style: fix CRLF line endings introduced by rebase

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

.idea/gradle.xml

@@ -11,6 +11,7 @@
             <option value="$PROJECT_DIR$" />
             <option value="$PROJECT_DIR$/modules" />
             <option value="$PROJECT_DIR$/modules/api" />
+            <option value="$PROJECT_DIR$/modules/backcore" />
             <option value="$PROJECT_DIR$/modules/core" />
             <option value="$PROJECT_DIR$/modules/io" />
             <option value="$PROJECT_DIR$/modules/rule" />

.idea/scala_compiler.xml

@@ -5,7 +5,7 @@
       <option name="deprecationWarnings" value="true" />
       <option name="uncheckedWarnings" value="true" />
     </profile>
-    <profile name="Gradle 2" modules="NowChessSystems.modules.core.main,NowChessSystems.modules.core.scoverage,NowChessSystems.modules.core.test,NowChessSystems.modules.io.main,NowChessSystems.modules.io.scoverage,NowChessSystems.modules.io.test,NowChessSystems.modules.rule.main,NowChessSystems.modules.rule.scoverage,NowChessSystems.modules.rule.test,NowChessSystems.modules.ui.main,NowChessSystems.modules.ui.scoverage,NowChessSystems.modules.ui.test">
+    <profile name="Gradle 2" modules="NowChessSystems.modules.backcore.integrationTest,NowChessSystems.modules.backcore.main,NowChessSystems.modules.backcore.native-test,NowChessSystems.modules.backcore.quarkus-generated-sources,NowChessSystems.modules.backcore.quarkus-test-generated-sources,NowChessSystems.modules.backcore.scoverage,NowChessSystems.modules.backcore.test,NowChessSystems.modules.core.main,NowChessSystems.modules.core.scoverage,NowChessSystems.modules.core.test,NowChessSystems.modules.io.main,NowChessSystems.modules.io.scoverage,NowChessSystems.modules.io.test,NowChessSystems.modules.rule.main,NowChessSystems.modules.rule.scoverage,NowChessSystems.modules.rule.test,NowChessSystems.modules.ui.main,NowChessSystems.modules.ui.scoverage,NowChessSystems.modules.ui.test">
       <option name="deprecationWarnings" value="true" />
       <option name="uncheckedWarnings" value="true" />
       <parameters>

.idea/scala_settings.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ScalaProjectSettings">
+    <option name="scala3DisclaimerShown" value="true" />
+  </component>
+</project>

build.gradle.kts

@@ -21,7 +21,15 @@ sonar {
             if (report.exists()) report.absolutePath else null
         }.joinToString(",")
 
+        val jacocoReports = subprojects.mapNotNull { subproject ->
+            val report = subproject.file("build/reports/jacoco/test/jacocoTestReport.xml")
+            if (report.exists()) report.absolutePath else null
+        }.joinToString(",")
+
         property("sonar.scala.coverage.reportPaths", scoverageReports)
+        if (jacocoReports.isNotEmpty()) {
+            property("sonar.coverage.jacoco.xmlReportPaths", jacocoReports)
+        }
     }
 }
 

gradle.properties

@@ -0,0 +1,5 @@
+quarkusPluginId=io.quarkus
+quarkusPluginVersion=3.32.4
+quarkusPlatformGroupId=io.quarkus.platform
+quarkusPlatformArtifactId=quarkus-bom
+quarkusPlatformVersion=3.32.4

modules/api/src/main/scala/de/nowchess/api/game/DrawReason.scala

@@ -5,5 +5,4 @@ enum DrawReason:
   case Stalemate
   case InsufficientMaterial
   case FiftyMoveRule
-  case ThreefoldRepetition
   case Agreement

modules/api/src/main/scala/de/nowchess/api/game/GameContext.scala

@@ -13,7 +13,6 @@ case class GameContext(
     halfMoveClock: Int,
     moves: List[Move],
     result: Option[GameResult] = None,
-    initialBoard: Board = Board.initial,
 ):
   /** Create new context with updated board. */
   def withBoard(newBoard: Board): GameContext = copy(board = newBoard)

modules/backcore/build.gradle.kts

@@ -0,0 +1,101 @@
+plugins {
+    id("scala")
+    id("org.scoverage") version "8.1"
+    id("io.quarkus")
+    id("jacoco")
+}
+
+@Suppress("UNCHECKED_CAST")
+val versions = rootProject.extra["VERSIONS"] as Map<String, String>
+
+repositories {
+    mavenCentral()
+    mavenLocal()
+}
+
+scala {
+    scalaVersion = versions["SCALA3"]!!
+}
+
+scoverage {
+    scoverageVersion.set(versions["SCOVERAGE"]!!)
+}
+
+tasks.withType<ScalaCompile> {
+    scalaCompileOptions.additionalParameters = listOf("-encoding", "UTF-8")
+}
+
+val quarkusPlatformGroupId: String by project
+val quarkusPlatformArtifactId: String by project
+val quarkusPlatformVersion: String by project
+
+dependencies {
+    implementation(project(":modules:api"))
+    implementation(project(":modules:core"))
+    implementation(project(":modules:io"))
+    implementation(project(":modules:rule"))
+
+    implementation(enforcedPlatform("${quarkusPlatformGroupId}:${quarkusPlatformArtifactId}:${quarkusPlatformVersion}"))
+    implementation("io.quarkus:quarkus-rest")
+    implementation("io.quarkus:quarkus-rest-jackson")
+    implementation("io.quarkus:quarkus-config-yaml")
+    implementation("io.quarkus:quarkus-arc")
+
+    implementation("com.fasterxml.jackson.module:jackson-module-scala_3:${versions["JACKSON_SCALA"]!!}")
+
+    testImplementation(platform("org.junit:junit-bom:${versions["JUNIT_BOM"]!!}"))
+    testImplementation("org.junit.jupiter:junit-jupiter")
+    testImplementation("org.scalatest:scalatest_3:${versions["SCALATEST"]!!}")
+    testImplementation("co.helmethair:scalatest-junit-runner:${versions["SCALATEST_JUNIT"]!!}")
+    testImplementation("io.quarkus:quarkus-junit5")
+    testImplementation("io.quarkus:quarkus-jacoco")
+    testImplementation("io.rest-assured:rest-assured")
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+}
+
+configurations.matching { !it.name.startsWith("scoverage") }.configureEach {
+    resolutionStrategy.force("org.scala-lang:scala-library:${versions["SCALA_LIBRARY"]!!}")
+}
+configurations.scoverage {
+    resolutionStrategy.eachDependency {
+        if (requested.group == "org.scoverage" && requested.name.startsWith("scalac-scoverage-plugin_")) {
+            useTarget("${requested.group}:scalac-scoverage-plugin_2.13.16:2.3.0")
+        }
+    }
+}
+
+group = "de.nowchess"
+version = "1.0-SNAPSHOT"
+
+tasks.withType<JavaCompile> {
+    options.encoding = "UTF-8"
+    options.compilerArgs.add("-parameters")
+}
+
+tasks.withType<Jar>().configureEach {
+    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
+}
+
+tasks.test {
+    useJUnitPlatform {
+        includeEngines("scalatest", "junit-jupiter")
+    }
+    testLogging {
+        events("passed", "skipped", "failed")
+    }
+    finalizedBy(tasks.named("jacocoTestReport"))
+}
+
+tasks.jacocoTestReport {
+    dependsOn(tasks.test)
+    executionData.setFrom(layout.buildDirectory.file("jacoco-quarkus.exec"))
+    sourceDirectories.setFrom(files("src/main/scala"))
+    classDirectories.setFrom(files(layout.buildDirectory.dir("classes/scala/main")))
+    reports {
+        xml.required.set(true)
+        xml.outputLocation.set(
+            layout.buildDirectory.file("reports/jacoco/test/jacocoTestReport.xml")
+        )
+        html.required.set(false)
+    }
+}

modules/backcore/src/main/resources/application.yml

@@ -0,0 +1,6 @@
+quarkus:
+  http:
+    port: 8080
+  jacoco:
+    data-file: ${user.dir}/build/jacoco-quarkus.exec
+    report: false

modules/backcore/src/main/scala/de/nowchess/backcore/config/JacksonConfig.scala

@@ -0,0 +1,11 @@
+package de.nowchess.backcore.config
+
+import com.fasterxml.jackson.databind.ObjectMapper
+import com.fasterxml.jackson.module.scala.DefaultScalaModule
+import io.quarkus.jackson.ObjectMapperCustomizer
+import jakarta.inject.Singleton
+
+@Singleton
+class JacksonConfig extends ObjectMapperCustomizer:
+  def customize(mapper: ObjectMapper): Unit =
+    mapper.registerModule(DefaultScalaModule)

