feat: Implement threefold repetition detection and update game rules

modules/api/CHANGELOG.md

@@ -34,3 +34,11 @@
 * NCS-14 implemented insufficient moves rule ([#30](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/30)) ([b0399a4](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b0399a4e489950083066c9538df9a84dcc7a4613))
 * NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
 * NCS-25 Add linters to keep quality up ([#27](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/27)) ([fd4e67d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fd4e67d4f782a7e955822d90cb909d0a81676fb2))
+##  (2026-04-16)
+
+### Features
+
+* NCS-13 Implement Threefold Repetition ([#31](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/31)) ([767d305](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/767d3051a76c266050b6335774d66e2db2273c16))
+* NCS-14 implemented insufficient moves rule ([#30](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/30)) ([b0399a4](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b0399a4e489950083066c9538df9a84dcc7a4613))
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
+* NCS-25 Add linters to keep quality up ([#27](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/27)) ([fd4e67d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fd4e67d4f782a7e955822d90cb909d0a81676fb2))

modules/api/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=5
+MINOR=6
 PATCH=0

modules/bot/src/test/scala/de/nowchess/bot/AlphaBetaSearchTest.scala

@@ -37,6 +37,7 @@ class AlphaBetaSearchTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val search = AlphaBetaSearch(stubRules, weights = EvaluationClassic)
@@ -54,6 +55,7 @@ class AlphaBetaSearchTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val search = AlphaBetaSearch(stubRules, weights = EvaluationClassic)
@@ -101,6 +103,7 @@ class AlphaBetaSearchTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = true
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val search = AlphaBetaSearch(stalematRules, weights = EvaluationClassic)
@@ -117,6 +120,7 @@ class AlphaBetaSearchTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = true
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val search = AlphaBetaSearch(insufficientRules, weights = EvaluationClassic)
@@ -133,6 +137,7 @@ class AlphaBetaSearchTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = true
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val search = AlphaBetaSearch(fiftyMoveRules, weights = EvaluationClassic)
@@ -159,6 +164,7 @@ class AlphaBetaSearchTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val search = AlphaBetaSearch(rulesWithCapture, weights = EvaluationClassic)
@@ -176,6 +182,7 @@ class AlphaBetaSearchTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val search = AlphaBetaSearch(rulesQuiet, weights = EvaluationClassic)

modules/bot/src/test/scala/de/nowchess/bot/ClassicalBotTest.scala

@@ -35,6 +35,7 @@ class ClassicalBotTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val bot  = ClassicalBot(BotDifficulty.Easy, stubRules)
@@ -65,6 +66,7 @@ class ClassicalBotTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val bot  = ClassicalBot(BotDifficulty.Easy, stubRules)
@@ -87,6 +89,7 @@ class ClassicalBotTest extends AnyFunSuite with Matchers:
       def isStalemate(context: GameContext): Boolean                       = false
       def isInsufficientMaterial(context: GameContext): Boolean            = false
       def isFiftyMoveRule(context: GameContext): Boolean                   = false
+      def isThreefoldRepetition(context: GameContext): Boolean            = false
       def applyMove(context: GameContext)(move: Move): GameContext         = context
 
     val context = GameContext.initial.copy(moves = List(repeatedMove, repeatedMove, repeatedMove))

