v4.0.0

Changed

• Position constructor accepts a single optional PositionData object instead
  of (board?, options?). Enables new Position(parse(fen)) for direct
  round-trip with @echecs/fen.
• PositionOptions type renamed to PositionData — adds board field
  alongside the existing 5 option fields.
• DeriveOptions extends Omit<PositionData, 'board'> instead of
  PositionOptions.

Removed

• PositionOptions type export — replaced by PositionData.

v3.1.0

Added

• Move type — { from: Square; promotion?: PromotionPieceType; to: Square }.
• PromotionPieceType type — Exclude<PieceType, 'king' | 'pawn'>.

v3.0.5

Changed

• added piece and square keywords

v3.0.4

Fixed

• Corrected constructor parameter type to ReadonlyMap in README.

v3.0.3

Fixed

• derive() constructor fast path — skips board allocation entirely via
  internal Array.isArray branch. ~2x faster than 3.0.2.

Removed

• SquareColor type export — unused across all @echecs packages.

v3.0.2

Fixed

• derive() no longer allocates a throwaway board array — constructor detects
  the internal fast path via Array.isArray, skipping the 128-element fill
  entirely. ~2x faster than 3.0.1, ~24x faster than 3.0.0.

v3.0.1

Fixed

• Position constructor board allocation — replaced Array.from with
  new Array(128).fill(0), ~12x faster derive() calls.

Changed

• Removed "Zero runtime dependencies" claim from README — package depends on
  @echecs/zobrist since 3.0.0.
• Removed fen and no-dependencies npm keywords.

Removed

• BACKLOG.md — all items completed.

v3.0.0

Added

• Position.prototype.reach(square, piece) method — from a square, return all
  squares the given piece can reach on the current board. Filters same-color
  pieces. Includes pawn pushes (single and double), captures, and en passant.
• Position.prototype.at(square) method — returns the piece on a square, or
  undefined if empty. Replaces piece().
• Lazy isCheck cache — computed once per position.
• @echecs/zobrist dependency — Polyglot standard Zobrist hash keys.

Changed

• Position internals rewritten to use bitmask 0x88 array as single source of
  truth. Map<Square, Piece> no longer stored internally.
• castlingRights, enPassantSquare, fullmoveNumber, halfmoveClock, and
  turn are now public readonly fields instead of getters.
• new Position() now creates an empty board. Pass STARTING_POSITION for the
  standard chess starting position: new Position(STARTING_POSITION).
• STARTING_POSITION is now a ReadonlyMap<Square, Piece> (the starting board
  map) instead of a Position instance.
• Constructor accepts ReadonlyMap<Square, Piece> instead of
  Map<Square, Piece>.
• isCheck reimplemented using reverse-lookup approach (from king, look outward
  for attackers) with the color trick — reuses reach internally.
• isValid reimplemented using the same approach.
• Zobrist hash now uses Polyglot standard keys for interoperability with opening
  books and other engines.
• Flattened internal module structure — removed internal/ directory.

Removed

• Position.prototype.attackers() method.
• Position.prototype.isAttacked() method.
• Position.prototype.piece() method — replaced by at().

v2.0.1

Fixed

• Docs CI workflow using renamed script.
• Lockfile out of sync with dependency versions.

v1.0.3

Fixed

• Added @preventExpand JSDoc tag to Square type alias so downstream TypeDoc
  (0.28+) renders it as a reference instead of expanding the 64-member union.