modules/backcore/src/main/scala/de/nowchess/backcore/dto/Dtos.scala

@@ -0,0 +1,57 @@
+package de.nowchess.backcore.dto
+
+import com.fasterxml.jackson.annotation.JsonInclude
+import com.fasterxml.jackson.annotation.JsonInclude.Include
+
+case class PlayerInfoDto(id: String, displayName: String)
+
+case class GameStateResponse(
+    fen: String,
+    pgn: String,
+    turn: String,
+    status: String,
+    @JsonInclude(Include.NON_ABSENT) winner: Option[String],
+    moves: List[String],
+    undoAvailable: Boolean,
+    redoAvailable: Boolean,
+)
+
+case class GameFullResponse(
+    gameId: String,
+    white: PlayerInfoDto,
+    black: PlayerInfoDto,
+    state: GameStateResponse,
+)
+
+case class OkResponse(ok: Boolean = true)
+
+@JsonInclude(Include.NON_ABSENT)
+case class ApiErrorResponse(
+    code: String,
+    message: String,
+    field: Option[String] = None,
+)
+
+// Requests
+case class CreateGameRequest(
+    white: Option[PlayerInfoDto] = None,
+    black: Option[PlayerInfoDto] = None,
+)
+
+case class ImportFenRequest(
+    fen: String = "",
+    white: Option[PlayerInfoDto] = None,
+    black: Option[PlayerInfoDto] = None,
+)
+
+case class ImportPgnRequest(pgn: String = "")
+
+case class LegalMoveDto(
+    from: String,
+    to: String,
+    uci: String,
+    moveType: String,
+    @JsonInclude(Include.NON_ABSENT) promotion: Option[String] = None,
+)
+
+case class LegalMovesResponse(moves: List[LegalMoveDto])

modules/backcore/src/main/scala/de/nowchess/backcore/game/GameId.scala

@@ -0,0 +1,10 @@
+package de.nowchess.backcore.game
+
+import java.security.SecureRandom
+
+object GameId:
+  private val chars  = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
+  private val random = SecureRandom()
+
+  def generate(): String =
+    (1 to 8).map(_ => chars(random.nextInt(chars.length))).mkString

modules/backcore/src/main/scala/de/nowchess/backcore/game/GameMapper.scala

@@ -0,0 +1,80 @@
+package de.nowchess.backcore.game
+
+import com.fasterxml.jackson.databind.ObjectMapper
+import com.fasterxml.jackson.module.scala.DefaultScalaModule
+import de.nowchess.api.board.Color
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.backcore.dto.*
+import de.nowchess.io.fen.FenExporter
+import de.nowchess.io.pgn.PgnExporter
+import de.nowchess.rules.sets.DefaultRules
+
+object GameMapper:
+  private val mapper = new ObjectMapper().registerModule(DefaultScalaModule)
+
+  def toGameFullJson(session: GameSession): String =
+    mapper.writeValueAsString(toGameFull(session))
+
+  def toGameFull(session: GameSession): GameFullResponse =
+    GameFullResponse(
+      gameId = session.gameId,
+      white = toPlayerInfo(session.white),
+      black = toPlayerInfo(session.black),
+      state = toGameState(session),
+    )
+
+  def toGameState(session: GameSession): GameStateResponse =
+    val (status, winner) = computeStatus(session)
+    GameStateResponse(
+      fen = FenExporter.exportGameContext(session.context),
+      pgn = buildPgn(session.context.moves),
+      turn = if session.context.turn == Color.White then "white" else "black",
+      status = status,
+      winner = winner,
+      moves = session.context.moves.map(moveToUci),
+      undoAvailable = session.invoker.canUndo,
+      redoAvailable = session.invoker.canRedo,
+    )
+
+  private def toPlayerInfo(p: de.nowchess.api.player.PlayerInfo): PlayerInfoDto =
+    PlayerInfoDto(id = p.id.value, displayName = p.displayName)
+
+  private def computeStatus(session: GameSession): (String, Option[String]) =
+    session.result match
+      case Some(GameResult.Checkmate(winner)) =>
+        val w = if winner == Color.White then "white" else "black"
+        ("checkmate", Some(w))
+      case Some(GameResult.Stalemate) =>
+        ("stalemate", None)
+      case Some(GameResult.Resign(winner)) =>
+        val w = if winner == Color.White then "white" else "black"
+        ("resign", Some(w))
+      case Some(GameResult.AgreedDraw) | Some(GameResult.FiftyMoveDraw) =>
+        ("draw", None)
+      case Some(GameResult.InsufficientMaterial) =>
+        ("insufficientMaterial", None)
+      case None =>
+        computeLiveStatus(session)
+
+  private def computeLiveStatus(session: GameSession): (String, Option[String]) =
+    val ctx = session.context
+    if DefaultRules.isCheck(ctx) then ("check", None)
+    else if session.drawOfferedBy.isDefined then ("drawOffered", None)
+    else if DefaultRules.isFiftyMoveRule(ctx) then ("fiftyMoveAvailable", None)
+    else ("started", None)
+
+  def moveToUci(move: Move): String =
+    val base = s"${move.from}${move.to}"
+    move.moveType match
+      case MoveType.Promotion(piece) =>
+        val suffix = piece match
+          case PromotionPiece.Queen  => "q"
+          case PromotionPiece.Rook   => "r"
+          case PromotionPiece.Bishop => "b"
+          case PromotionPiece.Knight => "n"
+        base + suffix
+      case _ => base
+
+  private def buildPgn(moves: List[Move]): String =
+    // Use PgnExporter with no headers to get move-text only (SAN notation)
+    PgnExporter.exportGame(Map.empty, moves)

modules/backcore/src/main/scala/de/nowchess/backcore/game/GameResult.scala

@@ -0,0 +1,12 @@
+package de.nowchess.backcore.game
+
+import de.nowchess.api.board.Color
+
+sealed trait GameResult
+object GameResult:
+  case class Checkmate(winner: Color) extends GameResult
+  case object Stalemate               extends GameResult
+  case class Resign(winner: Color)    extends GameResult
+  case object AgreedDraw              extends GameResult
+  case object FiftyMoveDraw           extends GameResult
+  case object InsufficientMaterial    extends GameResult

modules/backcore/src/main/scala/de/nowchess/backcore/game/GameSession.scala

@@ -0,0 +1,16 @@
+package de.nowchess.backcore.game
+
+import de.nowchess.api.board.Color
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.player.PlayerInfo
+import de.nowchess.chess.command.CommandInvoker
+
+case class GameSession(
+    gameId: String,
+    white: PlayerInfo,
+    black: PlayerInfo,
+    context: GameContext,
+    invoker: CommandInvoker,
+    drawOfferedBy: Option[Color] = None,
+    result: Option[GameResult] = None,
+)

