The U.S. economy failed to add jobs for the first time in almost a year, while the unemployment rate was stuck at 9.1%, sending stocks down and putting more pressure on policymakers to revive a moribund labor market. Nonfarm payrolls were unchanged last month—the worst result since a small decline in September 2010—as the government sector continued to shed jobs, the Labor Department said Friday. The private sector added only 17,000 jobs.