When the cost of American borrowing rises to heights unseen in nearly two decades, the tremor is felt not only on Wall Street but in the trading halls of Mumbai, Hong Kong, and Shanghai — a reminder that in a connected world, no market stands alone. On Thursday, Indian equities retreated sharply as US Treasury yields climbed to their highest since 2007, driven by unexpectedly strong American business activity that rekindled fears of further Federal Reserve tightening. Compounding the strain, crude oil prices surged past $100 a barrel, placing particular weight on India as one of the world's la