Analogue layer: put three terminations at each "corner" and regenerate incoming signals onto the other two paths - keeping the two directions on each bar separate, so each has one TX and one RX.
Digital layer: prefix each "packet" with N instructions, either "forward to the left" or "forward to the right" (having stripped the instruction), or "interpret locally". Then do some kind of tree search during the "pixel map it after" phase.
Disclaimer: I just farted this out and it might be rubbish.