modules/backcore/src/main/scala/de/nowchess/backcore/game/GameStore.scala

@@ -0,0 +1,260 @@
+package de.nowchess.backcore.game
+
+import de.nowchess.api.board.{Color, Square}
+import de.nowchess.api.game.GameContext
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.api.player.{PlayerId, PlayerInfo}
+import de.nowchess.backcore.dto.{CreateGameRequest, ImportFenRequest, PlayerInfoDto}
+import de.nowchess.chess.command.{CommandInvoker, MoveCommand, MoveResult}
+import de.nowchess.io.fen.FenParser
+import de.nowchess.io.pgn.PgnParser
+import de.nowchess.rules.sets.DefaultRules
+import jakarta.enterprise.context.ApplicationScoped
+
+import scala.collection.mutable
+
+@ApplicationScoped
+class GameStore:
+  private val games: mutable.Map[String, GameSession] = mutable.Map.empty
+
+  // ─── Create / Get ────────────────────────────────────────────────
+
+  def create(req: CreateGameRequest): GameSession = synchronized:
+    val id      = generateId()
+    val session = newSession(id, req.white, req.black, GameContext.initial)
+    games(id) = session
+    session
+
+  def get(id: String): Option[GameSession] = synchronized:
+    games.get(id)
+
+  // ─── Move-making ─────────────────────────────────────────────────
+
+  def applyMove(id: String, uci: String): Either[String, GameSession] = synchronized:
+    withSession(id): session =>
+      if session.result.isDefined then Left("Game is already over")
+      else
+        parseUci(uci) match
+          case None => Left(s"Invalid UCI notation: $uci")
+          case Some((from, to, promotion)) =>
+            val legalCandidates = DefaultRules.legalMoves(session.context)(from)
+            findMatchingMove(legalCandidates, to, promotion) match
+              case None => Left(s"$uci is not a legal move")
+              case Some(move) =>
+                val nextCtx = DefaultRules.applyMove(session.context)(move)
+                val prevCtx = session.context
+                val cmd = MoveCommand(
+                  from = move.from,
+                  to = move.to,
+                  moveResult = Some(MoveResult.Successful(nextCtx, prevCtx.board.pieceAt(move.to))),
+                  previousContext = Some(prevCtx),
+                )
+                session.invoker.execute(cmd)
+                val result  = detectGameOver(nextCtx)
+                val updated = session.copy(context = nextCtx, result = result)
+                games(id) = updated
+                Right(updated)
+
+  def legalMoves(id: String, square: Option[Square]): Either[String, List[Move]] = synchronized:
+    withSession(id): session =>
+      val moves = square match
+        case Some(sq) => DefaultRules.legalMoves(session.context)(sq)
+        case None     => DefaultRules.allLegalMoves(session.context)
+      Right(moves)
+
+  // ─── Undo / Redo ─────────────────────────────────────────────────
+
+  def undo(id: String): Either[String, GameSession] = synchronized:
+    withSession(id): session =>
+      if !session.invoker.canUndo then Left("No moves to undo")
+      else
+        val idx = session.invoker.getCurrentIndex
+        session.invoker.history(idx) match
+          case cmd: MoveCommand =>
+            cmd.previousContext match
+              case None => Left("Cannot undo: no previous context stored")
+              case Some(prevCtx) =>
+                session.invoker.undo()
+                val updated = session.copy(context = prevCtx, result = None, drawOfferedBy = None)
+                games(id) = updated
+                Right(updated)
+          case _ => Left("Cannot undo this command type")
+
+  def redo(id: String): Either[String, GameSession] = synchronized:
+    withSession(id): session =>
+      if !session.invoker.canRedo then Left("No moves to redo")
+      else
+        val idx = session.invoker.getCurrentIndex + 1
+        session.invoker.history(idx) match
+          case cmd: MoveCommand =>
+            cmd.moveResult match
+              case Some(MoveResult.Successful(nextCtx, _)) =>
+                session.invoker.redo()
+                val result  = detectGameOver(nextCtx)
+                val updated = session.copy(context = nextCtx, result = result)
+                games(id) = updated
+                Right(updated)
+              case _ => Left("Cannot redo: move result not available")
+          case _ => Left("Cannot redo this command type")
+
+  // ─── Resign ──────────────────────────────────────────────────────
+
+  def resign(id: String): Either[String, GameSession] = synchronized:
+    withSession(id): session =>
+      if session.result.isDefined then Left("Game is already over")
+      else
+        val winner  = session.context.turn.opposite
+        val updated = session.copy(result = Some(GameResult.Resign(winner)))
+        games(id) = updated
+        Right(updated)
+
+  // ─── Draw actions ────────────────────────────────────────────────
+
+  def drawAction(id: String, action: String): Either[String, GameSession] = synchronized:
+    withSession(id): session =>
+      if session.result.isDefined then Left("Game is already over")
+      else
+        action match
+          case "offer" =>
+            val updated = session.copy(drawOfferedBy = Some(session.context.turn))
+            games(id) = updated
+            Right(updated)
+          case "accept" =>
+            session.drawOfferedBy match
+              case None => Left("No draw offer to accept")
+              case Some(offerer) if offerer == session.context.turn =>
+                Left("Cannot accept your own draw offer")
+              case Some(_) =>
+                val updated = session.copy(result = Some(GameResult.AgreedDraw), drawOfferedBy = None)
+                games(id) = updated
+                Right(updated)
+          case "decline" =>
+            session.drawOfferedBy match
+              case None => Left("No draw offer to decline")
+              case Some(_) =>
+                val updated = session.copy(drawOfferedBy = None)
+                games(id) = updated
+                Right(updated)
+          case "claim" =>
+            if DefaultRules.isFiftyMoveRule(session.context) then
+              val updated = session.copy(result = Some(GameResult.FiftyMoveDraw))
+              games(id) = updated
+              Right(updated)
+            else Left("Fifty-move rule has not been triggered")
+          case other => Left(s"Unknown draw action: $other")
+
+  // ─── Import ──────────────────────────────────────────────────────
+
+  def importFen(req: ImportFenRequest): Either[String, GameSession] = synchronized:
+    FenParser.parseFen(req.fen) match
+      case Left(err) => Left(err)
+      case Right(ctx) =>
+        val id      = generateId()
+        val session = newSession(id, req.white, req.black, ctx)
+        games(id) = session
+        Right(session)
+
+  def importPgn(pgn: String, white: Option[PlayerInfoDto], black: Option[PlayerInfoDto]): Either[String, GameSession] =
+    synchronized:
+      PgnParser.validatePgn(pgn) match
+        case Left(err) => Left(err)
+        case Right(game) =>
+          val id      = generateId()
+          val session = newSession(id, white, black, GameContext.initial)
+          replayIntoSession(session, game.moves, GameContext.initial) match
+            case Left(err) => Left(err)
+            case Right(s) =>
+              games(id) = s
+              Right(s)
+
+  // ─── Private helpers ─────────────────────────────────────────────
+
+  private def withSession[A](id: String)(f: GameSession => Either[String, A]): Either[String, A] =
+    games.get(id) match
+      case None          => Left(s"Game $id not found")
+      case Some(session) => f(session)
+
+  private def generateId(): String =
+    var id = GameId.generate()
+    while games.contains(id) do id = GameId.generate()
+    id
+
+  private def newSession(
+      id: String,
+      white: Option[PlayerInfoDto],
+      black: Option[PlayerInfoDto],
+      ctx: GameContext,
+  ): GameSession =
+    GameSession(
+      gameId = id,
+      white = toPlayerInfo(white, "white", "White"),
+      black = toPlayerInfo(black, "black", "Black"),
+      context = ctx,
+      invoker = new CommandInvoker(),
+    )
+
+  private def toPlayerInfo(dto: Option[PlayerInfoDto], defaultId: String, defaultName: String): PlayerInfo =
+    dto.fold(PlayerInfo(PlayerId(defaultId), defaultName))(d => PlayerInfo(PlayerId(d.id), d.displayName))
+
+  private def parseUci(uci: String): Option[(Square, Square, Option[PromotionPiece])] =
+    if uci.length < 4 || uci.length > 5 then None
+    else
+      for
+        from <- Square.fromAlgebraic(uci.substring(0, 2))
+        to   <- Square.fromAlgebraic(uci.substring(2, 4))
+      yield
+        val promotion = if uci.length == 5 then parsePromotionChar(uci.charAt(4)) else None
+        (from, to, promotion)
+
+  private def parsePromotionChar(c: Char): Option[PromotionPiece] =
+    c match
+      case 'q' => Some(PromotionPiece.Queen)
+      case 'r' => Some(PromotionPiece.Rook)
+      case 'b' => Some(PromotionPiece.Bishop)
+      case 'n' => Some(PromotionPiece.Knight)
+      case _   => None
+
+  private def findMatchingMove(
+      candidates: List[Move],
+      to: Square,
+      promotion: Option[PromotionPiece],
+  ): Option[Move] =
+    candidates.filter(_.to == to) match
+      case Nil => None
+      case moves =>
+        promotion match
+          case Some(pp) => moves.find(_.moveType == MoveType.Promotion(pp))
+          case None =>
+            moves
+              .find(m => !m.moveType.isInstanceOf[MoveType.Promotion])
+              .orElse(moves.headOption)
+
+  private def detectGameOver(ctx: GameContext): Option[GameResult] =
+    if DefaultRules.isCheckmate(ctx) then Some(GameResult.Checkmate(ctx.turn.opposite))
+    else if DefaultRules.isStalemate(ctx) then Some(GameResult.Stalemate)
+    else if DefaultRules.isInsufficientMaterial(ctx) then Some(GameResult.InsufficientMaterial)
+    else None
+
+  private def replayIntoSession(
+      session: GameSession,
+      moves: List[Move],
+      startCtx: GameContext,
+  ): Either[String, GameSession] =
+    moves.foldLeft[Either[String, GameSession]](Right(session)):
+      case (Left(err), _) => Left(err)
+      case (Right(s), move) =>
+        val legal = DefaultRules.legalMoves(s.context)(move.from)
+        legal
+          .find(m => m.from == move.from && m.to == move.to && m.moveType == move.moveType)
+          .orElse(legal.find(m => m.from == move.from && m.to == move.to)) match
+          case None => Left(s"Illegal move in PGN: $move")
+          case Some(legalMove) =>
+            val nextCtx = DefaultRules.applyMove(s.context)(legalMove)
+            val cmd = MoveCommand(
+              from = legalMove.from,
+              to = legalMove.to,
+              moveResult = Some(MoveResult.Successful(nextCtx, s.context.board.pieceAt(legalMove.to))),
+              previousContext = Some(s.context),
+            )
+            s.invoker.execute(cmd)
+            Right(s.copy(context = nextCtx))

