Replace Stockfish book with PickleBook

[DMDTague]

Replaces the generic Stockfish-derived opening book with PickleBook: a pinned Lichess-Elite-derived strong-human repertoire re-keyed into Pickle's own Zobrist format and reweighted for Pickle's shallow D11 horizon.

Key behavior:

• source tree is derived from up to 80,000 strong non-bullet Lichess Elite games through 16 plies
• human move frequency is a prior, not the final weight
• rewards direct minor-piece development and castling
• penalizes repeated early queen moves, early king exposure, new pawn defects, prematurely opened positions, high reply branching, and high forcing-move density
• prunes low-fit alternatives rather than retaining every theoretically respectable branch
• explicit Scandinavian regression requires development-first ...Nf6 to outrank the early ...Qxd5 line; the tightened filter pushes ...Qxd5 below retention cutoff
• generated book currently contains 6,369 Pickle-fit positions and 13,325 weighted moves
• browser source label now reads PickleBook / Lichess Elite · horizon-weighted for Pickle
• preserves OwnBook toggle, mate-in-one priority, Syzygy behavior, promotion-mate regressions, hash invariant, D11 regression, WASM and web build

The compact upstream repertoire and its exact Git blob are pinned for deterministic regeneration. No opening-time network access is required.

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Project	Deployment	Actions	Updated
pickle	Ready	Preview	Sep 17, 2026 12:08am UTC

[coderabbitai]

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