add deploy yml for gitea

The DSP tests drive the same files the page loads, so there is no second
implementation to drift. The room tests put two real browsers through a
real room with a synthetic microphone, which covers everything except the
acoustics: slot rotation, leave and rejoin, and the stalled-device case
where a chirp must be withheld rather than sent late.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

.claude/settings.local.json

@@ -3,7 +3,9 @@
     "allow": [
       "Bash(dotnet test:*)",
       "Bash(dotnet build)",
-      "Bash(dir:*)"
+      "Bash(dir:*)",
+      "Bash(dotnet add:*)",
+      "Bash(dotnet build:*)"
     ],
     "deny": [],
     "ask": []

.github/workflows/deploy.yml

@@ -14,7 +14,9 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    # Pinned (not ubuntu-latest) to match the prod server's Ubuntu/glibc so the
+    # compiled libchess_engine.so loads there. Keep this == the server's release.
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -24,9 +26,16 @@ jobs:
         with:
           dotnet-version: '8.0.x'  # adjust if needed
       - name: Restore
-        run: dotnet restore
+        run: dotnet restore JoshHeaps.Net/JoshHeaps.Net.csproj
+
+      - name: Build native chess engine (libchess_engine.so)
+        run: |
+          cmake -S native/chess_engine -B native/chess_engine/build -DCMAKE_BUILD_TYPE=Release
+          cmake --build native/chess_engine/build
+          cp native/chess_engine/build/libchess_engine.so JoshHeaps.Net/Resources/
+
       - name: Publish
-        run: dotnet publish -c Release -o ./publish
+        run: dotnet publish JoshHeaps.Net/JoshHeaps.Net.csproj -c Release -o ./publish
 
       - name: Upload artifact
         uses: actions/upload-artifact@v4
@@ -45,6 +54,12 @@ jobs:
           name: site-publish
           path: publish
 
+      # GitHub artifacts don't preserve the Unix executable bit, so Stockfish (the only file
+      # the app spawns as a subprocess) arrives non-executable. Restore 755 here; rsync -a then
+      # carries it to the server, where the service user can run it regardless of file owner.
+      - name: Restore Stockfish executable bit
+        run: chmod 755 publish/Resources/stockfish-ubuntu-x86-64-sse41-popcnt
+
       - name: Prepare SSH
         run: |
           install -m 700 -d ~/.ssh
@@ -54,7 +69,9 @@ jobs:
 
       - name: Rsync to server
         run: |
-          rsync -az --delete -e "ssh -p ${{ secrets.SSH_PORT || 22 }} -i ~/.ssh/id_rsa" \
+          # --exclude chess-data: never let --delete remove the learned-engine training
+          # data, which lives in the deploy dir unless ChessEngine__WeightsPath is set.
+          rsync -az --delete --exclude 'chess-data' -e "ssh -p ${{ secrets.SSH_PORT || 22 }} -i ~/.ssh/id_rsa" \
             publish/ ${{ secrets.SSH_USER }}@${{ secrets.SSH_HOST }}:${{ secrets.TARGET_DIR }}/
 
       - name: Reload and restart service

.github/workflows/dotnet.yml

@@ -19,6 +19,6 @@ jobs:
       with:
         dotnet-version: 8.0.x
     - name: Restore dependencies
-      run: dotnet restore
+      run: dotnet restore JoshHeaps.Net.slnf
     - name: Build
-      run: dotnet build --no-restore
+      run: dotnet build JoshHeaps.Net.slnf --no-restore

.github/workflows/playwright-tests.yml

@@ -19,10 +19,10 @@ jobs:
         dotnet-version: 8.0.x
 
     - name: Restore dependencies
-      run: dotnet restore
+      run: dotnet restore JoshHeaps.Net.slnf
 
     - name: Build solution
-      run: dotnet build --no-restore
+      run: dotnet build JoshHeaps.Net.slnf --no-restore
 
     - name: Install Playwright browsers
       run: |

.gitignore

@@ -3,6 +3,9 @@
 ##
 ## Get latest from https://github.com/github/gitignore/blob/master/VisualStudio.gitignore
 
+# Learned chess engine weights (runtime training output, not source)
+chess-data/
+
 # User-specific files
 *.rsuser
 *.suo
@@ -361,3 +364,6 @@ MigrationBackup/
 
 # Fody - auto-generated XML schema
 FodyWeavers.xsd
+
+# Native chess engine CMake build output (the compiled .dll/.so are committed under Resources/)
+native/**/build/

JoshHeaps.Net.UiTests/EchoDspTests.cs

@@ -0,0 +1,296 @@
+using Microsoft.Playwright;
+using Microsoft.Playwright.NUnit;
+using NUnit.Framework;
+
+namespace JoshHeaps.Net.UiTests;
+
+/// <summary>
+/// Exercises the acoustic-ranging pipeline against a simulated room. The DSP runs in the browser
+/// because that is where it runs in production; these tests drive the same files the page loads,
+/// so there is no second implementation to drift.
+/// </summary>
+[TestFixture]
+public class EchoDspTests : PageTest
+{
+    private TestConfiguration Config => TestConfiguration.Instance;
+
+    public override BrowserNewContextOptions ContextOptions() => Config.GetBrowserContextOptions();
+
+    [SetUp]
+    public async Task LoadPipeline()
+    {
+        await Page.GotoAsync(Config.Test.BaseUrl);
+        await Page.AddScriptTagAsync(new() { Url = "/js/EchoScripts/EchoDsp.js" });
+        await Page.AddScriptTagAsync(new() { Url = "/js/EchoScripts/EchoSim.js" });
+    }
+
+    [Test]
+    public async Task Matched_Filter_Finds_The_Chirp_Within_One_Sample()
+    {
+        var error = await Page.EvaluateAsync<double>("""
+            () => {
+                const sampleRate = 48000;
+                const chirp = EchoDsp.makeChirp({ sampleRate, durationSeconds: 0.05, startHz: 2000, endHz: 8000 });
+                const recording = new Float32Array(sampleRate);
+                for (let i = 0; i < recording.length; i++) recording[i] = (Math.random() * 2 - 1) * 0.02;
+
+                const offset = 12345;
+                for (let i = 0; i < chirp.length; i++) recording[offset + i] += chirp[i] * 0.3;
+
+                const peak = EchoDsp.findFirstPeak(EchoDsp.matchedFilterEnvelope(recording, chirp));
+                return Math.abs(peak.index - offset);
+            }
+            """);
+
+        Assert.That(error, Is.LessThan(1.0), "arrival should be located to within a sample");
+    }
+
+    [Test]
+    public async Task A_Tone_Cannot_Be_Located_But_A_Chirp_Can()
+    {
+        var ratios = await Page.EvaluateAsync<double[]>("""
+            () => {
+                const sampleRate = 48000;
+                const sidelobeRatio = template => {
+                    const recording = new Float32Array(sampleRate / 2);
+                    const offset = 8000;
+                    for (let i = 0; i < template.length; i++) recording[offset + i] += template[i];
+
+                    const envelope = EchoDsp.matchedFilterEnvelope(recording, template);
+                    const peak = EchoDsp.maxInRange(envelope, 0, envelope.length);
+                    let highest = 0;
+                    for (let i = 0; i < envelope.length; i++) {
+                        if (Math.abs(i - peak.index) < 200) continue;
+                        highest = Math.max(highest, envelope[i]);
+                    }
+                    return highest / peak.value;
+                };
+
+                const chirp = EchoDsp.makeChirp({ sampleRate, durationSeconds: 0.05, startHz: 2000, endHz: 8000 });
+                const tone = EchoDsp.makeChirp({ sampleRate, durationSeconds: 0.05, startHz: 5000, endHz: 5000 });
+                return [sidelobeRatio(chirp), sidelobeRatio(tone)];
+            }
+            """);
+
+        Assert.That(ratios[1], Is.GreaterThan(0.5), "a tone should correlate almost as well far from the true arrival");
+        Assert.That(ratios[0], Is.LessThan(0.25), "a chirp should give one unambiguous arrival");
+    }
+
+    [Test]
+    public async Task Clock_Offset_And_Pipeline_Latency_Cancel()
+    {
+        var distance = await Page.EvaluateAsync<double>("""
+            () => {
+                const sampleRate = 48000;
+                const speedOfSound = 343;
+                const flight = (4.2 / speedOfSound) * sampleRate;
+                const slot = 0.4 * sampleRate;
+                const offsetB = 987654;
+                const latencyA = 0.031 * sampleRate;
+                const latencyB = 0.128 * sampleRate;
+
+                return EchoDsp.pairDistance({
+                    a1: latencyA,
+                    a2: slot + latencyB + flight,
+                    b1: offsetB + latencyA + flight,
+                    b2: offsetB + slot + latencyB,
+                    sampleRate,
+                    speedOfSound
+                });
+            }
+            """);
+
+        Assert.That(distance, Is.EqualTo(4.2).Within(0.001));
+    }
+
+    [Test]
+    public async Task Collocated_Devices_Read_Zero_Before_Calibration()
+    {
+        var distance = await Page.EvaluateAsync<double>("""
+            () => {
+                const sampleRate = 48000;
+                const speedOfSound = 343;
+                const spacing = (0.19 / speedOfSound) * sampleRate;
+                const slot = 0.4 * sampleRate;
+                const latencyA = 0.04 * sampleRate;
+                const latencyB = 0.11 * sampleRate;
+
+                // Two tabs on one machine: one speaker, one microphone, so the self path and the
+                // cross path are the same physical distance.
+                return EchoDsp.pairDistance({
+                    a1: latencyA + spacing,
+                    a2: slot + latencyB + spacing,
+                    b1: latencyA + spacing,
+                    b2: slot + latencyB + spacing,
+                    sampleRate,
+                    speedOfSound
+                });
+            }
+            """);
+
+        Assert.That(distance, Is.EqualTo(0).Within(0.001));
+    }
+
+    [Test]
+    public async Task Speaker_To_Microphone_Spacing_Is_Added_Back()
+    {
+        var distances = await Page.EvaluateAsync<double[]>("""
+            () => {
+                const sampleRate = 48000;
+                const speedOfSound = 343;
+                const truth = 3.0;
+                const epsilonA = 0.18;
+                const epsilonB = 0.04;
+                const samples = metres => (metres / speedOfSound) * sampleRate;
+                const slot = 0.4 * sampleRate;
+
+                const peaks = {
+                    a1: samples(epsilonA),
+                    a2: slot + samples(truth),
+                    b1: samples(truth),
+                    b2: slot + samples(epsilonB),
+                    sampleRate,
+                    speedOfSound
+                };
+
+                return [
+                    EchoDsp.pairDistance(peaks),
+                    EchoDsp.pairDistance({ ...peaks, epsilonA, epsilonB })
+                ];
+            }
+            """);
+
+        Assert.That(distances[0], Is.EqualTo(3.0 - 0.11).Within(0.005), "uncorrected range reads short");
+        Assert.That(distances[1], Is.EqualTo(3.0).Within(0.005), "correcting for spacing recovers the true range");
+    }
+
+    [Test]
+    public async Task Simulated_Room_Recovers_Distances_And_Layout()
+    {
+        var errors = await Page.EvaluateAsync<double[]>("""
+            () => {
+                const result = EchoSim.runRound({
+                    positions: [[0, 0], [3.2, 0], [3.0, 2.6], [0.4, 2.9], [1.7, 1.4]]
+                });
+                return [EchoSim.worstDistanceError(result), EchoSim.worstPositionError(result), result.keep.length];
+            }
+            """);
+
+        Assert.That(errors[2], Is.EqualTo(5), "every device should survive a clean round");
+        Assert.That(errors[0], Is.LessThan(0.05), "worst pairwise range error");
+        Assert.That(errors[1], Is.LessThan(0.15), "worst recovered position error");
+    }
+
+    [Test]
+    public async Task A_Reflection_Louder_Than_The_Direct_Path_Does_Not_Win()
+    {
+        var errors = await Page.EvaluateAsync<double[]>("""
+            () => {
+                const measure = relativeThreshold => EchoSim.worstDistanceError(EchoSim.runRound({
+                    positions: [[0, 0], [3.4, 0], [2.9, 2.7], [0.2, 2.5]],
+                    reflections: [{ extraMetres: 1.8, gain: 5 }],
+                    peakOptions: { relativeThreshold }
+                }));
+
+                return [measure(undefined), measure(0.5)];
+            }
+            """);
+
+        Assert.That(errors[0], Is.LessThan(0.05), "the first arrival is the distance, not the loudest one");
+        Assert.That(errors[1], Is.GreaterThan(1.5),
+            "a threshold high enough to miss the direct path must measure the reflection instead — this is what the default guards against");
+    }
+
+    [Test]
+    public async Task Echoes_Inside_The_Correlation_Lobe_Bound_The_Accuracy()
+    {
+        var errors = await Page.EvaluateAsync<double[]>("""
+            () => {
+                const positions = [[0, 0], [3.2, 0], [3.0, 2.6], [0.4, 2.9], [1.7, 1.4]];
+                const worst = reflectionExtraRange =>
+                    EchoSim.worstDistanceError(EchoSim.runRound({ positions, reflectionExtraRange }));
+
+                return [worst([0.4, 4.0]), worst([0.08, 0.4])];
+            }
+            """);
+
+        Assert.That(errors[0], Is.LessThan(0.01), "echoes well clear of the direct arrival are rejected outright");
+        Assert.That(errors[1], Is.LessThan(0.15),
+            "echoes arriving inside the correlation lobe cannot be separated and bias the range — this bounds what a device resting on a hard surface can achieve");
+    }
+
+    [Test]
+    public async Task A_Bad_Measurement_Is_Rejected_And_The_Layout_Survives()
+    {
+        var outcome = await Page.EvaluateAsync<double[]>("""
+            () => {
+                const positions = [[0, 0], [3.2, 0], [3.0, 2.6], [0.4, 2.9], [1.6, 1.3]];
+                const config = EchoSim.buildConfiguration({ positions });
+                const reports = EchoSim.detectAll(EchoSim.synthesizeRound(config), config);
+
+                reports[3].peaks[0] += 9000;
+
+                const solved = EchoDsp.solveRound(reports, { speedOfSound: config.speedOfSound });
+                const truth = solved.keep.map(index => positions[index]);
+                const aligned = EchoDsp.alignToReference(solved.points, truth);
+                const worst = Math.max(...aligned.map((point, i) => EchoSim.separation(point, truth[i])));
+                const brokenPairSurvived = solved.keep.includes(0) && solved.keep.includes(3);
+
+                return [solved.keep.length, brokenPairSurvived ? 1 : 0, worst];
+            }
+            """);
+
+        Assert.That(outcome[0], Is.EqualTo(4), "exactly one endpoint of the bad pair should be dropped");
+        Assert.That(outcome[1], Is.EqualTo(0), "the impossible pair must not survive");
+        Assert.That(outcome[2], Is.LessThan(0.2), "the remaining layout should be unpoisoned");
+    }
+
+    [Test]
+    public async Task Alignment_Undoes_An_Arbitrary_Rotation_And_Mirror()
+    {
+        var errors = await Page.EvaluateAsync<double[]>("""
+            () => {
+                const reference = [[0, 0], [3.4, 0], [2.9, 2.7], [0.2, 2.5]];
+                const scramble = (points, angle, mirror) => points.map(([x, y]) => {
+                    const mx = x * mirror;
+                    return [mx * Math.cos(angle) - y * Math.sin(angle) + 11, mx * Math.sin(angle) + y * Math.cos(angle) - 4];
+                });
+
+                const worst = mirror => {
+                    const aligned = EchoDsp.alignToReference(scramble(reference, 0.9, mirror), reference);
+                    return Math.max(...aligned.map((point, i) => EchoSim.separation(point, reference[i])));
+                };
+
+                return [worst(1), worst(-1)];
+            }
+            """);
+
+        Assert.That(errors[0], Is.LessThan(1e-9), "rotation and translation should be recovered exactly");
+        Assert.That(errors[1], Is.LessThan(1e-9), "a mirrored solve should be un-mirrored onto the reference");
+    }
+
+    [Test]
+    public async Task Consecutive_Frames_Do_Not_Rotate_Or_Flip()
+    {
+        var drift = await Page.EvaluateAsync<double>("""
+            () => {
+                const positions = [[0, 0], [3.2, 0], [3.0, 2.6], [0.4, 2.9]];
+                const first = EchoSim.runRound({ positions, seed: 11 });
+
+                const previous = new Array(positions.length).fill(null);
+                first.keep.forEach((device, i) => { previous[device] = first.points[i]; });
+
+                const config = EchoSim.buildConfiguration({ positions, seed: 22 });
+                const reports = EchoSim.detectAll(EchoSim.synthesizeRound(config), config);
+                const second = EchoDsp.solveRound(reports, {
+                    speedOfSound: config.speedOfSound,
+                    previousPoints: previous
+                });
+
+                return Math.max(...second.keep.map((device, i) => EchoSim.separation(second.points[i], previous[device])));
+            }
+            """);
+
+        Assert.That(drift, Is.LessThan(0.3), "a stationary room should not move between frames");
+    }
+}

JoshHeaps.Net.UiTests/EchoRoomTests.cs

@@ -0,0 +1,244 @@
+using Microsoft.Playwright;
+using Microsoft.Playwright.NUnit;
+using NUnit.Framework;
+
+namespace JoshHeaps.Net.UiTests;
+
+/// <summary>
+/// Drives two real browsers through a real room: the hub, the round scheduler, slot rotation,
+/// detection and the solve all run unchanged. Only the microphone is synthetic, so the answer is
+/// known in advance — this is everything except the acoustics.
+/// </summary>
+[TestFixture]
+public class EchoRoomTests : PlaywrightTest
+{
+    private const double TargetMetres = 2.5;
+    private IPlaywright? _playwright;
+    private IBrowser? _browser;
+    private readonly List<IBrowserContext> _contexts = [];
+    private TestConfiguration Config => TestConfiguration.Instance;
+
+    [OneTimeSetUp]
+    public async Task LaunchBrowser()
+    {
+        // Its own Playwright instance and browser: the fake-media launch flags have to be set at
+        // launch time, and the fixture-managed browser is already running by the time tests start.
+        _playwright = await Microsoft.Playwright.Playwright.CreateAsync();
+        _browser = await _playwright.Chromium.LaunchAsync(new BrowserTypeLaunchOptions
+        {
+            Headless = true,
+            Args =
+            [
+                "--use-fake-ui-for-media-stream",
+                "--use-fake-device-for-media-stream",
+                "--autoplay-policy=no-user-gesture-required"
+            ]
+        });
+    }
+
+    [OneTimeTearDown]
+    public async Task CloseBrowser()
+    {
+        if (_browser is not null) await _browser.CloseAsync();
+        _playwright?.Dispose();
+    }
+
+    [TearDown]
+    public async Task CloseContexts()
+    {
+        foreach (var context in _contexts) await context.CloseAsync();
+        _contexts.Clear();
+    }
+
+    [Test]
+    public async Task Two_Devices_Measure_The_Distance_Between_Them()
+    {
+        var roomCode = $"T{Random.Shared.Next(1000, 9999)}";
+        var first = await NewDeviceAsync(roomCode, "laptop");
+        var second = await NewDeviceAsync(roomCode, "phone");
+
+        await Expect(first.Locator("#echoRoster li")).ToHaveCountAsync(2);
+
+        var measured = await WaitForMeasurementAsync(first);
+        var alsoMeasured = await WaitForMeasurementAsync(second);
+
+        Assert.That(measured, Is.EqualTo(TargetMetres).Within(0.05), "the first device's range");
+        Assert.That(alsoMeasured, Is.EqualTo(TargetMetres).Within(0.05), "both devices should agree");
+    }
+
+    [Test]
+    public async Task A_Device_Leaving_Stops_The_Rounds_And_Rejoining_Resumes_Them()
+    {
+        var roomCode = $"T{Random.Shared.Next(1000, 9999)}";
+        var first = await NewDeviceAsync(roomCode, "laptop");
+        var second = await NewDeviceAsync(roomCode, "phone");
+
+        await WaitForMeasurementAsync(first);
+        await second.ClickAsync("#echoLeave");
+
+        await Expect(first.Locator("#echoRoster li")).ToHaveCountAsync(1);
+        await Expect(first.Locator("#echoStatus")).ToContainTextAsync("Waiting for a second device");
+
+        await second.ClickAsync("#echoJoin");
+        await Expect(first.Locator("#echoRoster li")).ToHaveCountAsync(2);
+        Assert.That(await WaitForMeasurementAsync(first), Is.EqualTo(TargetMetres).Within(0.05));
+    }
+
+    /// <summary>
+    /// A stalled main thread is the two-tabs-on-one-machine failure: only one tab is visible, so the
+    /// other gets throttled and its round handling runs late. A late chirp attributed to the wrong
+    /// slot yields a plausible-looking but completely wrong range, so the requirement is not "always
+    /// measures" — it is "never reports a wrong answer". A round it cannot hit must be sat out.
+    /// </summary>
+    [Test]
+    public async Task A_Stalled_Device_Sits_Rounds_Out_Instead_Of_Reporting_Nonsense()
+    {
+        var roomCode = $"T{Random.Shared.Next(1000, 9999)}";
+        var first = await NewDeviceAsync(roomCode, "laptop");
+        var second = await NewDeviceAsync(roomCode, "phone", stallMilliseconds: 900);
+
+        await Expect(first.Locator("#echoRoster li")).ToHaveCountAsync(2);
+        await first.EvaluateAsync("() => { window.__seen = []; }");
+        await first.EvaluateAsync("""
+            () => {
+                const original = EchoPage.renderSolved.bind(EchoPage);
+                EchoPage.renderSolved = update => {
+                    const range = update.solved?.matrix?.[0]?.[1];
+                    if (range != null) window.__seen.push(range);
+                    return original(update);
+                };
+            }
+            """);
+
+        await first.WaitForTimeoutAsync(20000);
+        var seen = await first.EvaluateAsync<double[]>("() => window.__seen");
+        var satOut = await second.EvaluateAsync<int>("() => EchoSession.skippedRounds");
+
+        TestContext.Out.WriteLine($"reported ranges: {string.Join(", ", seen.Select(r => r.ToString("0.000")))}, sat out: {satOut}");
+        Assert.That(satOut, Is.GreaterThan(0),
+            "the stall must actually have cost the device some slots, or this test proves nothing");
+        Assert.That(seen, Is.Not.Empty, "a stalled peer should still let some rounds through");
+        Assert.That(seen, Is.All.EqualTo(TargetMetres).Within(0.05),
+            "every range that gets reported must be right — a stalled device must sit the round out, not chirp late");
+    }
+
+    [Test]
+    public async Task The_Capture_Worklet_Keeps_A_Continuous_Readable_Stream()
+    {
+        var page = await NewDeviceAsync($"T{Random.Shared.Next(1000, 9999)}", "laptop", fakeMicrophone: false);
+
+        await page.WaitForFunctionAsync(
+            "() => EchoAudio.highestFrame > 48000",
+            null,
+            new PageWaitForFunctionOptions { Timeout = 15000, PollingInterval = 100 });
+
+        var capture = await page.EvaluateAsync<double[]>("""
+            () => [
+                EchoAudio.context.sampleRate,
+                EchoAudio.warnings.length,
+                EchoAudio.read(EchoAudio.highestFrame - 24000, 24000)?.length ?? 0,
+                EchoAudio.read(EchoAudio.highestFrame + 1000, 100) === null ? 1 : 0,
+                Math.abs(EchoAudio.frameAt(EchoAudio.context.currentTime) - EchoAudio.highestFrame)
+            ]
+            """);
+
+        Assert.That(capture[0], Is.EqualTo(48000), "the pipeline assumes it got the rate it asked for");
+        Assert.That(capture[1], Is.EqualTo(0), "a clean fake device should raise no capture warnings");
+        Assert.That(capture[2], Is.EqualTo(24000), "recent audio must be readable out of the ring");
+        Assert.That(capture[3], Is.EqualTo(1), "reads past the captured end must fail rather than return silence");
+        Assert.That(capture[4], Is.LessThan(48000),
+            "the frame index and the context clock must stay in the same domain — a scheduled playback time is converted straight into a recording position");
+    }
+
+    /// <summary>
+    /// A page joined to the room with its microphone replaced by a synthesizer. Every slot's chirp
+    /// is placed where a room of this geometry would put it, including a different unknown output
+    /// latency per slot so the cancellation is actually exercised.
+    /// </summary>
+    private async Task<IPage> NewDeviceAsync(
+        string roomCode,
+        string name,
+        bool fakeMicrophone = true,
+        int stallMilliseconds = 0)
+    {
+        var context = await _browser!.NewContextAsync(new BrowserNewContextOptions
+        {
+            IgnoreHTTPSErrors = true,
+            Permissions = ["microphone"]
+        });
+
+        _contexts.Add(context);
+        var page = await context.NewPageAsync();
+        page.Console += (_, message) =>
+        {
+            if (message.Type == "error") TestContext.Out.WriteLine($"[{name} console] {message.Text}");
+        };
+
+        await page.GotoAsync($"{Config.Test.BaseUrl}/echo?room={roomCode}");
+        await page.FillAsync("#echoName", name);
+        if (fakeMicrophone) await page.EvaluateAsync(FakeMicrophoneScript, TargetMetres);
+        if (stallMilliseconds > 0) await page.EvaluateAsync(StallScript, stallMilliseconds);
+        await page.ClickAsync("#echoJoin");
+
+        return page;
+    }
+
+    /// <summary>Blocks the main thread on every round announcement, the way a throttled tab does.</summary>
+    private const string StallScript = """
+        stallMs => {
+            const original = EchoSession.handleRoundStarting.bind(EchoSession);
+            EchoSession.handleRoundStarting = schedule => {
+                const until = performance.now() + stallMs;
+                while (performance.now() < until) { /* hold the thread */ }
+                return original(schedule);
+            };
+        }
+        """;
+
+    private static async Task<double> WaitForMeasurementAsync(IPage page)
+    {
+        await page.WaitForFunctionAsync(
+            "() => EchoPage.lastSolved?.solved?.matrix?.[0]?.[1] != null",
+            null,
+            new PageWaitForFunctionOptions { Timeout = 30000, PollingInterval = 250 });
+
+        return await page.EvaluateAsync<double>("() => EchoPage.lastSolved.solved.matrix[0][1]");
+    }
+
+    /// <summary>
+    /// Synthesizes what the microphone would have heard for this round. The device's own chirp is
+    /// placed at the frame it was actually scheduled for rather than at its nominal slot position,
+    /// so any drift between "when the round said to play" and "when playback was really booked"
+    /// reaches the detector instead of being papered over by the harness.
+    /// </summary>
+    private const string FakeMicrophoneScript = """
+        targetMetres => {
+            const speedOfSound = 343;
+            const epsilonMetres = 0.08;
+            const latencyBySlot = [1400, 5200, 2600, 7100, 900, 4300, 3300, 6000];
+
+            EchoAudio.read = (startFrame, length) => {
+                const round = EchoSession.pending ?? EchoSession.lastRound;
+                if (!round) return null;
+
+                const chirp = EchoSession.chirp;
+                const toSamples = metres => Math.round((metres / speedOfSound) * round.sampleRate);
+                const recording = new Float32Array(length);
+
+                round.schedule.slotOrder.forEach((_, slot) => {
+                    const own = slot === round.ownSlot;
+                    const origin = own
+                        ? round.scheduledFrame - round.windowStart
+                        : round.leadInSamples + slot * round.slotSamples;
+                    const at = origin + latencyBySlot[slot] + toSamples(own ? epsilonMetres : targetMetres);
+                    const amplitude = own ? 1.0 : 0.25;
+
+                    for (let i = 0; i < chirp.length && at + i < length; i++) recording[at + i] += chirp[i] * amplitude;
+                });
+
+                for (let i = 0; i < length; i++) recording[i] += (Math.random() * 2 - 1) * 0.01;
+                return recording;
+            };
+        }
+        """;
+}

