JoshHeaps.Net/Controllers/ChessController.cs

@@ -4,7 +4,6 @@ using JoshHeaps.Net.Services.Implementations;
 using JoshHeaps.Net.Services.Interfaces;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.SignalR;
-using System.Collections.Concurrent;
 
 namespace JoshHeaps.Net.Controllers;
 
@@ -16,24 +15,13 @@ public class ChessController(
     IChessEngineFactory engineFactory,
     IComputerMoveOrchestrator orchestrator,
     ILearnedWeightsStore weightsStore,
+    IGameStore gameStore,
+    ISelfPlayCoordinator selfPlay,
     IHubContext<ChessHub> chessHub) : ControllerBase
 {
-    /// <summary>
-    /// Store of ongoing games.
-    /// </summary>
-    private static readonly ConcurrentDictionary<Guid, GameState> _games = [];
-    private static readonly ConcurrentDictionary<Guid, Task> _gameRemovalTasks = [];
-    private static readonly ConcurrentDictionary<Guid, CancellationTokenSource> _gameRemovalCancellationTokens = [];
-
     private static readonly TimeSpan _computerGameTimeout = TimeSpan.FromHours(1);
     private static readonly TimeSpan _multiplayerGameTimeout = TimeSpan.FromDays(1);
     private static readonly TimeSpan _gameCleanupTimeout = TimeSpan.FromMinutes(1);
-    private static readonly TimeSpan _selfPlayMoveDelay = TimeSpan.FromSeconds(1);
-    private static readonly TimeSpan _selfPlayResultTimeout = TimeSpan.FromSeconds(30);
-
-    // Plies of random legal moves at the start of a training game, so self-play and
-    // engine-vs-engine games explore different lines instead of replaying one game.
-    private const int _openingRandomPlies = 4;
 
     /// <summary>
     /// Create a new chess game and store it in-memory.
@@ -43,7 +31,7 @@ public class ChessController(
     public ActionResult CreateGame(int difficulty = 20, string color = "random")
     {
         var gameState = chessService.CreateNewGame();
-        _games[gameState.GameId] = gameState;
+        gameStore.Add(gameState);
 
         gameState.IsVsComputer = true;
         gameState.WhiteJoined = true;
@@ -78,7 +66,7 @@ public class ChessController(
             });
         }
 
-        ScheduleRemoveGame(gameState.GameId, _computerGameTimeout);
+        gameStore.ScheduleRemove(gameState.GameId, _computerGameTimeout);
 
         return Ok(new
         {
@@ -102,31 +90,13 @@ public class ChessController(
         int? whiteSkill = null,
         int? blackSkill = null)
     {
-        var whiteKind = ParseEngineKind(whiteEngine);
+        var config = new SelfPlayConfig(
-        var blackKind = ParseEngineKind(blackEngine);
+            ParseEngineKind(whiteEngine), whiteSkill ?? difficulty,
+            ParseEngineKind(blackEngine), blackSkill ?? difficulty);
 
-        var gameState = chessService.CreateNewGame();
+        var (gameId, _) = selfPlay.StartGame(config);
-        _games[gameState.GameId] = gameState;
 
-        gameState.IsVsComputer = true;
+        return Ok(new { GameId = gameId });
-        gameState.IsComputerVsComputer = true;
-        gameState.WhiteJoined = true;
-        gameState.BlackJoined = true;
-        gameState.WhitePlayerId = Guid.NewGuid();
-        gameState.BlackPlayerId = Guid.NewGuid();
-        gameState.WhiteEngineKind = whiteKind;
-        gameState.BlackEngineKind = blackKind;
-        gameState.WhiteComputer = engineFactory.Create(whiteSkill ?? difficulty, whiteKind);
-        gameState.BlackComputer = engineFactory.Create(blackSkill ?? difficulty, blackKind);
-
-        // When the learned engine is playing, attach a trainer so the outcome can train it.
-        if (whiteKind == ChessEngineKind.CustomLearned || blackKind == ChessEngineKind.CustomLearned)
-            gameState.Trainer = weightsStore.CreateTrainer();
-
-        ScheduleRemoveGame(gameState.GameId, _computerGameTimeout);
-        StartSelfPlay(gameState);
-
-        return Ok(new { gameState.GameId });
     }
 