modules/core/CHANGELOG.md

@@ -260,3 +260,29 @@
 * correct test board positions and captureOutput/withInput interaction ([f0481e2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f0481e2561b779df00925b46ee281dc36a795150))
 * update main class path in build configuration and adjust VCS directory mapping ([7b1f8b1](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/7b1f8b117623d327232a1a92a8a44d18582e0189))
 * update move validation to check for king safety ([#13](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/13)) ([e5e20c5](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/e5e20c566e368b12ca1dc59680c34e9112bf6762))
+##  (2026-04-16)
+
+### Features
+
+* add GameRules stub with PositionStatus enum ([76d4168](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/76d4168038de23e5d6083d4e8f0504fbf31d15a3))
+* add MovedInCheck/Checkmate/Stalemate MoveResult variants (stub dispatch) ([8b7ec57](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/8b7ec57e5ea6ee1615a1883848a426dc07d26364))
+* implement GameRules with isInCheck, legalMoves, gameStatus ([94a02ff](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/94a02ff6849436d9496c70a0f16c21666dae8e4e))
+* implement legal castling ([#1](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/1)) ([00d326c](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/00d326c1ba67711fbe180f04e1100c3f01dd0254))
+* NCS-10 Implement Pawn Promotion ([#12](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/12)) ([13bfc16](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/13bfc16cfe25db78ec607db523ca6d993c13430c))
+* NCS-11 50-move rule ([#9](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/9)) ([412ed98](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/412ed986a95703a3b282276540153480ceed229d))
+* NCS-13 Implement Threefold Repetition ([#31](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/31)) ([767d305](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/767d3051a76c266050b6335774d66e2db2273c16))
+* NCS-14 implemented insufficient moves rule ([#30](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/30)) ([b0399a4](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b0399a4e489950083066c9538df9a84dcc7a4613))
+* NCS-16 Core Separation via Patterns ([#10](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/10)) ([1361dfc](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/1361dfc89553b146864fb8ff3526cf12cf3f293a))
+* NCS-17 Implement basic ScalaFX UI ([#14](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/14)) ([3ff8031](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/3ff80318b4f16c59733a46498581a5c27f048287))
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
+* NCS-25 Add linters to keep quality up ([#27](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/27)) ([fd4e67d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fd4e67d4f782a7e955822d90cb909d0a81676fb2))
+* NCS-6 Implementing FEN & PGN ([#7](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/7)) ([f28e69d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f28e69dc181416aa2f221fdc4b45c2cda5efbf07))
+* NCS-9 En passant implementation ([#8](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/8)) ([919beb3](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/919beb3b4bfa8caf2f90976a415fe9b19b7e9747))
+* wire check/checkmate/stalemate into processMove and gameLoop ([5264a22](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/5264a225418b885c5e6ea6411b96f85e38837f6c))
+
+### Bug Fixes
+
+* add missing kings to gameLoop capture test board ([aedd787](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/aedd787b77203c2af934751dba7b784eaf165032))
+* correct test board positions and captureOutput/withInput interaction ([f0481e2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/f0481e2561b779df00925b46ee281dc36a795150))
+* update main class path in build configuration and adjust VCS directory mapping ([7b1f8b1](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/7b1f8b117623d327232a1a92a8a44d18582e0189))
+* update move validation to check for king safety ([#13](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/13)) ([e5e20c5](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/e5e20c566e368b12ca1dc59680c34e9112bf6762))

modules/core/src/main/scala/de/nowchess/chess/engine/GameEngine.scala

@@ -19,20 +19,17 @@ class GameEngine(
     val ruleSet: RuleSet = DefaultRules,
     val participants: Map[Color, Participant] = Map(Color.White -> Human, Color.Black -> Human),
 ) extends Observable:
+  // Ensure that initialBoard is set correctly for threefold repetition detection
+  private val contextWithInitialBoard = if initialContext.moves.isEmpty && initialContext.board != initialContext.initialBoard then
+    initialContext.copy(initialBoard = initialContext.board)
+  else
+    initialContext
   @SuppressWarnings(Array("DisableSyntax.var"))
-  private var currentContext: GameContext = initialContext
+  private var currentContext: GameContext = contextWithInitialBoard
   private val invoker                     = new CommandInvoker()
 
-  /** Pending promotion: the Move that triggered it (from/to only, moveType filled in later). */
-  private case class PendingPromotion(from: Square, to: Square, contextBefore: GameContext)
-  @SuppressWarnings(Array("DisableSyntax.var"))
-  private var pendingPromotion: Option[PendingPromotion] = None
-
   private implicit val ec: ExecutionContext = ExecutionContext.global
 
-  /** True if a pawn promotion move is pending and needs a piece choice. */
-  def isPendingPromotion: Boolean = synchronized(pendingPromotion.isDefined)
-
   // Synchronized accessors for current state
   def board: Board         = synchronized(currentContext.board)
   def turn: Color          = synchronized(currentContext.turn)
@@ -67,11 +64,15 @@ class GameEngine(
           currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.FiftyMoveRule)))
           invoker.clear()
           notifyObservers(DrawEvent(currentContext, DrawReason.FiftyMoveRule))
+        else if ruleSet.isThreefoldRepetition(currentContext) then
+          currentContext = currentContext.withResult(Some(GameResult.Draw(DrawReason.ThreefoldRepetition)))
+          invoker.clear()
+          notifyObservers(DrawEvent(currentContext, DrawReason.ThreefoldRepetition))
         else
           notifyObservers(
             InvalidMoveEvent(
               currentContext,
-              "Draw cannot be claimed: the 50-move rule has not been triggered.",
+              "Draw cannot be claimed: neither the 50-move rule nor threefold repetition has been triggered.",
             ),
           )
 
