I put some pics up a couple of weeks ago of this in a more skeletal form. Here it is strung up. 13" scale with a zero fret. Rock maple neck and tuner support structure. Rosewood soundboard slightly radiused. Sitka spruce soundboard and body framing. Bhutan cypress around the sides. Less than 16" /400mm long, 2" /50mm deep, it would fit in a generous sized pocket.
It has little sound, and what there is sounds like it is coming down a very old telephone line. I need to smooth out/round over and strengthen the end of the body where the strings go in underneath. The D strings especially were jamming there, and I broke 4 trying to get them up to pitch. Rollers would be good if I can find something suitable. I will also try drilling a couple of soundholes in the soundboard or (one in the side) and fitting a removable back, attached with fridge magnet material.
As mandolins are about as portable as stringed instruments get, the whole idea might be considered to be a bit pointless, but it has been an interesting exercise in working out a way to make a mandolin as small as possible. Not quite there yet, but even if it doesn't have much sound, a internal piezo pickup and a small headphone amp would make it more practical as a compact travel instrument.