Function cross_context_service_for 

pub fn cross_context_service_for(
    name: &str,
    sdecl: &ServiceDecl,
) -> Option<CrossContextService>

Project one local on call handler into the CrossContextService shape both sides of a cross-context contract check need — a caller resolving a consumed service (crate::symbols::build_cross_context_info) and a callee stamping its own X-Bynk-Contract constant (crate::contract::own_contract_hashes). Sharing this one projection is the whole correctness argument for that symmetry: if the two sides ever diverged, a working deployment would 409 on every call instead of only on real skew. None when sdecl has no on call handler (e.g. an events-only or queue-only service).