I hate to be a Debbie Downer, but it's possible they're putting up the fence in anticipation of the Bruins playoff run. When they won the cup a few years ago, I was celebrating in the area of the future Merano.
This seems likely. The fence posts were 'behind' the sidewalk, in some cases by a foot or more. Seemed more like "let's keep people out of here for the time being" rather than "lets create some space to do work". Should have gotten a photo.