     private static ChessEngineKind ParseEngineKind(string value) => value.ToLowerInvariant() switch
@@ -145,12 +115,12 @@ public class ChessController(
     public ActionResult JoinGame()
     {
         Console.WriteLine("joining game");
-        GameState? gameState = _games.Values.FirstOrDefault(g => g.IsOpen);
+        GameState? gameState = gameStore.All.FirstOrDefault(g => g.IsOpen);
 
         if (gameState == null)
         {
             gameState = chessService.CreateNewGame();
-            _games[gameState.GameId] = gameState;
+            gameStore.Add(gameState);
         }
 
         Guid playerId = Guid.NewGuid();
@@ -168,7 +138,7 @@ public class ChessController(
             isWhite = false;
         }
 
-        ScheduleRemoveGame(gameState.GameId, _multiplayerGameTimeout);
+        gameStore.ScheduleRemove(gameState.GameId, _multiplayerGameTimeout);
 
         return Ok(new
         {
@@ -184,7 +154,7 @@ public class ChessController(
     [HttpGet("active")]
     public ActionResult GetActiveGames()
     {
-        var activeGames = _games.Values
+        var activeGames = gameStore.All
             // In-progress games, plus finished computer-vs-computer games still in their result window.
             .Where(g => g.WhiteJoined && g.BlackJoined
                 && ((!g.IsCheckmate && !g.IsStalemate && !g.IsForfeited && !g.IsThreefoldRepetition) || g.IsComputerVsComputer))
@@ -230,7 +200,7 @@ public class ChessController(
     [HttpGet("{gameId}")]
     public ActionResult GetGameState(Guid gameId)
     {
-        if (!_games.TryGetValue(gameId, out var gameState))
+        if (!gameStore.TryGet(gameId, out var gameState))
             return NotFound("Game not found");
 
         return Ok(gameState.ToDto());
@@ -243,7 +213,7 @@ public class ChessController(
     [HttpPost("move")]
     public async Task<ActionResult> MakeMove([FromBody] MoveDto moveDto)
     {
-        if (!_games.TryGetValue(moveDto.GameId, out var gameState))
+        if (!gameStore.TryGet(moveDto.GameId, out var gameState))
             return NotFound("Game not found");
 
         // Check if player is authorized to move
@@ -270,11 +240,11 @@ public class ChessController(
         var isGameOver = result.IsCheckmate || result.IsStalemate || result.IsThreefoldRepetition;
 
         if (isGameOver)
-            ScheduleRemoveGame(gameState.GameId, _gameCleanupTimeout);
+            gameStore.ScheduleRemove(gameState.GameId, _gameCleanupTimeout);
         else if (gameState.IsVsComputer)
-            ScheduleRemoveGame(gameState.GameId, _computerGameTimeout);
+            gameStore.ScheduleRemove(gameState.GameId, _computerGameTimeout);
         else
-            ScheduleRemoveGame(gameState.GameId, _multiplayerGameTimeout);
+            gameStore.ScheduleRemove(gameState.GameId, _multiplayerGameTimeout);
 
         var state = gameState.ToDto();
 
@@ -301,7 +271,7 @@ public class ChessController(
     [HttpPost("forfeit")]
     public async Task<ActionResult> Forfeit([FromBody] ForfeitDto forfeit)
     {
-        if (!_games.TryGetValue(forfeit.GameId, out var gameState))
+        if (!gameStore.TryGet(forfeit.GameId, out var gameState))
             return NotFound("Game not found");
 
         if (gameState.IsCheckmate || gameState.IsStalemate || gameState.IsForfeited)
@@ -319,7 +289,7 @@ public class ChessController(
         await chessHub.Clients.Group(gameState.GameId.ToString())
             .SendAsync("ReceiveGameOver", gameState.GameId.ToString(), gameState.Winner.ToString(), "forfeit");
 
