Partner leads the A♦. Firstly I wasn't expecting an unsupported Ace lead after this auction so it seemed reasonable to encourage the continuation, but playing the 10 with the Jack trapped didn't feel great. Since we only likely had 3 rounds to win before needing to switch (or if partner had 5 diamonds declarer would be forced to ruff) this didn't feel bad. Playing the 2 would surely lead to a club switch and I'd rather keep the Queen covered and not have partner broach a frozen suit - though, on the bidding it might not be frozen and he could have AJ10♣ to lead.
Such was my thinking at the table and I elected to play 10♦, partner followed with 4♦ and I was briefly optimistic he wanted to be on lead for the 3rd round
Partner's view was that I should have discouraged in diamonds as the Queen is a slow winner we'd probably get anyway and we clearly needed to force declarer in clubs. I'm not convinced by the logic of either statement (from what I could see) so would like some further views. Thus said, I can see that the extra club length does suggest this is the better suit to force declarer with, also wondering whether clubs could be frozen give that declarer holds at most 2 of them?