Function emit_helpers_for_owner 

pub fn emit_helpers_for_owner(
    out: &mut String,
    type_names: &[String],
    types: &HashMap<String, TypeDecl>,
    _owner_qualified: &str,
)

Emit serialise_<T> and deserialise_<T> for every named type the owner declares that crosses a boundary. owner_qualified is the qualified name used as the brand path so that refinement-violation messages identify the origin context.