StructuralConflict

A genuine structural conflict: two sides impose incompatible requirements on the same relation slot (Lindholm's Update/Update and Position/Position conflicts, section 6.3), and it isn't this code's job to guess a winner. slot names what's in contention (e.g. "content of u13d", or "successor after u1 under us"); baseValue/leftValue/rightValue are each side's value there, rendered as a string (None when a side has nothing there at all - e.g. a freshly inserted node has no base value).