JoshHeaps.Net.sln

@@ -1,26 +1,60 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio Version 17
-VisualStudioVersion = 17.9.34728.123
+# Visual Studio Version 18
+VisualStudioVersion = 18.6.11822.322 stable
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "JoshHeaps.Net", "JoshHeaps.Net\JoshHeaps.Net.csproj", "{9F0182CC-470F-4D1A-99F5-348D7921751E}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "JoshHeaps.Net.UiTests", "JoshHeaps.Net.UiTests\JoshHeaps.Net.UiTests.csproj", "{360264F4-8292-4EB3-B67D-98376C13438B}"
 EndProject
+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "chess_engine", "native\chess_engine\chess_engine\chess_engine.vcxproj", "{2579BBBC-1830-4342-BC10-0A4182DC84C7}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
+		Debug|x64 = Debug|x64
+		Debug|x86 = Debug|x86
 		Release|Any CPU = Release|Any CPU
+		Release|x64 = Release|x64
+		Release|x86 = Release|x86
 	EndGlobalSection
 	GlobalSection(ProjectConfigurationPlatforms) = postSolution
 		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Debug|x64.Build.0 = Debug|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Debug|x86.Build.0 = Debug|Any CPU
 		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Release|x64.ActiveCfg = Release|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Release|x64.Build.0 = Release|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Release|x86.ActiveCfg = Release|Any CPU
+		{9F0182CC-470F-4D1A-99F5-348D7921751E}.Release|x86.Build.0 = Release|Any CPU
 		{360264F4-8292-4EB3-B67D-98376C13438B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{360264F4-8292-4EB3-B67D-98376C13438B}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Debug|x64.Build.0 = Debug|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Debug|x86.Build.0 = Debug|Any CPU
 		{360264F4-8292-4EB3-B67D-98376C13438B}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{360264F4-8292-4EB3-B67D-98376C13438B}.Release|Any CPU.Build.0 = Release|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Release|x64.ActiveCfg = Release|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Release|x64.Build.0 = Release|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Release|x86.ActiveCfg = Release|Any CPU
+		{360264F4-8292-4EB3-B67D-98376C13438B}.Release|x86.Build.0 = Release|Any CPU
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Debug|Any CPU.ActiveCfg = Debug|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Debug|Any CPU.Build.0 = Debug|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Debug|x64.ActiveCfg = Debug|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Debug|x64.Build.0 = Debug|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Debug|x86.ActiveCfg = Debug|Win32
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Debug|x86.Build.0 = Debug|Win32
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Release|Any CPU.ActiveCfg = Release|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Release|Any CPU.Build.0 = Release|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Release|x64.ActiveCfg = Release|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Release|x64.Build.0 = Release|x64
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Release|x86.ActiveCfg = Release|Win32
+		{2579BBBC-1830-4342-BC10-0A4182DC84C7}.Release|x86.Build.0 = Release|Win32
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

JoshHeaps.Net.slnf

@@ -0,0 +1,9 @@
+{
+  "solution": {
+    "path": "JoshHeaps.Net.sln",
+    "projects": [
+      "JoshHeaps.Net\\JoshHeaps.Net.csproj",
+      "JoshHeaps.Net.UiTests\\JoshHeaps.Net.UiTests.csproj"
+    ]
+  }
+}

JoshHeaps.Net/.gitea/workflows/deploy.yml

@@ -0,0 +1,75 @@
+# .gitea/workflows/deploy.yml
+name: Build and Deploy
+
+on:
+  push:
+    branches: [ "master" ]
+  workflow_dispatch: {}
+
+concurrency:
+  group: deploy-${{ gitea.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build-deploy:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Install deploy tools
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends rsync openssh-client
+
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: '8.0.x'
+
+      - name: Restore
+        run: dotnet restore
+
+      - name: Publish
+        run: dotnet publish -c Release -o ./publish
+
+      - name: Prepare SSH
+        env:
+          SSH_KEY:  ${{ secrets.SSH_KEY }}
+          SSH_HOST: ${{ secrets.SSH_HOST }}
+          SSH_PORT: ${{ secrets.SSH_PORT }}
+        run: |
+          set -euo pipefail
+          PORT="${SSH_PORT:-22}"
+          install -m 700 -d ~/.ssh
+          printf '%s\n' "$SSH_KEY" > ~/.ssh/deploy_key
+          chmod 600 ~/.ssh/deploy_key
+          ssh-keyscan -p "$PORT" "$SSH_HOST" >> ~/.ssh/known_hosts 2>/dev/null
+
+      - name: Rsync to server
+        env:
+          SSH_HOST:   ${{ secrets.SSH_HOST }}
+          SSH_PORT:   ${{ secrets.SSH_PORT }}
+          SSH_USER:   ${{ secrets.SSH_USER }}
+          TARGET_DIR: ${{ secrets.TARGET_DIR }}
+        run: |
+          set -euo pipefail
+          PORT="${SSH_PORT:-22}"
+          rsync -az --delete \
+            -e "ssh -p $PORT -i ~/.ssh/deploy_key -o StrictHostKeyChecking=yes" \
+            publish/ "$SSH_USER@$SSH_HOST:$TARGET_DIR/"
+
+      - name: Restart service
+        env:
+          SSH_HOST:     ${{ secrets.SSH_HOST }}
+          SSH_PORT:     ${{ secrets.SSH_PORT }}
+          SSH_USER:     ${{ secrets.SSH_USER }}
+          SERVICE_NAME: ${{ secrets.SERVICE_NAME }}
+        run: |
+          set -euo pipefail
+          PORT="${SSH_PORT:-22}"
+          ssh -p "$PORT" -i ~/.ssh/deploy_key "$SSH_USER@$SSH_HOST" \
+            "sudo systemctl daemon-reload \
+             && sudo systemctl restart '$SERVICE_NAME' \
+             && systemctl --no-pager status '$SERVICE_NAME' --lines=0"

JoshHeaps.Net/Content/Blog/2026-03-06-my-first-post.md

@@ -0,0 +1,24 @@
+---
+title: My First Post
+date: 2026-03-06
+summary: Welcome to my blog! Here I'll share thoughts on software development, projects I'm working on, and things I find interesting.
+tags: [dev, personal]
+---
+
+# Welcome to My Blog
+
+I've been meaning to start writing about the things I build and learn, and I'm finally getting around to it.
+
+## What to Expect
+
+I plan to write about:
+
+- **Projects** I'm working on, like this website and the other things on my portfolio
+- **Software development** tips and patterns I find useful
+- **Problem solving** approaches that have helped me grow as a developer
+
+## Why a Blog?
+
+Building things is great, but explaining *how* and *why* you built them is just as valuable. Writing forces you to organize your thoughts, and hopefully someone else finds it useful along the way.
+
+Stay tuned for more posts!

JoshHeaps.Net/Controllers/BlogController.cs

@@ -0,0 +1,20 @@
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace JoshHeaps.Net.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public class BlogController(IBlogService blogService, IConfiguration configuration) : ControllerBase
+{
+    [HttpPost("invalidate")]
+    public IActionResult InvalidateCache([FromHeader(Name = "X-Invalidate-Key")] string? key)
+    {
+        var expectedKey = configuration["BlogApi:InvalidateKey"];
+        if (string.IsNullOrEmpty(expectedKey) || key != expectedKey)
+            return Unauthorized();
+
+        blogService.ClearCache();
+        return Ok();
+    }
+}

JoshHeaps.Net/Controllers/ChessController.cs

@@ -1,9 +1,9 @@
-using JoshHeaps.Net.Hubs;
+using JoshHeaps.Net.Hubs;
 using JoshHeaps.Net.Models;
+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;
 
@@ -11,16 +11,15 @@ namespace JoshHeaps.Net.Controllers;
 [Route("api/[controller]")]
 public class ChessController(
     IChessService chessService,
-    IHubContext<ChessHub> chessHub,
-    IBackgroundTaskQueue queue) : ControllerBase
+    IBackgroundTaskQueue queue,
+    IChessEngineFactory engineFactory,
+    IComputerMoveOrchestrator orchestrator,
+    ILearnedWeightsStore weightsStore,
+    IGameStore gameStore,
+    ISelfPlayCoordinator selfPlay,
+    AutoTrainingSettings autoTraining,
+    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);
@@ -30,38 +29,45 @@ public class ChessController(
     /// </summary>
     [HttpGet("new")]
     [HttpGet("new/{difficulty}")]
-    public ActionResult CreateGame(int difficulty = 20)
+    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;
         gameState.BlackJoined = true;
         Guid playerId = Guid.NewGuid();
         Guid computerId = Guid.NewGuid();
-        var isWhite = Random.Shared.Next(2) == 0;
+        var isWhite = color.ToLowerInvariant() switch
+        {
+            "white" => true,
+            "black" => false,
+            _ => Random.Shared.Next(2) == 0,
+        };
 
-        gameState.Computer = new(difficulty);
+        var computer = engineFactory.Create(difficulty);
 
         if (isWhite)
         {
             gameState.WhitePlayerId = playerId;
             gameState.BlackPlayerId = computerId;
+            gameState.BlackComputer = computer;
         }
         else
         {
             gameState.WhitePlayerId = computerId;
             gameState.BlackPlayerId = playerId;
+            gameState.WhiteComputer = computer;
             queue.Queue(async () =>
             {
                 // Give user's browser time to connect to signalR and such.
                 await Task.Delay(TimeSpan.FromSeconds(1));
-                await gameState.Computer.MakeMove(gameState, chessHub, chessService);
+                await orchestrator.PlayAsync(gameState);
             });
         }
 
-        ScheduleRemoveGame(gameState.GameId, _computerGameTimeout);
+        gameStore.ScheduleRemove(gameState.GameId, _computerGameTimeout);
 
         return Ok(new
         {
@@ -71,6 +77,55 @@ public class ChessController(
         });
     }
 
+    /// <summary>
+    /// Create a computer-vs-computer game and auto-play it move by move, broadcasting each
+    /// move so it can be watched on the spectator page. Each side's engine and skill can be
+    /// chosen independently; when the learned engine plays, the game also trains it.
+    /// </summary>
+    [HttpGet("watch/cpu")]
+    [HttpGet("watch/cpu/{difficulty}")]
+    public ActionResult CreateSelfPlayGame(
+        int difficulty = 4,
+        string whiteEngine = "custom",
+        string blackEngine = "custom",
+        int? whiteSkill = null,
+        int? blackSkill = null)
+    {
+        var config = new SelfPlayConfig(
+            ParseEngineKind(whiteEngine), whiteSkill ?? difficulty,
+            ParseEngineKind(blackEngine), blackSkill ?? difficulty);
+
+        var (gameId, _) = selfPlay.StartGame(config);
+
+        return Ok(new { GameId = gameId });
+    }
+
+    private static ChessEngineKind ParseEngineKind(string value) => value.ToLowerInvariant() switch
+    {
+        "stockfish" => ChessEngineKind.Stockfish,
+        "customlearned" or "learned" => ChessEngineKind.CustomLearned,
+        _ => ChessEngineKind.Custom
+    };
+
+    /// <summary>
+    /// Current number of background auto-training games (and the allowed maximum). Auto-training
+    /// itself runs only outside Development; this reflects the target the service is keeping.
+    /// </summary>
+    [HttpGet("autotrain")]
+    public ActionResult GetAutoTrain() =>
+        Ok(new { count = autoTraining.GameCount, max = AutoTrainingSettings.MaxGames });
+
+    /// <summary>
+    /// Set how many auto-training games run concurrently (clamped to 0..max; 0 pauses training).
+    /// Takes effect live — the background service tops up or drains toward the new count.
+    /// </summary>
+    [HttpPost("autotrain")]
+    public ActionResult SetAutoTrain([FromQuery] int count)
+    {
+        autoTraining.GameCount = count;   // clamped inside the setter
+        return Ok(new { count = autoTraining.GameCount, max = AutoTrainingSettings.MaxGames });
+    }
+
     /// <summary>
     /// Joins the "pool" of chess players.
     /// Test code expects to receive a GUID for the player
@@ -80,12 +135,12 @@ 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();
@@ -103,7 +158,7 @@ public class ChessController(
             isWhite = false;
         }
 
-        ScheduleRemoveGame(gameState.GameId, _multiplayerGameTimeout);
+        gameStore.ScheduleRemove(gameState.GameId, _multiplayerGameTimeout);
 
         return Ok(new
         {
@@ -113,41 +168,62 @@ public class ChessController(
         });
     }
 
+    /// <summary>
+    /// List in-progress games for spectators: both sides present and the game not yet decided.
+    /// </summary>
+    [HttpGet("active")]
+    public ActionResult GetActiveGames()
+    {
+        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))
+            .Select(g => new
+            {
+                g.GameId,
+                g.IsVsComputer,
+                g.IsComputerVsComputer,
+                WhiteEngine = g.WhiteEngineKind.ToString(),
+                BlackEngine = g.BlackEngineKind.ToString(),
+                CurrentPlayer = g.CurrentPlayer.ToString(),
+                MoveCount = g.MoveHistory.Count,
+                g.IsCheck
+            })
+            .OrderByDescending(g => g.MoveCount);
+
+        return Ok(activeGames);
+    }
+
+    /// <summary>
+    /// The learned engine's piece-square bonus table, for the weights-visualization page:
+    /// one 64-entry array per piece type (Pawn..King), white-relative (A1=0 .. H8=63).
+    /// </summary>
+    [HttpGet("weights")]
+    public ActionResult GetLearnedWeights()
+    {
+        var names = new[] { "Pawn", "Knight", "Bishop", "Rook", "Queen", "King" };
+        var featureNames = new[] { "Mobility N", "Mobility B", "Mobility R", "Mobility Q", "Passed", "Isolated", "Doubled", "King safety" };
+
+        var snapshot = weightsStore.Snapshot();
+
+        return Ok(new
+        {
+            mg = snapshot.Mg.Select((squares, i) => new { name = names[i], squares }),
+            eg = snapshot.Eg.Select((squares, i) => new { name = names[i], squares }),
+            features = snapshot.Features.Select((value, i) => new { name = featureNames[i], value })
+        });
+    }
+
     /// <summary>
     /// Get the state of an existing game by ID.
     /// </summary>
     [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");
 
-        var response = new
-        {
-            gameState.GameId,
-            CurrentPlayer = gameState.CurrentPlayer.ToString(),
-            gameState.IsCheck,
-            gameState.IsCheckmate,
-            gameState.IsStalemate,
-            EnPassantTarget = gameState.EnPassantTarget?.ToString() ?? null,
-            gameState.WhiteCanCastleKingside,
-            gameState.WhiteCanCastleQueenside,
-            gameState.BlackCanCastleKingside,
-            gameState.BlackCanCastleQueenside,
-            Pieces = gameState.Pieces
-                .Where(p => p.Position.Row >= 0)
-                .Select(p => new {
-                    p.Id,
-                    p.Type,
-                    p.Color,
-                    p.Position.Row,
-                    p.Position.Col,
-                    p.HasMoved
-                }),
-            gameState.MoveHistory
-        };
-
-        return Ok(response);
+        return Ok(gameState.ToDto());
     }
 
     /// <summary>
@@ -155,9 +231,9 @@ public class ChessController(
     /// The test passes a JSON body with a MoveDto.
     /// </summary>
     [HttpPost("move")]
-    public ActionResult MakeMove([FromBody] MoveDto moveDto)
+    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
@@ -181,17 +257,73 @@ public class ChessController(
         if (!result.Success)
             return BadRequest(result);
 
-        if (result.IsCheckmate || result.IsStalemate)
-            ScheduleRemoveGame(gameState.GameId, _gameCleanupTimeout);
+        var isGameOver = result.IsCheckmate || result.IsStalemate || result.IsThreefoldRepetition;
+
+        if (isGameOver)
+            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);
 
-        if (gameState.IsVsComputer && gameState.Computer is not null)
-            queue.Queue(() => gameState.Computer.MakeMove(gameState, chessHub, chessService));
+        var state = gameState.ToDto();
 
-        return Ok(result);
+        // Broadcast the move (with the full resulting state) to everyone watching this
+        // game. The mover also receives this echo but drops it via the version guard,
+        // since it already rendered the same state from this response.
+        await chessHub.Clients.Group(gameState.GameId.ToString())
+            .SendAsync("ReceiveMoveUpdate", gameState.GameId.ToString(), moveDto, result, state);
+
+        var sideToMoveEngine = gameState.CurrentPlayer == PieceColor.White
+            ? gameState.WhiteComputer
+            : gameState.BlackComputer;
+
+        if (!isGameOver && gameState.IsVsComputer && sideToMoveEngine is not null)
+            queue.Queue(() => orchestrator.PlayAsync(gameState));
+
+        return Ok(new { result, state });
+    }
+
+    /// <summary>
+    /// Forfeit a game on behalf of the calling player, handing the win to the opponent.
+    /// Used when a player abandons a game (e.g. starts a new one mid-game).
+    /// </summary>
+    [HttpPost("forfeit")]
+    public async Task<ActionResult> Forfeit([FromBody] ForfeitDto forfeit)
+    {
+        if (!gameStore.TryGet(forfeit.GameId, out var gameState))
+            return NotFound("Game not found");
+
+        if (gameState.IsCheckmate || gameState.IsStalemate || gameState.IsForfeited)
+            return Ok();
+
+        var isWhitePlayer = gameState.WhitePlayerId == forfeit.PlayerId;
+        var isBlackPlayer = gameState.BlackPlayerId == forfeit.PlayerId;
+
+        if (!isWhitePlayer && !isBlackPlayer)
+            return StatusCode(403, "You are not a player in this game.");
+
+        gameState.IsForfeited = true;
+        gameState.Winner = isWhitePlayer ? PieceColor.Black : PieceColor.White;
+
+        await chessHub.Clients.Group(gameState.GameId.ToString())
+            .SendAsync("ReceiveGameOver", gameState.GameId.ToString(), gameState.Winner.ToString(), "forfeit");
+
+        gameStore.ScheduleRemove(gameState.GameId, _gameCleanupTimeout);
+
+        return Ok();
+    }
+
+    /// <summary>
+    /// Export a game as PGN (works while the game is still in memory after it ends).
+    /// </summary>
+    [HttpGet("{gameId}/pgn")]
+    public ActionResult GetPgn(Guid gameId)
+    {
+        if (!gameStore.TryGet(gameId, out var gameState))
+            return NotFound("Game not found");
+
+        return Content(gameState.ToPgn(), "application/x-chess-pgn");
     }
 
     /// <summary>
@@ -200,7 +332,7 @@ 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);
@@ -214,7 +346,7 @@ 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)
@@ -226,39 +358,4 @@ public class ChessController(
 
         return Ok(allMoves);
     }
-
-    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) && game.Computer is not null)
-                    await game.Computer.DisposeAsync();
-
-                _games.Remove(id, out _);
-            }
-            catch (OperationCanceledException) { }
-            finally
-            {
-                if (_gameRemovalCancellationTokens.TryGetValue(id, out var currentCts) && currentCts == cts)
-                {
-                    _gameRemovalCancellationTokens.TryRemove(id, out _);
-                }
-
-                cts.Dispose();
-            }
-        });
-    }
 }

JoshHeaps.Net/Hubs/ChessHub.cs

@@ -1,5 +1,4 @@
-using JoshHeaps.Net.Models;
-using Microsoft.AspNetCore.SignalR;
+using Microsoft.AspNetCore.SignalR;
 
 namespace JoshHeaps.Net.Hubs;
 
@@ -11,11 +10,6 @@ public class ChessHub : Hub
         await Groups.AddToGroupAsync(Context.ConnectionId, gameId);
     }
 
-    public async Task MoveMade(string gameId, MoveDto moveDto, MoveResultDto moveResult)
-    {
-        await Clients.OthersInGroup(gameId).SendAsync("ReceiveMoveUpdate", gameId, moveDto, moveResult);
-    }
-
     public async Task LeaveWebsocketGroup(string gameId)
     {
         Console.WriteLine($"❌ Leaving group {gameId}");

