Oil refiners have stumbled into one of the best profit environments in years. Crude prices have fallen back to where they traded before the Iran war erupted. But gasoline, diesel, and jet fuel remain stubbornly expensive. That combination has pushed refining margins to extraordinary levels, giving refiners a windfall that few expected just weeks after the Strait of Hormuz reopened. The benchmark U.S. 3-2-1 crack spread—a closely watched measure of refining profitability—recently climbed above $60 per barrel, the highest level on record.…