KSP uses a tree graph structure for vessels, but added support for looping vessels (e.g. 4 station hubs connected in a square) by adding a physics joint at the final join that makes the ring, leaving the actual vessel as a tree.

Currently when trying to pass through this intra-vessel connection, FreeIVA shows "Go EVA" and "Hatch is obstructed, can't exit" on interaction. We should detect this kind of join and allow the hatches to be treated as connected.