"Foreclosing the common-fund rule would mean that McCutchen 'in effect . . . [paid] for the privilege of serving as US Airways' collection agent.' In the majority's view, 'McCutchen would not have foreseen that result when he signed on to the plan.' ... The dissent ... contends that McCutchen conceded that the terms of the plan require 'full reimbursement,' without any contribution by the airline to attorney's fees and expenses. Therefore, the dissent argues, '[t]he Court ... has no business deploying against petitioner an argument that was neither preserved ... nor fairly included within the question presented.'"