I decided to lead a spade which partner won with the king. The full layout:
Forcing dummy with a diamond ruff is the killing defence as it promotes a trump trick for partner. All we got in the end was a spade, heart and diamond trick. I thought of trying to cut down on diamond ruffs in dummy, but didn't think of the possibility of trump promotion by forcing dummy to ruff with a high card. Another one I got wrong.
Partner is of the philosphy that you should look at dummy, your hand and the bidding to decide what to do, so she doensn't play much in the way of signals beyond standard attitude and count, so the
♦8 was just saying she had values in diamonds. Teammates were two off in 4
♠. An interesting point is that if partner really wanted to go for a trump promotion by forcing dummy, she could have overtaken and lead a diamond back, rather than relying on me to work it out (which is always dangerous)
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I rank ...
1. ♠3. Try to reduce dummy's ruffing value. Hope partner ducks with ♠ Qxx.. Other options seem inferior.
2. ♦9. Suggest ♥ values.
3. ♥2. Perhaps partner can ruff ♥s.
4. ♣6. Perhaps partner can ruff ♣s