-        ScheduleRemoveGame(gameState.GameId, _gameCleanupTimeout);
+        gameStore.ScheduleRemove(gameState.GameId, _gameCleanupTimeout);
 
         return Ok();
     }
@@ -330,7 +300,7 @@ public class ChessController(
     [HttpGet("{gameId}/pgn")]
     public ActionResult GetPgn(Guid gameId)
     {
-        if (!_games.TryGetValue(gameId, out var gameState))
+        if (!gameStore.TryGet(gameId, out var gameState))
             return NotFound("Game not found");
 
         return Content(gameState.ToPgn(), "application/x-chess-pgn");
@@ -342,7 +312,7 @@ public class ChessController(
     [HttpGet("{gameId}/legalMoves/{pieceId}")]
     public ActionResult GetLegalMoves(Guid gameId, string pieceId)
     {
-        if (!_games.TryGetValue(gameId, out var gameState))
+        if (!gameStore.TryGet(gameId, out var gameState))
             return NotFound("Game not found");
 
         var moves = chessService.GetLegalMovesForPiece(gameState, pieceId);
@@ -356,7 +326,7 @@ public class ChessController(
     [HttpGet("{gameId}/legalMoves")]
     public ActionResult GetAllLegalMoves(Guid gameId)
     {
-        if (!_games.TryGetValue(gameId, out var gameState))
+        if (!gameStore.TryGet(gameId, out var gameState))
             return NotFound("Game not found");
 
         var allMoves = chessService.GetAllLegalMoves(gameState)
@@ -369,180 +339,4 @@ public class ChessController(
         return Ok(allMoves);
     }
 
