Even after Edwin Diaz went down for the season back in March, it was inconceivable the Mets, with their record highest payroll in history, would wind up sellers at the trading deadline. Yet here they are, raising the white flag over Flushing, beginning with the trading of David Robertson to the Marlins for a couple of low-level teenage “futures” plus agreeing to deal Max Scherzer to the Rangers and all but admitting they’ve been a $345 million catastrophe. And somewhere Steve Cohen is asking: “How did it come to this?” And, perhaps more importantly: “Where do we go from here?” How it came to this is mostly unexplainable.