JoshHeaps.Net/Hubs/EchoHub.cs

@@ -0,0 +1,52 @@
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.AspNetCore.SignalR;
+
+namespace JoshHeaps.Net.Hubs;
+
+/// <summary>
+/// Membership and peak reporting for acoustic ranging rooms. Nothing that arrives here is audio:
+/// a report is a handful of sample indices, and the geometry is solved on the clients.
+/// </summary>
+public class EchoHub(IEchoRoomStore rooms) : Hub
+{
+    /// <summary>Join (or create) a room and receive an id plus the current roster.</summary>
+    public async Task<EchoJoinResult> JoinRoom(string roomCode, string displayName, int sampleRate)
+    {
+        var result = rooms.Join(roomCode, Context.ConnectionId, displayName, sampleRate);
+        await Groups.AddToGroupAsync(Context.ConnectionId, GroupFor(result.RoomCode));
+        await Clients.Group(GroupFor(result.RoomCode)).SendAsync("RoomChanged", result.Room);
+
+        return result;
+    }
+
+    /// <summary>File this device's arrival indices for the room's open round.</summary>
+    public bool ReportRound(EchoPeakReport report) => rooms.Report(Context.ConnectionId, report);
+
+    /// <summary>
+    /// Server clock, for estimating each device's offset from it. Only needs to be good to a few
+    /// tens of milliseconds: it decides which chirp is whose, never how far away anything is.
+    /// </summary>
+    public long ServerTime() => DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
+
+    public async Task<bool> LeaveRoom() => await RemoveFromRoom();
+
+    public override async Task OnDisconnectedAsync(Exception? exception)
+    {
+        await RemoveFromRoom();
+        await base.OnDisconnectedAsync(exception);
+    }
+
+    internal static string GroupFor(string roomCode) => $"echo:{roomCode.ToUpperInvariant()}";
+
+    private async Task<bool> RemoveFromRoom()
+    {
+        var (roomCode, room) = rooms.Leave(Context.ConnectionId);
+        if (roomCode is null) return false;
+
+        await Groups.RemoveFromGroupAsync(Context.ConnectionId, GroupFor(roomCode));
+        if (room is not null) await Clients.Group(GroupFor(roomCode)).SendAsync("RoomChanged", room);
+
+        return true;
+    }
+}

JoshHeaps.Net/JoshHeaps.Net.csproj

@@ -5,6 +5,7 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <UserSecretsId>53ed685c-bdff-4306-8cc2-9fbe55c85713</UserSecretsId>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
   <ItemGroup>
@@ -28,4 +29,16 @@
     <PackageReference Include="Microsoft.AspNetCore.SignalR.Common" Version="8.0.7" />
   </ItemGroup>
 
+  <!-- Builds the native engine and refreshes Resources\chess_engine.dll (via its post-build copy)
+       only inside Visual Studio, which has the C++ tools. The dotnet CLI can't build a .vcxproj,
+       so this is skipped by `dotnet build`/`dotnet publish` (incl. the Linux CI, which deploys the
+       libchess_engine.so instead). ReferenceOutputAssembly=false: build-ordering only, not a
+       managed reference to the native DLL. -->
+  <ItemGroup Condition="'$(BuildingInsideVisualStudio)' == 'true'">
+    <ProjectReference Include="..\native\chess_engine\chess_engine\chess_engine.vcxproj">
+      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+      <Private>false</Private>
+    </ProjectReference>
+  </ItemGroup>
+
 </Project>

JoshHeaps.Net/Models/BlogPost.cs

@@ -0,0 +1,12 @@
+namespace JoshHeaps.Net.Models;
+
+public class BlogPost
+{
+    public long Id { get; set; }
+    public string Slug { get; set; } = string.Empty;
+    public string Title { get; set; } = string.Empty;
+    public DateTime PublishedDate { get; set; }
+    public string Summary { get; set; } = string.Empty;
+    public List<string> Tags { get; set; } = [];
+    public string HtmlContent { get; set; } = string.Empty;
+}

JoshHeaps.Net/Models/EchoModels.cs

@@ -0,0 +1,84 @@
+namespace JoshHeaps.Net.Models;
+
+/// <summary>A device taking part in a ranging room.</summary>
+public sealed class EchoDevice
+{
+    public required string DeviceId { get; init; }
+    public required string ConnectionId { get; init; }
+    public required string DisplayName { get; set; }
+    public int SampleRate { get; set; }
+}
+
+/// <summary>
+/// One chirp cycle: every device plays in turn, and every device listens to the whole thing.
+/// </summary>
+public sealed class EchoRound
+{
+    public required string RoundId { get; init; }
+    public required string[] SlotOrder { get; init; }
+    public int SlotMilliseconds { get; init; }
+    public DateTimeOffset Deadline { get; init; }
+    public Dictionary<string, EchoPeakReport> Reports { get; } = [];
+}
+
+/// <summary>
+/// What one device heard. Peaks are fractional sample indices into that device's own continuous
+/// recording, one per slot, null where a chirp was not detected. Nothing else is ever uploaded.
+/// </summary>
+public sealed class EchoPeakReport
+{
+    public required string DeviceId { get; init; }
+    public required string RoundId { get; init; }
+    public int Slot { get; init; }
+    public int SampleRate { get; init; }
+    public double Epsilon { get; init; }
+    public double?[] Peaks { get; init; } = [];
+}
+
+public sealed class EchoJoinResult
+{
+    public required string DeviceId { get; init; }
+    public required string RoomCode { get; init; }
+    public required EchoRoomSnapshot Room { get; init; }
+}
+
+public sealed class EchoRoomSnapshot
+{
+    public required string RoomCode { get; init; }
+    public required EchoDeviceSnapshot[] Devices { get; init; }
+}
+
+public sealed class EchoDeviceSnapshot
+{
+    public required string DeviceId { get; init; }
+    public required string DisplayName { get; init; }
+    public int SampleRate { get; init; }
+}
+
+/// <summary>Tells every device when to chirp: its own slot index and how long a slot lasts.</summary>
+public sealed class EchoRoundSchedule
+{
+    public required string RoundId { get; init; }
+    public required string[] SlotOrder { get; init; }
+    public int SlotMilliseconds { get; init; }
+    public int TailMilliseconds { get; init; }
+
+    /// <summary>
+    /// When slot zero should sound, in server time, set far enough ahead that every device can
+    /// receive the message and book the playback before it arrives. Devices schedule against this
+    /// rather than against message arrival, so one slow client cannot drag its chirp into another
+    /// device's slot and invalidate the round for everybody.
+    /// </summary>
+    public long StartsAtUnixMs { get; init; }
+}
+
+/// <summary>
+/// Every device's peaks for one round, broadcast unchanged. Each client solves the geometry itself
+/// so the server never needs the ranging maths.
+/// </summary>
+public sealed class EchoRoundResult
+{
+    public required string RoundId { get; init; }
+    public required string[] SlotOrder { get; init; }
+    public required EchoPeakReport[] Reports { get; init; }
+}

JoshHeaps.Net/Models/ForfeitDto.cs

@@ -0,0 +1,7 @@
+namespace JoshHeaps.Net.Models;
+
+public class ForfeitDto
+{
+    public Guid GameId { get; set; }
+    public Guid PlayerId { get; set; }
+}

JoshHeaps.Net/Models/GameState.cs

@@ -1,4 +1,5 @@
 using JoshHeaps.Net.Services.Implementations;
+using JoshHeaps.Net.Services.Interfaces;
 
 namespace JoshHeaps.Net.Models;
 
@@ -28,10 +29,25 @@ public class GameState
     public bool IsCheck { get; set; }
     public bool IsCheckmate { get; set; }
     public bool IsStalemate { get; set; }
+    public bool IsThreefoldRepetition { get; set; }
+    public bool IsForfeited { get; set; } = false;
+
+    // The color that won, when the game ended by forfeit (null while the game is live).
+    public PieceColor? Winner { get; set; }
 
     // Keep a history of moves if desired
     public List<string> MoveHistory { get; set; }
 
+    // Position keys (FEN placement/side/castling/en-passant) for threefold-repetition detection.
+    public List<string> PositionHistory { get; set; }
+
+    // Moves in standard algebraic notation (SAN), in order, for PGN export.
+    public List<string> SanHistory { get; set; }
+
+    // Half-moves since the last capture or pawn move (the FEN 50-move clock). Also tells
+    // us how many trailing PositionHistory entries belong to the current repetition window.
+    public int HalfmoveClock { get; set; }
+
     // A list of all pieces to quickly reference them (optional but convenient).
     // Alternatively, you can iterate the Board array.
     public List<ChessPiece> Pieces { get; set; }
@@ -42,8 +58,22 @@ public class GameState
     public Guid BlackPlayerId { get; set; }
 
     public bool IsVsComputer { get; set; } = false;
+    public bool IsComputerVsComputer { get; set; } = false;
 
-    public Stockfish? Computer { get; set; }
+    // The engine playing each side (null for a human). In a human-vs-computer game only the
+    // computer's side is set; the orchestrator picks the engine for whoever is to move.
+    public IChessEngine? WhiteComputer { get; set; }
+    public IChessEngine? BlackComputer { get; set; }
+
+    // Which engine implementation each side uses — lets game-over handling know which side(s)
+    // are the learning engine, and lets spectators see who is playing.
+    public ChessEngineKind WhiteEngineKind { get; set; }
+    public ChessEngineKind BlackEngineKind { get; set; }
+
+    // Native per-game training accumulator (nint.Zero when this game isn't training the
+    // learned engine). The engine records each played position into it and applies the
+    // result on game over.
+    public nint Trainer { get; set; }
 
     // optional: convenience
     public bool IsOpen => !WhiteJoined || !BlackJoined;
@@ -54,5 +84,7 @@ public class GameState
         Board = new ChessPiece[8, 8];
         Pieces = [];
         MoveHistory = [];
+        PositionHistory = [];
+        SanHistory = [];
     }
 }

JoshHeaps.Net/Models/GameStateDto.cs

@@ -0,0 +1,61 @@
+using System.Linq;
+
+namespace JoshHeaps.Net.Models;
+
+/// <summary>
+/// A single piece as sent to the client. Captured pieces keep their original
+/// type and color; their position is meaningless and omitted.
+/// </summary>
+public record ChessPieceDto(string Id, PieceType Type, PieceColor Color, int Row, int Col, bool HasMoved);
+
+/// <summary>
+/// The full board state pushed to clients. The same shape is returned by the
+/// state endpoint, the move endpoint, and every SignalR move broadcast, so the
+/// client always renders from one authoritative payload instead of re-fetching.
+/// </summary>
+public record GameStateDto(
+    Guid GameId,
+    string CurrentPlayer,
+    bool IsCheck,
+    bool IsCheckmate,
+    bool IsStalemate,
+    bool IsThreefoldRepetition,
+    string? EnPassantTarget,
+    bool WhiteCanCastleKingside,
+    bool WhiteCanCastleQueenside,
+    bool BlackCanCastleKingside,
+    bool BlackCanCastleQueenside,
+    IReadOnlyList<ChessPieceDto> Pieces,
+    IReadOnlyList<ChessPieceDto> CapturedPieces,
+    IReadOnlyList<string> MoveHistory,
+    // Moves in standard algebraic notation, for the move-list panel.
+    IReadOnlyList<string> SanHistory,
+    // Monotonic ply counter the client uses to drop stale or echoed updates.
+    int Version);
+
+public static class GameStateMapper
+{
+    public static GameStateDto ToDto(this GameState gameState) => new(
+        gameState.GameId,
+        gameState.CurrentPlayer.ToString(),
+        gameState.IsCheck,
+        gameState.IsCheckmate,
+        gameState.IsStalemate,
+        gameState.IsThreefoldRepetition,
+        gameState.EnPassantTarget?.ToString(),
+        gameState.WhiteCanCastleKingside,
+        gameState.WhiteCanCastleQueenside,
+        gameState.BlackCanCastleKingside,
+        gameState.BlackCanCastleQueenside,
+        gameState.Pieces
+            .Where(p => p.Position.Row >= 0)
+            .Select(p => new ChessPieceDto(p.Id, p.Type, p.Color, p.Position.Row, p.Position.Col, p.HasMoved))
+            .ToList(),
+        gameState.Pieces
+            .Where(p => p.Position.Row < 0)
+            .Select(p => new ChessPieceDto(p.Id, p.Type, p.Color, p.Position.Row, p.Position.Col, p.HasMoved))
+            .ToList(),
+        gameState.MoveHistory,
+        gameState.SanHistory,
+        gameState.MoveHistory.Count);
+}

JoshHeaps.Net/Models/LearnedWeightsSnapshot.cs

@@ -0,0 +1,9 @@
+namespace JoshHeaps.Net.Models;
+
+/// <summary>
+/// A copy of the learned engine's weights for display: midgame and endgame piece-square
+/// tables (one 64-entry array per piece, in canonical Pawn..King order, white-relative
+/// A1=0..H8=63) plus the feature weights (mobility N/B/R/Q, passed, isolated, doubled,
+/// king safety).
+/// </summary>
+public sealed record LearnedWeightsSnapshot(int[][] Mg, int[][] Eg, int[] Features);

JoshHeaps.Net/Models/MoveResultDto.cs

@@ -7,4 +7,5 @@ public class MoveResultDto
     public bool IsCheck { get; set; }
     public bool IsCheckmate { get; set; }
     public bool IsStalemate { get; set; }
+    public bool IsThreefoldRepetition { get; set; }
 }

JoshHeaps.Net/Pages/Blog.cshtml

@@ -0,0 +1,49 @@
+@page
+@model JoshHeaps.Net.Pages.BlogModel
+@{
+    ViewData["Title"] = "Blog - JoshHeaps.Net";
+    Layout = "_Layout";
+}
+
+<div class="blog-index">
+    <h1 class="blog-title">Blog</h1>
+
+    @if (Model.ActiveTag is not null)
+    {
+        <div class="blog-filter">
+            <span>Filtered by: <strong>@Model.ActiveTag</strong></span>
+            <a href="/blog">Clear filter</a>
+        </div>
+    }
+
+    @if (Model.Posts.Count == 0)
+    {
+        <p class="blog-empty">No posts yet. Check back soon!</p>
+    }
+
+    <div class="blog-list">
+        @foreach (var post in Model.Posts)
+        {
+            <article class="blog-card">
+                <a href="/blog/@post.Slug" class="blog-card-link">
+                    <h2 class="blog-card-title">@post.Title</h2>
+                </a>
+                <time class="blog-card-date" datetime="@post.PublishedDate.ToString("yyyy-MM-dd")">
+                    @post.PublishedDate.ToString("MMMM d, yyyy")
+                </time>
+                <p class="blog-card-summary">@post.Summary</p>
+                <div class="blog-card-tags">
+                    @foreach (var tag in post.Tags)
+                    {
+                        <a href="/blog?tag=@tag" class="blog-tag">@tag</a>
+                    }
+                </div>
+            </article>
+        }
+    </div>
+</div>
+
+@section Styles {
+    <link href="/css/variables.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
+    <link href="/css/blog/index.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
+}

JoshHeaps.Net/Pages/Blog.cshtml.cs

@@ -0,0 +1,26 @@
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace JoshHeaps.Net.Pages;
+
+public class BlogModel : PageModel
+{
+    private readonly IBlogService _blogService;
+
+    public List<BlogPost> Posts { get; set; } = [];
+    public string? ActiveTag { get; set; }
+
+    public BlogModel(IBlogService blogService)
+    {
+        _blogService = blogService;
+    }
+
+    public async Task OnGetAsync(string? tag)
+    {
+        ActiveTag = tag;
+        Posts = tag is not null
+            ? await _blogService.GetPostsByTagAsync(tag)
+            : await _blogService.GetAllPostsAsync();
+    }
+}

JoshHeaps.Net/Pages/Blog/Post.cshtml

@@ -0,0 +1,38 @@
+@page "/blog/{slug}"
+@model JoshHeaps.Net.Pages.Blog.PostModel
+@{
+    ViewData["Title"] = Model.Post!.Title + " - JoshHeaps.Net";
+    Layout = "_Layout";
+}
+
+<article class="blog-post">
+    <a href="/blog" class="blog-back">&larr; Back to blog</a>
+
+    <header class="blog-post-header">
+        <h1 class="blog-post-title">@Model.Post.Title</h1>
+        <time class="blog-post-date" datetime="@Model.Post.PublishedDate.ToString("yyyy-MM-dd")">
+            @Model.Post.PublishedDate.ToString("MMMM d, yyyy")
+        </time>
+        <div class="blog-post-tags">
+            @foreach (var tag in Model.Post.Tags)
+            {
+                <a href="/blog?tag=@tag" class="blog-tag">@tag</a>
+            }
+        </div>
+    </header>
+
+    <div class="post-content">
+        @Html.Raw(Model.Post.HtmlContent)
+    </div>
+</article>
+
+@section Styles {
+    <link href="/css/variables.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
+    <link href="/css/blog/post.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
+    <link href="/css/blog/prism-tomorrow.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
+}
+
+@section Scripts {
+    <script src="https://cdn.jsdelivr.net/npm/prismjs@1/components/prism-core.min.js"></script>
+    <script src="https://cdn.jsdelivr.net/npm/prismjs@1/plugins/autoloader/prism-autoloader.min.js"></script>
+}

JoshHeaps.Net/Pages/Blog/Post.cshtml.cs

@@ -0,0 +1,28 @@
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace JoshHeaps.Net.Pages.Blog;
+
+public class PostModel : PageModel
+{
+    private readonly IBlogService _blogService;
+
+    public BlogPost? Post { get; set; }
+
+    public PostModel(IBlogService blogService)
+    {
+        _blogService = blogService;
+    }
+
+    public async Task<IActionResult> OnGetAsync(string slug)
+    {
+        Post = await _blogService.GetPostBySlugAsync(slug);
+
+        if (Post is null)
+            return NotFound();
+
+        return Page();
+    }
+}

JoshHeaps.Net/Pages/Chess.cshtml

@@ -6,7 +6,14 @@
 }
 
 <div id="chessContainer">
-    <div id="boardContainer">
+    <section id="boardArea">
+        <div class="playerBar" id="topPlayerBar">
+            <span class="playerDot black"></span>
+            <span class="playerName">Opponent</span>
+            <div class="capturedTray" id="captured-top"></div>
+            <span class="advantage" id="advantage-top"></span>
+        </div>
+
         <div id="chessBoard">
             <!-- Placeholder squares -->
             @for (int i = 0; i < 64; i++)
@@ -14,16 +21,41 @@
                 <div id="square-@i" class="chessSquare @( (i + i / 8) % 2 == 0 ? "light" : "dark" )"></div>
             }
         </div>
-    </div>
 
-    <div id="textContainer" class="sideContent">
-        <h1>Chess</h1>
-        <p>Click a button to start a game :)</p>
-    </div>
+        <div class="playerBar" id="bottomPlayerBar">
+            <span class="playerDot white"></span>
+            <span class="playerName">You</span>
+            <div class="capturedTray" id="captured-bottom"></div>
+            <span class="advantage" id="advantage-bottom"></span>
+        </div>
+    </section>
 
-    <div id="buttonContainer" class="sideContent">
-        <button id="startGameBtn" onclick="startNewGame()">Start New Game</button>
-        <button id="startCPUGame" onclick="startCPUGame()">Vs CPU</button>
+    <aside id="gamePanel">
+        <header class="panelHeader">
+            <span class="panelLogo">&#9822;</span>
+            <h1>Chess</h1>
+            <button id="menuClose" class="iconBtn" aria-label="Close menu" onclick="closeMenu()">&times;</button>
+        </header>
+
+        <div id="moveList">
+            <p class="movePlaceholder">Moves will appear here once a game begins.</p>
+        </div>
+
+        <div id="statusLine">Start a game to play.</div>
+
+        <div id="panelButtons">
+            <button id="startGameBtn" class="btn btn-primary" onclick="startNewGame()">New Game</button>
+            <button id="startCPUGame" class="btn btn-secondary" onclick="startCPUGame()">Play vs CPU</button>
+            <button id="copyPgnBtn" class="btn btn-ghost" onclick="copyPgn()" style="display: none">Copy PGN</button>
+            <a id="watchLink" href="/watch">Watch other games &rarr;</a>
+        </div>
+    </aside>
+
+    <div id="menuBackdrop" onclick="closeMenu()"></div>
+
+    <div id="mobileBar">
+        <span id="mobileStatus">Start a game to play.</span>
+        <button id="menuToggle" class="btn btn-primary" onclick="toggleMenu()">Menu</button>
     </div>
 </div>
 
@@ -57,19 +89,31 @@
     </div>
 </div>
 
+<div id="colorModal" style="display: none;">
+    <p>Play as:</p>
+    <div id="colorButtonContainer">
+        <button onclick="selectColor('white')">White</button>
+        <button onclick="selectColor('black')">Black</button>
+        <button onclick="selectColor('random')">Random</button>
+    </div>
+</div>
+
 @section Scripts {
     <script src="~/js/signalr/signalr.min.js"></script>
-    <script src="~/js/ChessScripts/GameState.js"></script>
-    <script src="~/js/ChessScripts/ChessUtils.js"></script>
-    <script src="~/js/ChessScripts/ChessAPI.js"></script>
-    <script src="~/js/ChessScripts/ChessSignalR.js"></script>
-    <script src="~/js/ChessScripts/ChessInteractions.js"></script>
-    <script src="~/js/ChessScripts/ChessBoard.js"></script>
-    <script src="~/js/ChessScripts/ChessModals.js"></script>
-    <script src="~/js/ChessScripts/chessMain.js"></script>
+    <script src="~/js/ChessScripts/GameState.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/ChessScripts/ChessUtils.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/ChessScripts/ChessAPI.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/ChessScripts/ChessSignalR.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/ChessScripts/ChessInteractions.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/ChessScripts/ChessBoard.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/ChessScripts/ChessModals.js?v=@ViewData["cssVersion"]"></script>
+    <script src="~/js/ChessScripts/chessMain.js?v=@ViewData["cssVersion"]"></script>
 }
 
 @section Styles {
+    <link rel="preconnect" href="https://fonts.googleapis.com" />
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
+    <link href="https://fonts.googleapis.com/css2?family=Outfit:wght@400;500;600;700;800&display=swap" rel="stylesheet" />
     <link rel="stylesheet" href="~/css/chess/game.css?v=@ViewData["cssVersion"]" />
     <link rel="stylesheet" href="~/css/chess/site.css?v=@ViewData["cssVersion"]" />
 }

JoshHeaps.Net/Pages/Echo.cshtml

@@ -0,0 +1,70 @@
+@page
+@model JoshHeaps.Net.Pages.EchoModel
+@{
+    Layout = "_Layout";
+    ViewData["Title"] = "Echo";
+}
+
+<div id="echoHeader">
+    <h1>Echo</h1>
+    <p class="echo-blurb">
+        Two devices measure the distance between them by chirping at each other and timing the answer.
+        Each one records continuously and only ever compares arrivals inside its own recording, so no
+        clock synchronisation is needed and the unknown audio latency cancels out.
+    </p>
+    <p class="echo-privacy">Only sample numbers leave your device. The recording never does.</p>
+</div>
+
+<div id="echoControls">
+    <label>Room <input id="echoRoom" type="text" maxlength="6" autocomplete="off" spellcheck="false" /></label>
+    <label>Name <input id="echoName" type="text" maxlength="16" placeholder="this device" autocomplete="off" /></label>
+    <label>
+        Speaker to mic (m)
+        <input id="echoEpsilon" type="number" min="0" max="0.5" step="0.01" />
+    </label>
+    <button id="echoJoin">Join and listen</button>
+    <button id="echoLeave" hidden>Leave</button>
+</div>
+
+<p id="echoStatus" class="echo-status">Pick a room, then open the same room on a second device.</p>
+<p class="echo-share">Join link: <a id="echoShareLink" href="#"></a></p>
+<div id="echoWarnings"></div>
+
+<div id="echoReadout" class="echo-readout"><span class="echo-readout-idle">not measuring</span></div>
+
+<div id="echoPanels">
+    <section class="echo-panel">
+        <h2>Devices</h2>
+        <ul id="echoRoster"></ul>
+    </section>
+    <section class="echo-panel">
+        <h2>Ranges</h2>
+        <div id="echoPairs"></div>
+    </section>
+    <section class="echo-panel">
+        <h2>Timing</h2>
+        <p class="echo-hint">How far each chirp landed from its slot. Steady means the arrivals are being matched to the right devices.</p>
+        <div id="echoDiagnostics"></div>
+    </section>
+</div>
+
+<section class="echo-panel echo-panel-wide">
+    <h2>Matched filter</h2>
+    <p class="echo-hint">Each spike is a chirp arriving. The bright one is this device hearing itself.</p>
+    <canvas id="echoTrace"></canvas>
+</section>
+
+<a class="echo-back" href="/">&larr; Back</a>
+
+@section Scripts {
+    <script src="~/js/signalr/signalr.min.js"></script>
+    <script src="~/js/EchoScripts/EchoDsp.js"></script>
+    <script src="~/js/EchoScripts/EchoAudio.js"></script>
+    <script src="~/js/EchoScripts/EchoSession.js"></script>
+    <script src="~/js/EchoScripts/echoMain.js"></script>
+}
+
+@section Styles {
+    <link rel="stylesheet" href="~/css/variables.css?v=@ViewData["cssVersion"]" />
+    <link rel="stylesheet" href="~/css/echo/echo.css?v=@ViewData["cssVersion"]" />
+}

