setFaultProfile

Replace the active FaultProfile atomically.

Frames held in a FaultProfile.ReorderWindow are released by the swap rather than stranded in a window the new profile will never fill (#2882): each outbound frame goes to its own route, each inbound frame to incoming, in the order they arrived. This function cannot suspend, so the release runs in the seam's scope — a frame sent straight after the swap can overtake it. A released frame that finds the link already closed counts in framesDropped.