There’s something called the Chapman Stick

Like a steinberger?

I know nothing about guitars, but I’ve seen Ichika Nito with these ibanez guitars. They don’t have a head, and the strings go all the way to the other side, making the guitar more compact.

nee dass ist unmöglich

You can get pretty close on any guitar by mounting a bigsby to it

But what (I think) you’re asking for essentially is a guitar where the actual vibrating length of the string is equal to the overall length of the instrument. This is not often done, as it limits your options significantly in terms of what standard components you can use (such as if you want to switch to a higher mass bridge).

But they exist! Look up the strandberg boden line of guitars. Headless + bottom tuning, although there is still a bit of material on either side