This looks like a special way to keep the gunk out of a derailleur cable. The rubber tube has a metal connector at one end that holds the cable with a grub screw. There is a strange swinging stop that attaches to the frame stop, and looks like they work together in such a way that I couldn’t steal the swinging stop for another bike.
A friend returned a bike I put together for them, and included an old Cannondale! Yay! But… 1.25” headtube, blown Judy fork, bent derailleur.
Kind of made me mad, since I’d just got a new bike (the Fitz), and sold a bike (the Swobo), and I was looking to downsize not metastasize. Which is why there isn’t any kind of documentation to this weirdo bike.
It was also a bad sign that my friend “CannonDave” who will drive four hours to buy a $50 Cannondale frame wouldn’t take the whole bike off my hands for free.