modules/backcore/src/main/scala/de/nowchess/backcore/resource/GameResource.scala

@@ -0,0 +1,99 @@
+package de.nowchess.backcore.resource
+
+import de.nowchess.backcore.dto.*
+import de.nowchess.backcore.game.{GameMapper, GameStore}
+import jakarta.enterprise.context.ApplicationScoped
+import jakarta.inject.Inject
+import jakarta.ws.rs.*
+import jakarta.ws.rs.core.{MediaType, Response}
+
+@Path("/api/board/game")
+@Produces(Array(MediaType.APPLICATION_JSON))
+@ApplicationScoped
+class GameResource @Inject() (store: GameStore):
+
+  @POST
+  @Consumes(Array(MediaType.APPLICATION_JSON))
+  def createGame(req: CreateGameRequest): Response =
+    val session = store.create(Option(req).getOrElse(CreateGameRequest()))
+    Response.status(201).entity(GameMapper.toGameFull(session)).build()
+
+  @GET
+  @Path("/{gameId}")
+  def getGame(@PathParam("gameId") gameId: String): Response =
+    store.get(gameId) match
+      case Some(session) => Response.ok(GameMapper.toGameFull(session)).build()
+      case None =>
+        Response
+          .status(404)
+          .entity(ApiErrorResponse("GAME_NOT_FOUND", s"Game $gameId not found"))
+          .build()
+
+  @GET
+  @Path("/{gameId}/stream")
+  @Produces(Array("application/x-ndjson"))
+  def streamGame(@PathParam("gameId") gameId: String): Response =
+    store.get(gameId) match
+      case None =>
+        Response
+          .status(404)
+          .`type`(MediaType.APPLICATION_JSON)
+          .entity(ApiErrorResponse("GAME_NOT_FOUND", s"Game $gameId not found"))
+          .build()
+      case Some(session) =>
+        // Simplified: return a single-line NDJSON snapshot of the current game state
+        val event = s"""{"type":"gameFull","game":${GameMapper.toGameFullJson(session)}}"""
+        Response.ok(event + "\n").build()
+
+  @POST
+  @Path("/{gameId}/resign")
+  def resignGame(@PathParam("gameId") gameId: String): Response =
+    store.resign(gameId) match
+      case Right(_) => Response.ok(OkResponse()).build()
+      case Left(err) if err.contains("not found") =>
+        Response.status(404).entity(ApiErrorResponse("GAME_NOT_FOUND", err)).build()
+      case Left(err) =>
+        Response.status(400).entity(ApiErrorResponse("RESIGN_ERROR", err)).build()
+
+  @POST
+  @Path("/{gameId}/draw/{action}")
+  def drawAction(
+      @PathParam("gameId") gameId: String,
+      @PathParam("action") action: String,
+  ): Response =
+    store.drawAction(gameId, action) match
+      case Right(_) => Response.ok(OkResponse()).build()
+      case Left(err) if err.contains("not found") =>
+        Response.status(404).entity(ApiErrorResponse("GAME_NOT_FOUND", err)).build()
+      case Left(err) =>
+        Response.status(400).entity(ApiErrorResponse("DRAW_ERROR", err)).build()
+
+  @GET
+  @Path("/{gameId}/export/fen")
+  @Produces(Array(MediaType.TEXT_PLAIN))
+  def exportFen(@PathParam("gameId") gameId: String): Response =
+    store.get(gameId) match
+      case None =>
+        Response
+          .status(404)
+          .`type`(MediaType.APPLICATION_JSON)
+          .entity(ApiErrorResponse("GAME_NOT_FOUND", s"Game $gameId not found"))
+          .build()
+      case Some(session) =>
+        import de.nowchess.io.fen.FenExporter
+        Response.ok(FenExporter.exportGameContext(session.context)).build()
+
+  @GET
+  @Path("/{gameId}/export/pgn")
+  @Produces(Array("application/x-chess-pgn"))
+  def exportPgn(@PathParam("gameId") gameId: String): Response =
+    store.get(gameId) match
+      case None =>
+        Response
+          .status(404)
+          .`type`(MediaType.APPLICATION_JSON)
+          .entity(ApiErrorResponse("GAME_NOT_FOUND", s"Game $gameId not found"))
+          .build()
+      case Some(session) =>
+        import de.nowchess.io.pgn.PgnExporter
+        Response.ok(PgnExporter.exportGameContext(session.context)).build()

modules/backcore/src/main/scala/de/nowchess/backcore/resource/ImportResource.scala

@@ -0,0 +1,29 @@
+package de.nowchess.backcore.resource
+
+import de.nowchess.backcore.dto.{ApiErrorResponse, ImportFenRequest, ImportPgnRequest}
+import de.nowchess.backcore.game.{GameMapper, GameStore}
+import jakarta.enterprise.context.ApplicationScoped
+import jakarta.inject.Inject
+import jakarta.ws.rs.*
+import jakarta.ws.rs.core.{MediaType, Response}
+
+@Path("/api/board/game/import")
+@Produces(Array(MediaType.APPLICATION_JSON))
+@Consumes(Array(MediaType.APPLICATION_JSON))
+@ApplicationScoped
+class ImportResource @Inject() (store: GameStore):
+
+  @POST
+  @Path("/fen")
+  def importFen(req: ImportFenRequest): Response =
+    store.importFen(Option(req).getOrElse(ImportFenRequest())) match
+      case Right(session) => Response.status(201).entity(GameMapper.toGameFull(session)).build()
+      case Left(err)      => Response.status(400).entity(ApiErrorResponse("INVALID_FEN", err)).build()
+
+  @POST
+  @Path("/pgn")
+  def importPgn(req: ImportPgnRequest): Response =
+    val body = Option(req).getOrElse(ImportPgnRequest())
+    store.importPgn(body.pgn, None, None) match
+      case Right(session) => Response.status(201).entity(GameMapper.toGameFull(session)).build()
+      case Left(err)      => Response.status(400).entity(ApiErrorResponse("INVALID_PGN", err)).build()

modules/backcore/src/main/scala/de/nowchess/backcore/resource/MoveResource.scala

@@ -0,0 +1,87 @@
+package de.nowchess.backcore.resource
+
+import de.nowchess.api.board.Square
+import de.nowchess.api.move.{Move, MoveType, PromotionPiece}
+import de.nowchess.backcore.dto.*
+import de.nowchess.backcore.game.{GameMapper, GameStore}
+import jakarta.enterprise.context.ApplicationScoped
+import jakarta.inject.Inject
+import jakarta.ws.rs.*
+import jakarta.ws.rs.core.{MediaType, Response}
+
+@Path("/api/board/game")
+@Produces(Array(MediaType.APPLICATION_JSON))
+@ApplicationScoped
+class MoveResource @Inject() (store: GameStore):
+
+  @POST
+  @Path("/{gameId}/move/{uci}")
+  def makeMove(
+      @PathParam("gameId") gameId: String,
+      @PathParam("uci") uci: String,
+  ): Response =
+    store.applyMove(gameId, uci) match
+      case Right(session) => Response.ok(GameMapper.toGameState(session)).build()
+      case Left(err) if err.contains("not found") =>
+        Response.status(404).entity(ApiErrorResponse("GAME_NOT_FOUND", err)).build()
+      case Left(err) =>
+        Response.status(400).entity(ApiErrorResponse("INVALID_MOVE", err)).build()
+
+  @GET
+  @Path("/{gameId}/moves")
+  def getLegalMoves(
+      @PathParam("gameId") gameId: String,
+      @QueryParam("square") squareParam: String,
+  ): Response =
+    val square = Option(squareParam).flatMap(Square.fromAlgebraic)
+    store.legalMoves(gameId, square) match
+      case Right(moves) =>
+        val dtos = moves.map(toLegalMoveDto)
+        Response.ok(LegalMovesResponse(dtos)).build()
+      case Left(err) if err.contains("not found") =>
+        Response.status(404).entity(ApiErrorResponse("GAME_NOT_FOUND", err)).build()
+      case Left(err) =>
+        Response.status(400).entity(ApiErrorResponse("ERROR", err)).build()
+
+  @POST
+  @Path("/{gameId}/undo")
+  def undoMove(@PathParam("gameId") gameId: String): Response =
+    store.undo(gameId) match
+      case Right(session) => Response.ok(GameMapper.toGameState(session)).build()
+      case Left(err) if err.contains("not found") =>
+        Response.status(404).entity(ApiErrorResponse("GAME_NOT_FOUND", err)).build()
+      case Left(err) =>
+        Response.status(400).entity(ApiErrorResponse("UNDO_NOT_AVAILABLE", err)).build()
+
+  @POST
+  @Path("/{gameId}/redo")
+  def redoMove(@PathParam("gameId") gameId: String): Response =
+    store.redo(gameId) match
+      case Right(session) => Response.ok(GameMapper.toGameState(session)).build()
+      case Left(err) if err.contains("not found") =>
+        Response.status(404).entity(ApiErrorResponse("GAME_NOT_FOUND", err)).build()
+      case Left(err) =>
+        Response.status(400).entity(ApiErrorResponse("REDO_NOT_AVAILABLE", err)).build()
+
+  private def toLegalMoveDto(move: Move): LegalMoveDto =
+    val uci = GameMapper.moveToUci(move)
+    val (moveType, promotion) = move.moveType match
+      case MoveType.Normal(true)    => ("capture", None)
+      case MoveType.Normal(false)   => ("normal", None)
+      case MoveType.CastleKingside  => ("castleKingside", None)
+      case MoveType.CastleQueenside => ("castleQueenside", None)
+      case MoveType.EnPassant       => ("enPassant", None)
+      case MoveType.Promotion(pp) =>
+        val pName = pp match
+          case PromotionPiece.Queen  => "queen"
+          case PromotionPiece.Rook   => "rook"
+          case PromotionPiece.Bishop => "bishop"
+          case PromotionPiece.Knight => "knight"
+        ("promotion", Some(pName))
+    LegalMoveDto(
+      from = move.from.toString,
+      to = move.to.toString,
+      uci = uci,
+      moveType = moveType,
+      promotion = promotion,
+    )

modules/backcore/src/test/scala/de/nowchess/backcore/BackcoreStartupTest.scala

@@ -0,0 +1,11 @@
+package de.nowchess.backcore
+
+import io.quarkus.test.junit.QuarkusTest
+import org.junit.jupiter.api.Test
+
+@QuarkusTest
+class BackcoreStartupTest:
+  @Test
+  def applicationStarts(): Unit =
+    // If we get here the Quarkus container started successfully
+    ()

modules/backcore/src/test/scala/de/nowchess/backcore/resource/GameResourceTest.scala

@@ -0,0 +1,67 @@
+package de.nowchess.backcore.resource
+
+import io.quarkus.test.junit.QuarkusTest
+import io.restassured.RestAssured
+import org.hamcrest.Matchers.{equalTo, matchesPattern, notNullValue}
+import org.junit.jupiter.api.Test
+
+@QuarkusTest
+class GameResourceTest:
+
+  @Test
+  def createGameReturns201WithGameId(): Unit =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .body("gameId", matchesPattern("[A-Za-z0-9]{8}"))
+      .body("state.fen", notNullValue())
+      .body("state.turn", equalTo("white"))
+      .body("state.status", equalTo("started"))
+
+  @Test
+  def createGameWithPlayersReturns201(): Unit =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("""{"white":{"id":"p1","displayName":"Alice"},"black":{"id":"p2","displayName":"Bob"}}""")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .body("white.id", equalTo("p1"))
+      .body("black.displayName", equalTo("Bob"))
+
+  @Test
+  def getGameReturns200ForExistingGame(): Unit =
+    val gameId = RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .extract()
+      .path[String]("gameId")
+
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId")
+      .`then`()
+      .statusCode(200)
+      .body("gameId", equalTo(gameId))
+
+  @Test
+  def getGameReturns404ForUnknownId(): Unit =
+    RestAssured
+      .`given`()
+      .when()
+      .get("/api/board/game/XXXXXXXX")
+      .`then`()
+      .statusCode(404)

modules/backcore/src/test/scala/de/nowchess/backcore/resource/ImportExportTest.scala

