Snow arrives in East Cambridge sideways, funneled off the river and down the brick canyons toward Kendall Square. J&J Property Maintenance is already out in it, plowing lots and driveways and cutting walkways down to bare pavement while the streetlights are still the brightest thing going. Salt goes down at the steps and the curb cuts, because the hard part of a Cambridge storm is never the open drive — it is the six feet between a door and the street. By the time the first commuters come through, the way is open and ordinary shoes will do. The work stays close to home: Cambridge and the cities beside it, storm after storm.