Function try_registered_client_proc 

pub fn try_registered_client_proc() -> Option<&'static ProcMeshRef>

Returns the externally-registered client proc mesh, or None if none was registered. Non-bootstrapping: reads only the registration (.get(), never get_or_init), so it never spins up GLOBAL_CONTEXT. This getter has a single source of truth: it reads only the external registration; a coexisting Rust GLOBAL_CONTEXT root is ignored, with no fallback (unlike try_this_host, which does consult GLOBAL_CONTEXT).