-    /// <summary>
-    /// Drives a computer-vs-computer game: keeps asking the side-to-move's engine for its
-    /// move (which applies and broadcasts it) until the game ends or is removed. Training
-    /// games get a randomized opening and feed their result back into the learned weights.
-    /// </summary>
-    private void StartSelfPlay(GameState gameState)
-    {
-        queue.Queue(async () =>
-        {
-            // Give spectators a moment to join the SignalR group before the first move.
-            await Task.Delay(TimeSpan.FromSeconds(1));
-
-            // Training games open with random moves so they don't replay the same line.
-            if (gameState.Trainer != nint.Zero)
-                for (int i = 0; i < _openingRandomPlies && _games.ContainsKey(gameState.GameId) && !IsGameOver(gameState); i++)
-                {
-                    await orchestrator.PlayRandomMoveAsync(gameState);
-                    await Task.Delay(_selfPlayMoveDelay);
-                }
-
-            while (_games.ContainsKey(gameState.GameId) && !IsGameOver(gameState))
-            {
-                try
-                {
-                    await orchestrator.PlayAsync(gameState);
-                }
-                catch (Exception ex)
-                {
-                    Console.WriteLine($"Self-play game {gameState.GameId} stopped: {ex.Message}");
-                    break;
-                }
-
-                await Task.Delay(_selfPlayMoveDelay);
-            }
-
-            ApplyLearning(gameState);
-
-            // Leave the finished game in place briefly so spectators can see the result.
-            if (_games.ContainsKey(gameState.GameId))
-                ScheduleRemoveGame(gameState.GameId, _selfPlayResultTimeout);
-        });
-    }
-
-    private static bool IsGameOver(GameState gameState) =>
-        gameState.IsCheckmate || gameState.IsStalemate || gameState.IsThreefoldRepetition || gameState.IsForfeited;
-
-    /// <summary>
-    /// Feeds a finished training game's result into the learned weights, then frees the
-    /// trainer. Both sides teach the table — the winner's squares/features up, the loser's
-    /// down. A checkmate is a full-strength result; a material-imbalance draw is a half-
-    /// strength win for the lower-material side (holding a draw while down material is a
-    /// success; only drawing while up is a failure). A balanced draw, forfeit, or unfinished
-    /// game teaches nothing (but the trainer is still freed).
-    /// </summary>
-    private void ApplyLearning(GameState gameState)
-    {
-        if (gameState.Trainer == nint.Zero)
-            return;
-
-        if (TryDetermineOutcome(gameState, out var winner, out var weight))
-            weightsStore.ApplyResult(gameState.Trainer, winner, weight);
-
-        weightsStore.DestroyTrainer(gameState.Trainer);
-        gameState.Trainer = nint.Zero;
-    }
-
-    /// <summary>
-    /// Determines the trainable outcome of a finished game: the winning color and the reward
-    /// weight. Returns false when the game teaches nothing (balanced draw, forfeit, unfinished).
-    /// </summary>
-    private static bool TryDetermineOutcome(GameState gameState, out PieceColor winner, out double weight)
-    {
-        winner = PieceColor.White;
-        weight = 1.0;
-
-        if (gameState.IsCheckmate)
-        {
-            // The side to move is the mated one, so the winner is the other color.
-            winner = gameState.CurrentPlayer == PieceColor.White ? PieceColor.Black : PieceColor.White;
-            return true;
-        }
-
-        if (gameState.IsStalemate || gameState.IsThreefoldRepetition)
-        {
-            var (white, black) = MaterialCounts(gameState);
-
-            if (white == black)
-                return false;                 // a balanced draw carries no signal
-
-            winner = white < black ? PieceColor.White : PieceColor.Black;
-            weight = 0.5;
-            return true;
-        }
-
-        return false;                         // forfeit / unfinished
-    }
-
-    /// <summary>Total non-king material per side (P=1, N=B=3, R=5, Q=9), for draw adjudication.</summary>
-    private static (int white, int black) MaterialCounts(GameState gameState)
-    {
-        int white = 0, black = 0;
-
-        for (int row = 0; row < 8; row++)
-            for (int col = 0; col < 8; col++)
-            {
-                var piece = gameState.Board[row, col];
-
-                if (piece is null)
-                    continue;
-
-                int value = piece.Type switch
-                {
-                    PieceType.Pawn => 1,
-                    PieceType.Knight => 3,
-                    PieceType.Bishop => 3,
-                    PieceType.Rook => 5,
-                    PieceType.Queen => 9,
-                    _ => 0
-                };
-
-                if (piece.Color == PieceColor.White)
-                    white += value;
-                else
-                    black += value;
-            }
-
-        return (white, black);
-    }
-
-    private static void ScheduleRemoveGame(Guid id, TimeSpan delay)
-    {
-        if (_gameRemovalCancellationTokens.TryRemove(id, out var oldCts))
-        {
-            oldCts.Cancel();
-            oldCts.Dispose();
-        }
-
-        var cts = new CancellationTokenSource();
-        _gameRemovalCancellationTokens[id] = cts;
-
-        _gameRemovalTasks[id] = Task.Run(async () =>
-        {
-            try
-            {
-                await Task.Delay(delay, cts.Token);
-
-                if (_games.TryGetValue(id, out var game))
-                {
-                    if (game.WhiteComputer is not null)
-                        await game.WhiteComputer.DisposeAsync();
-                    if (game.BlackComputer is not null)
-                        await game.BlackComputer.DisposeAsync();
-
-                    // Free the trainer if the game never reached ApplyLearning (e.g. timed out).
-                    // The native ABI is shared via CustomChessEngine's import resolver.
-                    if (game.Trainer != nint.Zero)
-                    {
-                        CustomChessEngine.NativeMethods.trainer_destroy(game.Trainer);
-                        game.Trainer = nint.Zero;
-                    }
-                }
-
-                _games.Remove(id, out _);
-            }
-            catch (OperationCanceledException) { }
-            finally
-            {
-                if (_gameRemovalCancellationTokens.TryGetValue(id, out var currentCts) && currentCts == cts)
-                {
-                    _gameRemovalCancellationTokens.TryRemove(id, out _);
-                }
-
-                cts.Dispose();
-            }
-        });
-    }
 }

