Sorry again for being slow to post the solution to this one. Below was the actual hand.
You'll notice that I fell from grace and made the play that (double dummy, on this particular lie) is worst possible. I think Ben (Inquiry) got it exactly right with the heart return (taking the time to count the hand and place possible cards...always a good idea), although wyman and I both believed partner's signal in spades. I don't think I thought about it well at the table. I thought the situation might be one of the following two, which need a spade switch now:
Note that only the spade return (whichever spade you think is most deceptive, probably the Ten is better than what I did) will give declarer even a chance to go down. I had fixated in my mind that the situation was like this, even though some patient thought would show it couldn't be.
Wyman's construction is another reason to lead a spade.
This is more reasonable than what I was considering. In fact partner has made things a little more difficult than it should be by pitching an "encouraging" low spade.
What's the correct play? Ben would have won as the cards were (and is probably correct in general); Wyman had a reasonable thought that was incorrect this time; I was not thinking.
The main lesson again:
"Wrong thoughts are good. Correct thoughts are great. No thoughts are bad."