In the ancient calculus of war and commerce, the price of oil has long served as a barometer of the world's unease. On Thursday, as American and Iranian forces exchanged direct military strikes, crude oil crossed $100 per barrel — a threshold that markets treat less as a number than as a verdict. The breach was swift and unambiguous, a signal that traders believe the conflict carries real consequences for the flow of energy from one of the planet's most vital producing regions, and that ordinary people, from commuters to small business owners, will bear the cost of that uncertainty.