JoshHeaps.Net/Program.cs

@@ -26,10 +26,19 @@ builder.Services.Configure<ChessEngineOptions>(configuration.GetSection(ChessEng
 builder.Services.AddSingleton<ILearnedWeightsStore, LearnedWeightsStore>();
 builder.Services.AddSingleton<IChessEngineFactory, ChessEngineFactory>();
 builder.Services.AddSingleton<IComputerMoveOrchestrator, ComputerMoveOrchestrator>();
+builder.Services.AddSingleton<IGameStore, GameStore>();
+builder.Services.AddSingleton<ISelfPlayCoordinator, SelfPlayCoordinator>();
 
 if (!builder.Environment.IsDevelopment())
+{
     builder.Services.AddHostedService<AutoIpUpdateService>();
 
+    // Continuously train the learned engine against Stockfish in the background. Toggle off
+    // via ChessEngine:AutoTrain (env ChessEngine__AutoTrain=false) without a redeploy.
+    if (configuration.GetValue($"{ChessEngineOptions.SectionName}:{nameof(ChessEngineOptions.AutoTrain)}", true))
+        builder.Services.AddHostedService<AutoTrainingService>();
+}
+
 var app = builder.Build();
 
 // Configure the HTTP request pipeline.

JoshHeaps.Net/Services/Implementations/AutoTrainingService.cs

@@ -0,0 +1,55 @@
+using JoshHeaps.Net.Services.Interfaces;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// Continuously trains the learned engine in the background: two self-play games run in
+/// parallel, the learned engine (skill 6) against Stockfish (skill 20), one with Stockfish as
+/// black and one as white. Each slot is independent — when its game finishes it immediately
+/// starts another under the same conditions, without waiting on the other slot. Registered
+/// only outside Development and gated by the ChessEngine:AutoTrain config flag.
+/// </summary>
+public sealed class AutoTrainingService(
+    ISelfPlayCoordinator coordinator,
+    ILogger<AutoTrainingService> logger) : BackgroundService
+{
+    private const int LearnedSkill = 6;
+    private const int StockfishSkill = 20;
+    private static readonly TimeSpan _restartBackoff = TimeSpan.FromSeconds(5);
+
+    protected override Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        // Learned plays both colors so the model trains symmetrically; each slot is its own loop.
+        var stockfishBlack = RunSlot(
+            new SelfPlayConfig(ChessEngineKind.CustomLearned, LearnedSkill, ChessEngineKind.Stockfish, StockfishSkill),
+            stoppingToken);
+        var stockfishWhite = RunSlot(
+            new SelfPlayConfig(ChessEngineKind.Stockfish, StockfishSkill, ChessEngineKind.CustomLearned, LearnedSkill),
+            stoppingToken);
+
+        return Task.WhenAll(stockfishBlack, stockfishWhite);
+    }
+
+    private async Task RunSlot(SelfPlayConfig config, CancellationToken stoppingToken)
+    {
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await coordinator.StartGame(config, stoppingToken).Completion;
+            }
+            catch (OperationCanceledException)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                // Most likely an engine failing to start (e.g. Stockfish). Back off so a
+                // persistent failure doesn't spin a tight loop, then try again.
+                logger.LogError(ex, "Auto-training game failed to start; retrying after backoff.");
+                try { await Task.Delay(_restartBackoff, stoppingToken); }
+                catch (OperationCanceledException) { break; }
+            }
+        }
+    }
+}

JoshHeaps.Net/Services/Implementations/ChessEngineFactory.cs

@@ -29,6 +29,13 @@ public sealed class ChessEngineOptions
     /// clashes. Override via the <c>ChessEngine__WeightsPath</c> environment variable.
     /// </summary>
     public string? WeightsPath { get; set; }
+
+    /// <summary>
+    /// When true (and outside Development), a background service continuously plays the learned
+    /// engine against Stockfish to train it. Set to false to stop auto-training without a
+    /// redeploy. Override via the <c>ChessEngine__AutoTrain</c> environment variable.
+    /// </summary>
+    public bool AutoTrain { get; set; } = true;
 }
 
 /// <summary>Creates the configured <see cref="IChessEngine"/> per game.</summary>

