Before falling asleep I thought I would jot more thoughts.
Some major behind-the-scenes problems are that I am storing joseki as 10-by-10 tiles, just because that is slightly more natural for me to think about. Which is a problem, because joseki are being played on a 19-by-19 board. Actually the joseki are one dimensional lines of numbers, but those are somewhat more confusing.
I told it to pretend a same-color stone on some rotation or reflection of C7 : C10 was more or less one of the other stones. In the name of half-asleep ad hoc solutions being an approach to doing programming. It panics if it sees a wrong-color extension and is embarrassing for everyone involved.