It's taken the little seedling a while to recover its roots but I'm happy to say it's putting on new leaves and doing splendidly. I moved the pot out into the rain last night because there's something magical about rain water. With any luck that magic will soak in and given some time I'll have a sweet little tree.
I don't expect to get any fruit off it, since this is zone 7 and it probably wouldn't survive winters out of doors but it'll make a nice potted exotic for the porch in summer. If I ever have a green house or live in a warmer climate I can plant it and perhaps one day pluck a juicy grapefruit from its branches and boast that I grew it from a seed.