@@ -87,11 +88,11 @@ class GameEngine(
                 s"Invalid move format '$moveInput'. Use coordinate notation, e.g. e2e4.",
               ),
             )
-          case Some((from, to)) =>
-            handleParsedMove(from, to)
+          case Some((from, to, promotionPiece: Option[PromotionPiece])) =>
+            handleParsedMove(from, to, promotionPiece)
   }
 
-  private def handleParsedMove(from: Square, to: Square): Unit =
+  private def handleParsedMove(from: Square, to: Square, promotionPiece: Option[PromotionPiece]): Unit =
     currentContext.board.pieceAt(from) match
       case None =>
         notifyObservers(InvalidMoveEvent(currentContext, "No piece on that square."))
@@ -104,11 +105,13 @@ class GameEngine(
         candidates match
           case Nil =>
             notifyObservers(InvalidMoveEvent(currentContext, "Illegal move."))
-          case moves if isPromotionMove(piece, to) =>
-            // Multiple moves (one per promotion piece) — ask user to choose
-            val contextBefore = currentContext
-            pendingPromotion = Some(PendingPromotion(from, to, contextBefore))
-            notifyObservers(PromotionRequiredEvent(currentContext, from, to))
+          case _ if isPromotionMove(piece, to) =>
+            if promotionPiece.isEmpty then
+              notifyObservers(InvalidMoveEvent(currentContext, "Promotion piece required: append q, r, b, or n to the move."))
+            else
+              candidates.find(_.moveType == MoveType.Promotion(promotionPiece.get)) match
+                case None       => notifyObservers(InvalidMoveEvent(currentContext, "Error completing promotion: no matching legal move."))
+                case Some(move) => executeMove(move)
           case move :: _ =>
             executeMove(move)
 
@@ -118,21 +121,6 @@ class GameEngine(
       to.rank.ordinal == promoRank
     }
 
-  /** Apply a player's promotion piece choice. Must only be called when isPendingPromotion is true.
-    */
-  def completePromotion(piece: PromotionPiece): Unit = synchronized {
-    pendingPromotion match
-      case None =>
-        notifyObservers(InvalidMoveEvent(currentContext, "No promotion pending."))
-      case Some(pending) =>
-        pendingPromotion = None
-        val move = Move(pending.from, pending.to, MoveType.Promotion(piece))
-        // Verify it's actually legal
-        val legal = ruleSet.legalMoves(currentContext)(pending.from)
-        if legal.contains(move) then executeMove(move)
-        else notifyObservers(InvalidMoveEvent(currentContext, "Error completing promotion."))
-  }
-
   /** Undo the last move. */
   def undo(): Unit = synchronized(performUndo())
 
@@ -154,11 +142,10 @@ class GameEngine(
   private def replayGame(ctx: GameContext): Either[String, Unit] =
     val savedContext = currentContext
     currentContext = GameContext.initial
-    pendingPromotion = None
     invoker.clear()
 
     if ctx.moves.isEmpty then
-      currentContext = ctx
+      currentContext = ctx.copy(initialBoard = ctx.board)
       Right(())
     else replayMoves(ctx.moves, savedContext)
 
@@ -170,14 +157,13 @@ class GameEngine(
     result
 
   private def applyReplayMove(move: Move): Either[String, Unit] =
-    handleParsedMove(move.from, move.to)
-    move.moveType match
-      case MoveType.Promotion(pp) if pendingPromotion.isDefined =>
-        completePromotion(pp)
-        Right(())
-      case MoveType.Promotion(_) =>
-        Left(s"Promotion required for move ${move.from}${move.to}")
-      case _ => Right(())
+    val legal     = ruleSet.legalMoves(currentContext)(move.from)
+    val candidate = move.moveType match
+      case MoveType.Promotion(pp) => legal.find(m => m.to == move.to && m.moveType == MoveType.Promotion(pp))
+      case _                      => legal.find(_.to == move.to)
+    candidate match
+      case None     => Left("Illegal move.")
+      case Some(lm) => executeMove(lm); Right(())
 
