Thanks a lot!
About disappearing line - the puzzle encourages player to think a bit, predict paths in their head, find the suitable crossing, and then get serotonin from being correct :) With lines always visible player would be able to just spam STOPs in different places without even thinking, until the paths intersect, check quickly for their length, and press "Run". Not much of a puzzle this way, don't you think?
Although I consider adding a toggle in settings, for lines to be always visible, in post-jam version.