Santa Rosa sectional 3/26 (part 1)

MPs

r/r, we're in second, they bid
1D - 1H - 1S - 4H

Partner leads the CQ, we see

---------K965
---------Q3
---------QJ53
---------AT8
---------------------Q42
---------------------A8
---------------------AKT872
---------------------42
---------
---------closed
---------hand
---------

Declarer wins the CK in hand and plays a heart to the Q. Right or wrong, I win the HA. Now what?

After partner's unfortunate lead, it looks like declarer will make three club tricks (unless he was dealt stiff K). I was worried about declarer being able to shed a diamond on the club if he was 3712, which is not terribly unlikely. Partner probably would have led a diamond if she had a stiff, so she rates to have 2 or 3. If she had 7 clubs, she _might_ have preempted (the suit is pretty bad and she probably doesn't have any outside cards.)

So I try to cash the DK. Declarer ruffs, draws trumps, hooks the club, sets up the diamond for a spade pitch, making 6.

I missed that even if we pick up a diamond trick, declarer can still pitch a spade on the club. Therefore, I should just leave things alone and exit passively with a trump. I think the only time it is right to cash a top diamond is when declarer is specifically 3712 with the AJ of spades.