JoshHeaps.Net/Services/Implementations/GameStore.cs

@@ -0,0 +1,69 @@
+using System.Collections.Concurrent;
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// In-memory game registry with a delayed-removal lifecycle. Singleton: the game state is
+/// process-wide, not per-request, so it lives in a service rather than static controller fields.
+/// </summary>
+public sealed class GameStore(ILearnedWeightsStore weightsStore) : IGameStore
+{
+    private readonly ConcurrentDictionary<Guid, GameState> _games = [];
+    private readonly ConcurrentDictionary<Guid, Task> _removalTasks = [];
+    private readonly ConcurrentDictionary<Guid, CancellationTokenSource> _removalCts = [];
+
+    public void Add(GameState game) => _games[game.GameId] = game;
+
+    public bool TryGet(Guid id, out GameState game) => _games.TryGetValue(id, out game!);
+
+    public bool Contains(Guid id) => _games.ContainsKey(id);
+
+    public IReadOnlyCollection<GameState> All => [.. _games.Values];
+
+    public void ScheduleRemove(Guid id, TimeSpan delay)
+    {
+        if (_removalCts.TryRemove(id, out var oldCts))
+        {
+            oldCts.Cancel();
+            oldCts.Dispose();
+        }
+
+        var cts = new CancellationTokenSource();
+        _removalCts[id] = cts;
+
+        _removalTasks[id] = Task.Run(async () =>
+        {
+            try
+            {
+                await Task.Delay(delay, cts.Token);
+
+                if (_games.TryGetValue(id, out var game))
+                {
+                    if (game.WhiteComputer is not null)
+                        await game.WhiteComputer.DisposeAsync();
+                    if (game.BlackComputer is not null)
+                        await game.BlackComputer.DisposeAsync();
+
+                    // Free the trainer if the game never reached ApplyLearning (e.g. timed out).
+                    if (game.Trainer != nint.Zero)
+                    {
+                        weightsStore.DestroyTrainer(game.Trainer);
+                        game.Trainer = nint.Zero;
+                    }
+                }
+
+                _games.Remove(id, out _);
+            }
+            catch (OperationCanceledException) { }
+            finally
+            {
+                if (_removalCts.TryGetValue(id, out var currentCts) && currentCts == cts)
+                    _removalCts.TryRemove(id, out _);
+
+                cts.Dispose();
+            }
+        });
+    }
+}