   /** Export the current game context using the provided exporter. */
   def exportGame(exporter: GameContextExport): String = synchronized {
@@ -186,7 +172,11 @@ class GameEngine(
 
   /** Load an arbitrary board position, clearing all history and undo/redo state. */
   def loadPosition(newContext: GameContext): Unit = synchronized {
-    currentContext = newContext
+    val contextWithInitialBoard = if newContext.moves.isEmpty then
+      newContext.copy(initialBoard = newContext.board)
+    else
+      newContext
+    currentContext = contextWithInitialBoard
     invoker.clear()
     notifyObservers(BoardResetEvent(currentContext))
   }
@@ -243,10 +233,7 @@ class GameEngine(
     else if ruleSet.isCheck(currentContext) then notifyObservers(CheckDetectedEvent(currentContext))
 
     if currentContext.halfMoveClock >= 100 then notifyObservers(FiftyMoveRuleAvailableEvent(currentContext))
-
-    // Request bot move if it's the opponent bot's turn
-    if ruleSet.isCheckmate(currentContext) || ruleSet.isStalemate(currentContext) then
-      () // Game is over, don't request bot move
+    if ruleSet.isThreefoldRepetition(currentContext) then notifyObservers(ThreefoldRepetitionAvailableEvent(currentContext))
     else requestBotMoveIfNeeded()
 
   private def translateMoveToNotation(move: Move, boardBefore: Board): String =
@@ -336,7 +323,7 @@ class GameEngine(
       if ruleSet.isCheckmate(currentContext) then
         val winner = currentContext.turn.opposite
         notifyObservers(CheckmateEvent(currentContext, winner))
-      else if ruleSet.isStalemate(currentContext) then notifyObservers(StalemateEvent(currentContext))
+      else if ruleSet.isStalemate(currentContext) then notifyObservers(DrawEvent(currentContext, DrawReason.Stalemate))
     }
 
   private def performUndo(): Unit =

modules/core/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=13
+MINOR=14
 PATCH=0

modules/io/CHANGELOG.md

@@ -47,3 +47,12 @@
 * NCS-29 JSON - Cherry Picked ([#28](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/28)) ([dbcafd2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/dbcafd286993e0604a6fa286c5543581a149439e))
 * NCS-30 FEN Parser using ParserCombinators ([#21](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/21)) ([b4bc72f](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b4bc72f7e49f94d6e1bc805c68680e5fe8ef8e36))
 * NCS-31 FastParse FEN ([#22](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/22)) ([7a045d3](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/7a045d31d757bbc5aa6f4bad2664ebe8b8519cac))
+##  (2026-04-16)
+
+### Features
+
+* NCS-14 implemented insufficient moves rule ([#30](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/30)) ([b0399a4](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b0399a4e489950083066c9538df9a84dcc7a4613))
+* NCS-25 Add linters to keep quality up ([#27](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/27)) ([fd4e67d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fd4e67d4f782a7e955822d90cb909d0a81676fb2))
+* NCS-29 JSON - Cherry Picked ([#28](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/28)) ([dbcafd2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/dbcafd286993e0604a6fa286c5543581a149439e))
+* NCS-30 FEN Parser using ParserCombinators ([#21](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/21)) ([b4bc72f](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b4bc72f7e49f94d6e1bc805c68680e5fe8ef8e36))
+* NCS-31 FastParse FEN ([#22](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/22)) ([7a045d3](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/7a045d31d757bbc5aa6f4bad2664ebe8b8519cac))

modules/io/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=7
+MINOR=8
 PATCH=0

modules/rule/CHANGELOG.md

@@ -44,3 +44,14 @@
 ### Bug Fixes
 
 * NCS-32 Queenside Castle doesn't care about pieces in the way ([#23](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/23)) ([fe8e3c0](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fe8e3c05397f433bfa34d1999e9738c82790adf7))
+##  (2026-04-16)
+
+### Features
+
+* NCS-13 Implement Threefold Repetition ([#31](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/31)) ([767d305](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/767d3051a76c266050b6335774d66e2db2273c16))
+* NCS-14 implemented insufficient moves rule ([#30](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/30)) ([b0399a4](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b0399a4e489950083066c9538df9a84dcc7a4613))
+* NCS-25 Add linters to keep quality up ([#27](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/27)) ([fd4e67d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fd4e67d4f782a7e955822d90cb909d0a81676fb2))
+
+### Bug Fixes
+
+* NCS-32 Queenside Castle doesn't care about pieces in the way ([#23](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/23)) ([fe8e3c0](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fe8e3c05397f433bfa34d1999e9738c82790adf7))

modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala

@@ -458,18 +458,11 @@ object DefaultRules extends RuleSet:
   private def squareColor(sq: Square): Int = (sq.file.ordinal + sq.rank.ordinal) % 2
 
   private def insufficientMaterial(board: Board): Boolean =
-    val nonKings = board.pieces.toList.filter(_._2.pieceType != PieceType.King)
+    val nonKings = board.pieces.toList.filter { case (_, p) => p.pieceType != PieceType.King }
     nonKings match
-      case Nil => true
+      case Nil                                                                                => true
       case List((_, p)) if p.pieceType == PieceType.Bishop || p.pieceType == PieceType.Knight => true
-      case List((sq1, p1), (sq2, p2))
-          if p1.pieceType == PieceType.Bishop && p2.pieceType == PieceType.Bishop
-            && p1.color != p2.color
-            && squareColor(sq1) == squareColor(sq2) =>
-        true
-      case bishops
-          if bishops.forall(_._2.pieceType == PieceType.Bishop)
-            && bishops.map(_._2.color).distinct.size == 1
-            && bishops.map(e => squareColor(e._1)).distinct.size == 1 =>
-        true
+      case bishops if bishops.forall { case (_, p) => p.pieceType == PieceType.Bishop }       =>
+        // All non-king pieces are bishops: draw only if they all share the same square color
+        bishops.map { case (sq, _) => squareColor(sq) }.distinct.sizeIs == 1
       case _ => false

modules/rule/src/test/scala/de/nowchess/rule/DefaultRulesTest.scala

@@ -29,15 +29,10 @@ class DefaultRulesTest extends AnyFunSuite with Matchers:
 
   test("pawn can capture diagonally"):
     // FEN: white pawn e4, black pawn d5
-    val fen     = "8/8/8/3p4/4P3/8/8/8 w - - 0 1"
-    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
-    val moves   = rules.allLegalMoves(context)
-    val captures = moves.filter { m =>
-      m.from == Square(File.E, Rank.R4) && (m.moveType match
-        case _: MoveType.Normal => true
-        case _                  => false
-      )
-    }
+    val fen      = "8/8/8/3p4/4P3/8/8/8 w - - 0 1"
+    val context  = FenParser.parseFen(fen).fold(_ => fail(), identity)
+    val moves    = rules.allLegalMoves(context)
+    val captures = moves.filter(m => m.from == Square(File.E, Rank.R4) && (m.moveType match { case _: MoveType.Normal => true; case _ => false }))
     captures.exists(m => m.to == Square(File.D, Rank.R5)) shouldBe true
 
   test("pawn cannot move backward"):

modules/rule/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=2
+MINOR=3
 PATCH=0

modules/ui/CHANGELOG.md

@@ -79,3 +79,15 @@
 * NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
 * NCS-25 Add linters to keep quality up ([#27](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/27)) ([fd4e67d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fd4e67d4f782a7e955822d90cb909d0a81676fb2))
 * NCS-29 JSON - Cherry Picked ([#28](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/28)) ([dbcafd2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/dbcafd286993e0604a6fa286c5543581a149439e))
+##  (2026-04-16)
+
+### Features
+
+* NCS-10 Implement Pawn Promotion ([#12](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/12)) ([13bfc16](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/13bfc16cfe25db78ec607db523ca6d993c13430c))
+* NCS-13 Implement Threefold Repetition ([#31](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/31)) ([767d305](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/767d3051a76c266050b6335774d66e2db2273c16))
+* NCS-14 implemented insufficient moves rule ([#30](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/30)) ([b0399a4](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/b0399a4e489950083066c9538df9a84dcc7a4613))
+* NCS-16 Core Separation via Patterns ([#10](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/10)) ([1361dfc](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/1361dfc89553b146864fb8ff3526cf12cf3f293a))
+* NCS-17 Implement basic ScalaFX UI ([#14](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/14)) ([3ff8031](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/3ff80318b4f16c59733a46498581a5c27f048287))
+* NCS-21 Write Scripts to automate certain tasks ([#15](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/15)) ([8051871](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/80518719d536a087d339fe02530825dc07f8b388))
+* NCS-25 Add linters to keep quality up ([#27](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/27)) ([fd4e67d](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/fd4e67d4f782a7e955822d90cb909d0a81676fb2))
+* NCS-29 JSON - Cherry Picked ([#28](https://git.janis-eccarius.de/NowChess/NowChessSystems/issues/28)) ([dbcafd2](https://git.janis-eccarius.de/NowChess/NowChessSystems/commit/dbcafd286993e0604a6fa286c5543581a149439e))

