Landed fair before the bag, landed fair past the bag, never touched foul ground
Ok, I just looked at the replay (which I should have done before I posted the first time; I apologize for my laziness), and it looked to me like the first bounce was foul, the second (in front of the bag) was on the line, and the third (behind the bag) was inside the line, based on which I'm inclined to conclude it was fair as it passed over the bag.
In my sluggishness this morning I was using the wrong rule. I thought the ball was a line drive, and since it landed fair, it had to be fair when it crossed the bag. But, of course, on a ball hit beyond the bag on the fly, it doesn't matter where it is as it crosses the bag: all that matters is where it lands. The fact that people were concerned about whether it was fair when it crossed the bag means that the ball must have bounced at least once before the bag, which means that spin, curious bounces, etc, could produce almost any kind of path.
I shall now go get some coffee so I'm not quite as thick.