I may be missing something as well.
If
♦ are 4-0, I am reduced to guessing whether LHO is 2=5=0=6 or 1=5=0=7....I will be driving out the
♦ K (unless for some strange reason he ducks twice) and then hoping to run the
♠...stay tuned as to how I play the suit

.... I suspect, based on the 5
♣ call, that I will go for 1=3 split.
If RHO has the Kxx
♦, and wins the first
♦ to lead a
♥, I ruff and DO NOT pull trump.. I cross to the
♠K, to guard against LHO having 0=5=1=7, and now I can hook the
♠ and return to dummy in trump, while pulling RHO's last trump.
Obviously, if RHO ducks the
♦10, I leave trump alone, and play the
♠ to the K and back.... he can take his trump King whenever he wants it... I still have complete control.
If LHO is 0=6=0=7 or 0=5=0=8, I'm not making, unless I peeked, but that is unlikely.... (both that he has that shape and that I peeked)
Sorry, Frances, it is the middle of a long, hot afternoon, in the office on a holiday Monday when I should be golfing or taking the dogs to the beach... but I don't see the concern about which
♦ to play on the 10. Not doubt you will elucidate the issue, and I will be red-faced
'one of the great markers of the advance of human kindness is the howls you will hear from the Men of God' Johann Hari
1♠ 2♠ x P
P 3♣ P P
x P 3♠ P
4♣ P 4♠ P
P 5♣ P P 5♦
all pass