PARIS — Manuel Valls, a center-leaning former prime minister who rallied France together after extremist attacks, will confront stalwart Socialist Benoît Hamon in the country’s left-wing presidential primary runoff next week. Whoever wins the Jan. 29 primary runoff will face the April-May presidential election battling more popular candidates from the far right to the far left riding frustration with immigration and economic stagnation. Tough-talking, center-leaning Valls jumped in the presidential race in December a few days after President François Hollande declined to seek re-election —acknowledging his personal unpopularity would lead his Socialist party to defeat in the presidential battle. Valls has faced fierce attacks from harder-left rivals who associate him with Hollande’s unpopular moves to relax labor protections to encourage hiring. A former junior minister and education minister, he left the government in 2014 after he expressed disagreement with Valls’ pro-business policies.