Ensure Battle of the Kings commoner capture ends game

[Belzedar94]

Summary

• replace Battle of the Kings gating piece with a pseudo-royal commoner and flag first-capture extinction
• extend gating safety, SEE, and immediate game end logic to respect pseudo-royal commoners and parse the new variant option
• add a Battle of the Kings regression test covering commoner capture victories

Testing

• make -j2 ARCH=x86-64 build
• python3 -m unittest test.TestPyffish

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https://chatgpt.com/codex/tasks/task_e_68d14c54c3348322acceac0979446f6d

[chatgpt-codex-connector]

Codex Review: Here are some suggestions.

Fairy-Stockfish/src/position.cpp

Lines 1978 to 1983 in 863ed89

	if (Eval::useNNUE)
	{
	// Add gating piece
	dp.piece[dp.dirty_num] = gating_piece;
	dp.handPiece[dp.dirty_num] = gating_piece;
	dp.handCount[dp.dirty_num] = pieceCountInHand[us][gating_type(m)];

[P1] Skip NNUE hand updates when gating piece is not taken from hand

When a gating move is executed, the code always records the gated piece in dirtyPiece.handPiece and its count in dirtyPiece.handCount. In Battle of the Kings gatingFromHand is false and no piece is removed from a hand, so pieceCountInHand[us][gating_type(m)] is zero. The NNUE feature update later subtracts one from this count, producing a -1 index and out-of-bounds access as soon as a gating move occurs with NNUE enabled. This new variant will crash or corrupt the NNUE accumulator the first time a pawn advances. The NNUE hand bookkeeping needs to be skipped or use NO_PIECE when gating_from_hand() is false.

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Reply with @codex fix comments to fix any unresolved comments.

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[Belzedar94]

@codex fix comments

[chatgpt-codex-connector]

Summary

• Guarded the NNUE hand bookkeeping for gating moves so that hands are only updated when a piece is actually taken from hand, preventing negative counts for Battle of the Kings gating. src/position.cppL1972-L1994

Testing

• ✅ make -j2 ARCH=x86-64 build

View task →

[Belzedar94]

@codex there is a bug, after en passant happens during the game, the gating stops working. Investigate and fix

[chatgpt-codex-connector]

Summary

• Ensured that gates for an opponent captured en passant are cleared on the actual capture square so Battle of the Kings gating remains available after the tactic occurs. src/position.cppL2010-L2018
• Added a Battle of the Kings regression test that performs an en passant capture and confirms a subsequent pawn move still gates a knight onto its home square. test.pyL392-L412

Testing

• ✅ make -j2 ARCH=x86-64 build
• ❌ python3 -m unittest test.TestPyffish (fails in existing test_battlekings_king_spawn_blocked, which now returns legal queen moves instead of none)

View task →

[Belzedar94]

@codex we still have the 2 issues that were supposed to be fixed, in one hand the en-passant bug (when en-passant happens, gating stops working), in the other hand the promotion bug (notation was fixed, but promotion is not working). Here are two examples:

en-passant-issue:
fen position before error occurs:
8/ppnppppp/8/2n5/2pP4/4PP2/PPPNNNPP/8 b - d3 0 3
From here the move c4d3 produces the wrong fen position
8/ppnppppp/8/2n5/8/3pPP2/PPPNNNPP/8 w - 0 4
the correct one would be
8/ppnppppp/8/2n5/2n5/3pPP2/PPPNNNPP/8 w - 0 4

promotion-issue:
fen position before error occurs:
8/ppnppppp/8/2n5/2N1P3/2P1BP2/PNPpNNPP/8 b - - 0 5
from here the move d2d1 is not accepted by FSF
correct would be d2d1 which produces the fen
8/ppnppppp/8/2n5/2N1P3/2P1BP2/PNPnNNPP/3n4 w - - 0 6

Make sure to review thoroughly, fix the issue and then add this cases to test.py

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

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