@@ -0,0 +1,177 @@
+package de.nowchess.backcore.resource
+
+import io.quarkus.test.junit.QuarkusTest
+import io.restassured.RestAssured
+import org.hamcrest.Matchers.{containsString, equalTo, matchesPattern, notNullValue}
+import org.junit.jupiter.api.Test
+
+@QuarkusTest
+class ImportExportTest:
+
+  private val startFen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
+
+  // ─── Import FEN ────────────────────────────────────────────────
+
+  @Test
+  def importFenReturns201WithCorrectPosition(): Unit =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body(s"""{"fen":"$startFen"}""")
+      .when()
+      .post("/api/board/game/import/fen")
+      .`then`()
+      .statusCode(201)
+      .body("gameId", matchesPattern("[A-Za-z0-9]{8}"))
+      .body("state.fen", equalTo(startFen))
+      .body("state.turn", equalTo("white"))
+
+  @Test
+  def importFenWithCustomPositionWorks(): Unit =
+    val fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1"
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body(s"""{"fen":"$fen"}""")
+      .when()
+      .post("/api/board/game/import/fen")
+      .`then`()
+      .statusCode(201)
+      .body("state.fen", equalTo(fen))
+      .body("state.turn", equalTo("black"))
+
+  @Test
+  def importFenWithInvalidFenReturns400(): Unit =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("""{"fen":"not-a-fen"}""")
+      .when()
+      .post("/api/board/game/import/fen")
+      .`then`()
+      .statusCode(400)
+
+  // ─── Import PGN ────────────────────────────────────────────────
+
+  @Test
+  def importPgnReturns201(): Unit =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("""{"pgn":"1. e4 e5 2. Nf3 Nc6 *"}""")
+      .when()
+      .post("/api/board/game/import/pgn")
+      .`then`()
+      .statusCode(201)
+      .body("gameId", matchesPattern("[A-Za-z0-9]{8}"))
+      .body("state.turn", equalTo("white"))
+
+  @Test
+  def importPgnWithInvalidPgnReturns400(): Unit =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("""{"pgn":"1. z9 *"}""")
+      .when()
+      .post("/api/board/game/import/pgn")
+      .`then`()
+      .statusCode(400)
+
+  // ─── Export FEN ────────────────────────────────────────────────
+
+  @Test
+  def exportFenReturnsStartingFen(): Unit =
+    val gameId = RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .extract()
+      .path[String]("gameId")
+
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId/export/fen")
+      .`then`()
+      .statusCode(200)
+      .body(equalTo(startFen))
+
+  @Test
+  def exportFenOnUnknownGameReturns404(): Unit =
+    RestAssured
+      .`given`()
+      .when()
+      .get("/api/board/game/XXXXXXXX/export/fen")
+      .`then`()
+      .statusCode(404)
+
+  // ─── Export PGN ────────────────────────────────────────────────
+
+  @Test
+  def exportPgnReturnsText(): Unit =
+    val gameId = RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .extract()
+      .path[String]("gameId")
+
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/move/e2e4")
+      .`then`()
+      .statusCode(200)
+
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId/export/pgn")
+      .`then`()
+      .statusCode(200)
+      .body(containsString("e4"))
+
+  // ─── Stream ────────────────────────────────────────────────────
+
+  @Test
+  def streamReturnsNdjsonSnapshot(): Unit =
+    val gameId = RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .extract()
+      .path[String]("gameId")
+
+    val body = RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId/stream")
+      .`then`()
+      .statusCode(200)
+      .contentType("application/x-ndjson")
+      .extract()
+      .body()
+      .asString()
+
+    assert(body.trim.startsWith("""{"type":"gameFull""""), s"Expected gameFull event, got: $body")
+
+  @Test
+  def streamOnUnknownGameReturns404(): Unit =
+    RestAssured
+      .`given`()
+      .when()
+      .get("/api/board/game/XXXXXXXX/stream")
+      .`then`()
+      .statusCode(404)

modules/backcore/src/test/scala/de/nowchess/backcore/resource/MoveResourceTest.scala

@@ -0,0 +1,84 @@
+package de.nowchess.backcore.resource
+
+import io.quarkus.test.junit.QuarkusTest
+import io.restassured.RestAssured
+import org.hamcrest.Matchers.{containsString, empty, equalTo, hasItem, hasItems, not, notNullValue}
+import org.junit.jupiter.api.Test
+
+@QuarkusTest
+class MoveResourceTest:
+
+  private def createGame(): String =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .extract()
+      .path[String]("gameId")
+
+  @Test
+  def makeMoveReturns200WithUpdatedFen(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/move/e2e4")
+      .`then`()
+      .statusCode(200)
+      .body("fen", containsString("4P3")) // e4 pawn present in FEN
+      .body("turn", equalTo("black"))
+      .body("moves", hasItem("e2e4"))
+
+  @Test
+  def makeMoveOnUnknownGameReturns404(): Unit =
+    RestAssured
+      .`given`()
+      .when()
+      .post("/api/board/game/XXXXXXXX/move/e2e4")
+      .`then`()
+      .statusCode(404)
+
+  @Test
+  def illegalMoveReturns400(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/move/e2e5") // illegal — pawns can't jump 3 squares
+      .`then`()
+      .statusCode(400)
+
+  @Test
+  def getLegalMovesReturnsNonEmptyList(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId/moves")
+      .`then`()
+      .statusCode(200)
+      .body("moves", not(empty()))
+
+  @Test
+  def getLegalMovesFilteredBySquareReturnsCorrectMoves(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId/moves?square=e2")
+      .`then`()
+      .statusCode(200)
+      .body("moves.uci", hasItems("e2e3", "e2e4"))
+
+  @Test
+  def getLegalMovesOnUnknownGameReturns404(): Unit =
+    RestAssured
+      .`given`()
+      .when()
+      .get("/api/board/game/XXXXXXXX/moves")
+      .`then`()
+      .statusCode(404)

modules/backcore/src/test/scala/de/nowchess/backcore/resource/ResignDrawTest.scala

@@ -0,0 +1,168 @@
+package de.nowchess.backcore.resource
+
+import io.quarkus.test.junit.QuarkusTest
+import io.restassured.RestAssured
+import org.hamcrest.Matchers.{equalTo, notNullValue}
+import org.junit.jupiter.api.Test
+
+@QuarkusTest
+class ResignDrawTest:
+
+  private def createGame(): String =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .extract()
+      .path[String]("gameId")
+
+  // ─── Resign ────────────────────────────────────────────────────
+
+  @Test
+  def resignReturns200(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/resign")
+      .`then`()
+      .statusCode(200)
+      .body("ok", equalTo(true))
+
+  @Test
+  def afterResignGameShowsResignStatusAndWinner(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/resign")
+      .`then`()
+      .statusCode(200)
+
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId")
+      .`then`()
+      .statusCode(200)
+      .body("state.status", equalTo("resign"))
+      .body("state.winner", notNullValue())
+
+  @Test
+  def resignOnUnknownGameReturns404(): Unit =
+    RestAssured
+      .`given`()
+      .when()
+      .post("/api/board/game/XXXXXXXX/resign")
+      .`then`()
+      .statusCode(404)
+
+  // ─── Draw ──────────────────────────────────────────────────────
+
+  @Test
+  def offerDrawSetsDrawOfferedStatus(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/draw/offer")
+      .`then`()
+      .statusCode(200)
+      .body("ok", equalTo(true))
+
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId")
+      .`then`()
+      .statusCode(200)
+      .body("state.status", equalTo("drawOffered"))
+
+  @Test
+  def acceptDrawAfterOfferSetsDrawStatus(): Unit =
+    val gameId = createGame()
+    // White offers
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/draw/offer")
+      .`then`()
+      .statusCode(200)
+
+    // Black moves so it's black's turn... actually the API doesn't enforce turn-based draw accept.
+    // White offered, so black (opponent) accepts — but since there's no auth, we just call accept.
+    // The GameStore checks drawOfferedBy != turn to allow accept.
+    // White offered on white's turn, so black needs to accept — but current turn is still white.
+    // We need to make a move first to switch turns.
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/move/e2e4")
+      .`then`()
+      .statusCode(200)
+
+    // Now it's black's turn and white offered the draw — black accepts
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/draw/accept")
+      .`then`()
+      .statusCode(200)
+      .body("ok", equalTo(true))
+
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId")
+      .`then`()
+      .statusCode(200)
+      .body("state.status", equalTo("draw"))
+
+  @Test
+  def declineDrawClearsOffer(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/draw/offer")
+      .`then`()
+      .statusCode(200)
+
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/draw/decline")
+      .`then`()
+      .statusCode(200)
+      .body("ok", equalTo(true))
+
+    RestAssured
+      .`given`()
+      .when()
+      .get(s"/api/board/game/$gameId")
+      .`then`()
+      .statusCode(200)
+      .body("state.status", equalTo("started"))
+
+  @Test
+  def acceptWithoutOfferReturns400(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/draw/accept")
+      .`then`()
+      .statusCode(400)
+
+  @Test
+  def drawOnUnknownGameReturns404(): Unit =
+    RestAssured
+      .`given`()
+      .when()
+      .post("/api/board/game/XXXXXXXX/draw/offer")
+      .`then`()
+      .statusCode(404)

