refactor: migrate GameRules.legalMoves signature to GameContext

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/core/src/main/scala/de/nowchess/chess/logic/GameRules.scala

@@ -1,6 +1,7 @@
 package de.nowchess.chess.logic
 
 import de.nowchess.api.board.*
+import de.nowchess.chess.logic.GameContext
 
 enum PositionStatus:
   case Normal, InCheck, Mated, Drawn
@@ -19,13 +20,13 @@ object GameRules:
       }
 
   /** All (from, to) moves for `color` that do not leave their own king in check. */
-  def legalMoves(board: Board, color: Color): Set[(Square, Square)] =
+  def legalMoves(ctx: GameContext, color: Color): Set[(Square, Square)] =
-    board.pieces
+    ctx.board.pieces
       .collect { case (from, piece) if piece.color == color => from }
       .flatMap { from =>
-        MoveValidator.legalTargets(board, from)
+        MoveValidator.legalTargets(ctx.board, from)
           .filter { to =>
-            val (newBoard, _) = board.withMove(from, to)
+            val (newBoard, _) = ctx.board.withMove(from, to)
             !isInCheck(newBoard, color)
           }
           .map(to => from -> to)
@@ -34,7 +35,7 @@ object GameRules:
 
   /** Position status for the side whose turn it is (`color`). */
   def gameStatus(board: Board, color: Color): PositionStatus =
-    val moves   = legalMoves(board, color)
+    val moves   = legalMoves(GameContext(board), color)
     val inCheck = isInCheck(board, color)
     if moves.isEmpty && inCheck then PositionStatus.Mated
     else if moves.isEmpty       then PositionStatus.Drawn

modules/core/src/test/scala/de/nowchess/chess/logic/GameRulesTest.scala

@@ -1,6 +1,7 @@
 package de.nowchess.chess.logic
 
 import de.nowchess.api.board.*
+import de.nowchess.chess.logic.GameContext
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 
@@ -9,6 +10,9 @@ class GameRulesTest extends AnyFunSuite with Matchers:
   private def sq(f: File, r: Rank): Square = Square(f, r)
   private def board(entries: (Square, Piece)*): Board = Board(entries.toMap)
 
+  /** Wrap a board in a GameContext with no castling rights — for non-castling tests. */
+  private def ctx(entries: (Square, Piece)*): GameContext = GameContext(Board(entries.toMap))
+
   // ──── isInCheck ──────────────────────────────────────────────────────
 
   test("isInCheck: king attacked by enemy rook on same rank"):
@@ -36,22 +40,20 @@ class GameRulesTest extends AnyFunSuite with Matchers:
   test("legalMoves: move that exposes own king to rook is excluded"):
     // White King E1, White Rook E4 (pinned on E-file), Black Rook E8
     // Moving the White Rook off the E-file would expose the king
-    val b = board(
+    val moves = GameRules.legalMoves(ctx(
       sq(File.E, Rank.R1) -> Piece.WhiteKing,
       sq(File.E, Rank.R4) -> Piece.WhiteRook,
       sq(File.E, Rank.R8) -> Piece.BlackRook
-    )
+    ), Color.White)
-    val moves = GameRules.legalMoves(b, Color.White)
     moves should not contain (sq(File.E, Rank.R4) -> sq(File.D, Rank.R4))
 
   test("legalMoves: move that blocks check is included"):
     // White King E1 in check from Black Rook E8; White Rook A5 can interpose on E5
-    val b = board(
+    val moves = GameRules.legalMoves(ctx(
       sq(File.E, Rank.R1) -> Piece.WhiteKing,
       sq(File.A, Rank.R5) -> Piece.WhiteRook,
       sq(File.E, Rank.R8) -> Piece.BlackRook
-    )
+    ), Color.White)
-    val moves = GameRules.legalMoves(b, Color.White)
     moves should contain(sq(File.A, Rank.R5) -> sq(File.E, Rank.R5))
 
   // ──── gameStatus ──────────────────────────────────────────────────────