I definitely should have raised immediately. But they had let us buy the previous two hands for much lower than we deserved and I was greedy. Karma reared its ugly head, I suppose. The full deal, which makes me look rather worse than partner, I think:
Partner led a low club to my ace. I cashed the A of spades looking for a signal; declarer played the J and partner the 5, which I couldn't read. Reasoning that if partner had an honor sequence in diamonds he might have led from it, I led a diamond back looking for the AQ in partner's hand and they wrapped up 11 tricks.
I didn't give declarer enough credit, since he has to have something for his bidding, but I was picturing
KJx
??QT9xx
Kx
9
with a missing heart honor (since I was trying to give partner something close to an opening hand in my mind).
Declarer did think for a bit before playing the J of spades, so maybe I should have decided he couldn't hold KJx, but he usually thinks for a bit before he plays any card. My partner will be gratified to see that an honor lead is not automatic on the auction. The misdefense is clearly my fault. What could I have done so that we had a better chance of getting it right? Should I just trust that declarer is not going to bid this way without some sort of diamond control?