constructible local type.