Function is_simple_non_opaque_param 

pub fn is_simple_non_opaque_param(ty: &TypeRef) -> bool

Check if a param type is safe for non-opaque delegation (no complex conversions needed). Vec and Map params can cause type mismatches (e.g. Vec vs &&str).

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. This lets fluent-builder methods like with_extension(self, key: String, value: Value) -> Self be auto-generated instead of being rejected as non-delegatable.