With the pressure bid, Opener was forced to raise clubs at a level that made it very uncomfortable for Responder to show that his club bid was "manufactured" and that he had spade support. I mean, 4♠ works, except that the range for 4♠ is now minimum GF to seriously interested in slam. How does one handle this, let alone moving toward slam?
Flags work here:
4♦ = club power acceptance
4♥ = spade power raise
4♠ = normal spade raise
5♠ = non-interesting club resolution
Then, a bit later, another intervention:
In this sequence, GP suggests a different structure than would be expected. The risk of further trouble (we actually heard 5♥ next from Advancer) is greatest when Opener has shortness in hearts. With length and an honor control, in contrast, high-level heart competition is of reduced risk. So, it seems that the fourth-suit splinter (4♦) would be better delayed through 3♥ to allow 4♦ to show something different, something heart-shortness oriented.
Our thoughts for spade raises:
4♣ = good clubs, maybe no diamond control, heart shortness control
4♦ = diamond control, heart stiff
4♥ = diamond control, heart void
4♠ = no heart control
3♥ = catch-all, typically with a heart honor control
In other words, focus on the immediate need to show as much as you can immediately when Opener has heart shortness.
In practice, the opponents were red and we were white. Advancer bid 5♥, doubled for +800, but our slam was making. Had Responder known that Opener had a diamond control and a heart void, his K-QJ combo of honors would have grown up and the slam might have been bid successfully.
I'm not sure how this translates into other auctions, but it seems like a steps structure works best when spades will be agreed. In other words, if the overcall had been diamonds, 4♥ would still show the void and 4♦ the stiff.