modules/backcore/src/test/scala/de/nowchess/backcore/resource/UndoRedoTest.scala

@@ -0,0 +1,88 @@
+package de.nowchess.backcore.resource
+
+import io.quarkus.test.junit.QuarkusTest
+import io.restassured.RestAssured
+import org.hamcrest.Matchers.{containsString, equalTo}
+import org.junit.jupiter.api.Test
+
+@QuarkusTest
+class UndoRedoTest:
+
+  private val initialFen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
+
+  private def createGame(): String =
+    RestAssured
+      .`given`()
+      .contentType("application/json")
+      .body("{}")
+      .when()
+      .post("/api/board/game")
+      .`then`()
+      .statusCode(201)
+      .extract()
+      .path[String]("gameId")
+
+  @Test
+  def undoAfterMoveRestoresOriginalPosition(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/move/e2e4")
+      .`then`()
+      .statusCode(200)
+
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/undo")
+      .`then`()
+      .statusCode(200)
+      .body("fen", equalTo(initialFen))
+      .body("undoAvailable", equalTo(false))
+
+  @Test
+  def redoAfterUndoRestoresMovedPosition(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/move/e2e4")
+      .`then`()
+      .statusCode(200)
+
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/undo")
+      .`then`()
+      .statusCode(200)
+
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/redo")
+      .`then`()
+      .statusCode(200)
+      .body("fen", containsString("4P3"))
+      .body("turn", equalTo("black"))
+
+  @Test
+  def undoWithNoHistoryReturns400(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/undo")
+      .`then`()
+      .statusCode(400)
+
+  @Test
+  def redoWithNoRedoStackReturns400(): Unit =
+    val gameId = createGame()
+    RestAssured
+      .`given`()
+      .when()
+      .post(s"/api/board/game/$gameId/redo")
+      .`then`()
+      .statusCode(400)

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

@@ -17,13 +17,8 @@ class GameEngine(
     val initialContext: GameContext = GameContext.initial,
     val ruleSet: RuleSet = DefaultRules,
 ) 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 = contextWithInitialBoard
+  private var currentContext: GameContext = initialContext
   private val invoker                     = new CommandInvoker()
 
   /** Pending promotion: the Move that triggered it (from/to only, moveType filled in later). */
@@ -68,15 +63,11 @@ 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: neither the 50-move rule nor threefold repetition has been triggered.",
+              "Draw cannot be claimed: the 50-move rule has not been triggered.",
             ),
           )
 
@@ -163,7 +154,7 @@ class GameEngine(
     invoker.clear()
 
     if ctx.moves.isEmpty then
-      currentContext = ctx.copy(initialBoard = ctx.board)
+      currentContext = ctx
       Right(())
     else replayMoves(ctx.moves, savedContext)
 
@@ -191,11 +182,7 @@ class GameEngine(
 
   /** Load an arbitrary board position, clearing all history and undo/redo state. */
   def loadPosition(newContext: GameContext): Unit = synchronized {
-    val contextWithInitialBoard = if newContext.moves.isEmpty then
-      newContext.copy(initialBoard = newContext.board)
-    else
-      newContext
-    currentContext = contextWithInitialBoard
+    currentContext = newContext
     pendingPromotion = None
     invoker.clear()
     notifyObservers(BoardResetEvent(currentContext))
@@ -250,7 +237,6 @@ class GameEngine(
     else if ruleSet.isCheck(currentContext) then notifyObservers(CheckDetectedEvent(currentContext))
 
     if currentContext.halfMoveClock >= 100 then notifyObservers(FiftyMoveRuleAvailableEvent(currentContext))
-    if ruleSet.isThreefoldRepetition(currentContext) then notifyObservers(ThreefoldRepetitionAvailableEvent(currentContext))
 
   private def translateMoveToNotation(move: Move, boardBefore: Board): String =
     move.moveType match

modules/core/src/main/scala/de/nowchess/chess/observer/Observer.scala

@@ -56,11 +56,6 @@ case class FiftyMoveRuleAvailableEvent(
     context: GameContext,
 ) extends GameEvent
 
-/** Fired after any move where the same position occurs for the third time — threefold repetition is now claimable. */
-case class ThreefoldRepetitionAvailableEvent(
-    context: GameContext,
-) extends GameEvent
-
 /** Fired when a move is undone, carrying PGN notation of the reversed move. */
 case class MoveUndoneEvent(
     context: GameContext,

modules/core/src/test/scala/de/nowchess/chess/command/CommandInvokerBranchTest.scala

@@ -18,8 +18,8 @@ class CommandInvokerBranchTest extends AnyFunSuite with Matchers:
       initialShouldFailOnUndo: Boolean = false,
       initialShouldFailOnExecute: Boolean = false,
   ) extends Command:
-    val shouldFailOnUndo    = new java.util.concurrent.atomic.AtomicBoolean(initialShouldFailOnUndo)
-    val shouldFailOnExecute = new java.util.concurrent.atomic.AtomicBoolean(initialShouldFailOnExecute)
+    val shouldFailOnUndo             = new java.util.concurrent.atomic.AtomicBoolean(initialShouldFailOnUndo)
+    val shouldFailOnExecute          = new java.util.concurrent.atomic.AtomicBoolean(initialShouldFailOnExecute)
     override def execute(): Boolean  = !shouldFailOnExecute.get()
     override def undo(): Boolean     = !shouldFailOnUndo.get()
     override def description: String = "Conditional fail"

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineIntegrationTest.scala

@@ -69,7 +69,9 @@ class GameEngineIntegrationTest extends AnyFunSuite with Matchers:
 
     engine.context shouldBe target
     engine.commandHistory shouldBe empty
-    events.lastOption.exists { case _: de.nowchess.chess.observer.BoardResetEvent => true; case _ => false } shouldBe true
+    events.lastOption.exists {
+      case _: de.nowchess.chess.observer.BoardResetEvent => true; case _ => false
+    } shouldBe true
 
   test("redo event includes captured piece description when replaying a capture"):
     val engine = new GameEngine()
@@ -98,7 +100,6 @@ class GameEngineIntegrationTest 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 = DefaultRules.applyMove(context)(move)
 
     val engine = new GameEngine(ruleSet = permissiveRules)
@@ -120,7 +121,6 @@ class GameEngineIntegrationTest 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 engine = new GameEngine(ruleSet = noLegalMoves)

modules/core/src/test/scala/de/nowchess/chess/engine/GameEngineOutcomesTest.scala

@@ -221,75 +221,3 @@ class GameEngineOutcomesTest extends AnyFunSuite with Matchers:
     evt.isDefined shouldBe true
     evt.get.reason shouldBe DrawReason.InsufficientMaterial
     engine.context.result shouldBe Some(GameResult.Draw(DrawReason.InsufficientMaterial))
-
-  // ── Threefold Repetition ──────────────────────────────────────────
-
-  test("draw command rejected when neither 50-move rule nor threefold repetition available"):
-    val engine   = EngineTestHelpers.makeEngine()
-    val observer = new EngineTestHelpers.MockObserver()
-    engine.subscribe(observer)
-
-    engine.processUserInput("e2e4")
-    observer.clear()
-
-    engine.processUserInput("draw")
-
-    observer.hasEvent[InvalidMoveEvent] shouldBe true
-
-  test("threefold repetition fires ThreefoldRepetitionAvailableEvent after 8-move shuffle"):
-    val engine   = EngineTestHelpers.makeEngine()
-    val observer = new EngineTestHelpers.MockObserver()
-    engine.subscribe(observer)
-
-    // Both knights shuffle home: initial position occurs 3 times on move 8 (Ng8)
-    engine.processUserInput("g1f3")
-    engine.processUserInput("g8f6")
-    engine.processUserInput("f3g1")
-    engine.processUserInput("f6g8")
-    engine.processUserInput("g1f3")
-    engine.processUserInput("g8f6")
-    engine.processUserInput("f3g1")
-    observer.clear()
-
-    engine.processUserInput("f6g8")  // 3rd occurrence of initial position
-
-    observer.hasEvent[ThreefoldRepetitionAvailableEvent] shouldBe true
-    engine.context.result shouldBe None  // claimable, not automatic
-
-  test("draw claim via threefold repetition ends game with DrawEvent"):
-    val engine   = EngineTestHelpers.makeEngine()
-    val observer = new EngineTestHelpers.MockObserver()
-    engine.subscribe(observer)
-
-    engine.processUserInput("g1f3")
-    engine.processUserInput("g8f6")
-    engine.processUserInput("f3g1")
-    engine.processUserInput("f6g8")
-    engine.processUserInput("g1f3")
-    engine.processUserInput("g8f6")
-    engine.processUserInput("f3g1")
-    engine.processUserInput("f6g8")  // threefold now available
-
-    observer.clear()
-    engine.processUserInput("draw")
-
-    val evt = observer.getEvent[DrawEvent]
-    evt.isDefined shouldBe true
-    evt.get.reason shouldBe DrawReason.ThreefoldRepetition
-    engine.context.result shouldBe Some(GameResult.Draw(DrawReason.ThreefoldRepetition))
-
-  test("loadPosition with non-empty moves preserves context as-is"):
-    val engine   = EngineTestHelpers.makeEngine()
-    val observer = new EngineTestHelpers.MockObserver()
-    engine.subscribe(observer)
-
-    // Build a context that already has a move in its history
-    val move = de.nowchess.api.move.Move(
-      de.nowchess.api.board.Square(de.nowchess.api.board.File.E, de.nowchess.api.board.Rank.R2),
-      de.nowchess.api.board.Square(de.nowchess.api.board.File.E, de.nowchess.api.board.Rank.R4),
-    )
-    val ctxWithMove = de.nowchess.api.game.GameContext.initial.withMove(move)
-
-    engine.loadPosition(ctxWithMove)
-
-    observer.hasEvent[BoardResetEvent] shouldBe true

modules/core/src/test/scala/de/nowchess/chess/engine/GameEnginePromotionTest.scala

