During some data migration I hit an issue where my data for supplierProductId was too long. So I looked up the fields and noticed that the order item entity had a different type for the field than the supplier product entity. I think it would be a good idea to pick one so the two fields can be treated consistently. I would vote for id-long, but I think either way it would be good to have them be the same type. There are other fields that have this issue too if you are interested?
<field name="supplierProductId" type="id-long"></field>
<field name="supplierProductId" type="id"></field>