As always, thanks to everyone for their replies. I probably should have mentioned that we were not playing 2/1. Partner would not be interested in any subtle inferences about my heart length anyway; he had a heart void. The hand was approximately (my hand repeated for convenience)
At our table, I declared 4♥
on the lead of the (singleton) ♣
2. I flew Ace, crossed in diamonds, and played 3 rounds of trump. My RHO didn't think I could have (only) 6 hearts and (as many as) 4 clubs, so he exited with a spade. Making 4.
At the other table, the auction was something like: 1♦
. My teammate thought opener was showing the ♠
A, and thus led a heart from ♠
KTx. Making 6.
I think any reasonable set of agreements should let you stop in 5♣
with these cards; time for more discussion with partner.