JoshHeaps.Net/Pages/Echo.cshtml.cs

@@ -0,0 +1,11 @@
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace JoshHeaps.Net.Pages
+{
+    public class EchoModel : PageModel
+    {
+        public void OnGet()
+        {
+        }
+    }
+}

JoshHeaps.Net/Pages/Index.cshtml

@@ -1,115 +1,116 @@
-@page
+@page
 @model JoshHeaps.Net.Pages.IndexModel
 @{
     ViewData["Title"] = "JoshHeaps.Net";
     Layout = "_Layout";
 }
 
-<header id="Header">
-    <a class="headerOption" onclick="showClickedContents('projects')">./ Projects</a>
-    <a class="headerOption" onclick="showClickedContents('demos')">./ Demos</a>
-    <a class="headerOption" onclick="showClickedContents('contact')">./ Contact me</a>
-</header>
-
-<div id="WelcomeMessage"></div>
-
-<div id="ProjectsBox">
-    <div id="ChessProject" class="projectContainer">
-        <div class="displayBox diagonal-section-left">
-            <a target="_blank" href="https://github.com/JoshHeaps/JoshHeaps.Net/blob/master/JoshHeaps.Net/Pages/Chess.cshtml">
-                <img id="ChessImage" class="projectImage projectImageLeft" src="/images/Chess.jpg" title="Chessboard"/>
-            </a>
-        </div>
-        <div id="ChessText" class="projectTextRight">
-            <h2 id="ChessTitle" class="projectHeaderRight projectHeader">Chess</h2>
-            <p id="ChessDescription" class="projectDescriptionRight projectDescription">
-                As someone who loves chess, I wanted to create a chess game that I could play with my friends and family. It was made using .NET razor pages, a .NET web api backend, and a good amount of javascript on the frontend. Feel free to check it out in the demos below :)
-            </p>
-        </div>
+<nav id="Header">
+    <span class="site-name">josh heaps</span>
+    <div class="nav-links">
+        <a class="nav-link" onclick="showClickedContents('projects')">Projects</a>
+        <a class="nav-link" onclick="showClickedContents('demos')">Demos</a>
+        <a class="nav-link" onclick="showClickedContents('blog')">Blog</a>
+        <a class="nav-link" onclick="showClickedContents('contact')">Contact</a>
     </div>
+</nav>
 
-    <div id="CompilerProject" class="projectContainer">
-        <div id="CompilerText" class="projectTextLeft">
-            <h2 id="CompilerTitle" class="projectHeaderLeft projectHeader">Compiler</h2>
-            <p id="CompilerDescription" class="projectDescriptionLeft projectDescription">
-                I love solving problems, and figuring out how things work. What better way to do both than writing a compiler myself? This project is a compiler that I wrote in C# on .NET 8.0. It takes in a simple language that I created, outputs the corresponding common intermediate language (CIL), and executes it. I plan to add more features in the future.
-            </p>
-        </div>
-        <div class="displayBox diagonal-section-right">
-            <a target="_blank" href="https://github.com/JoshHeaps/CILCompiler">
-                <img id="CompilerImage" class="projectImage projectImageRight" src="/images/CompilerDemo.png" title="Compiler Input and Output"/>
+<section id="Hero">
+    <div id="WelcomeMessage"></div>
+</section>
+
+<section id="ProjectsBox">
+    <h2 class="section-title">Projects</h2>
+    <div class="projects-grid">
+        <article class="project-card">
+            <a href="https://github.com/JoshHeaps/JoshHeaps.Net/blob/master/JoshHeaps.Net/Pages/Chess.cshtml" target="_blank" class="project-image-link">
+                <img class="projectImage" src="/images/Chess.jpg" alt="Chessboard" />
             </a>
-        </div>
-    </div>
+            <div class="project-info">
+                <h3 class="project-title">Chess</h3>
+                <p class="project-description">As someone who loves chess, I wanted to create a chess game that I could play with my friends and family. It was made using .NET razor pages, a .NET web api backend, and a good amount of javascript on the frontend. Feel free to check it out in the demos below :)</p>
+                <a class="project-link" href="https://github.com/JoshHeaps/JoshHeaps.Net/blob/master/JoshHeaps.Net/Pages/Chess.cshtml" target="_blank">View on GitHub &rarr;</a>
+            </div>
+        </article>
 
-    <div id="CloudStorageProject" class="projectContainer">
-        <div class="displayBox diagonal-section-left">
-            <a target="_blank" href="https://media.joshheaps.net">
-                <img id="CloudStorageImage" class="projectImage projectImageLeft" src="/images/CloudStorageDemo.png" title="CloudStorageScreenshot" />
+        <article class="project-card">
+            <a href="https://github.com/JoshHeaps/CILCompiler" target="_blank" class="project-image-link">
+                <img class="projectImage" src="/images/CompilerDemo.png" alt="Compiler Input and Output" />
             </a>
-        </div>
-        <div id="CloudStorageText" class="projectTextRight">
-            <h2 id="CloudStorageTitle" class="projectHeaderRight projectHeader">Image Cloud Storage</h2>
-            <p id="CloudStorageDescription" class="projectDescriptionRight projectDescription">
-                My wife and I LOVE to take pictures and videos of our kids, but we do not like paying for extra cloud storage. I made this for my family so we can upload pictures to my server, share them with each other, and now we don't need to worry about how much space we're using.
-            </p>
-        </div>
-    </div>
-</div>
+            <div class="project-info">
+                <h3 class="project-title">Compiler</h3>
+                <p class="project-description">I love solving problems, and figuring out how things work. What better way to do both than writing a compiler myself? This project is a compiler that I wrote in C# on .NET 8.0. It takes in a simple language that I created, outputs the corresponding common intermediate language (CIL), and executes it. I plan to add more features in the future.</p>
+                <a class="project-link" href="https://github.com/JoshHeaps/CILCompiler" target="_blank">View on GitHub &rarr;</a>
+            </div>
+        </article>
 
-<div id="DemosBox" class="displayBox">
-    <h2 id="DemoHeader">Demos</h2>
+        <article class="project-card">
+            <a href="https://media.joshheaps.net" target="_blank" class="project-image-link">
+                <img class="projectImage" src="/images/CloudStorageDemo.png" alt="Cloud Storage Screenshot" />
+            </a>
+            <div class="project-info">
+                <h3 class="project-title">Image Cloud Storage</h3>
+                <p class="project-description">My wife and I LOVE to take pictures and videos of our kids, but we do not like paying for extra cloud storage. I made this for my family so we can upload pictures to my server, share them with each other, and now we don't need to worry about how much space we're using.</p>
+                <a class="project-link" href="https://media.joshheaps.net" target="_blank">View Live Demo &rarr;</a>
+            </div>
+        </article>
+    </div>
+</section>
+
+<section id="DemosBox">
+    <h2 class="section-title">Demos</h2>
     <div id="buttonWrapper">
-        <button id="ChessDemo" class="demoButton" onclick="window.location.href='/chess'">
-            Play Chess
-        </button>
-        <button id="ParticleDemo" class="demoButton" onclick="window.location.href='/particles'">
-            Particle Simulator
-        </button>
-        <button id="MemoryLane" class="demoButton" onclick="window.location.href='/memorylane'">
-            Memory Lane
-        </button>
-        <button id="CloadStorageDemo" class="demoButton" onclick="window.location.href='https://media.joshheaps.net'">
-            Cloud Image Storage
-        </button>
-        <button id="MoreFiller" class="demoButton">
-            More coming soon...
-        </button>
+        <button class="demoButton" onclick="window.location.href='/chess'">Play Chess</button>
+        <button class="demoButton" onclick="window.location.href='/watch'">Watch Live Chess</button>
+        <button class="demoButton" onclick="window.location.href='/particles'">Particle Simulator</button>
+        <button class="demoButton" onclick="window.location.href='/memorylane'">Memory Lane</button>
+        <button class="demoButton" onclick="window.location.href='https://media.joshheaps.net'">Cloud Image Storage</button>
+        <button id="MoreFiller" class="demoButton">More coming soon...</button>
     </div>
-</div>
+</section>
+
+<section id="BlogBox">
+    <h2 class="section-title">Latest Posts</h2>
+    <div id="blogPostsList">
+        @foreach (var post in Model.LatestPosts)
+        {
+            <div class="blog-teaser-item">
+                <a class="blog-teaser-title" href="/blog/@post.Slug">@post.Title</a>
+                <span class="blog-teaser-date">@post.PublishedDate.ToString("MMMM d, yyyy")</span>
+                <p class="blog-teaser-summary">@post.Summary</p>
+            </div>
+        }
+    </div>
+    <a class="blog-view-all" href="/blog">View all posts &rarr;</a>
+</section>
 
 <footer id="Contacts">
-    <svg viewBox="0 0 16 16" class="social-icon">
-        <a id="GithubLink" class="social-link" href="https://github.com/JoshHeaps" target="_blank">
+    <a class="social-link" href="https://github.com/JoshHeaps" target="_blank">
+        <svg viewBox="0 0 16 16" class="social-icon">
             <path d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0016 8c0-4.42-3.58-8-8-8z"></path>
-            <rect width="100%" height="100%" fill="transparent" />
-        </a>
-    </svg>
-
-    <svg viewBox="0 0 24 24" class="social-icon">
-        <a id="LinkedinLink" class="social-link" href="https://www.linkedin.com/in/josh-heaps/" target="_blank">
+        </svg>
+    </a>
+    <a class="social-link" href="https://www.linkedin.com/in/josh-heaps/" target="_blank">
+        <svg viewBox="0 0 24 24" class="social-icon">
             <path d="M20.5 2h-17A1.5 1.5 0 002 3.5v17A1.5 1.5 0 003.5 22h17a1.5 1.5 0 001.5-1.5v-17A1.5 1.5 0 0020.5 2zM8 19H5v-9h3zM6.5 8.25A1.75 1.75 0 118.3 6.5a1.78 1.78 0 01-1.8 1.75zM19 19h-3v-4.74c0-1.42-.6-1.93-1.38-1.93A1.74 1.74 0 0013 14.19a.66.66 0 000 .14V19h-3v-9h2.9v1.3a3.11 3.11 0 012.7-1.4c1.55 0 3.36.86 3.36 3.66z"></path>
-            <rect width="100%" height="100%" fill="transparent" />
-        </a>
-    </svg>
-
-    <svg viewBox="0 -4 31 31" class="social-icon" preserveAspectRatio="none">
-        <a id="GmailLink" class="social-link" href="mailto:[email protected]">
+        </svg>
+    </a>
+    <a class="social-link" href="mailto:[email protected]">
+        <svg viewBox="0 -4 31 31" class="social-icon" preserveAspectRatio="none">
             <path d="m0 3.23863636v2.72727273l3.12784091 3.02727273 3.69034091 2.08636368.68181818-4.59034095-.68181818-4.27329546-1.90909091-1.43181818c-2.02329546-1.51704546-4.90909091-.07329545-4.90909091 2.45454545"/>
             <path d="m23.1818182 2.21590909-.6818182 4.32954546.6818182 4.53409095 3.3494318-1.65852277 3.46875-3.45511364v-2.72727273c0-2.5278409-2.8857955-3.97159091-4.9090909-2.45454545z"/>
             <path d="m2.04545455 22.6704545h4.77272727v-11.590909l-6.81818182-5.11363641v14.65909091c0 1.1301136.91534091 2.0454545 2.04545455 2.0454545"/>
             <path d="m23.1818182 22.6704545h4.7727273c1.1301136 0 2.0454545-.9153409 2.0454545-2.0454545v-14.65909091l-6.8181818 5.11363641z"/>
             <path d="m15 8.35227273-8.18181818-6.13636364v8.86363641l8.18181818 6.1363636 8.1818182-6.1363636v-8.86363641z"/>
-            <rect width="100%" height="100%" fill="transparent" />
-        </a>
-    </svg>
+        </svg>
+    </a>
 </footer>
 
 @section Styles {
+    <link href="/css/variables.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
     <link href="/css/home/site.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
     <link href="/css/home/project.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
-    <link href="/css/home/imageLeftProject.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
-    <link href="/css/home/imageRightProject.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
+    <link href="/css/home/blog.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
     <link href="/css/home/footer.css?v=@ViewData["cssVersion"]" rel="stylesheet" type="text/css" />
 }
 

JoshHeaps.Net/Pages/Index.cshtml.cs

@@ -1,12 +1,17 @@
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
 using Microsoft.AspNetCore.Mvc.RazorPages;
 
 namespace JoshHeaps.Net.Pages
 {
-    public class IndexModel() : PageModel
+    public class IndexModel(IBlogService blogService) : PageModel
     {
-        public void OnGet()
-        {
+        public List<BlogPost> LatestPosts { get; set; } = [];
 
+        public async Task OnGetAsync()
+        {
+            var allPosts = await blogService.GetAllPostsAsync();
+            LatestPosts = allPosts.Take(3).ToList();
         }
     }
 }

JoshHeaps.Net/Pages/Watch.cshtml

@@ -0,0 +1,61 @@
+@page
+@model JoshHeaps.Net.Pages.WatchModel
+@{
+    Layout = "_Layout";
+    ViewData["Title"] = "Watch Chess";
+}
+
+<div id="watchHeader">
+    <h1>Live Chess</h1>
+    <p id="watchStatus">Loading games…</p>
+    <div id="watchControls">
+        <fieldset class="enginePicker">
+            <legend>White</legend>
+            <select id="whiteEngine">
+                <option value="custom">Custom (v1)</option>
+                <option value="customLearned" selected>Custom (Learned)</option>
+                <option value="stockfish">Stockfish</option>
+            </select>
+            <select id="whiteSkill">
+                @for (int i = 1; i <= 20; i++)
+                {
+                    <option value="@i" @(i == 4 ? "selected" : "")>@i</option>
+                }
+            </select>
+        </fieldset>
+        <fieldset class="enginePicker">
+            <legend>Black</legend>
+            <select id="blackEngine">
+                <option value="custom" selected>Custom (v1)</option>
+                <option value="customLearned">Custom (Learned)</option>
+                <option value="stockfish">Stockfish</option>
+            </select>
+            <select id="blackSkill">
+                @for (int i = 1; i <= 20; i++)
+                {
+                    <option value="@i" @(i == 4 ? "selected" : "")>@i</option>
+                }
+            </select>
+        </fieldset>
+        <button id="startCpuVsCpu" onclick="Spectate.startCpuGame()">Watch CPU vs CPU</button>
+        <fieldset class="enginePicker">
+            <legend>Auto-train games</legend>
+            <input id="autoTrainCount" type="number" min="0" max="16" step="1" />
+            <button id="applyAutoTrain" onclick="Spectate.setAutoTrainCount()">Apply</button>
+        </fieldset>
+    </div>
+    <a id="backToPlay" href="/chess">← Play a game</a>
+    <a id="viewWeights" href="/weights">View learned weights →</a>
+</div>
+
+<div id="gamesFeed"></div>
+
+@section Scripts {
+    <script src="~/js/signalr/signalr.min.js"></script>
+    <script src="~/js/ChessScripts/Spectate.js"></script>
+}
+
+@section Styles {
+    <link rel="stylesheet" href="~/css/chess/game.css?v=@ViewData["cssVersion"]" />
+    <link rel="stylesheet" href="~/css/chess/spectate.css?v=@ViewData["cssVersion"]" />
+}

JoshHeaps.Net/Pages/Watch.cshtml.cs

@@ -0,0 +1,11 @@
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace JoshHeaps.Net.Pages
+{
+    public class WatchModel : PageModel
+    {
+        public void OnGet()
+        {
+        }
+    }
+}

JoshHeaps.Net/Pages/Weights.cshtml

@@ -0,0 +1,44 @@
+@page
+@model JoshHeaps.Net.Pages.WeightsModel
+@{
+    Layout = "_Layout";
+    ViewData["Title"] = "Learned Weights";
+}
+
+<div id="weightsHeader">
+    <h1>Learned Piece-Square Weights</h1>
+    <p id="weightsStatus">Where the learned engine thinks each piece belongs.</p>
+    <div id="weightsControls">
+        <div class="heatLegend">
+            <span>low</span>
+            <span class="legendBar"></span>
+            <span>high</span>
+        </div>
+        <button id="refreshWeights" onclick="Weights.refresh()">Refresh</button>
+    </div>
+    <a id="backToWatch" href="/watch">← Watch / train</a>
+</div>
+
+<section class="weightsSection">
+    <h2>Feature weights</h2>
+    <p class="sectionHint">Learned value of each contextual feature (per normalized unit). Mobility is per piece type; passed pawns are endgame-weighted, king safety midgame-weighted.</p>
+    <div id="featureWeights" class="featurePanel"></div>
+</section>
+
+<section class="weightsSection">
+    <h2>Midgame tables</h2>
+    <div id="weightsGridMg" class="weightsGrid"></div>
+</section>
+
+<section class="weightsSection">
+    <h2>Endgame tables</h2>
+    <div id="weightsGridEg" class="weightsGrid"></div>
+</section>
+
+@section Scripts {
+    <script src="~/js/ChessScripts/Weights.js"></script>
+}
+
+@section Styles {
+    <link rel="stylesheet" href="~/css/chess/weights.css?v=@ViewData["cssVersion"]" />
+}

JoshHeaps.Net/Pages/Weights.cshtml.cs

@@ -0,0 +1,11 @@
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace JoshHeaps.Net.Pages
+{
+    public class WeightsModel : PageModel
+    {
+        public void OnGet()
+        {
+        }
+    }
+}

JoshHeaps.Net/Pages/_Layout.cshtml

@@ -1,6 +1,6 @@
 @{
     Layout = null;
-    ViewData["cssVersion"] = "1.0.2"; // <--- change this once to bust cache
+    ViewData["cssVersion"] = "1.0.7"; // <--- change this once to bust cache
 }
 
 <!DOCTYPE html>

JoshHeaps.Net/Program.cs

@@ -1,6 +1,7 @@
 using JoshHeaps.Net.Hubs;
 using JoshHeaps.Net.Services.Implementations;
 using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.Extensions.Options;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -12,12 +13,40 @@ builder.Services.AddControllers();
 
 builder.Services.AddSignalR();
 
+builder.Services.AddHttpClient("BlogApi", client =>
+{
+    var baseUrl = configuration["BlogApi:BaseUrl"] ?? "https://media.joshheaps.net";
+    client.BaseAddress = new Uri(baseUrl);
+    client.Timeout = TimeSpan.FromSeconds(10);
+});
+builder.Services.AddSingleton<IBlogService, BlogService>();
 builder.Services.AddSingleton<IChessService, ChessService>();
 builder.Services.AddSingleton<IBackgroundTaskQueue, BackgroundTaskQueue>();
 
+builder.Services.Configure<ChessEngineOptions>(configuration.GetSection(ChessEngineOptions.SectionName));
+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>();
+builder.Services.AddSingleton<AutoTrainingSettings>();
+
+builder.Services.Configure<EchoRoundSettings>(configuration.GetSection(EchoRoundSettings.SectionName));
+builder.Services.AddSingleton(provider =>
+    provider.GetRequiredService<IOptions<EchoRoundSettings>>().Value);
+builder.Services.AddSingleton<IEchoRoomStore, EchoRoomStore>();
+builder.Services.AddHostedService<EchoRoundService>();
+
 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.
@@ -50,4 +79,6 @@ app.MapControllers();
 
 app.MapHub<ChessHub>("/chessHub");
 
+app.MapHub<EchoHub>("/echoHub");
+
 app.Run();

JoshHeaps.Net/Properties/launchSettings.json

@@ -11,6 +11,7 @@
     "profiles": {
         "http": {
             "commandName": "Project",
+            "nativeDebugging": true,
             "dotnetRunMessages": true,
             "launchBrowser": true,
             "applicationUrl": "http://localhost:5200",
@@ -20,6 +21,7 @@
         },
         "https": {
             "commandName": "Project",
+            "nativeDebugging": true,
             "dotnetRunMessages": true,
             "launchBrowser": true,
             "applicationUrl": "https://localhost:7118;http://localhost:5200",

JoshHeaps.Net/Services/Implementations/AutoTrainingService.cs

@@ -0,0 +1,73 @@
+using JoshHeaps.Net.Services.Interfaces;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// Continuously trains the learned engine in the background by keeping a configurable number of
+/// self-play games running — the learned engine (skill 6) against Stockfish (skill 20), alternating
+/// which color Stockfish takes so the model trains on both. The target count is read live from
+/// <see cref="AutoTrainingSettings"/> (adjustable from the website): when a game finishes another
+/// starts to refill the pool, raising the count starts more, and lowering it lets the surplus drain
+/// as games finish (0 pauses training). Registered only outside Development and gated by the
+/// ChessEngine:AutoTrain config flag.
+/// </summary>
+public sealed class AutoTrainingService(
+    ISelfPlayCoordinator coordinator,
+    AutoTrainingSettings settings,
+    ILogger<AutoTrainingService> logger) : BackgroundService
+{
+    private const int LearnedSkill = 6;
+    private const int StockfishSkill = 20;
+    private static readonly TimeSpan _restartBackoff = TimeSpan.FromSeconds(5);
+    private static readonly TimeSpan _pollInterval = TimeSpan.FromSeconds(2);
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        var running = new List<Task>();
+        int started = 0;
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            running.RemoveAll(t => t.IsCompleted);
+
+            int desired = settings.GameCount;
+            bool startFailed = false;
+
+            while (running.Count < desired && !stoppingToken.IsCancellationRequested)
+            {
+                // Alternate Stockfish's color so the learned engine trains as both white and black.
+                var config = started++ % 2 == 0
+                    ? new SelfPlayConfig(ChessEngineKind.CustomLearned, LearnedSkill, ChessEngineKind.Stockfish, StockfishSkill)
+                    : new SelfPlayConfig(ChessEngineKind.Stockfish, StockfishSkill, ChessEngineKind.CustomLearned, LearnedSkill);
+
+                try
+                {
+                    var (_, completion) = coordinator.StartGame(config, stoppingToken);
+                    running.Add(completion);
+                }
+                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, "Failed to start an auto-training game; retrying after backoff.");
+                    startFailed = true;
+                    break;
+                }
+            }
+
+            try
+            {
+                if (startFailed)
+                    await Task.Delay(_restartBackoff, stoppingToken);
+                else if (running.Count > 0)
+                    // Wake when any game finishes (to refill) or after a short poll (to pick up a
+                    // count increase promptly).
+                    await Task.WhenAny(Task.WhenAny(running), Task.Delay(_pollInterval, stoppingToken));
+                else
+                    // Pool is empty (count is 0) — just poll for the count to change.
+                    await Task.Delay(_pollInterval, stoppingToken);
+            }
+            catch (OperationCanceledException) { break; }
+        }
+    }
+}

