Wild swings in world financial markets this week have shown how events in China can potentially disrupt the Federal Reserve’s carefully scripted policy plans. The turmoil, triggered by a rout in Chinese markets, also flagged a broader risk that the U.S. central bank may struggle to meet its inflation target until the rest of the world plays along. As they try to nudge U.S. interest rates away from zero, policymakers might have to rethink a basic assumption that solid economic growth and swelling payrolls at home are enough to do the job even as the world’s second-largest economy stutters.