Function resolve_json_param_name 

pub(crate) fn resolve_json_param_name(
    arg: &str,
    param_names: &[String],
) -> String

Resolve a simple parameter-name reference in a JSON contract arg string to the arg:N positional form. Complex expressions (containing function calls, field access, etc.) are left unchanged — they are handled later by the expression parser which already knows how to resolve named parameters.