JoshHeaps.Net/Services/Implementations/AutoTrainingSettings.cs

@@ -0,0 +1,31 @@
+using Microsoft.Extensions.Options;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// Runtime-adjustable auto-training settings. Singleton so the value set from the website (via the
+/// chess controller) is seen live by the background <see cref="AutoTrainingService"/>. Seeded from
+/// <see cref="ChessEngineOptions.AutoTrainGameCount"/> and clamped to a sane range.
+/// </summary>
+public sealed class AutoTrainingSettings
+{
+    /// <summary>Upper bound on concurrent auto-training games (each spawns a Stockfish + a learned engine).</summary>
+    public const int MaxGames = 16;
+
+    private int _gameCount;
+
+    public AutoTrainingSettings(IOptions<ChessEngineOptions> options)
+        => _gameCount = Clamp(options.Value.AutoTrainGameCount);
+
+    /// <summary>
+    /// Number of auto-training games to keep running concurrently. 0 pauses auto-training.
+    /// Reads/writes are atomic; the background service reads this every cycle.
+    /// </summary>
+    public int GameCount
+    {
+        get => Volatile.Read(ref _gameCount);
+        set => Volatile.Write(ref _gameCount, Clamp(value));
+    }
+
+    private static int Clamp(int n) => Math.Clamp(n, 0, MaxGames);
+}

JoshHeaps.Net/Services/Implementations/BlogService.cs

@@ -0,0 +1,94 @@
+using System.Collections.Concurrent;
+using System.Text.Json;
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+public class BlogService : IBlogService
+{
+    private readonly HttpClient _httpClient;
+    private readonly ILogger<BlogService> _logger;
+    private readonly TimeSpan _cacheTtl = TimeSpan.FromMinutes(5);
+
+    private readonly ConcurrentDictionary<string, CacheEntry> _cache = new();
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNameCaseInsensitive = true
+    };
+
+    public BlogService(IHttpClientFactory httpClientFactory, ILogger<BlogService> logger)
+    {
+        _httpClient = httpClientFactory.CreateClient("BlogApi");
+        _logger = logger;
+    }
+
+    public async Task<List<BlogPost>> GetAllPostsAsync()
+    {
+        return await GetCachedAsync("all_posts",
+            () => FetchAsync<List<BlogPost>>("api/blog/posts")) ?? [];
+    }
+
+    public async Task<BlogPost?> GetPostBySlugAsync(string slug)
+    {
+        return await GetCachedAsync($"post_{slug}",
+            () => FetchAsync<BlogPost>($"api/blog/posts/{Uri.EscapeDataString(slug)}"));
+    }
+
+    public async Task<List<BlogPost>> GetPostsByTagAsync(string tag)
+    {
+        return await GetCachedAsync($"tag_{tag}",
+            () => FetchAsync<List<BlogPost>>($"api/blog/posts/tags/{Uri.EscapeDataString(tag)}")) ?? [];
+    }
+
+    private async Task<T?> FetchAsync<T>(string path) where T : class
+    {
+        try
+        {
+            var response = await _httpClient.GetAsync(path);
+            if (!response.IsSuccessStatusCode)
+            {
+                _logger.LogWarning("Blog API returned {StatusCode} for {Path}", response.StatusCode, path);
+                return null;
+            }
+
+            var json = await response.Content.ReadAsStringAsync();
+            return JsonSerializer.Deserialize<T>(json, JsonOptions);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to fetch from blog API: {Path}", path);
+            return null;
+        }
+    }
+
+    private async Task<T?> GetCachedAsync<T>(string key, Func<Task<T?>> factory) where T : class
+    {
+        if (_cache.TryGetValue(key, out var entry) && entry.ExpiresAt > DateTime.UtcNow)
+            return (T?)entry.Value;
+
+        var result = await factory();
+
+        if (result is not null)
+        {
+            _cache[key] = new CacheEntry(result, DateTime.UtcNow.Add(_cacheTtl));
+        }
+        else if (entry is not null)
+        {
+            // API unreachable — serve stale cache
+            _logger.LogWarning("Serving stale cache for key {Key}", key);
+            return (T?)entry.Value;
+        }
+
+        return result;
+    }
+
+    public void ClearCache()
+    {
+        _cache.Clear();
+        _logger.LogInformation("Blog cache cleared");
+    }
+
+    private record CacheEntry(object Value, DateTime ExpiresAt);
+}

JoshHeaps.Net/Services/Implementations/ChessEngineFactory.cs

@@ -0,0 +1,64 @@
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.Extensions.Options;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>The available chess engine implementations.</summary>
+public enum ChessEngineKind
+{
+    Stockfish,
+    Custom,
+
+    /// <summary>The custom engine with the reinforcement-learned piece-square evaluation.</summary>
+    CustomLearned
+}
+
+/// <summary>Configuration selecting which <see cref="IChessEngine"/> to use.</summary>
+public sealed class ChessEngineOptions
+{
+    public const string SectionName = "ChessEngine";
+
+    public ChessEngineKind Engine { get; set; } = ChessEngineKind.Stockfish;
+
+    /// <summary>
+    /// Absolute path to the learned-weights file. Leave null to default to
+    /// <c>{ContentRoot}/chess-data/learned-weights.txt</c> (fine for local dev). In
+    /// production set this to a stable, service-writable location OUTSIDE the deploy
+    /// directory (e.g. <c>/var/lib/joshheaps/chess-data/learned-weights.txt</c>) so the
+    /// trained weights survive deploys and avoid deploy-user vs service-user permission
+    /// 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>
+    /// How many auto-training games run concurrently (when <see cref="AutoTrain"/> is on). This is
+    /// the starting value; it can be changed at runtime from the website. Override the default via
+    /// the <c>ChessEngine__AutoTrainGameCount</c> environment variable.
+    /// </summary>
+    public int AutoTrainGameCount { get; set; } = 2;
+}
+
+/// <summary>Creates the configured <see cref="IChessEngine"/> per game.</summary>
+public sealed class ChessEngineFactory(
+    IOptions<ChessEngineOptions> options,
+    ILearnedWeightsStore weightsStore) : IChessEngineFactory
+{
+    private readonly ChessEngineKind _kind = options.Value.Engine;
+
+    public IChessEngine Create(int skill) => Create(skill, _kind);
+
+    public IChessEngine Create(int skill, ChessEngineKind kind) => kind switch
+    {
+        ChessEngineKind.Custom => new CustomChessEngine(skill),
+        ChessEngineKind.CustomLearned => new CustomChessEngine(skill, EngineVariant.Learned, weightsStore.WeightsFilePath),
+        ChessEngineKind.Stockfish => new Stockfish(skill),
+        _ => throw new InvalidOperationException($"Unknown chess engine '{kind}'.")
+    };
+}

JoshHeaps.Net/Services/Implementations/ChessEngineHelpers.cs

@@ -0,0 +1,153 @@
+using JoshHeaps.Net.Models;
+using System.Text;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+public static class ChessEngineHelpers
+{
+    public static MoveDto ToMoveDto(
+        this string uci,
+        GameState gameState,
+        Guid playerId)
+    {
+        int fCol = uci[0] - 'a', fRow = 7 - (uci[1] - '1');
+        int tCol = uci[2] - 'a', tRow = 7 - (uci[3] - '1');
+
+        var piece = gameState.Board[fRow, fCol]
+                    ?? throw new Exception("No piece at source square");
+
+        PieceType? promo = uci.Length == 5 ? uci[4] switch
+        {
+            'q' => PieceType.Queen,
+            'r' => PieceType.Rook,
+            'b' => PieceType.Bishop,
+            'n' => PieceType.Knight,
+            _ => null
+        } : null;
+
+        return new MoveDto
+        {
+            GameId = gameState.GameId,
+            PlayerId = playerId,
+            PieceId = piece.Id,
+            TargetRow = tRow,
+            TargetCol = tCol,
+            PromotionChoice = promo,
+            SourceCol = fCol,
+            SourceRow = fRow,
+        };
+    }
+
+    /// <summary>
+    /// Convert a 2-D board array (rank 8 = row 0, file a = col 0) to a FEN string.
+    /// Only piece placement + active colour + castling are computed; the rest use
+    /// safe defaults (-, 0, 1).  That is all the engine needs.
+    /// </summary>
+    public static string ToFen(this GameState gs)
+    {
+        var sb = new StringBuilder(64);
+
+        /* 1) piece placement */
+        for (int row = 0; row < 8; row++)
+        {
+            int empty = 0;
+
+            for (int col = 0; col < 8; col++)
+            {
+                var p = gs.Board[row, col];
+
+                if (p is null)
+                {
+                    empty++;
+                }
+                else
+                {
+                    if (empty > 0) { sb.Append(empty); empty = 0; }
+                    sb.Append(ToFenChar(p));                 // ← unchanged helper
+                }
+            }
+
+            if (empty > 0) sb.Append(empty);
+            if (row < 7) sb.Append('/');
+        }
+
+        /* 2) active colour */
+        sb.Append(gs.CurrentPlayer == PieceColor.White ? " w " : " b ");
+
+        /* 3) castling rights (from GameState flags) */
+        sb.Append(GetCastlingFlags(gs));
+
+        /* 4) en-passant target square */
+        sb.Append(' ');
+        sb.Append(gs.EnPassantTarget.HasValue
+            ? Alg(gs.EnPassantTarget.Value)
+            : "-");
+
+        /* 5-6) half-move clock + full-move number  */
+        int fullMoves = gs.MoveHistory.Count / 2 + 1;
+        sb.Append(' ').Append(gs.HalfmoveClock).Append(' ').Append(fullMoves);
+
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// The prior positions since the last irreversible move (capture/pawn move), as
+    /// completed FEN strings, oldest first and excluding the current position. This is
+    /// the repetition window the engine needs to detect threefold/50-move draws that a
+    /// single FEN can't express.
+    /// </summary>
+    public static IReadOnlyList<string> RepetitionHistory(this GameState gs)
+    {
+        int clock = gs.HalfmoveClock;
+        int count = gs.PositionHistory.Count;
+        int start = count - 1 - clock;        // PositionHistory ends with the current position
+
+        if (clock <= 0 || start < 0)
+            return Array.Empty<string>();
+
+        var fens = new List<string>(clock);
+
+        for (int i = start; i < count - 1; i++)
+            fens.Add(gs.PositionHistory[i] + " 0 1");   // complete the 4-field key into a parseable FEN
+
+        return fens;
+    }
+
+    /* ---------- helpers ---------- */
+
+    private static string GetCastlingFlags(GameState gs)
+    {
+        var flags = new StringBuilder(4);
+
+        if (gs.WhiteCanCastleKingside) flags.Append('K');
+        if (gs.WhiteCanCastleQueenside) flags.Append('Q');
+        if (gs.BlackCanCastleKingside) flags.Append('k');
+        if (gs.BlackCanCastleQueenside) flags.Append('q');
+
+        return flags.Length == 0 ? "-" : flags.ToString();
+    }
+
+    private static string Alg(Position p)
+    {
+        char file = (char)('a' + p.Col);
+        int rank = 8 - p.Row;
+        return $"{file}{rank}";
+    }
+
+    private static char ToFenChar(ChessPiece p) => p switch
+    {
+        { Type: PieceType.Pawn, Color: PieceColor.White } => 'P',
+        { Type: PieceType.Pawn, Color: PieceColor.Black } => 'p',
+        { Type: PieceType.Knight, Color: PieceColor.White } => 'N',
+        { Type: PieceType.Knight, Color: PieceColor.Black } => 'n',
+        { Type: PieceType.Bishop, Color: PieceColor.White } => 'B',
+        { Type: PieceType.Bishop, Color: PieceColor.Black } => 'b',
+        { Type: PieceType.Rook, Color: PieceColor.White } => 'R',
+        { Type: PieceType.Rook, Color: PieceColor.Black } => 'r',
+        { Type: PieceType.Queen, Color: PieceColor.White } => 'Q',
+        { Type: PieceType.Queen, Color: PieceColor.Black } => 'q',
+        { Type: PieceType.King, Color: PieceColor.White } => 'K',
+        { Type: PieceType.King, Color: PieceColor.Black } => 'k',
+        _ => throw new ArgumentOutOfRangeException(nameof(p))
+    };
+}

JoshHeaps.Net/Services/Implementations/ChessService.cs

@@ -22,12 +22,14 @@ public class ChessService : IChessService
 
         gameState.Pieces.Clear();
         gameState.MoveHistory.Clear();
+        gameState.SanHistory.Clear();
 
         gameState.WhiteCanCastleKingside = true;
         gameState.WhiteCanCastleQueenside = true;
         gameState.BlackCanCastleKingside = true;
         gameState.BlackCanCastleQueenside = true;
         gameState.EnPassantTarget = null;
+        gameState.HalfmoveClock = 0;
 
         SetupBlackPieces(gameState);
         SetupWhitePieces(gameState);
@@ -35,6 +37,9 @@ public class ChessService : IChessService
         gameState.CurrentPlayer = PieceColor.White;
 
         UpdateCheckStatus(gameState);
+
+        gameState.PositionHistory.Clear();
+        gameState.PositionHistory.Add(PositionKey(gameState));
     }
 
     private static void SetupBlackPieces(GameState gs)
@@ -137,12 +142,23 @@ public class ChessService : IChessService
         if (!legalMoves.Any(m => m.Row == moveDto.TargetRow && m.Col == moveDto.TargetCol))
             return new MoveResultDto { Success = false, Message = "Illegal move." };
 
+        // SAN is built before the move (needs the pre-move board for captures/disambiguation);
+        // the check/mate suffix is appended after UpdateCheckStatus.
+        var sanBase = BuildSan(gameState, piece, targetPos, moveDto);
+
         PerformMove(gameState, piece, targetPos, moveDto);
 
         UpdateCheckStatus(gameState);
 
         var notation = $"{piece.Id}:{piece.Position}->{targetPos}";
         gameState.MoveHistory.Add(notation);
+        gameState.SanHistory.Add(sanBase + (gameState.IsCheckmate ? "#" : gameState.IsCheck ? "+" : ""));
+
+        var positionKey = PositionKey(gameState);
+        gameState.PositionHistory.Add(positionKey);
+
+        if (gameState.PositionHistory.Count(k => k == positionKey) >= 3)
+            gameState.IsThreefoldRepetition = true;
 
         return new MoveResultDto
         {
@@ -150,14 +166,95 @@ public class ChessService : IChessService
             Message = "Move successful.",
             IsCheck = gameState.IsCheck,
             IsCheckmate = gameState.IsCheckmate,
-            IsStalemate = gameState.IsStalemate
+            IsStalemate = gameState.IsStalemate,
+            IsThreefoldRepetition = gameState.IsThreefoldRepetition
         };
     }
 
+    /// <summary>
+    /// Build the standard-algebraic notation for a move from the position BEFORE it is
+    /// applied (the check/mate suffix is added by the caller afterward).
+    /// </summary>
+    private string BuildSan(GameState gs, ChessPiece piece, Position target, MoveDto moveDto)
+    {
+        var from = piece.Position;
+
+        if (piece.Type == PieceType.King && Math.Abs(target.Col - from.Col) == 2)
+            return target.Col > from.Col ? "O-O" : "O-O-O";
+
+        bool targetOccupied = gs.Board[target.Row, target.Col] != null;
+        bool isEnPassant = piece.Type == PieceType.Pawn && from.Col != target.Col && !targetOccupied;
+        bool isCapture = targetOccupied || isEnPassant;
+        string dest = SquareName(target);
+
+        if (piece.Type == PieceType.Pawn)
+        {
+            var san = isCapture ? $"{FileChar(from.Col)}x{dest}" : dest;
+
+            bool promotes = (piece.Color == PieceColor.White && target.Row == 0)
+                         || (piece.Color == PieceColor.Black && target.Row == 7);
+
+            if (promotes)
+                san += "=" + PieceLetter(moveDto.PromotionChoice ?? PieceType.Queen);
+
+            return san;
+        }
+
+        return $"{PieceLetter(piece.Type)}{Disambiguation(gs, piece, target)}{(isCapture ? "x" : "")}{dest}";
+    }
+
+    /// <summary>
+    /// SAN disambiguation: when another piece of the same type and color can also reach the
+    /// target, qualify the origin by file, else rank, else both.
+    /// </summary>
+    private string Disambiguation(GameState gs, ChessPiece piece, Position target)
+    {
+        var rivals = gs.Pieces
+            .Where(p => p.Id != piece.Id && p.Type == piece.Type && p.Color == piece.Color && p.Position.Row >= 0)
+            .Where(p => GetLegalMovesForPiece(gs, p.Id).Any(m => m.Row == target.Row && m.Col == target.Col))
+            .ToList();
+
+        if (rivals.Count == 0)
+            return "";
+
+        if (rivals.All(p => p.Position.Col != piece.Position.Col))
+            return FileChar(piece.Position.Col).ToString();
+
+        if (rivals.All(p => p.Position.Row != piece.Position.Row))
+            return (8 - piece.Position.Row).ToString();
+
+        return $"{FileChar(piece.Position.Col)}{8 - piece.Position.Row}";
+    }
+
+    private static char FileChar(int col) => (char)('a' + col);
+
+    private static string SquareName(Position p) => $"{FileChar(p.Col)}{8 - p.Row}";
+
+    private static string PieceLetter(PieceType type) => type switch
+    {
+        PieceType.Knight => "N",
+        PieceType.Bishop => "B",
+        PieceType.Rook   => "R",
+        PieceType.Queen  => "Q",
+        PieceType.King   => "K",
+        _                => ""
+    };
+
+    /// <summary>
+    /// The repetition signature of a position: the first four FEN fields — piece placement,
+    /// side to move, castling rights, and en-passant target. Move counters are excluded.
+    /// </summary>
+    private static string PositionKey(GameState gs)
+    {
+        var fields = gs.ToFen().Split(' ');
+        return string.Join(' ', fields.Take(4));
+    }
+
     private static void PerformMove(GameState gs, ChessPiece piece, Position targetPos, MoveDto moveDto)
     {
         var oldPos = piece.Position;
         var captured = gs.Board[targetPos.Row, targetPos.Col];
+        var isPawnMove = piece.Type == PieceType.Pawn;   // captured before promotion can change Type
 
         HandleEnPassantIfNeeded(gs, piece, targetPos, ref captured);
 
@@ -179,6 +276,9 @@ public class ChessService : IChessService
 
         UpdateCastlingRights(gs, piece, oldPos);
 
+        // Reset the 50-move clock on captures and pawn moves (irreversible); else advance it.
+        gs.HalfmoveClock = (isPawnMove || captured != null) ? 0 : gs.HalfmoveClock + 1;
+
         gs.CurrentPlayer = gs.CurrentPlayer == PieceColor.White
             ? PieceColor.Black
             : PieceColor.White;

JoshHeaps.Net/Services/Implementations/ComputerMoveOrchestrator.cs

@@ -0,0 +1,70 @@
+using JoshHeaps.Net.Hubs;
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.AspNetCore.SignalR;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// Engine-agnostic glue for computer moves: get a move from the engine, apply it
+/// through the rules service, and broadcast it to the game's clients.
+/// </summary>
+public sealed class ComputerMoveOrchestrator(
+    IHubContext<ChessHub> chessHub,
+    IChessService chessService,
+    ILearnedWeightsStore weightsStore) : IComputerMoveOrchestrator
+{
+    public async Task<(MoveDto move, MoveResultDto result)> PlayAsync(GameState state)
+    {
+        var engine = (state.CurrentPlayer == PieceColor.White ? state.WhiteComputer : state.BlackComputer)
+            ?? throw new InvalidOperationException($"No engine is set for {state.CurrentPlayer} in game {state.GameId}.");
+
+        var uci = await engine.GetBestMoveAsync(state.ToFen(), state.RepetitionHistory());
+        var move = uci.ToMoveDto(state, CurrentPlayerId(state));
+
+        return await ApplyAndBroadcastAsync(state, move);
+    }
+
+    public async Task PlayRandomMoveAsync(GameState state)
+    {
+        var options = chessService.GetAllLegalMoves(state);
+
+        // No legal moves means the game is already over; let the caller's loop detect it.
+        if (options.Count == 0)
+            return;
+
+        var (piece, moves) = options[Random.Shared.Next(options.Count)];
+        var target = moves[Random.Shared.Next(moves.Count)];
+
+        var move = new MoveDto
+        {
+            GameId = state.GameId,
+            PlayerId = CurrentPlayerId(state),
+            PieceId = piece.Id,
+            SourceRow = piece.Position.Row,
+            SourceCol = piece.Position.Col,
+            TargetRow = target.Row,
+            TargetCol = target.Col,
+            PromotionChoice = null   // a pawn cannot reach the last rank within the opening plies
+        };
+
+        await ApplyAndBroadcastAsync(state, move);
+    }
+
+    private async Task<(MoveDto move, MoveResultDto result)> ApplyAndBroadcastAsync(GameState state, MoveDto move)
+    {
+        var result = chessService.MakeMove(state, move);
+
+        // Record the played position for training (no-op for non-training games).
+        if (state.Trainer != nint.Zero)
+            weightsStore.Record(state.Trainer, state.ToFen());
+
+        await chessHub.Clients.Group(state.GameId.ToString())
+            .SendAsync("ReceiveMoveUpdate", state.GameId.ToString(), move, result, state.ToDto());
+
+        return (move, result);
+    }
+
+    private static Guid CurrentPlayerId(GameState state) =>
+        state.CurrentPlayer == PieceColor.White ? state.WhitePlayerId : state.BlackPlayerId;
+}

