Stocks drifted on Wall Street and oil prices fell for the first time in a week, even as heavy fighting in the Middle East again threatened to slow the global flow of oil. The S&P 500 was mostly unchanged Friday. The Dow Jones Industrial Average added 0.5%, and the Nasdaq composite fell 0.6%. All three indexes finished the week lower. After shooting to $102 a barrel a day earlier, Brent crude fell almost 4% to settle at $96.78 a barrel. Treasury yields moved lower in the bond market. European markets rose and Asian markets closed lower.