How to handle .see and "visibility" explicitly

Any incoming or outgoing line to another switch is “invisible” (that peer’s IP:PORT isn’t automatically shared with anyone) until that switch sends itself back inside a .see request at any point. From then on, that switch is visible and can be re-announced out via another .see to any other switch.

Switches may prioritize visible lines/taps/etc over non-visible ones, so as to encourage everyone to be visible if at all possible.