modules/ui/build.gradle.kts

@@ -38,11 +38,6 @@ tasks.withType<ScalaCompile> {
     scalaCompileOptions.additionalParameters = listOf("-encoding", "UTF-8")
 }
 
-// Disable scalafix for UI module due to mutable state requirements
-tasks.matching { it.name.startsWith("scalafix") }.configureEach {
-    enabled = false
-}
-
 tasks.named<JavaExec>("run") {
     jvmArgs("-Dfile.encoding=UTF-8", "-Dstdout.encoding=UTF-8", "-Dstderr.encoding=UTF-8")
     standardInput = System.`in`

modules/ui/src/main/scala/de/nowchess/ui/terminal/TerminalUI.scala

@@ -1,7 +1,8 @@
 package de.nowchess.ui.terminal
 
+import java.util.concurrent.atomic.AtomicBoolean
 import scala.io.StdIn
-import de.nowchess.api.move.PromotionPiece
+import de.nowchess.api.game.DrawReason
 import de.nowchess.chess.engine.GameEngine
 import de.nowchess.chess.observer.*
 import de.nowchess.ui.utils.Renderer
@@ -10,8 +11,7 @@ import de.nowchess.ui.utils.Renderer
   * I/O and user interaction in the terminal.
   */
 class TerminalUI(engine: GameEngine) extends Observer:
-  private val running           = new AtomicBoolean(true)
-  private val awaitingPromotion = new AtomicBoolean(false)
+  private val running = new AtomicBoolean(true)
 
   /** Called by GameEngine whenever a game event occurs. */
   override def onGameEvent(event: GameEvent): Unit =
@@ -63,9 +63,6 @@ class TerminalUI(engine: GameEngine) extends Observer:
         print(Renderer.render(e.context.board))
         printPrompt(e.context.turn)
 
-      case _: PromotionRequiredEvent =>
-        println("Promote to: q=Queen, r=Rook, b=Bishop, n=Knight")
-        awaitingPromotion.set(true)
       case _: FiftyMoveRuleAvailableEvent =>
         println("50-move rule is now available — type 'draw' to claim.")
 
@@ -91,24 +88,14 @@ class TerminalUI(engine: GameEngine) extends Observer:
     while running.get() do
       val input = Option(StdIn.readLine()).getOrElse("quit").trim
       synchronized {
-        if awaitingPromotion.get() then
-          input.toLowerCase match
-            case "q" => awaitingPromotion.set(false); engine.completePromotion(PromotionPiece.Queen)
-            case "r" => awaitingPromotion.set(false); engine.completePromotion(PromotionPiece.Rook)
-            case "b" => awaitingPromotion.set(false); engine.completePromotion(PromotionPiece.Bishop)
-            case "n" => awaitingPromotion.set(false); engine.completePromotion(PromotionPiece.Knight)
-            case _ =>
-              println("Invalid choice. Enter q, r, b, or n.")
-              println("Promote to: q=Queen, r=Rook, b=Bishop, n=Knight")
-        else
-          input.toLowerCase match
-            case "quit" | "q" =>
-              running.set(false)
-              println("Game over. Goodbye!")
-            case "" =>
-              printPrompt(engine.turn)
-            case _ =>
-              engine.processUserInput(input)
+        input.toLowerCase match
+          case "quit" | "q" =>
+            running.set(false)
+            println("Game over. Goodbye!")
+          case "" =>
+            printPrompt(engine.turn)
+          case _ =>
+            engine.processUserInput(input)
       }
 
     // Unsubscribe when done

modules/ui/versions.env

@@ -1,3 +1,3 @@
 MAJOR=0
-MINOR=10
+MINOR=11
 PATCH=0