Shortest-proof-game challenge

It was a long one, but I looked a little more and found a longer one. Maybe it holds the current move length record.

This was a good one. ...Rf4! Is a nice touch. Is it your composition?

Yep. Felt like making a captureless game.

I don't know if anyone is working on #6783. I'll help by giving the move count, which is proof game in 38.5. For another hint, although not longest, it might still hold the move length record for a capture-free unique SPG which includes a castling move.

SOLV'D

Tough solve. Took longer than it should to notice the bolt hole on e7 for wK.

Very impressive work. I wonder if the 41.5 move proof game for #6784 will be as tough.

Second position, non-unique SPG in 24.0.

First position, non-unique SPG in 23.0.

Took me a while to make a position with this "theme", if you will

Should be a unique 17.5 PG. All white pawns on the 3rd rank, very nice.

Unique SPG, confirmed by Stelvio.

Why stop at the 3rd rank? Here's one with the pawns on the 5th.

Solution is unique, verified by Jacobi

20.0 moves

What is the fastest unique SPG that can accomplish this theme (in general)?

E. Minerva, 2005

Leither, does the theme require a double check by an en passant capture? If so, you're looking for something shorter than your position's unique SPG in 15.5.

Theme is Valladao task; the double check is only to force an en passant

So it needs castling, en passant, and promotion. The 8.5 move game at #6799 should be the winner.

I'd like to see if I can find a unique SPG shorter than yours that ends with double check by en passant capture, even if it's not a known task. Do you have any ideas?

I've located a position by Gerd Wilts and Norbert Geissler, 1996, that does the trick.

Proof game in 7.0.