JoshHeaps.Net/Services/Implementations/CustomChessEngine.cs

@@ -0,0 +1,162 @@
+using JoshHeaps.Net.Services.Interfaces;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>Which evaluation the native engine uses.</summary>
+public enum EngineVariant
+{
+    /// <summary>The hand-crafted evaluation.</summary>
+    Classic,
+
+    /// <summary>Material plus a learned per-square bonus table loaded from a weights file.</summary>
+    Learned
+}
+
+/// <summary>
+/// Middleman wrapper over the native custom chess engine (chess_engine.dll / libchess_engine.so).
+/// Shares <see cref="IChessEngine"/> with <see cref="Stockfish"/> so the two are swappable.
+/// The boundary contract is FEN string in, UCI move string out — identical to Stockfish.
+/// </summary>
+public sealed partial class CustomChessEngine : IChessEngine
+{
+    private readonly EngineSafeHandle _handle;
+
+    public int Skill { get; }
+
+    public CustomChessEngine(int skill = 20, EngineVariant variant = EngineVariant.Classic, string? weightsPath = null)
+    {
+        Skill = skill;
+
+        // weights= must come last: the native side reads the path as the rest of the
+        // string, which lets it contain ';' and spaces.
+        var options = variant == EngineVariant.Learned
+            ? $"skill={skill};variant=learned;weights={weightsPath}"
+            : $"skill={skill}";
+
+        var handle = NativeMethods.engine_create(options);
+
+        if (handle == IntPtr.Zero)
+            throw new InvalidOperationException("Native chess engine failed to initialize (engine_create returned null).");
+
+        _handle = new EngineSafeHandle(handle);
+    }
+
+    public Task<string> GetBestMoveAsync(string fen, IReadOnlyList<string> historyFens) =>
+        Task.Run(() => GetBestMove(fen, string.Join('\n', historyFens)));
+
+    private unsafe string GetBestMove(string fen, string history)
+    {
+        const int bufferLength = 16;            // longest UCI move is 5 chars ("e7e8q") + NUL
+        byte* buffer = stackalloc byte[bufferLength];
+
+        var added = false;
+
+        try
+        {
+            _handle.DangerousAddRef(ref added);
+            var code = NativeMethods.engine_best_move(_handle.DangerousGetHandle(), fen, history, buffer, bufferLength);
+
+            if (code != 0)
+                throw new InvalidOperationException($"Native chess engine failed to produce a move for FEN '{fen}' (engine_best_move returned {code}).");
+
+            return Marshal.PtrToStringUTF8((IntPtr)buffer)
+                ?? throw new InvalidOperationException("Native chess engine returned an empty move.");
+        }
+        finally
+        {
+            if (added)
+                _handle.DangerousRelease();
+        }
+    }
+
+    public ValueTask DisposeAsync()
+    {
+        _handle.Dispose();
+        return ValueTask.CompletedTask;
+    }
+
+    /// <summary>Guarantees the native handle is released exactly once via engine_destroy.</summary>
+    private sealed class EngineSafeHandle : SafeHandle
+    {
+        public EngineSafeHandle(IntPtr handle) : base(IntPtr.Zero, ownsHandle: true) => SetHandle(handle);
+
+        public override bool IsInvalid => handle == IntPtr.Zero;
+
+        protected override bool ReleaseHandle()
+        {
+            NativeMethods.engine_destroy(handle);
+            return true;
+        }
+    }
+
+    /// <summary>
+    /// P/Invoke surface for chess_engine.(dll|so). The resolver maps the logical name
+    /// "chess_engine" to the platform binary in the Resources folder (mirrors Stockfish).
+    /// Internal so <see cref="LearnedWeightsStore"/> can share the single import resolver.
+    /// </summary>
+    internal static partial class NativeMethods
+    {
+        private const string LibName = "chess_engine";
+
+        static NativeMethods() =>
+            NativeLibrary.SetDllImportResolver(typeof(NativeMethods).Assembly, Resolve);
+
+        private static IntPtr Resolve(string libraryName, Assembly assembly, DllImportSearchPath? searchPath)
+        {
+            if (libraryName != LibName)
+                return IntPtr.Zero;
+
+            var fileName = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
+                ? "chess_engine.dll"
+                : "libchess_engine.so";
+
+            var path = Path.Combine(AppContext.BaseDirectory, "Resources", fileName);
+
+            if (NativeLibrary.TryLoad(path, out var handle))
+                return handle;
+
+            return NativeLibrary.Load(libraryName, assembly, searchPath);
+        }
+
+        [LibraryImport(LibName, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial IntPtr engine_create(string? options);
+
+        [LibraryImport(LibName, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static unsafe partial int engine_best_move(IntPtr engine, string fen, string history, byte* outBuffer, int outLength);
+
+        [LibraryImport(LibName)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial void engine_destroy(IntPtr engine);
+
+        // ---- Learned-weights / training ABI (see chess_engine.h) ----
+
+        [LibraryImport(LibName, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial void learned_load(string path);
+
+        [LibraryImport(LibName)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static unsafe partial int weights_snapshot(int* outBuf, int outLen);
+
+        [LibraryImport(LibName)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial IntPtr trainer_create();
+
+        [LibraryImport(LibName, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial void trainer_record(IntPtr trainer, string fen);
+
+        [LibraryImport(LibName)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial void trainer_apply(IntPtr trainer, int winner, double weight);
+
+        [LibraryImport(LibName)]
+        [UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+        internal static partial void trainer_destroy(IntPtr trainer);
+    }
+}

JoshHeaps.Net/Services/Implementations/EchoRoomStore.cs

@@ -0,0 +1,189 @@
+using System.Collections.Concurrent;
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// In-memory ranging rooms. Singleton: rooms are process-wide and short-lived, and the site runs
+/// as a single instance, so there is nothing to persist and no backplane to coordinate.
+/// </summary>
+public sealed class EchoRoomStore : IEchoRoomStore
+{
+    private sealed class Room
+    {
+        public required string Code { get; init; }
+        public List<EchoDevice> Devices { get; } = [];
+        public EchoRound? Round { get; set; }
+        public int RoundCounter { get; set; }
+        public DateTimeOffset LastActivity { get; set; } = DateTimeOffset.UtcNow;
+    }
+
+    private readonly ConcurrentDictionary<string, Room> _rooms = new(StringComparer.OrdinalIgnoreCase);
+    private readonly ConcurrentDictionary<string, string> _roomsByConnection = [];
+
+    public EchoJoinResult Join(string roomCode, string connectionId, string displayName, int sampleRate)
+    {
+        var room = _rooms.GetOrAdd(roomCode, code => new Room { Code = code });
+        var device = new EchoDevice
+        {
+            DeviceId = Guid.NewGuid().ToString("N")[..8],
+            ConnectionId = connectionId,
+            DisplayName = displayName,
+            SampleRate = sampleRate
+        };
+
+        lock (room)
+        {
+            room.Devices.RemoveAll(existing => existing.ConnectionId == connectionId);
+            room.Devices.Add(device);
+            room.LastActivity = DateTimeOffset.UtcNow;
+            _roomsByConnection[connectionId] = room.Code;
+
+            return new EchoJoinResult { DeviceId = device.DeviceId, RoomCode = room.Code, Room = SnapshotLocked(room) };
+        }
+    }
+
+    public (string? roomCode, EchoRoomSnapshot? room) Leave(string connectionId)
+    {
+        if (!_roomsByConnection.TryRemove(connectionId, out var roomCode)) return (null, null);
+        if (!_rooms.TryGetValue(roomCode, out var room)) return (roomCode, null);
+
+        lock (room)
+        {
+            room.Devices.RemoveAll(device => device.ConnectionId == connectionId);
+            room.Round = null;
+            room.LastActivity = DateTimeOffset.UtcNow;
+
+            if (room.Devices.Count == 0) _rooms.TryRemove(roomCode, out _);
+
+            return (roomCode, SnapshotLocked(room));
+        }
+    }
+
+    public EchoRoomSnapshot? Snapshot(string roomCode)
+    {
+        if (!_rooms.TryGetValue(roomCode, out var room)) return null;
+
+        lock (room) return SnapshotLocked(room);
+    }
+
+    public IReadOnlyCollection<string> MeasurableRooms =>
+        [.. _rooms.Values.Where(room => room.Devices.Count >= 2).Select(room => room.Code)];
+
+    public EchoRoundSchedule? StartRound(
+        string roomCode,
+        int slotMilliseconds,
+        int tailMilliseconds,
+        TimeSpan lead,
+        TimeSpan grace)
+    {
+        if (!_rooms.TryGetValue(roomCode, out var room)) return null;
+
+        lock (room)
+        {
+            if (room.Round is not null || room.Devices.Count < 2) return null;
+
+            var slotOrder = RotatedSlotOrder(room);
+            var startsAt = DateTimeOffset.UtcNow + lead;
+            var duration = TimeSpan.FromMilliseconds(slotOrder.Length * slotMilliseconds + tailMilliseconds);
+
+            room.Round = new EchoRound
+            {
+                RoundId = Guid.NewGuid().ToString("N")[..12],
+                SlotOrder = slotOrder,
+                SlotMilliseconds = slotMilliseconds,
+                Deadline = startsAt + duration + grace
+            };
+            room.LastActivity = DateTimeOffset.UtcNow;
+
+            return new EchoRoundSchedule
+            {
+                RoundId = room.Round.RoundId,
+                SlotOrder = slotOrder,
+                SlotMilliseconds = slotMilliseconds,
+                TailMilliseconds = tailMilliseconds,
+                StartsAtUnixMs = startsAt.ToUnixTimeMilliseconds()
+            };
+        }
+    }
+
+    public bool Report(string connectionId, EchoPeakReport report)
+    {
+        var device = FindDevice(connectionId, out var room);
+        if (device is null || room is null) return false;
+
+        lock (room)
+        {
+            if (room.Round?.RoundId != report.RoundId) return false;
+            if (!room.Round.SlotOrder.Contains(device.DeviceId)) return false;
+
+            room.Round.Reports[device.DeviceId] = report;
+            room.LastActivity = DateTimeOffset.UtcNow;
+            return true;
+        }
+    }
+
+    public EchoRoundResult? TryCloseRound(string roomCode)
+    {
+        if (!_rooms.TryGetValue(roomCode, out var room)) return null;
+
+        lock (room)
+        {
+            var round = room.Round;
+            if (round is null) return null;
+
+            var everyoneReported = round.SlotOrder.All(round.Reports.ContainsKey);
+            if (!everyoneReported && DateTimeOffset.UtcNow < round.Deadline) return null;
+
+            room.Round = null;
+
+            return new EchoRoundResult
+            {
+                RoundId = round.RoundId,
+                SlotOrder = round.SlotOrder,
+                Reports = [.. round.SlotOrder.Where(round.Reports.ContainsKey).Select(id => round.Reports[id])]
+            };
+        }
+    }
+
+    public int PruneIdle(TimeSpan idleFor)
+    {
+        var cutoff = DateTimeOffset.UtcNow - idleFor;
+        var stale = _rooms.Values.Where(room => room.LastActivity < cutoff).Select(room => room.Code).ToList();
+
+        foreach (var code in stale) _rooms.TryRemove(code, out _);
+
+        return stale.Count;
+    }
+
+    private static EchoRoomSnapshot SnapshotLocked(Room room) =>
+        new()
+        {
+            RoomCode = room.Code,
+            Devices =
+            [
+                .. room.Devices.Select(device => new EchoDeviceSnapshot
+                {
+                    DeviceId = device.DeviceId,
+                    DisplayName = device.DisplayName,
+                    SampleRate = device.SampleRate
+                })
+            ]
+        };
+
+    private static string[] RotatedSlotOrder(Room room)
+    {
+        var offset = room.RoundCounter++ % room.Devices.Count;
+        return [.. room.Devices.Skip(offset).Concat(room.Devices.Take(offset)).Select(device => device.DeviceId)];
+    }
+
+    private EchoDevice? FindDevice(string connectionId, out Room? room)
+    {
+        room = null;
+        if (!_roomsByConnection.TryGetValue(connectionId, out var roomCode)) return null;
+        if (!_rooms.TryGetValue(roomCode, out room)) return null;
+
+        lock (room) return room.Devices.FirstOrDefault(device => device.ConnectionId == connectionId);
+    }
+}

JoshHeaps.Net/Services/Implementations/EchoRoundService.cs

@@ -0,0 +1,107 @@
+using JoshHeaps.Net.Hubs;
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.AspNetCore.SignalR;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+public sealed class EchoRoundSettings
+{
+    public const string SectionName = "Echo";
+
+    /// <summary>
+    /// Slot length. Wide enough that no device's chirp can land in another's search window once
+    /// unknown output latency (tens of milliseconds, different per device) and message jitter are
+    /// accounted for.
+    /// </summary>
+    public int SlotMilliseconds { get; set; } = 500;
+
+    /// <summary>Time after the last chirp for propagation, detection and reporting.</summary>
+    public int TailMilliseconds { get; set; } = 700;
+
+    public int GraceMilliseconds { get; set; } = 1500;
+    public int GapMilliseconds { get; set; } = 250;
+    public int IdleRoomMinutes { get; set; } = 10;
+
+    /// <summary>
+    /// How far ahead a round is announced. Must exceed the worst message delivery plus client
+    /// stall, or a device will find its slot already gone and sit the round out.
+    /// </summary>
+    public int LeadMilliseconds { get; set; } = 600;
+}
+
+/// <summary>
+/// Drives continuous ranging: opens a round for every room that has two or more devices, closes it
+/// once everyone has reported or the deadline passes, and broadcasts the raw peak table.
+/// </summary>
+public sealed class EchoRoundService(
+    IEchoRoomStore rooms,
+    IHubContext<EchoHub> hub,
+    EchoRoundSettings settings,
+    ILogger<EchoRoundService> logger) : BackgroundService
+{
+    private readonly Dictionary<string, DateTimeOffset> _nextRoundAllowedAt = [];
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        var lastPrune = DateTimeOffset.UtcNow;
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await TickAsync();
+                lastPrune = PruneIfDue(lastPrune);
+            }
+            catch (Exception error)
+            {
+                logger.LogError(error, "Echo round tick failed");
+            }
+
+            await Task.Delay(50, stoppingToken);
+        }
+    }
+
+    private async Task TickAsync()
+    {
+        foreach (var roomCode in rooms.MeasurableRooms)
+        {
+            await CloseFinishedRoundAsync(roomCode);
+            await OpenRoundIfDueAsync(roomCode);
+        }
+    }
+
+    private async Task CloseFinishedRoundAsync(string roomCode)
+    {
+        var result = rooms.TryCloseRound(roomCode);
+        if (result is null) return;
+
+        _nextRoundAllowedAt[roomCode] = DateTimeOffset.UtcNow.AddMilliseconds(settings.GapMilliseconds);
+        await hub.Clients.Group(EchoHub.GroupFor(roomCode)).SendAsync("RoundComplete", result);
+    }
+
+    private async Task OpenRoundIfDueAsync(string roomCode)
+    {
+        if (_nextRoundAllowedAt.TryGetValue(roomCode, out var earliest) && DateTimeOffset.UtcNow < earliest) return;
+
+        var schedule = rooms.StartRound(
+            roomCode,
+            settings.SlotMilliseconds,
+            settings.TailMilliseconds,
+            TimeSpan.FromMilliseconds(settings.LeadMilliseconds),
+            TimeSpan.FromMilliseconds(settings.GraceMilliseconds));
+
+        if (schedule is null) return;
+
+        await hub.Clients.Group(EchoHub.GroupFor(roomCode)).SendAsync("RoundStarting", schedule);
+    }
+
+    private DateTimeOffset PruneIfDue(DateTimeOffset lastPrune)
+    {
+        if (DateTimeOffset.UtcNow - lastPrune < TimeSpan.FromMinutes(1)) return lastPrune;
+
+        var pruned = rooms.PruneIdle(TimeSpan.FromMinutes(settings.IdleRoomMinutes));
+        if (pruned > 0) logger.LogInformation("Pruned {Count} idle echo room(s)", pruned);
+
+        return DateTimeOffset.UtcNow;
+    }
+}

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/LearnedWeightsStore.cs

@@ -0,0 +1,84 @@
+using JoshHeaps.Net.Models;
+using JoshHeaps.Net.Services.Interfaces;
+using Microsoft.Extensions.Options;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+/// <summary>
+/// Managed facade over the native learned-weights model (see <see cref="ILearnedWeightsStore"/>).
+/// On construction it points the native engine at the weights file; everything else delegates
+/// to the shared native ABI in <see cref="CustomChessEngine"/>.
+/// </summary>
+public sealed class LearnedWeightsStore : ILearnedWeightsStore
+{
+    private const int Pieces = 6;       // Pawn..King
+    private const int Squares = 64;
+    private const int Features = 8;     // mobility N/B/R/Q, passed, isolated, doubled, king safety
+
+    public string WeightsFilePath { get; }
+
+    public LearnedWeightsStore(IHostEnvironment env, IOptions<ChessEngineOptions> options, ILogger<LearnedWeightsStore> logger)
+    {
+        // Prefer the configured path (production points this outside the deploy dir); fall
+        // back to the content root for local dev.
+        var configured = options.Value.WeightsPath;
+        WeightsFilePath = string.IsNullOrWhiteSpace(configured)
+            ? Path.Combine(env.ContentRootPath, "chess-data", "learned-weights.txt")
+            : configured;
+
+        // A missing/unwritable/misconfigured path must not take down the whole app — the
+        // learned engine just plays from a neutral table and can't persist training.
+        try
+        {
+            Directory.CreateDirectory(Path.GetDirectoryName(WeightsFilePath)!);
+            CustomChessEngine.NativeMethods.learned_load(WeightsFilePath);
+        }
+        catch (Exception ex)
+        {
+            logger.LogError(ex,
+                "Could not initialize the learned-weights store at {Path}. The learned engine will " +
+                "play from a neutral table and training will not persist. In production set " +
+                "ChessEngine:WeightsPath (env ChessEngine__WeightsPath) to a service-writable directory.",
+                WeightsFilePath);
+        }
+    }
+
+    public nint CreateTrainer() => CustomChessEngine.NativeMethods.trainer_create();
+
+    public void Record(nint trainer, string fen) =>
+        CustomChessEngine.NativeMethods.trainer_record(trainer, fen);
+
+    public void ApplyResult(nint trainer, PieceColor winner, double weight) =>
+        CustomChessEngine.NativeMethods.trainer_apply(trainer, winner == PieceColor.White ? 0 : 1, weight);
+
+    public void DestroyTrainer(nint trainer) =>
+        CustomChessEngine.NativeMethods.trainer_destroy(trainer);
+
+    public LearnedWeightsSnapshot Snapshot()
+    {
+        const int total = Pieces * Squares * 2 + Features;
+        var buffer = new int[total];
+
+        unsafe
+        {
+            fixed (int* p = buffer)
+                CustomChessEngine.NativeMethods.weights_snapshot(p, total);
+        }
+
+        var mg = new int[Pieces][];
+        var eg = new int[Pieces][];
+
+        for (int piece = 0; piece < Pieces; piece++)
+        {
+            mg[piece] = new int[Squares];
+            eg[piece] = new int[Squares];
+            Array.Copy(buffer, piece * Squares, mg[piece], 0, Squares);
+            Array.Copy(buffer, Pieces * Squares + piece * Squares, eg[piece], 0, Squares);
+        }
+
+        var features = new int[Features];
+        Array.Copy(buffer, Pieces * Squares * 2, features, 0, Features);
+
+        return new LearnedWeightsSnapshot(mg, eg, features);
+    }
+}

JoshHeaps.Net/Services/Implementations/PgnExporter.cs

@@ -0,0 +1,50 @@
+using JoshHeaps.Net.Models;
+using System.Text;
+
+namespace JoshHeaps.Net.Services.Implementations;
+
+public static class PgnExporter
+{
+    /// <summary>
+    /// Render a game as PGN: the standard seven-tag header plus the SAN movetext and result.
+    /// </summary>
+    public static string ToPgn(this GameState gs)
+    {
+        var result = ResultTag(gs);
+        var name = gs.IsComputerVsComputer ? "Computer" : null;
+
+        var sb = new StringBuilder();
+        sb.AppendLine("[Event \"JoshHeaps.Net Chess\"]");
+        sb.AppendLine("[Site \"joshheaps.net\"]");
+        sb.AppendLine($"[Date \"{DateTime.Now:yyyy.MM.dd}\"]");
+        sb.AppendLine($"[White \"{name ?? "White"}\"]");
+        sb.AppendLine($"[Black \"{name ?? "Black"}\"]");
+        sb.AppendLine($"[Result \"{result}\"]");
+        sb.AppendLine();
+
+        for (int i = 0; i < gs.SanHistory.Count; i++)
+        {
+            if (i % 2 == 0)
+                sb.Append(i / 2 + 1).Append(". ");
+
+            sb.Append(gs.SanHistory[i]).Append(' ');
+        }
+
+        sb.Append(result);
+        return sb.ToString();
+    }
+
+    private static string ResultTag(GameState gs)
+    {
+        if (gs.IsCheckmate)
+            return gs.CurrentPlayer == PieceColor.White ? "0-1" : "1-0";
+
+        if (gs.IsStalemate || gs.IsThreefoldRepetition)
+            return "1/2-1/2";
+
+        if (gs.IsForfeited)
+            return gs.Winner == PieceColor.White ? "1-0" : "0-1";
+
+        return "*";
+    }
+}

JoshHeaps.Net/Services/Implementations/SelfPlayCoordinator.cs

@@ -0,0 +1,257 @@
+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);
+
+    // Abandon a game that goes this long without a move being played — i.e. an engine (usually
+    // Stockfish) that crashed or froze. The game is killed with no result recorded; if it was an
+    // auto-training game the trainer schedules a replacement once this one's task completes.
+    private static readonly TimeSpan _idleTimeout = TimeSpan.FromSeconds(60);
+
+    // 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 (or a frozen
+    /// engine) just ends the game and the trainer is always freed, so callers can await or ignore.
+    /// </summary>
+    private async Task RunAsync(GameState gameState, CancellationToken cancellationToken)
+    {
+        bool aborted = false;
+
+        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);
+                }
+
+            var lastMoveCount = gameState.MoveHistory.Count;
+            var lastProgress = DateTime.UtcNow;
+
+            while (IsLive(gameState, cancellationToken))
+            {
+                await PlayMoveWithTimeoutAsync(gameState, cancellationToken);
+
+                // Watchdog: abandon the game if it stops making moves (a crashed or frozen engine
+                // can leave PlayAsync returning without progressing). Reset the clock on a real
+                // move; otherwise bail once nothing has happened for the idle timeout.
+                if (gameState.MoveHistory.Count != lastMoveCount)
+                {
+                    lastMoveCount = gameState.MoveHistory.Count;
+                    lastProgress = DateTime.UtcNow;
+                }
+                else if (DateTime.UtcNow - lastProgress > _idleTimeout)
+                    throw new TimeoutException("no move played within the idle timeout");
+
+                await Task.Delay(_selfPlayMoveDelay, cancellationToken);
+            }
+        }
+        catch (OperationCanceledException) { aborted = true; /* service shutting down */ }
+        catch (TimeoutException)
+        {
+            aborted = true;
+            Console.WriteLine($"Self-play game {gameState.GameId} abandoned: no move for over " +
+                              $"{_idleTimeout.TotalSeconds:n0}s (likely a crashed or frozen engine).");
+        }
+        catch (Exception ex)
+        {
+            aborted = true;
+            Console.WriteLine($"Self-play game {gameState.GameId} stopped: {ex.Message}");
+        }
+
+        // A clean finish trains the learned engine; an abandoned game (cancelled, crashed, or
+        // idle past the timeout) records nothing and just frees its trainer.
+        if (aborted)
+            DiscardTraining(gameState);
+        else
+            ApplyLearning(gameState);
+
+        // A clean finish lingers briefly so spectators see the result; an abandoned game is torn
+        // down immediately so its engines (and any crashed/frozen Stockfish process) are released.
+        if (gameStore.Contains(gameState.GameId))
+            gameStore.ScheduleRemove(gameState.GameId, aborted ? TimeSpan.Zero : _selfPlayResultTimeout);
+    }
+
+    /// <summary>
+    /// Plays one engine move, abandoning it if it exceeds <see cref="_idleTimeout"/> (throwing
+    /// <see cref="TimeoutException"/>) so a single hung move can't block the loop forever. The
+    /// abandoned move's eventual fault — it errors once the game's engines are disposed — is
+    /// observed so it isn't an unobserved task exception.
+    /// </summary>
+    private async Task PlayMoveWithTimeoutAsync(GameState gameState, CancellationToken cancellationToken)
+    {
+        var play = orchestrator.PlayAsync(gameState);
+        try
+        {
+            await play.WaitAsync(_idleTimeout, cancellationToken);
+        }
+        catch (TimeoutException)
+        {
+            _ = play.ContinueWith(static t => { _ = t.Exception; }, TaskScheduler.Default);
+            throw;
+        }
+    }
+
+    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>
+    /// Frees an abandoned game's trainer without recording any result — a cancelled, crashed, or
+    /// idle-timed-out game teaches the model nothing.
+    /// </summary>
+    private void DiscardTraining(GameState gameState)
+    {
+        if (gameState.Trainer == nint.Zero)
+            return;
+
+        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/Implementations/Stockfish.cs

@@ -1,22 +1,19 @@
-using JoshHeaps.Net.Hubs;
-using JoshHeaps.Net.Models;
 using JoshHeaps.Net.Services.Interfaces;
-using Microsoft.AspNetCore.SignalR;
 using System.Diagnostics;
-using System.Reflection;
 using System.Runtime.InteropServices;
-using System.Text;
 using System.Threading.Channels;
 
 namespace JoshHeaps.Net.Services.Implementations;
 
-public sealed class Stockfish : IAsyncDisposable
+public sealed class Stockfish : IChessEngine
 {
     private readonly Process _p;
     private readonly StreamWriter _stdin;
     private readonly Channel<string> _stdout = Channel.CreateUnbounded<string>();
     private readonly int _skill;
 
+    public int Skill => _skill;
+
     public Stockfish(int skill = 20, int hash = 256)
     {
         _skill = skill;
@@ -77,8 +74,9 @@ public sealed class Stockfish : IAsyncDisposable
         WaitFor("readyok").GetAwaiter().GetResult();
     }
 
