How Many Diamond Winners?

5 4 3
K 6 2
10 4
Q J 9 8 6
Q 9 K J 10 8 2
J 7 3 8
A 9 6 2 K 8 7
K 7 3 2 A 5 4
A 7
A Q 10 9 5 4
Q J 5 3
10

East opened with a spade, South overcalled with two hearts and that ended the bidding. How many diamond winners does declarer have coming on this hand? Of course, the answer should be one. East must cover the 10 in dummy, and West must conquer one of the other honors, either on second round or (if declarer is out of trump in dummy), he can duck that round and hold the A 9 tenace over declarer's last honor in the suit. As for ruffing potential, yes, it looks as though declarer could establish the highest diamond in two leads and ruff a low diamond for only two losers in the suit, but I would call that a heart winner. However, that's neither here nor there. Declarer didn't do that, and the defense should be inhibiting a second diamond winner in any event. You can only do your best and take advantage of declarer's mistakes when there are some.
West led the queen of spades in deference to his partner's bid, South winning and drawing trump in three rounds. East sluffed two low clubs. Declarer then led the 10 of clubs, won by East, who laid down the king of spades and continued the suit, which was ruffed by declarer as West, at his first discard, played the 9 of diamonds, evidently to show he had something good in that suit! A diamond was led, West going low, East capturing the 10. The 10 of spades was now led, declarer ruffing as West pitched a small club. The diamond queen was led, captured by the ace, the king of clubs was led, ruffed by declarer. And now declarer laid down the jack of diamonds and then the 5, the last diamond out.
One overtrick. Where did a defender go wrong, and could he have known? Well, that was made pretty clear in the above discussion. A 9 6 2? You shouldn't be discarding a suit like that, or at least until it's a choice between that and another unhappy choice. This is one of those dad-gummed computer hands, and I have no idea why defenders were programmed to toss out 9's in their best suit! That's the suit you want to save! Not discard.
You might note two things. The first is simple mathematics and obvious. If East captures the 10 with the king and West one of the other honors with the ace, the 9 will hold up fourth round. And secondly, please note that you don't hafta signal your partner. Declarer has no entries to the clubs, which East makes clear by sluffing two low clubs. So West has seen 'em all and can sluff all the clubs he wants with impunity and sit back and wait for his diamonds.
You don't need to signal your partner if declarer eventually has to come to the suit, and you don't want to signal if it costs you a valuable card!