You play UDCA (discards are UDCA too)
You lead the spade. Right or wrong, partner cashes the ♠AK and declarer follows. The analysis on whether or not he should isn't relevant.
It should be clear that you need a club shift. How can you get partner's cooperation to lead a club instead of simply playing a 3rd spade trying to get you an uppercut, or kill dummy's spade tricks?