IMP Scoring, Jack of spades lead.
You are North and your partner didn't rebid 1♠ but it seems to have saved you from a potentially dangerous ♦ lead. How would you have continued in partner's seat? You seem to have a couple of options:
1) Win in hand, cash the A♣ and unblock the K♥, hoping for 3-3 ♥s if the King of ♣s isn't singleton.
2) Win in dummy with the K♠ and overtake the ♣Queen, trying to establish ♣s.
3) Win in dummy with the ♠K and run the ♣Q, crossing to hand with the ♥K and try to set up ♣s.