Function is_writeback_param 

pub fn is_writeback_param(
    param: &ParamDef,
    opaque_types: &AHashSet<String>,
) -> bool

Whether param is a &mut T parameter whose T is a non-opaque (serde DTO) named type.

Opaque named types are excluded: the host holds a live handle for those, so a backend that mutates through the handle is already correct and must not be rewritten. ~keep