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fix(chess): support long game history and export - #127
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0xferit
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September 21, 2026 13:03
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Long PGNs now retain their full move history through import, copying, undo, and export. Previously, the 601st ply wrote beyond the native history array, while an 800-entry move buffer also failed during SAN or HTML conversion.
Dynamic history requires value-based position copying. Reconstructing a copy from FEN while retaining its undo records lost the native history those records referred to, so undo followed by a new move could write at a negative history index. Copies now retain independent repetition history and the halfmove counter. The history length is the sole source of the current history ply; the exported legacy capacity constant remains available for source compatibility.
The import, plain/HTML export, and copy/undo regressions were observed failing under sanitizers before the fix. A separate repetition test also fails without sanitizers when copying falls back to FEN, and verifies that undoing the original leaves the copy independent. Validation covers ASan and Xcode UBSan, Release builds, and an 804-ply document read/save/reopen. Native history checks through 1,000 plies and move-generation/SAN round trips match the baseline.