@@ -173,8 +173,6 @@ class GameEnginePromotionTest extends AnyFunSuite with Matchers:
         DefaultRules.isInsufficientMaterial(context)
       def isFiftyMoveRule(context: GameContext): Boolean =
         DefaultRules.isFiftyMoveRule(context)
-      def isThreefoldRepetition(context: GameContext): Boolean =
-        DefaultRules.isThreefoldRepetition(context)
       def applyMove(context: GameContext)(move: Move): GameContext =
         DefaultRules.applyMove(context)(move)
 

modules/io/src/test/scala/de/nowchess/io/fen/FenParserFastParseTest.scala

@@ -70,58 +70,66 @@ class FenParserFastParseTest extends AnyFunSuite with Matchers:
     FenParserFastParse.parseBoard("8pp/8/8/8/8/8/8/8") shouldBe None
 
   test("parseFen handles all individual castling rights"):
-    FenParserFastParse.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w K - 0 1").fold(_ => fail(), ctx =>
-      ctx.castlingRights.whiteKingSide shouldBe true
-      ctx.castlingRights.whiteQueenSide shouldBe false
-      ctx.castlingRights.blackKingSide shouldBe false
-      ctx.castlingRights.blackQueenSide shouldBe false
-    )
+    FenParserFastParse
+      .parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w K - 0 1")
+      .fold(
+        _ => fail(),
+        ctx =>
+          ctx.castlingRights.whiteKingSide shouldBe true
+          ctx.castlingRights.whiteQueenSide shouldBe false
+          ctx.castlingRights.blackKingSide shouldBe false
+          ctx.castlingRights.blackQueenSide shouldBe false,
+      )
 
-    FenParserFastParse.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w Q - 0 1").fold(_ => fail(), ctx =>
-      ctx.castlingRights.whiteQueenSide shouldBe true
-      ctx.castlingRights.whiteKingSide shouldBe false
-    )
+    FenParserFastParse
+      .parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w Q - 0 1")
+      .fold(
+        _ => fail(),
+        ctx =>
+          ctx.castlingRights.whiteQueenSide shouldBe true
+          ctx.castlingRights.whiteKingSide shouldBe false,
+      )
 
-    FenParserFastParse.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w k - 0 1").fold(_ => fail(), ctx =>
-      ctx.castlingRights.blackKingSide shouldBe true
-      ctx.castlingRights.whiteKingSide shouldBe false
-    )
+    FenParserFastParse
+      .parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w k - 0 1")
+      .fold(
+        _ => fail(),
+        ctx =>
+          ctx.castlingRights.blackKingSide shouldBe true
+          ctx.castlingRights.whiteKingSide shouldBe false,
+      )
 
-    FenParserFastParse.parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w q - 0 1").fold(_ => fail(), ctx =>
-      ctx.castlingRights.blackQueenSide shouldBe true
-      ctx.castlingRights.whiteKingSide shouldBe false
-    )
+    FenParserFastParse
+      .parseFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w q - 0 1")
+      .fold(
+        _ => fail(),
+        ctx =>
+          ctx.castlingRights.blackQueenSide shouldBe true
+          ctx.castlingRights.whiteKingSide shouldBe false,
+      )
 
   test("parseFen parses all en passant squares"):
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - a3 0 1").fold(_ => fail(), ctx =>
-      ctx.enPassantSquare shouldBe Some(Square(File.A, Rank.R3))
-    )
+    FenParserFastParse
+      .parseFen("8/8/8/8/8/8/8/8 w - a3 0 1")
+      .fold(_ => fail(), ctx => ctx.enPassantSquare shouldBe Some(Square(File.A, Rank.R3)))
 
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - h6 0 1").fold(_ => fail(), ctx =>
-      ctx.enPassantSquare shouldBe Some(Square(File.H, Rank.R6))
-    )
+    FenParserFastParse
+      .parseFen("8/8/8/8/8/8/8/8 w - h6 0 1")
+      .fold(_ => fail(), ctx => ctx.enPassantSquare shouldBe Some(Square(File.H, Rank.R6)))
 
   test("parseFen parses different halfMove and fullMove clocks"):
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - - 5 10").fold(_ => fail(), ctx =>
-      ctx.halfMoveClock shouldBe 5
-    )
+    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - - 5 10").fold(_ => fail(), ctx => ctx.halfMoveClock shouldBe 5)
 
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - - 0 100").fold(_ => fail(), ctx =>
-      ctx.halfMoveClock shouldBe 0
-    )
+    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - - 0 100").fold(_ => fail(), ctx => ctx.halfMoveClock shouldBe 0)
 
   test("parseBoard parses boards with mixed empty and piece tokens"):
     val mixed = "8/1p1p1p1p/8/1P1P1P1P/8/8/8/8"
     FenParserFastParse.parseBoard(mixed) should not be empty
 
   test("parseFen handles turn transitions"):
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - - 0 1").fold(_ => fail(), ctx =>
-      ctx.turn shouldBe Color.White
-    )
+    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w - - 0 1").fold(_ => fail(), ctx => ctx.turn shouldBe Color.White)
 
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 b - - 0 1").fold(_ => fail(), ctx =>
-      ctx.turn shouldBe Color.Black
-    )
+    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 b - - 0 1").fold(_ => fail(), ctx => ctx.turn shouldBe Color.Black)
 
   test("parseFen rejects invalid piece characters"):
     FenParserFastParse.parseFen("8x/8/8/8/8/8/8/8 w - - 0 1").isLeft shouldBe true
@@ -133,7 +141,7 @@ class FenParserFastParseTest extends AnyFunSuite with Matchers:
   test("parseBoard tests all piece types in various positions"):
     // Test each piece type: pawn, rook, knight, bishop, queen, king (both colors)
     val allPieces = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
-    val parsed = FenParserFastParse.parseBoard(allPieces)
+    val parsed    = FenParserFastParse.parseBoard(allPieces)
     parsed.map(_.pieces.size) shouldBe Some(32)
     parsed.map(_.pieceAt(Square(File.A, Rank.R8))) shouldBe Some(Some(Piece.BlackRook))
     parsed.map(_.pieceAt(Square(File.B, Rank.R8))) shouldBe Some(Some(Piece.BlackKnight))
@@ -150,25 +158,33 @@ class FenParserFastParseTest extends AnyFunSuite with Matchers:
     FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 b - - 0 1").fold(_ => fail(), _.turn shouldBe Color.Black)
 
   test("parseFen tests all castling combinations"):
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w KQkq - 0 1").fold(_ => fail(), ctx =>
-      ctx.castlingRights.whiteKingSide shouldBe true
-      ctx.castlingRights.whiteQueenSide shouldBe true
-      ctx.castlingRights.blackKingSide shouldBe true
-      ctx.castlingRights.blackQueenSide shouldBe true
-    )
+    FenParserFastParse
+      .parseFen("8/8/8/8/8/8/8/8 w KQkq - 0 1")
+      .fold(
+        _ => fail(),
+        ctx =>
+          ctx.castlingRights.whiteKingSide shouldBe true
+          ctx.castlingRights.whiteQueenSide shouldBe true
+          ctx.castlingRights.blackKingSide shouldBe true
+          ctx.castlingRights.blackQueenSide shouldBe true,
+      )
 
-    FenParserFastParse.parseFen("8/8/8/8/8/8/8/8 w Kq - 0 1").fold(_ => fail(), ctx =>
-      ctx.castlingRights.whiteKingSide shouldBe true
-      ctx.castlingRights.whiteQueenSide shouldBe false
-      ctx.castlingRights.blackKingSide shouldBe false
-      ctx.castlingRights.blackQueenSide shouldBe true
-    )
+    FenParserFastParse
+      .parseFen("8/8/8/8/8/8/8/8 w Kq - 0 1")
+      .fold(
+        _ => fail(),
+        ctx =>
+          ctx.castlingRights.whiteKingSide shouldBe true
+          ctx.castlingRights.whiteQueenSide shouldBe false
+          ctx.castlingRights.blackKingSide shouldBe false
+          ctx.castlingRights.blackQueenSide shouldBe true,
+      )
 
   test("parseFen tests all en passant files"):
     for file <- Seq("a", "b", "c", "d", "e", "f", "g", "h") do
-      FenParserFastParse.parseFen(s"8/8/8/8/8/8/8/8 w - ${file}3 0 1").fold(_ => fail(), ctx =>
-        ctx.enPassantSquare should not be empty
-      )
+      FenParserFastParse
+        .parseFen(s"8/8/8/8/8/8/8/8 w - ${file}3 0 1")
+        .fold(_ => fail(), ctx => ctx.enPassantSquare should not be empty)
 
   test("parseBoard with mixed pieces and empty squares"):
     FenParserFastParse.parseBoard("r1bqkb1r/pppppppp/2n2n2/8/8/2N2N2/PPPPPPPP/R1BQKB1R") should not be empty

modules/rule/src/main/scala/de/nowchess/rules/RuleSet.scala

@@ -32,9 +32,6 @@ trait RuleSet:
   /** True if halfMoveClock >= 100 (50-move rule). */
   def isFiftyMoveRule(context: GameContext): Boolean
 
