Here is the full winning line
[White "New game"]
[FEN "1B1k4/3p4/1Kp5/PpP2p2/1PqP1P2/8/1P6/8 w - - 0 0"]
1. a6 Kc8 2. a7 Qa2 3. Bd6 Qa4 4. Be7 Qa2 5. Bh4 Qa4 6. b3 Qa3 7. Bg3 Qa2 8.
Bf2 Qa1 9. Be1 Qa2 10. Bd2 Qa1 11. Bc1 d5 12. Be3 Qa3 13. Bf2 Qa2 14. Bh4 Qa3
15. Bf6 Qa1 16. Be5 Qa3 17. Bb8 Qa2 18. Be5 Qa3 19. Bf6 Qa1 20. Bh4 Qa3 21. Bg3
Qa2 22. Bf2 Qa1 23. Be1 Qa2 24. Bd2 Qa3 25. Bc3 Qa2 26. Bb2 *[/pgn]
I have been looking at this (human only). It seems to be zugzwang related. IE black queen must stay on a file or white wins. But the black queen only has 3 squares it can use. White would love to play Bb2 with the black queen on a2, so that now either queen move loses the queen and the game, or a king move allows white's king to get to b7 and the a pawn promotes.
So the question is, can white somehow force a position where the black queen is at a3, the white bishop covers a1 from c3, forcing the black queen to go to a2. Now Bb2 wins outright.
So white wants to have Qa3 as the reply to Bc3, then Bb2 doesn't work because of Qa2, so back to the drawing board. How to get black queen to a3 with the white bishop able to move to c3. Because now the black queen only has a2 as a move since bishop covers a1, and after Bb2 black is zugged and lost.
Is this forceable? I could not find a way to do it, but I didn't spend very much time trying.
Looking at the PGN, the exact scenario I explained happened. Black queen on a3, white bishop moved to c3, now black queen only has a2, and after Bb2 it is over. Why not play Qa1 on move 24? Now Bc3 doesn't work as black plays Qa3, and now Bb2 doesn't work, since after Qa2 white is now forced to move, breaking the zugzwang.
Maybe I am overlooking something. But I don't see how that can be a forced win that takes that many moves. Chess engines might well botch it due to 2-fold == 3-fold repetition issues. I let Crafty play it out from the initial position several times and it ended in a draw each time. It clearly and instantly recognizes the final position in your list of moves is dead lost for black, however...