JoshHeaps.Net/Services/Implementations/SelfPlayCoordinator.cs

@@ -0,0 +1,189 @@
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// Runs CPU-vs-CPU games: builds the game and engines, plays a randomized opening (for training
+/// variety), drives the move loop to completion, then trains the learned engine from the result.
+/// </summary>
+public sealed class SelfPlayCoordinator(
+    IChessService chessService,
+    IChessEngineFactory engineFactory,
+    IComputerMoveOrchestrator orchestrator,
+    ILearnedWeightsStore weightsStore,
+    IGameStore gameStore) : ISelfPlayCoordinator
+{
+    private static readonly TimeSpan _computerGameTimeout = TimeSpan.FromHours(1);
+    private static readonly TimeSpan _selfPlayMoveDelay = TimeSpan.FromSeconds(1);
+    private static readonly TimeSpan _selfPlayResultTimeout = TimeSpan.FromSeconds(30);
+
+    // Plies of random legal moves at the start of a training game, so self-play and
+    // engine-vs-engine games explore different lines instead of replaying one game.
+    private const int _openingRandomPlies = 4;
+
+    public (Guid GameId, Task Completion) StartGame(SelfPlayConfig config, CancellationToken cancellationToken = default)
+    {
+        var whiteComputer = engineFactory.Create(config.WhiteSkill, config.WhiteKind);
+        IChessEngine blackComputer;
+        try
+        {
+            blackComputer = engineFactory.Create(config.BlackSkill, config.BlackKind);
+        }
+        catch
+        {
+            // Don't leak the first engine if the second fails to start (e.g. Stockfish process).
+            whiteComputer.DisposeAsync().AsTask().GetAwaiter().GetResult();
+            throw;
+        }
+
+        var gameState = chessService.CreateNewGame();
+        gameState.IsVsComputer = true;
+        gameState.IsComputerVsComputer = true;
+        gameState.WhiteJoined = true;
+        gameState.BlackJoined = true;
+        gameState.WhitePlayerId = Guid.NewGuid();
+        gameState.BlackPlayerId = Guid.NewGuid();
+        gameState.WhiteEngineKind = config.WhiteKind;
+        gameState.BlackEngineKind = config.BlackKind;
+        gameState.WhiteComputer = whiteComputer;
+        gameState.BlackComputer = blackComputer;
+
+        // When the learned engine is playing, attach a trainer so the outcome can train it.
+        if (config.WhiteKind == ChessEngineKind.CustomLearned || config.BlackKind == ChessEngineKind.CustomLearned)
+            gameState.Trainer = weightsStore.CreateTrainer();
+
+        gameStore.Add(gameState);
+        gameStore.ScheduleRemove(gameState.GameId, _computerGameTimeout);
+
+        var completion = Task.Run(() => RunAsync(gameState, cancellationToken));
+        return (gameState.GameId, completion);
+    }
+
+    /// <summary>
+    /// Drives the game to completion, then trains from it. Never throws — a failure just ends
+    /// the game (and the trainer is always freed), so callers can safely await or ignore it.
+    /// </summary>
+    private async Task RunAsync(GameState gameState, CancellationToken cancellationToken)
+    {
+        try
+        {
+            // Give spectators a moment to join the SignalR group before the first move.
+            await Task.Delay(_selfPlayMoveDelay, cancellationToken);
+
+            // Training games open with random moves so they don't replay the same line.
+            if (gameState.Trainer != nint.Zero)
+                for (int i = 0; i < _openingRandomPlies && IsLive(gameState, cancellationToken); i++)
+                {
+                    await orchestrator.PlayRandomMoveAsync(gameState);
+                    await Task.Delay(_selfPlayMoveDelay, cancellationToken);
+                }
+
+            while (IsLive(gameState, cancellationToken))
+            {
+                await orchestrator.PlayAsync(gameState);
+                await Task.Delay(_selfPlayMoveDelay, cancellationToken);
+            }
+        }
+        catch (OperationCanceledException) { /* service shutting down */ }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"Self-play game {gameState.GameId} stopped: {ex.Message}");
+        }
+
+        ApplyLearning(gameState);
+
+        // Leave the finished game in place briefly so spectators can see the result.
+        if (gameStore.Contains(gameState.GameId))
+            gameStore.ScheduleRemove(gameState.GameId, _selfPlayResultTimeout);
+    }
+
+    private bool IsLive(GameState gameState, CancellationToken cancellationToken) =>
+        !cancellationToken.IsCancellationRequested
+        && gameStore.Contains(gameState.GameId)
+        && !IsGameOver(gameState);
+
+    private static bool IsGameOver(GameState gameState) =>
+        gameState.IsCheckmate || gameState.IsStalemate || gameState.IsThreefoldRepetition || gameState.IsForfeited;
+
+    /// <summary>
+    /// Feeds a finished training game's result into the learned weights, then frees the trainer.
+    /// A checkmate is a full-strength result; a material-imbalance draw is a half-strength win
+    /// for the lower-material side (holding a draw while down material is a success; only drawing
+    /// while up is a failure). A balanced draw, forfeit, or unfinished game teaches nothing.
+    /// </summary>
+    private void ApplyLearning(GameState gameState)
+    {
+        if (gameState.Trainer == nint.Zero)
+            return;
+
+        if (TryDetermineOutcome(gameState, out var winner, out var weight))
+            weightsStore.ApplyResult(gameState.Trainer, winner, weight);
+
+        weightsStore.DestroyTrainer(gameState.Trainer);
+        gameState.Trainer = nint.Zero;
+    }
+
+    /// <summary>
+    /// Determines the trainable outcome of a finished game: the winning color and the reward
+    /// weight. Returns false when the game teaches nothing (balanced draw, forfeit, unfinished).
+    /// </summary>
+    private static bool TryDetermineOutcome(GameState gameState, out PieceColor winner, out double weight)
+    {
+        winner = PieceColor.White;
+        weight = 1.0;
+
+        if (gameState.IsCheckmate)
+        {
+            // The side to move is the mated one, so the winner is the other color.
+            winner = gameState.CurrentPlayer == PieceColor.White ? PieceColor.Black : PieceColor.White;
+            return true;
+        }
+
+        if (gameState.IsStalemate || gameState.IsThreefoldRepetition)
+        {
+            var (white, black) = MaterialCounts(gameState);
+
+            if (white == black)
+                return false;                 // a balanced draw carries no signal
+
+            winner = white < black ? PieceColor.White : PieceColor.Black;
+            weight = 0.5;
+            return true;
+        }
+
+        return false;                         // forfeit / unfinished
+    }
+
+    /// <summary>Total non-king material per side (P=1, N=B=3, R=5, Q=9), for draw adjudication.</summary>
+    private static (int white, int black) MaterialCounts(GameState gameState)
+    {
+        int white = 0, black = 0;
+
+        for (int row = 0; row < 8; row++)
+            for (int col = 0; col < 8; col++)
+            {
+                var piece = gameState.Board[row, col];
+
+                if (piece is null)
+                    continue;
+
+                int value = piece.Type switch
+                {
+                    PieceType.Pawn => 1,
+                    PieceType.Knight => 3,
+                    PieceType.Bishop => 3,
+                    PieceType.Rook => 5,
+                    PieceType.Queen => 9,
+                    _ => 0
+                };
+
+                if (piece.Color == PieceColor.White)
+                    white += value;
+                else
+                    black += value;
+            }
+
+        return (white, black);
+    }
+}