-  /** True if the same position has occurred 3 times (including current position). */
-  def isThreefoldRepetition(context: GameContext): Boolean
-
   /** Apply a legal move to produce the next game context. Handles all special move types: castling, en passant,
     * promotion. Updates castling rights, en passant square, half-move clock, turn, and move history.
     */

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

@@ -11,14 +11,6 @@ import scala.annotation.tailrec
   */
 object DefaultRules extends RuleSet:
 
-  /** Represents a position for threefold repetition (board state + turn + castling + en passant). */
-  private case class Position(
-      board: Board,
-      turn: Color,
-      castlingRights: CastlingRights,
-      enPassantSquare: Option[Square],
-  )
-
   // ── Direction vectors ──────────────────────────────────────────────
   private val RookDirs: List[(Int, Int)]   = List((1, 0), (-1, 0), (0, 1), (0, -1))
   private val BishopDirs: List[(Int, Int)] = List((1, 1), (1, -1), (-1, 1), (-1, -1))
@@ -70,46 +62,6 @@ object DefaultRules extends RuleSet:
   override def isFiftyMoveRule(context: GameContext): Boolean =
     context.halfMoveClock >= 100
 
-  override def isThreefoldRepetition(context: GameContext): Boolean =
-    val currentPosition = Position(
-      board = context.board,
-      turn = context.turn,
-      castlingRights = context.castlingRights,
-      enPassantSquare = context.enPassantSquare,
-    )
-    countPositionOccurrences(context, currentPosition) >= 3
-
-  private def countPositionOccurrences(context: GameContext, targetPosition: Position): Int =
-    try
-      var count     = 0
-      var tempCtx   = GameContext(
-        board = context.initialBoard,
-        turn = Color.White,
-        castlingRights = CastlingRights.Initial,
-        enPassantSquare = None,
-        halfMoveClock = 0,
-        moves = List.empty,
-        initialBoard = context.initialBoard,
-      )
-      var tempPos   = Position(tempCtx.board, tempCtx.turn, tempCtx.castlingRights, tempCtx.enPassantSquare)
-      if tempPos == targetPosition then count += 1
-
-      for move <- context.moves do
-        tempCtx = applyMove(tempCtx)(move)
-        tempPos = Position(
-          board = tempCtx.board,
-          turn = tempCtx.turn,
-          castlingRights = tempCtx.castlingRights,
-          enPassantSquare = tempCtx.enPassantSquare,
-        )
-        if tempPos == targetPosition then count += 1
-
-      count
-    catch
-      case _: Exception =>
-        // If replay fails, conservatively count only the current position (never triggers a draw)
-        1
-
   // ── Sliding pieces (Bishop, Rook, Queen) ───────────────────────────
 
   private def slidingMoves(

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

@@ -29,10 +29,12 @@ 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"):
@@ -175,48 +177,3 @@ class DefaultRulesTest extends AnyFunSuite with Matchers:
 
     // White is in check; only moves that block or move the king are legal
     moves.nonEmpty shouldBe true
-
-  // ── Threefold Repetition ─────────────────────────────────────────
-
-  test("threefold repetition returns false for initial position with no moves"):
-    val context = GameContext.initial
-    rules.isThreefoldRepetition(context) shouldBe false
-
-  test("threefold repetition returns false after single move"):
-    val fen     = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
-    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
-    val move1   = Move(Square(File.E, Rank.R2), Square(File.E, Rank.R4))
-    val ctx1    = rules.applyMove(context)(move1)
-
-    rules.isThreefoldRepetition(ctx1) shouldBe false
-
-  test("threefold repetition detects repeated position after back-and-forth moves"):
-    // Both knights shuffle back and forth: initial position (White to move) occurs 3 times
-    val fen     = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
-    val context = FenParser.parseFen(fen).fold(_ => fail(), identity)
-
-    val nf3 = Move(Square(File.G, Rank.R1), Square(File.F, Rank.R3))
-    val nf6 = Move(Square(File.G, Rank.R8), Square(File.F, Rank.R6))
-    val ng1 = Move(Square(File.F, Rank.R3), Square(File.G, Rank.R1))
-    val ng8 = Move(Square(File.F, Rank.R6), Square(File.G, Rank.R8))
-
-    // After 8 moves the starting position (White to move, both knights home) has occurred 3 times
-    val ctx = List(nf3, nf6, ng1, ng8, nf3, nf6, ng1, ng8)
-      .foldLeft(context)(rules.applyMove(_)(_))
-
-    rules.isThreefoldRepetition(ctx) shouldBe true
-
-  test("threefold repetition catch block returns false for inconsistent context"):
-    // A context whose moves cannot be replayed from initialBoard (forces the catch path)
-    val m = Move(Square(File.E, Rank.R5), Square(File.E, Rank.R6))  // e5→e6, no pawn there in initial board
-    val brokenCtx = GameContext(
-      board = Board.initial,
-      turn = Color.White,
-      castlingRights = CastlingRights.Initial,
-      enPassantSquare = None,
-      halfMoveClock = 0,
-      moves = List(m),
-      initialBoard = Board.initial,
-    )
-    // Replay will fail → catch returns 1 → 1 >= 3 is false
-    rules.isThreefoldRepetition(brokenCtx) shouldBe false

modules/ui/src/main/scala/de/nowchess/ui/gui/ChessBoardView.scala

@@ -266,7 +266,8 @@ class ChessBoardView(val stage: Stage, private val engine: GameEngine) extends B
         case Some(piece) =>
           Seq(bgRect) ++ PieceSprites.loadPieceImage(piece, squareSize * 0.8).toSeq
         case None =>
-          Seq(bgRect)): Seq[scalafx.scene.Node]
+          Seq(bgRect)
+      ): Seq[scalafx.scene.Node]
     }
 
   def showMessage(msg: String): Unit =

modules/ui/src/main/scala/de/nowchess/ui/gui/ChessGUI.scala

@@ -30,9 +30,9 @@ class ChessGUIApp extends JFXApplication:
     stage.scene = new Scene {
       root = boardView
       // Load CSS if available
-      try {
+      try
         Option(getClass.getResource("/styles.css")).foreach(url => stylesheets.add(url.toExternalForm))
-      } catch {
+      catch {
         case _: Exception => // CSS is optional
       }
     }

modules/ui/src/main/scala/de/nowchess/ui/gui/GUIObserver.scala

@@ -36,7 +36,6 @@ class GUIObserver(private val boardView: ChessBoardView) extends Observer:
             case DrawReason.Stalemate            => "Stalemate! The game is a draw."
             case DrawReason.InsufficientMaterial => "Draw by insufficient material."
             case DrawReason.FiftyMoveRule        => "Draw claimed under the 50-move rule."
-            case DrawReason.ThreefoldRepetition  => "Draw by threefold repetition."
             case DrawReason.Agreement            => "Draw by agreement."
           showAlert(AlertType.Information, "Game Over", msg)
 
@@ -53,9 +52,6 @@ class GUIObserver(private val boardView: ChessBoardView) extends Observer:
         case e: FiftyMoveRuleAvailableEvent =>
           boardView.showMessage("50-move rule is now available — type 'draw' to claim.")
 
-        case e: ThreefoldRepetitionAvailableEvent =>
-          boardView.showMessage("Threefold repetition is now available — type 'draw' to claim.")
-
         case e: MoveUndoneEvent =>
           boardView.updateBoard(e.context.board, e.context.turn)
           boardView.showMessage(s"↶ Undo: ${e.pgnNotation}")

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

@@ -50,7 +50,6 @@ class TerminalUI(engine: GameEngine) extends Observer:
           case DrawReason.Stalemate            => "Stalemate! The game is a draw."
           case DrawReason.InsufficientMaterial => "Draw by insufficient material."
           case DrawReason.FiftyMoveRule        => "Draw claimed under the 50-move rule."
-          case DrawReason.ThreefoldRepetition  => "Draw by threefold repetition."
           case DrawReason.Agreement            => "Draw by agreement."
         println(msg)
         println()
@@ -71,9 +70,6 @@ class TerminalUI(engine: GameEngine) extends Observer:
       case _: FiftyMoveRuleAvailableEvent =>
         println("50-move rule is now available — type 'draw' to claim.")
 
-      case _: ThreefoldRepetitionAvailableEvent =>
-        println("Threefold repetition is now available — type 'draw' to claim.")
-
       case e: PgnLoadedEvent =>
         println("PGN loaded successfully.")
         println()

settings.gradle.kts

@@ -1,8 +1,23 @@
 rootProject.name = "NowChessSystems"
+
+pluginManagement {
+    val quarkusPluginVersion: String by settings
+    val quarkusPluginId: String by settings
+    repositories {
+        mavenCentral()
+        gradlePluginPortal()
+        mavenLocal()
+    }
+    plugins {
+        id(quarkusPluginId) version quarkusPluginVersion
+    }
+}
+
 include(
     "modules:core",
     "modules:api",
     "modules:io",
     "modules:rule",
     "modules:ui",
-)
+    "modules:backcore",
+)