How 49ers have addressed their offensive line puzzle in NFL free agency

The 49ers might already have the pieces in place to assemble their starting offensive line.Veteran lineman Robert Jones on Monday agreed to a one-year contract with the 49ers. He is viewed as a potential starter at left guard, which is the only spot on the 49ers’ offensive line where there was a vacancy.A year ago, the 49ers started three different players at left guard. Spencer Burford, who opened the year as the 49ers’ top backup tackle, ended up starting the final 11 weeks, including both postseason games.Burford last week signed with the Las Vegas Raiders as a free agent. Ben Bartch, who opened as the starting left guard, remains unsigned as a free agent. Connor Colby started six games as a rookie before his demotion from the lineup.The 49ers last season rushed for just 3.8 yards per attempt. Quarterbacks Brock Purdy and Mac Jones were sacked 27 times, a figure that tied for fifth-best in the NFL.The 49ers checked in at No. 5 in PFF’s offensive line rankings, behind only Denver, Indianapolis, Chicago and the L.A. Rams. PFF tracks and grades every player and unit on every NFL team.The 49ers still have some degree of uncertainty at left tackle until they...