BOSTON (AP) — Democrat Michelle Wu has emerged the top vote-getter in a runoff election for the next mayor of Boston, but the race to decide her opponent in November is too early to call. Wu, a city councilor, easily won Tuesday’s preliminary balloting. Three other candidates — acting mayor Kim Janey and fellow city council members Andrea Campbell and Annissa Essaibi George — were locked in a tight race for the second spot. Janey and Campbell conceded defeat late Tuesday night. All four are candidates of color, as is John Barros, Boston’s former economic development chief and the only man in contention. Barros trailed well behind the four women.