Three in the morning near Davis Square, and the storm has stopped but the streets have not been given back yet — just the orange flash of a beacon working its way along a row of buried driveways. Urban Builders does the winter work in Somerville: plowing, cutting driveways and aprons open, shoveling walks and stairs down to the surface, and laying salt where the sun never reaches. These streets are narrow, the parking is tight, and there is nowhere to put the snow, so the plan matters as much as the blade. The reward comes at daybreak, when a car backs out cleanly and nobody has to think about how that happened. Then the next storm lines up over the harbor.