A shroud of black netting has enveloped the proposed City Hall Annex at the corner of Laura and Duval streets, as contractors begin the busiest part of the renovations to the old Haverty’s building owned by the Police and Fire Pension Fund. Fund Executive Director John Keane said the netting is to keep in debris as workers resurface the concrete floors, remortar the brick walls, install windows and pour new pads for the elevator. Keane said he is still shooting for an Oct. 1 completion date, after which City departments will move in and determine the final interior layout. “We’ve got a good grasp on the basic floor plan,” he said, “but the specifics on the individual agencies occupying the space have yet to be determined by the City.”