Across the United States, the price of energy has crossed into uncharted territory — diesel surpassing six dollars a gallon for the first time, gasoline at seasonal records — as geopolitical tensions with Iran ripple outward from distant diplomatic rooms into the daily arithmetic of American households. Economists have put a number to the disruption: roughly $860 more per year for the average family, a figure that translates the abstractions of foreign policy into groceries ungotten and savings untouched. It is a reminder, as old as trade itself, that the world's fault lines do not stay where