-    public async Task<string> GetBestMoveAsync(string fen)
+    public async Task<string> GetBestMoveAsync(string fen, IReadOnlyList<string> historyFens)
     {
+        // historyFens is unused: Stockfish tracks repetition from the position it's given.
         Send($"position fen {fen}");
         Send($"go depth {_skill}");
         string? best = null;
@@ -109,145 +107,4 @@ public sealed class Stockfish : IAsyncDisposable
         await _p.WaitForExitAsync();
         _p.Dispose();
     }
-
-    public async Task MakeMove(GameState state, IHubContext<ChessHub> chessHub, IChessService chessService)
-    {
-        var move = await GetBestMoveAsync(state.ToFen());
-
-        var moveDto = move.ToMoveDto(
-            state,
-            state.CurrentPlayer == PieceColor.White
-                ? state.WhitePlayerId
-                : state.BlackPlayerId);
-
-        var result = chessService.MakeMove(state, moveDto);
-
-        await chessHub.Clients.Group(state.GameId.ToString()).SendAsync("ReceiveMoveUpdate", state.GameId.ToString(), moveDto, result);
-    }
-}
-
-public static class StockfishHelpers
-{
-    public static MoveDto ToMoveDto(
-        this string uci,
-        GameState gameState,
-        Guid playerId)
-    {
-        int fCol = uci[0] - 'a', fRow = 7 - (uci[1] - '1');
-        int tCol = uci[2] - 'a', tRow = 7 - (uci[3] - '1');
-
-        var piece = gameState.Board[fRow, fCol]
-                    ?? throw new Exception("No piece at source square");
-
-        PieceType? promo = uci.Length == 5 ? uci[4] switch
-        {
-            'q' => PieceType.Queen,
-            'r' => PieceType.Rook,
-            'b' => PieceType.Bishop,
-            'n' => PieceType.Knight,
-            _ => null
-        } : null;
-
-        return new MoveDto
-        {
-            GameId = gameState.GameId,
-            PlayerId = playerId,
-            PieceId = piece.Id,
-            TargetRow = tRow,
-            TargetCol = tCol,
-            PromotionChoice = promo,
-            SourceCol = fCol,
-            SourceRow = fRow,
-        };
-    }
-
-    /// <summary>
-    /// Convert a 2-D board array (rank 8 = row 0, file a = col 0) to a FEN string.
-    /// Only piece placement + active colour + castling are computed; the rest use
-    /// safe defaults (-, 0, 1).  That is all Stockfish needs.
-    /// </summary>
-    public static string ToFen(this GameState gs)
-    {
-        var sb = new StringBuilder(64);
-
-        /* 1) piece placement */
-        for (int row = 0; row < 8; row++)
-        {
-            int empty = 0;
-
-            for (int col = 0; col < 8; col++)
-            {
-                var p = gs.Board[row, col];
-
-                if (p is null)
-                {
-                    empty++;
-                }
-                else
-                {
-                    if (empty > 0) { sb.Append(empty); empty = 0; }
-                    sb.Append(ToFenChar(p));                 // ← unchanged helper
-                }
-            }
-
-            if (empty > 0) sb.Append(empty);
-            if (row < 7) sb.Append('/');
-        }
-
-        /* 2) active colour */
-        sb.Append(gs.CurrentPlayer == PieceColor.White ? " w " : " b ");
-
-        /* 3) castling rights (from GameState flags) */
-        sb.Append(GetCastlingFlags(gs));
-
-        /* 4) en-passant target square */
-        sb.Append(' ');
-        sb.Append(gs.EnPassantTarget.HasValue
-            ? Alg(gs.EnPassantTarget.Value)
-            : "-");
-
-        /* 5-6) half-move clock + full-move number  */
-        int fullMoves = gs.MoveHistory.Count / 2 + 1;
-        sb.Append(" 0 ").Append(fullMoves);
-
-        return sb.ToString();
-    }
-
-    /* ---------- helpers ---------- */
-
-    private static string GetCastlingFlags(GameState gs)
-    {
-        var flags = new StringBuilder(4);
-
-        if (gs.WhiteCanCastleKingside) flags.Append('K');
-        if (gs.WhiteCanCastleQueenside) flags.Append('Q');
-        if (gs.BlackCanCastleKingside) flags.Append('k');
-        if (gs.BlackCanCastleQueenside) flags.Append('q');
-
-        return flags.Length == 0 ? "-" : flags.ToString();
-    }
-
-    private static string Alg(Position p)
-    {
-        char file = (char)('a' + p.Col);
-        int rank = 8 - p.Row;
-        return $"{file}{rank}";
-    }
-
-    private static char ToFenChar(ChessPiece p) => p switch
-    {
-        { Type: PieceType.Pawn, Color: PieceColor.White } => 'P',
-        { Type: PieceType.Pawn, Color: PieceColor.Black } => 'p',
-        { Type: PieceType.Knight, Color: PieceColor.White } => 'N',
-        { Type: PieceType.Knight, Color: PieceColor.Black } => 'n',
-        { Type: PieceType.Bishop, Color: PieceColor.White } => 'B',
-        { Type: PieceType.Bishop, Color: PieceColor.Black } => 'b',
-        { Type: PieceType.Rook, Color: PieceColor.White } => 'R',
-        { Type: PieceType.Rook, Color: PieceColor.Black } => 'r',
-        { Type: PieceType.Queen, Color: PieceColor.White } => 'Q',
-        { Type: PieceType.Queen, Color: PieceColor.Black } => 'q',
-        { Type: PieceType.King, Color: PieceColor.White } => 'K',
-        { Type: PieceType.King, Color: PieceColor.Black } => 'k',
-        _ => throw new ArgumentOutOfRangeException(nameof(p))
-    };
 }

JoshHeaps.Net/Services/Interfaces/IBlogService.cs

@@ -0,0 +1,11 @@
+using JoshHeaps.Net.Models;
+
+namespace JoshHeaps.Net.Services.Interfaces;
+
+public interface IBlogService
+{
+    Task<List<BlogPost>> GetAllPostsAsync();
+    Task<BlogPost?> GetPostBySlugAsync(string slug);
+    Task<List<BlogPost>> GetPostsByTagAsync(string tag);
+    void ClearCache();
+}

JoshHeaps.Net/Services/Interfaces/IChessEngine.cs

@@ -0,0 +1,24 @@
+namespace JoshHeaps.Net.Services.Interfaces;
+
+/// <summary>
+/// An AI move-selection engine (e.g. Stockfish or the custom native engine).
+/// Selects a move for a position; it does not enforce rules or broadcast updates.
+/// Implementations own unmanaged resources, hence <see cref="IAsyncDisposable"/>.
+/// </summary>
+public interface IChessEngine : IAsyncDisposable
+{
+    /// <summary>The engine's playing strength / search depth.</summary>
+    int Skill { get; }
+
+    /// <summary>
+    /// Returns the engine's chosen move in UCI long-algebraic form (e.g. "e2e4", "e7e8q").
+    /// </summary>
+    /// <param name="fen">The current position as a FEN string.</param>
+    /// <param name="historyFens">
+    /// Prior positions since the last irreversible move, oldest first, excluding the
+    /// current one — lets the engine detect threefold/50-move draws the FEN can't carry.
+    /// May be empty.
+    /// </param>
+    /// <returns>The selected move as a UCI string.</returns>
+    Task<string> GetBestMoveAsync(string fen, IReadOnlyList<string> historyFens);
+}

JoshHeaps.Net/Services/Interfaces/IChessEngineFactory.cs

@@ -0,0 +1,27 @@
+using JoshHeaps.Net.Services.Implementations;
+
+namespace JoshHeaps.Net.Services.Interfaces;
+
+/// <summary>
+/// Creates <see cref="IChessEngine"/> instances, choosing the implementation from configuration.
+/// </summary>
+public interface IChessEngineFactory
+{
+    /// <summary>
+    /// Creates a new engine instance for a single game using the configured default engine.
+    /// The caller owns and disposes it.
+    /// </summary>
+    /// <param name="skill">The desired playing strength / search depth.</param>
+    /// <returns>A new, owned <see cref="IChessEngine"/>.</returns>
+    IChessEngine Create(int skill);
+
+    /// <summary>
+    /// Creates a new engine instance for a single game using an explicitly chosen engine
+    /// (e.g. for picking a different engine per side in a CPU-vs-CPU game). The caller owns
+    /// and disposes it.
+    /// </summary>
+    /// <param name="skill">The desired playing strength / search depth.</param>
+    /// <param name="kind">The engine implementation to create.</param>
+    /// <returns>A new, owned <see cref="IChessEngine"/>.</returns>
+    IChessEngine Create(int skill, ChessEngineKind kind);
+}

JoshHeaps.Net/Services/Interfaces/IComputerMoveOrchestrator.cs

@@ -0,0 +1,26 @@
+using JoshHeaps.Net.Models;
+
+namespace JoshHeaps.Net.Services.Interfaces;
+
+/// <summary>
+/// Drives a computer move: asks the side-to-move's engine for a move, applies it through
+/// the rules service, and broadcasts the result to the game's clients.
+/// </summary>
+public interface IComputerMoveOrchestrator
+{
+    /// <summary>
+    /// Has the side-to-move's engine pick a move for the current position, applies it, and
+    /// broadcasts it. The engine is taken from the game's per-side computer assignments.
+    /// </summary>
+    /// <param name="state">The game to play a move in.</param>
+    /// <returns>The applied move and its result.</returns>
+    Task<(MoveDto move, MoveResultDto result)> PlayAsync(GameState state);
+
+    /// <summary>
+    /// Plays a uniformly-random legal move for the side to move (no engine), applying and
+    /// broadcasting it. Used to randomize the opening of training games so self-play and
+    /// engine-vs-engine games don't replay the same line every time.
+    /// </summary>
+    /// <param name="state">The game to play a random move in.</param>
+    Task PlayRandomMoveAsync(GameState state);
+}

JoshHeaps.Net/Services/Interfaces/IEchoRoomStore.cs

@@ -0,0 +1,45 @@
+using JoshHeaps.Net.Models;
+
+namespace JoshHeaps.Net.Services.Interfaces;
+
+/// <summary>
+/// Process-wide registry of ranging rooms. Holds only device identity and the sample indices each
+/// device reported, so the server is a scheduler and a relay — it never sees audio.
+/// </summary>
+public interface IEchoRoomStore
+{
+    /// <summary>Add a device to a room, creating the room if this is the first arrival.</summary>
+    EchoJoinResult Join(string roomCode, string connectionId, string displayName, int sampleRate);
+
+    /// <summary>Remove whichever device owns this connection, returning the room it left.</summary>
+    (string? roomCode, EchoRoomSnapshot? room) Leave(string connectionId);
+
+    /// <summary>Snapshot of a room's roster, or null if the room is gone.</summary>
+    EchoRoomSnapshot? Snapshot(string roomCode);
+
+    /// <summary>Room codes with at least two devices, which is the minimum for a measurement.</summary>
+    IReadOnlyCollection<string> MeasurableRooms { get; }
+
+    /// <summary>
+    /// Open a new round for a room, rotating which device chirps first so no single device is
+    /// permanently the slot-order anchor.
+    /// </summary>
+    EchoRoundSchedule? StartRound(
+        string roomCode,
+        int slotMilliseconds,
+        int tailMilliseconds,
+        TimeSpan lead,
+        TimeSpan grace);
+
+    /// <summary>File a device's peaks against the room's open round.</summary>
+    bool Report(string connectionId, EchoPeakReport report);
+
+    /// <summary>
+    /// Close the open round if every device has reported or its deadline has passed, returning the
+    /// reports to broadcast.
+    /// </summary>
+    EchoRoundResult? TryCloseRound(string roomCode);
+
+    /// <summary>Drop rooms that have had no activity for longer than <paramref name="idleFor"/>.</summary>
+    int PruneIdle(TimeSpan idleFor);
+}

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/ILearnedWeightsStore.cs

@@ -0,0 +1,33 @@
+using JoshHeaps.Net.Models;
+
+namespace JoshHeaps.Net.Services.Interfaces;
+
+/// <summary>
+/// Thin managed facade over the native learned-weights model. The weights, all feature
+/// computation, per-game accumulation, the update rule, and persistence live in the native
+/// engine; this just points it at the weights file, hands out per-game trainers, and reads
+/// the table back for visualization.
+/// </summary>
+public interface ILearnedWeightsStore
+{
+    /// <summary>Absolute path to the weights file the native engine loads and saves.</summary>
+    string WeightsFilePath { get; }
+
+    /// <summary>A copy of the current weights (midgame/endgame tables + feature weights).</summary>
+    LearnedWeightsSnapshot Snapshot();
+
+    /// <summary>Creates a per-game training accumulator. The caller owns it (see <see cref="DestroyTrainer"/>).</summary>
+    nint CreateTrainer();
+
+    /// <summary>Records one played position (post-move FEN) into a trainer.</summary>
+    void Record(nint trainer, string fen);
+
+    /// <summary>
+    /// Applies a finished game's outcome to the global weights (and saves): rewards the
+    /// winner's squares/features, punishes the loser's, scaled by <paramref name="weight"/>.
+    /// </summary>
+    void ApplyResult(nint trainer, PieceColor winner, double weight);
+
+    /// <summary>Frees a trainer. Safe to call with <see cref="nint.Zero"/>.</summary>
+    void DestroyTrainer(nint trainer);
+}

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);
+}

JoshHeaps.Net/appsettings.Development.json

@@ -5,5 +5,8 @@
       "Default": "Information",
       "Microsoft.AspNetCore": "Warning"
     }
+  },
+  "ChessEngine": {
+    "Engine": "Custom"
   }
 }

JoshHeaps.Net/appsettings.json

@@ -5,5 +5,12 @@
       "Microsoft.AspNetCore": "Warning"
     }
   },
-  "AllowedHosts": "*"
+  "AllowedHosts": "*",
+  "BlogApi": {
+    "BaseUrl": "https://media.joshheaps.net",
+    "InvalidateKey": "CHANGE_ME"
+  },
+  "ChessEngine": {
+    "Engine": "Custom"
+  }
 }

JoshHeaps.Net/wwwroot/css/blog/index.css

@@ -0,0 +1,126 @@
+*, *::before, *::after {
+    box-sizing: border-box;
+}
+
+body {
+    margin: 0;
+    background-color: var(--color-bg);
+    color: var(--color-text);
+    overflow-x: hidden;
+    font-family: var(--font-body);
+    line-height: 1.6;
+}
+
+.blog-index {
+    max-width: 800px;
+    margin: 0 auto;
+    padding: 4rem clamp(1.5rem, 5vw, 3rem);
+}
+
+.blog-title {
+    color: var(--color-heading);
+    font-size: clamp(1.75rem, 3vw, 2.25rem);
+    font-weight: 700;
+    letter-spacing: -0.02em;
+    margin: 0 0 2.5rem;
+}
+
+.blog-filter {
+    display: flex;
+    align-items: center;
+    gap: 1rem;
+    margin-bottom: 2rem;
+    color: var(--color-text-muted);
+    font-size: 0.875rem;
+}
+
+.blog-filter strong {
+    color: var(--color-heading-secondary);
+}
+
+.blog-filter a {
+    color: var(--color-accent);
+    text-decoration: none;
+    transition: color 0.2s;
+}
+
+.blog-filter a:hover {
+    color: var(--color-accent-hover);
+}
+
+.blog-empty {
+    color: var(--color-text-subtle);
+    font-style: italic;
+    font-size: 1rem;
+}
+
+.blog-list {
+    display: flex;
+    flex-direction: column;
+    gap: 1rem;
+}
+
+.blog-card {
+    padding: 1.5rem 1.75rem;
+    border-left: 2px solid var(--color-accent-border);
+    background: var(--color-surface);
+    border-radius: 0 8px 8px 0;
+    transition: background 0.2s;
+}
+
+.blog-card:hover {
+    background: var(--color-surface-hover);
+}
+
+.blog-card-link {
+    text-decoration: none;
+}
+
+.blog-card-title {
+    color: var(--color-heading-secondary);
+    font-size: 1.25rem;
+    font-weight: 600;
+    margin: 0 0 0.3rem;
+    letter-spacing: -0.01em;
+    transition: color 0.2s;
+}
+
+.blog-card-link:hover .blog-card-title {
+    color: var(--color-accent);
+}
+
+.blog-card-date {
+    color: var(--color-text-subtle);
+    font-size: 0.75rem;
+    display: block;
+    margin-bottom: 0.5rem;
+}
+
+.blog-card-summary {
+    color: var(--color-text-muted);
+    margin: 0;
+    line-height: 1.6;
+    font-size: 0.875rem;
+}
+
+.blog-card-tags {
+    display: flex;
+    gap: 0.4rem;
+    flex-wrap: wrap;
+    margin-top: 0.75rem;
+}
+
+.blog-tag {
+    background: var(--color-surface-raised);
+    color: var(--color-text-muted);
+    padding: 0.2rem 0.6rem;
+    border-radius: 4px;
+    font-size: 0.7rem;
+    text-decoration: none;
+    transition: background 0.2s, color 0.2s;
+}
+
+.blog-tag:hover {
+    background: var(--color-surface-raised-hover);
+    color: var(--color-heading-secondary);
+}

JoshHeaps.Net/wwwroot/css/blog/post.css

@@ -0,0 +1,184 @@
+*, *::before, *::after {
+    box-sizing: border-box;
+}
+
+body {
+    margin: 0;
+    background-color: var(--color-bg);
+    color: var(--color-text);
+    overflow-x: hidden;
+    font-family: var(--font-body);
+    line-height: 1.6;
+}
+
+.blog-post {
+    max-width: 800px;
+    margin: 0 auto;
+    padding: 4rem clamp(1.5rem, 5vw, 3rem);
+}
+
+.blog-back {
+    color: var(--color-text-subtle);
+    text-decoration: none;
+    font-size: 0.85rem;
+    transition: color 0.2s;
+}
+
+.blog-back:hover {
+    color: var(--color-heading-secondary);
+}
+
+.blog-post-header {
+    margin: 2.5rem 0 2.5rem;
+}
+
+.blog-post-title {
+    color: var(--color-heading);
+    font-size: clamp(1.75rem, 3vw, 2.25rem);
+    font-weight: 700;
+    letter-spacing: -0.02em;
+    margin: 0 0 0.5rem;
+    line-height: 1.25;
+}
+
+.blog-post-date {
+    color: var(--color-text-subtle);
+    font-size: 0.8rem;
+    display: block;
+}
+
+.blog-post-tags {
+    display: flex;
+    gap: 0.4rem;
+    flex-wrap: wrap;
+    margin-top: 0.75rem;
+}
+
+.blog-tag {
+    background: var(--color-surface-raised);
+    color: var(--color-text-muted);
+    padding: 0.2rem 0.6rem;
+    border-radius: 4px;
+    font-size: 0.7rem;
+    text-decoration: none;
+    transition: background 0.2s, color 0.2s;
+}
+
+.blog-tag:hover {
+    background: var(--color-surface-raised-hover);
+    color: var(--color-heading-secondary);
+}
+
+/* ── Post Content ── */
+
+.post-content {
+    color: var(--color-text);
+    line-height: 1.8;
+    font-size: 1rem;
+}
+
+.post-content h1,
+.post-content h2,
+.post-content h3,
+.post-content h4 {
+    color: var(--color-heading-secondary);
+    margin-top: 2rem;
+    margin-bottom: 0.75rem;
+    letter-spacing: -0.01em;
+}
+
+.post-content h1 { font-size: 1.6rem; }
+.post-content h2 { font-size: 1.35rem; }
+.post-content h3 { font-size: 1.15rem; }
+
+.post-content p {
+    margin: 0 0 1.25rem;
+}
+
+.post-content a {
+    color: var(--color-accent);
+    text-decoration: none;
+    transition: color 0.2s;
+}
+
+.post-content a:hover {
+    color: var(--color-accent-hover);
+}
+
+.post-content ul,
+.post-content ol {
+    margin: 0 0 1.25rem 1.5rem;
+}
+
+.post-content li {
+    margin-bottom: 0.4rem;
+}
+
+.post-content code {
+    background: var(--color-surface-raised);
+    color: var(--color-heading-secondary);
+    padding: 0.15rem 0.4rem;
+    border-radius: 4px;
+    font-size: 0.85em;
+    font-family: var(--font-mono);
+}
+
+.post-content pre {
+    background: var(--color-surface);
+    border: 1px solid var(--color-border);
+    border-radius: 8px;
+    padding: 1.25rem 1.5rem;
+    overflow-x: auto;
+    margin: 0 0 1.25rem;
+    scrollbar-width: thin;
+    scrollbar-color: var(--color-border) transparent;
+}
+
+.post-content pre::-webkit-scrollbar {
+    height: 6px;
+}
+
+.post-content pre::-webkit-scrollbar-track {
+    background: transparent;
+}
+
+.post-content pre::-webkit-scrollbar-thumb {
+    background: var(--color-border);
+    border-radius: 3px;
+}
+
+.post-content pre[class*="language-"] {
+    background: var(--color-surface);
+}
+
+.post-content pre code {
+    background: none;
+    color: var(--prism-text);
+    padding: 0;
+    font-size: 0.85rem;
+}
+
+.post-content blockquote {
+    border-left: 2px solid var(--color-accent-border);
+    margin: 0 0 1.25rem;
+    padding: 0.75rem 1.25rem;
+    color: var(--color-text-muted);
+    background: var(--color-surface);
+    border-radius: 0 8px 8px 0;
+}
+
+.post-content img {
+    max-width: 100%;
+    border-radius: 8px;
+    margin: 1.25rem 0;
+}
+
+.post-content strong {
+    color: var(--color-heading-secondary);
+}
+
+.post-content hr {
+    border: none;
+    border-top: 1px solid var(--color-border);
+    margin: 2rem 0;
+}

JoshHeaps.Net/wwwroot/css/blog/prism-tomorrow.css

@@ -0,0 +1,154 @@
+/* Prism.js Tomorrow Night theme (customized) */
+/* Original: https://github.com/PrismJS/prism/blob/master/themes/prism-tomorrow.css */
+
+/* ============================================
+   Theme colors — edit these to restyle
+   ============================================ */
+:root {
+    --prism-background:   #0a0a0a;
+    --prism-text:         #909090;
+    --prism-comment:      #555;
+    --prism-punctuation:  #707070;
+    --prism-tag:          #09ff00;
+    --prism-function:     #fff;
+    --prism-boolean:      #1ab815;
+    --prism-number:       #1ab815;
+    --prism-property:     #c8c8c8;
+    --prism-class:        #c8c8c8;
+    --prism-keyword:      #09ff00;
+    --prism-string:       #43c760;
+    --prism-variable:     #43c760;
+    --prism-operator:     #999;
+    --prism-inserted:     #09ff00;
+}
+
+code[class*="language-"],
+pre[class*="language-"] {
+    color: var(--prism-text);
+    background: none;
+    font-family: var(--font-mono);
+    font-size: 1em;
+    text-align: left;
+    white-space: pre;
+    word-spacing: normal;
+    word-break: normal;
+    word-wrap: normal;
+    line-height: 1.5;
+    tab-size: 4;
+    hyphens: none;
+}
+
+pre[class*="language-"] {
+    padding: 1em;
+    margin: 0.5em 0;
+    overflow: auto;
+}
+
+:not(pre) > code[class*="language-"],
+pre[class*="language-"] {
+    background: var(--prism-background);
+}
+
+:not(pre) > code[class*="language-"] {
+    padding: 0.1em;
+    border-radius: 0.3em;
+    white-space: normal;
+}
+
+/* Comments */
+.token.comment,
+.token.block-comment,
+.token.prolog,
+.token.doctype,
+.token.cdata {
+    color: var(--prism-comment);
+}
+
+/* Punctuation */
+.token.punctuation {
+    color: var(--prism-punctuation);
+}
+
+/* Tags, attributes, deleted */
+.token.tag,
+.token.attr-name,
+.token.namespace,
+.token.deleted {
+    color: var(--prism-tag);
+}
+
+/* Function names */
+.token.function-name,
+.token.function {
+    color: var(--prism-function);
+}
+
+/* Booleans */
+.token.boolean {
+    color: var(--prism-boolean);
+}
+
+/* Numbers */
+.token.number {
+    color: var(--prism-number);
+}
+
+/* Properties */
+.token.property {
+    color: var(--prism-property);
+}
+
+/* Classes, constants, symbols */
+.token.class-name,
+.token.constant,
+.token.symbol {
+    color: var(--prism-class);
+}
+
+/* Keywords, selectors, builtins */
+.token.selector,
+.token.important,
+.token.atrule,
+.token.keyword,
+.token.builtin {
+    color: var(--prism-keyword);
+}
+
+/* Strings, chars, attr values, regex */
+.token.string,
+.token.char,
+.token.attr-value,
+.token.regex {
+    color: var(--prism-string);
+}
+
+/* Variables */
+.token.variable {
+    color: var(--prism-variable);
+}
+
+/* Operators, entities, URLs */
+.token.operator,
+.token.entity,
+.token.url {
+    color: var(--prism-operator);
+}
+
+/* Inserted */
+.token.inserted {
+    color: var(--prism-inserted);
+}
+
+/* Formatting */
+.token.bold,
+.token.important {
+    font-weight: 700;
+}
+
+.token.italic {
+    font-style: italic;
+}
+
+.token.entity {
+    cursor: help;
+}

