I worked your version of the Gilded Rose Kata today. I'm going to use it as an exercise for the OK.rb group tonight. Thanks for preparing this for us.
Anyway, I was butting horns with a couple of your specs and just thought I would mention that I'm not sure I agree with them. Conjured items "degrade in Quality twice as fast as normal items." To me, that means they are -2 before the sell date, but -4 afterward (twice as fast as the normal -2).
I went looking around to see if I could find an official answer to this question. I didn't really. However, at least one other person who has worked with your code agrees with me.
So, this changes the specs if you feel it's warranted.
I believe conjured items should degrade at -4 after the sell date.
Good luck with your OK.rb group.