Function is_delegatable_param 

pub fn is_delegatable_param(
    ty: &TypeRef,
    _opaque_types: &AHashSet<String>,
) -> bool

A param type is delegatable if it’s simple, or a Named type (opaque → Arc unwrap, non-opaque → .into()).

Json is delegatable: the binding takes a JSON string and gen_call_args emits serde_json::from_str(...) to bridge it into the core serde_json::Value parameter. All Rust-based bindings already depend on serde_json (Json field round-tripping uses it).