JoshHeaps.Net/Services/Interfaces/IGameStore.cs

@@ -0,0 +1,29 @@
+using JoshHeaps.Net.Models;
+
+namespace JoshHeaps.Net.Services.Interfaces;
+
+/// <summary>
+/// Process-wide registry of in-memory games and their cleanup lifecycle. Shared by the HTTP
+/// controller (human and single-computer games) and the self-play coordinator (CPU-vs-CPU and
+/// auto-training games), so every game is reachable from one place for lookup and spectating.
+/// </summary>
+public interface IGameStore
+{
+    /// <summary>Add (or replace) a game in the registry.</summary>
+    void Add(GameState game);
+
+    /// <summary>Look a game up by id.</summary>
+    bool TryGet(Guid id, out GameState game);
+
+    /// <summary>Whether a game with this id is still in the registry.</summary>
+    bool Contains(Guid id);
+
+    /// <summary>Snapshot of all games currently in the registry.</summary>
+    IReadOnlyCollection<GameState> All { get; }
+
+    /// <summary>
+    /// Schedule removal of a game after <paramref name="delay"/>, cancelling any prior schedule
+    /// for it. On removal the game's engines are disposed and any training accumulator freed.
+    /// </summary>
+    void ScheduleRemove(Guid id, TimeSpan delay);
+}

JoshHeaps.Net/Services/Interfaces/ISelfPlayCoordinator.cs

@@ -0,0 +1,23 @@
+using JoshHeaps.Net.Services.Implementations;
+
+namespace JoshHeaps.Net.Services.Interfaces;
+
+/// <summary>Per-side engine and strength for a CPU-vs-CPU game.</summary>
+public sealed record SelfPlayConfig(
+    ChessEngineKind WhiteKind, int WhiteSkill,
+    ChessEngineKind BlackKind, int BlackSkill);
+
+/// <summary>
+/// Creates and runs CPU-vs-CPU games to completion: randomized opening, move loop, and (when
+/// the learned engine plays) feeding the result back into the learned weights. Used by the
+/// spectator "watch" endpoint and by the auto-trainer.
+/// </summary>
+public interface ISelfPlayCoordinator
+{
+    /// <summary>
+    /// Create, register, and start running a self-play game. Returns immediately with the new
+    /// game's id and a task that completes when the game finishes (or is cancelled). Callers
+    /// that only need the id can ignore the task; the auto-trainer awaits it to start the next.
+    /// </summary>
+    (Guid GameId, Task Completion) StartGame(SelfPlayConfig config, CancellationToken cancellationToken = default);
+}