Mission Hill climbs at an angle nobody forgets in January, when a half-inch of ice can shut a sidewalk down entirely. Rios Snow Removal, LLC works those Boston grades through the night — plowing what a truck can reach, shoveling what it cannot, and salting the pitched walks and stairs where the real danger lives. Storms arrive here in long bands, so the route runs more than once and the last pass counts as much as the first. Down to pavement, treated, and passable before anyone starts walking to work: that is the whole scorecard. There are few better sights at five in the morning than a hill with its footing back.