JoshHeaps.Net/wwwroot/css/chess/game.css

@@ -1,12 +1,4 @@
-#boardContainer {
-    position: relative;
-    width: fit-content;
-    margin: 2vw auto;
-}
-
-#chessBoard {
-    width: 60vw;
-    height: 60vw;
+#chessBoard {
     display: grid;
     grid-template-columns: repeat(8, 1fr);
     grid-template-rows: repeat(8, 1fr);
@@ -165,6 +157,47 @@
     pointer-events: none; /* ensures img doesn't steal the click */
 }
 
+#colorModal {
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    transform: translate(-50%, -50%);
+    background-color: #1e1e1e;
+    padding: 20px;
+    border-radius: 10px;
+    box-shadow: 0 0 20px rgba(0,0,0,0.6);
+    color: white;
+    z-index: 1000;
+    text-align: center;
+}
+
+#colorModal p {
+    margin-bottom: 15px;
+    font-size: 18px;
+    font-weight: bold;
+}
+
+#colorButtonContainer {
+    display: flex;
+    gap: 10px;
+    justify-content: center;
+}
+
+#colorButtonContainer button {
+    background-color: #2c2c2c;
+    border: none;
+    padding: 10px 18px;
+    border-radius: 8px;
+    cursor: pointer;
+    transition: transform 0.2s ease;
+    color: white;
+}
+
+#colorButtonContainer button:hover {
+    transform: scale(1.1);
+    background-color: #3a3a3a;
+}
+
 .chessSquare .coordinate-label {
     position: absolute;
     font-size: 1.2vw;

JoshHeaps.Net/wwwroot/css/chess/site.css

@@ -1,137 +1,429 @@
-html, body {
-    background-color: #2b2c30;
-    color: #d6d6d6;
-    cursor: default;
+:root {
+    --bg: #2b2c30;
+    --panel: #21232a;
+    --panel-row: rgba(255, 255, 255, 0.035);
+    --bar: #1e2026;
+    --accent: #8cd5ed;
+    --accent-ink: #10222a;
+    --text: #d6d6d6;
+    --muted: #8b8f99;
+    --line: #34373f;
+    --bar-h: clamp(34px, 5.5vh, 50px);
+    --radius: 12px;
+    --font: 'Outfit', system-ui, -apple-system, Segoe UI, sans-serif;
+}
+
+html, body {
     height: 100%;
     margin: 0;
+    background: var(--bg);
+    color: var(--text);
+    font-family: var(--font);
+    cursor: default;
+    /* The chess page is a fixed, single-screen app: never scroll. */
+    overflow: hidden;
 }
 
-#startGameBtn {
-    background-color: #8cd5ed;
-    color: #262626;
-    border-radius: 30px;
-    border: 0px;
-    cursor: pointer;
-    order: 1;
-    padding: 2vh;
-    margin: 2vh;
+main {
+    height: 100%;
 }
 
-#startCPUGame {
-    background-color: #8cd5ed;
-    color: #262626;
-    border-radius: 30px;
-    border: 0px;
-    cursor: pointer;
-    order: 1;
-    padding: 2vh;
-    margin: 2vh;
-}
+/* ---- Layout ------------------------------------------------------------ */
 
+/* Portrait / narrow: board on top, panel stacked below. */
 #chessContainer {
+    height: 100vh;
+    height: 100dvh;
+    box-sizing: border-box;
     display: flex;
     flex-direction: column;
     align-items: center;
-    justify-content: space-evenly;
-    height: 100vh;
-    box-sizing: border-box;
-    padding: 5vw;
+    gap: clamp(8px, 1.6vh, 16px);
+    padding: clamp(10px, 2vh, 20px);
+    overflow: hidden;
+}
+
+#boardArea {
+    display: flex;
+    flex-direction: column;
+    gap: 6px;
+    flex: 0 0 auto;
+    width: min(94vw, 56vh);
 }
 
 #chessBoard {
-    aspect-ratio: 1 / 1;
-    width: 90vw; /* use the smaller of width or height */
+    width: 100%;
     height: auto;
-    max-height: 90vw;
+    aspect-ratio: 1 / 1;
+    border-radius: 6px;
+    overflow: hidden;
+    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.45);
 }
 
-#boardContainer {
-    align-content: center;
-    flex-grow: 1;
-}
-
-.sideContent {
+#gamePanel {
+    width: min(94vw, 56vh);
+    flex: 1 1 auto;
+    min-height: 0;
     display: flex;
     flex-direction: column;
-    align-content: center;
-    justify-content: center;
-    text-align: center;
+    background: var(--panel);
+    border-radius: var(--radius);
+    overflow: hidden;
+    box-shadow: 0 6px 24px rgba(0, 0, 0, 0.35);
 }
 
-#textContainer {
-    flex-direction: column;
-    order: -1;
-    flex-shrink: 1;
-    font-size: large;
-    margin: 5vw;
-}
-
-#buttonContainer {
-    flex-grow: 3;
-}
-
-/* Put UI to left/right when screen is short */
+/* Landscape / wide: board left, game panel right (chess.com style). */
 @media (min-aspect-ratio: 1/1) {
     #chessContainer {
-        display: grid;
-        grid-template-columns: auto, auto;
-        grid-template-rows: auto, auto;
-        align-items: center;
         flex-direction: row;
+        align-items: center;
         justify-content: center;
-        align-items: center;
-        height: 100vh;
-        padding: 0;
+        gap: clamp(16px, 3vw, 48px);
+        padding: clamp(12px, 3vh, 28px);
     }
 
-    .sideContent {
-        display: flex;
-        flex-direction: column;
-        flex-grow: 1;
-        flex-shrink: 0;
-        align-items: center;
-        text-align: center;
-        padding: min(5vw, 5vh);
-    }
-
-    #boardContainer {
-        grid-row: 1 / span 2;
-        grid-column: 1;
-    }
-
-    #textContainer {
-        grid-row: 1;
-        grid-column: 2;
-        text-align: center;
-        font-size: x-large;
-    }
-
-    #buttonContainer {
-        grid-row: 2;
-        grid-column: 2;
-        text-align: left;
-        align-self: start;
-    }
-
-    #startGameBtn {
-        padding: 1vw;
-        font-size: large;
-    }
-
-    #startCPUGame {
-        padding: 1vw;
-        margin: 1vw;
-        font-size: large;
+    #boardArea {
+        width: auto;
+        height: 100%;
+        justify-content: center;
+        flex: 0 0 auto;
     }
 
     #chessBoard {
-        aspect-ratio: 1 / 1;
-        flex-shrink: 1;
-        width: min(90vh, 90vw);
-        max-height: 90vh;
+        width: min(72vh, 54vw);
+        height: min(72vh, 54vw);
     }
 
-    #difficultyButtonContainer {
-        grid-template-columns: repeat(10, 1fr);
+    .playerBar {
+        width: min(72vh, 54vw);
+    }
+
+    #gamePanel {
+        width: clamp(300px, 26vw, 380px);
+        height: min(86vh, 100%);
+        align-self: center;
+    }
+}
+
+/* ---- Player bars ------------------------------------------------------- */
+
+.playerBar {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+    width: 100%;
+    box-sizing: border-box;
+    height: var(--bar-h);
+    padding: 0 12px;
+    background: var(--bar);
+    border-radius: 8px;
+}
+
+.playerDot {
+    width: 14px;
+    height: 14px;
+    border-radius: 50%;
+    flex: 0 0 auto;
+}
+
+.playerDot.white {
+    background: #ededed;
+    box-shadow: 0 0 0 1px rgba(0, 0, 0, 0.4) inset;
+}
+
+.playerDot.black {
+    background: #2c2c2c;
+    box-shadow: 0 0 0 1px #565656 inset;
+}
+
+.playerName {
+    font-weight: 600;
+    white-space: nowrap;
+}
+
+.capturedTray {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    gap: 1px;
+    flex: 1;
+    min-width: 0;
+    overflow: hidden;
+}
+
+.capturedPiece {
+    height: clamp(15px, calc(var(--bar-h) * 0.58), 26px);
+    width: auto;
+    margin-right: -5px;
+}
+
+.advantage {
+    margin-left: auto;
+    font-weight: 700;
+    color: var(--accent);
+    white-space: nowrap;
+}
+
+/* ---- Game panel -------------------------------------------------------- */
+
+.panelHeader {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+    padding: 14px 16px;
+    border-bottom: 1px solid var(--line);
+    flex: 0 0 auto;
+}
+
+.panelLogo {
+    font-size: 1.5rem;
+    color: var(--accent);
+    line-height: 1;
+}
+
+.panelHeader h1 {
+    margin: 0;
+    font-size: 1.25rem;
+    font-weight: 700;
+    letter-spacing: 0.01em;
+}
+
+#moveList {
+    flex: 1 1 auto;
+    min-height: 0;
+    overflow-y: auto;
+    padding: 6px 0;
+}
+
+.movePlaceholder {
+    margin: 0;
+    padding: 18px 16px;
+    color: var(--muted);
+    font-size: 0.95rem;
+}
+
+.moveRow {
+    display: grid;
+    grid-template-columns: 2.4em 1fr 1fr;
+    align-items: center;
+    gap: 6px;
+    padding: 4px 14px;
+    font-size: 0.98rem;
+}
+
+.moveRow:nth-child(odd) {
+    background: var(--panel-row);
+}
+
+.moveNum {
+    color: var(--muted);
+    font-variant-numeric: tabular-nums;
+}
+
+.moveSan {
+    padding: 2px 7px;
+    border-radius: 5px;
+}
+
+.moveSan.latest {
+    background: var(--accent);
+    color: var(--accent-ink);
+    font-weight: 600;
+}
+
+#statusLine {
+    flex: 0 0 auto;
+    padding: 12px 16px;
+    border-top: 1px solid var(--line);
+    color: var(--muted);
+    font-weight: 500;
+}
+
+#statusLine.alert {
+    color: var(--accent);
+    font-weight: 700;
+}
+
+#panelButtons {
+    flex: 0 0 auto;
+    display: flex;
+    flex-direction: column;
+    gap: 10px;
+    padding: 14px 16px 16px;
+    border-top: 1px solid var(--line);
+}
+
+.btn {
+    font-family: inherit;
+    font-weight: 600;
+    font-size: clamp(0.92rem, 1vw, 1.05rem);
+    border: 0;
+    border-radius: 8px;
+    padding: clamp(10px, 1.4vh, 14px) 16px;
+    cursor: pointer;
+    transition: transform 0.08s ease, filter 0.15s ease, background 0.15s ease;
+}
+
+.btn:active {
+    transform: translateY(1px);
+}
+
+.btn-primary {
+    background: var(--accent);
+    color: var(--accent-ink);
+}
+
+.btn-primary:hover {
+    filter: brightness(1.08);
+}
+
+.btn-secondary {
+    background: #363a44;
+    color: var(--text);
+}
+
+.btn-secondary:hover {
+    background: #424752;
+}
+
+.btn-ghost {
+    background: transparent;
+    color: var(--accent);
+    border: 1px solid var(--line);
+}
+
+.btn-ghost:hover {
+    background: #2a2e37;
+}
+
+#watchLink {
+    color: var(--muted);
+    text-decoration: none;
+    text-align: center;
+    font-size: 0.9rem;
+    margin-top: 2px;
+}
+
+#watchLink:hover {
+    color: var(--accent);
+}
+
+/* ---- Mobile chrome (hidden on desktop) --------------------------------- */
+
+.iconBtn {
+    background: transparent;
+    border: 0;
+    color: var(--text);
+    font-size: 1.7rem;
+    line-height: 1;
+    cursor: pointer;
+    padding: 0 4px;
+}
+
+.iconBtn:hover {
+    color: var(--accent);
+}
+
+#menuClose {
+    margin-left: auto;
+}
+
+/* Default (tablet/desktop): no mobile bar, menu button, or sheet chrome. */
+#mobileBar,
+#menuBackdrop,
+#menuClose {
+    display: none;
+}
+
+/* ---- Phone layout ------------------------------------------------------ */
+/* The full panel doesn't fit alongside a usable board on a phone, so we show
+   the board + a slim status/menu bar, and tuck the move list and secondary
+   actions into a slide-up sheet. The page itself still never scrolls. */
+@media (max-width: 640px) {
+    #chessContainer {
+        flex-direction: column;
+        justify-content: flex-start;
+        gap: 8px;
+        padding: 8px;
+    }
+
+    #boardArea {
+        width: min(94vw, 60vh);
+        flex: 0 0 auto;
+    }
+
+    .playerBar {
+        width: 100%;
+    }
+
+    /* Right rail becomes a hidden bottom sheet, revealed by the Menu button. */
+    #gamePanel {
+        display: none;
+        position: fixed;
+        left: 0;
+        right: 0;
+        bottom: 0;
+        top: auto;
+        width: 100%;
+        height: auto;
+        max-height: 85dvh;
+        border-radius: 16px 16px 0 0;
+        z-index: 60;
+        box-shadow: 0 -8px 30px rgba(0, 0, 0, 0.5);
+    }
+
+    body.menu-open #gamePanel {
+        display: flex;
+    }
+
+    /* The slim bar already shows status, so hide the sheet's inline copy. */
+    #gamePanel #statusLine {
+        display: none;
+    }
+
+    #menuClose {
+        display: block;
+    }
+
+    #menuBackdrop {
+        position: fixed;
+        inset: 0;
+        background: rgba(0, 0, 0, 0.55);
+        z-index: 55;
+    }
+
+    body.menu-open #menuBackdrop {
+        display: block;
+    }
+
+    #mobileBar {
+        display: flex;
+        align-items: center;
+        gap: 10px;
+        width: min(94vw, 60vh);
+        flex: 0 0 auto;
+        box-sizing: border-box;
+        background: var(--panel);
+        border-radius: 10px;
+        padding: 8px 10px;
+    }
+
+    #mobileStatus {
+        flex: 1;
+        min-width: 0;
+        color: var(--muted);
+        font-weight: 600;
+        white-space: nowrap;
+        overflow: hidden;
+        text-overflow: ellipsis;
+    }
+
+    #mobileStatus.alert {
+        color: var(--accent);
+    }
+
+    #mobileBar #menuToggle {
+        flex: 0 0 auto;
+        padding: 10px 20px;
     }
 }

JoshHeaps.Net/wwwroot/css/chess/spectate.css

@@ -0,0 +1,165 @@
+html, body {
+    background-color: #2b2c30;
+    color: #d6d6d6;
+    margin: 0;
+}
+
+#watchHeader {
+    text-align: center;
+    padding: 2rem 1rem 0;
+}
+
+#watchHeader h1 {
+    margin: 0;
+}
+
+#watchStatus {
+    color: #9a9a9a;
+}
+
+#watchControls {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    flex-wrap: wrap;
+    gap: 0.75rem;
+    margin: 1rem 0;
+}
+
+.enginePicker {
+    display: flex;
+    align-items: center;
+    gap: 0.4rem;
+    border: 1px solid #444;
+    border-radius: 8px;
+    padding: 0.3rem 0.6rem 0.5rem;
+}
+
+.enginePicker legend {
+    color: #9a9a9a;
+    font-size: 0.8rem;
+    padding: 0 0.3rem;
+}
+
+#watchControls select {
+    background-color: #1e1e1e;
+    color: #d6d6d6;
+    border: 1px solid #444;
+    border-radius: 6px;
+    padding: 0.4rem;
+}
+
+#startCpuVsCpu {
+    background-color: #8cd5ed;
+    color: #262626;
+    border: 0;
+    border-radius: 30px;
+    padding: 0.6rem 1.2rem;
+    cursor: pointer;
+}
+
+#startCpuVsCpu:hover {
+    background-color: #a5e0f2;
+}
+
+#backToPlay {
+    color: #8cd5ed;
+    text-decoration: none;
+}
+
+#backToPlay:hover {
+    text-decoration: underline;
+}
+
+#gamesFeed {
+    display: grid;
+    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
+    gap: 1.5rem;
+    padding: 2rem;
+    box-sizing: border-box;
+}
+
+.gameCard {
+    background-color: #1e1e1e;
+    border-radius: 10px;
+    padding: 1rem;
+    box-shadow: 0 0 12px rgba(0, 0, 0, 0.4);
+    position: relative;
+    cursor: pointer;
+}
+
+.gameResult {
+    text-align: center;
+    font-weight: bold;
+    color: #8cd5ed;
+    margin-top: 0.75rem;
+}
+
+.copyPgnBtn {
+    display: block;
+    margin: 0.75rem auto 0;
+    background-color: #8cd5ed;
+    color: #262626;
+    border: 0;
+    border-radius: 30px;
+    padding: 0.5rem 1rem;
+    cursor: pointer;
+}
+
+.copyPgnBtn:hover {
+    background-color: #a5e0f2;
+}
+
+.backButton {
+    display: none;
+}
+
+body.fullscreen-open {
+    overflow: hidden;
+}
+
+.gameCard.fullscreen {
+    position: fixed;
+    inset: 0;
+    z-index: 1000;
+    margin: 0;
+    border-radius: 0;
+    cursor: default;
+    background-color: #2b2c30;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+}
+
+.gameCard.fullscreen .miniBoard {
+    width: min(90vh, 90vw);
+    height: min(90vh, 90vw);
+}
+
+.gameCard.fullscreen .backButton {
+    display: inline-block;
+    position: absolute;
+    top: 1rem;
+    left: 1rem;
+    background-color: #8cd5ed;
+    color: #262626;
+    border: 0;
+    border-radius: 30px;
+    padding: 0.6rem 1.2rem;
+    cursor: pointer;
+}
+
+.gameCardHeader {
+    text-align: center;
+    font-weight: bold;
+    margin-bottom: 0.75rem;
+}
+
+.miniBoard {
+    width: 100%;
+    aspect-ratio: 1 / 1;
+    display: grid;
+    grid-template-columns: repeat(8, 1fr);
+    grid-template-rows: repeat(8, 1fr);
+}

JoshHeaps.Net/wwwroot/css/chess/weights.css

@@ -0,0 +1,187 @@
+body {
+    margin: 0;
+    background-color: #141414;
+    color: #d6d6d6;
+    font-family: "Segoe UI", system-ui, sans-serif;
+}
+
+#weightsHeader {
+    text-align: center;
+    padding: 1.5rem 1rem 0.5rem;
+}
+
+#weightsHeader h1 {
+    margin: 0 0 0.25rem;
+    font-size: 1.6rem;
+}
+
+#weightsStatus {
+    color: #9a9a9a;
+    margin: 0.25rem 0 1rem;
+}
+
+#weightsControls {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    gap: 1.25rem;
+    margin-bottom: 0.5rem;
+}
+
+.heatLegend {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+    font-size: 0.8rem;
+    color: #9a9a9a;
+}
+
+.legendBar {
+    width: 120px;
+    height: 10px;
+    border-radius: 5px;
+    background: linear-gradient(to right, rgba(232, 74, 74, 1), #2a2a2a, rgba(74, 134, 232, 1));
+}
+
+#refreshWeights {
+    background-color: #8cd5ed;
+    color: #262626;
+    border: 0;
+    border-radius: 30px;
+    padding: 0.5rem 1.1rem;
+    cursor: pointer;
+}
+
+#refreshWeights:hover {
+    background-color: #a5e0f2;
+}
+
+#backToWatch {
+    display: inline-block;
+    margin-top: 0.5rem;
+    color: #8cd5ed;
+    text-decoration: none;
+}
+
+.weightsSection {
+    margin: 0 auto;
+    max-width: 1200px;
+    padding: 0.5rem 1rem;
+}
+
+.weightsSection h2 {
+    text-align: center;
+    font-size: 1.2rem;
+    margin: 1rem 0 0.25rem;
+}
+
+.sectionHint {
+    text-align: center;
+    color: #9a9a9a;
+    font-size: 0.8rem;
+    margin: 0 0 0.75rem;
+}
+
+.weightsGrid {
+    display: flex;
+    flex-wrap: wrap;
+    justify-content: center;
+    gap: 1.25rem;
+    padding: 0.5rem 0;
+}
+
+.featurePanel {
+    max-width: 520px;
+    margin: 0 auto;
+    display: flex;
+    flex-direction: column;
+    gap: 0.4rem;
+}
+
+.featureRow {
+    display: flex;
+    align-items: center;
+    gap: 0.6rem;
+}
+
+.featureLabel {
+    flex: 0 0 6.5rem;
+    font-size: 0.8rem;
+    color: #c8c8c8;
+    text-align: right;
+}
+
+.featureTrack {
+    flex: 1 1 auto;
+    height: 14px;
+    background-color: #232323;
+    border-radius: 7px;
+    overflow: hidden;
+}
+
+.featureBar {
+    height: 100%;
+    border-radius: 7px;
+    min-width: 2px;
+}
+
+.featureValue {
+    flex: 0 0 3rem;
+    font-size: 0.8rem;
+    color: #e8e8e8;
+    text-align: left;
+}
+
+.weightBoard {
+    background-color: #1c1c1c;
+    border: 1px solid #2e2e2e;
+    border-radius: 10px;
+    padding: 0.75rem;
+}
+
+.weightBoardHeader {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+    margin-bottom: 0.5rem;
+    font-weight: 600;
+}
+
+.weightBoardIcon {
+    width: 22px;
+    height: 22px;
+}
+
+.weightRange {
+    margin-left: auto;
+    font-weight: 400;
+    font-size: 0.75rem;
+    color: #888;
+}
+
+.miniHeat {
+    display: grid;
+    grid-template-columns: 1.1rem repeat(8, 34px);
+}
+
+.heatSquare {
+    width: 34px;
+    height: 34px;
+    box-sizing: border-box;
+    border: 1px solid #2a2a2a;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    font-size: 0.62rem;
+    color: #f0f0f0;
+    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.8);
+}
+
+.heatLabel {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    padding: 2px 0;
+    font-size: 0.6rem;
+    color: #777;
+}

JoshHeaps.Net/wwwroot/css/echo/echo.css

@@ -0,0 +1,287 @@
+body {
+    background: var(--color-bg);
+    color: var(--color-text);
+    font-family: var(--font-body);
+    margin: 0;
+    padding: 2rem 1.25rem 4rem;
+}
+
+#echoHeader {
+    max-width: 46rem;
+    margin: 0 auto 1.5rem;
+}
+
+#echoHeader h1 {
+    color: var(--color-heading);
+    font-size: 2.4rem;
+    letter-spacing: -0.02em;
+    margin: 0 0 0.6rem;
+}
+
+.echo-blurb {
+    line-height: 1.6;
+    margin: 0 0 0.5rem;
+}
+
+.echo-privacy {
+    color: var(--color-text-subtle);
+    font-family: var(--font-mono);
+    font-size: 0.8rem;
+    margin: 0;
+}
+
+#echoControls {
+    align-items: flex-end;
+    display: flex;
+    flex-wrap: wrap;
+    gap: 0.75rem;
+    margin: 0 auto 1rem;
+    max-width: 46rem;
+}
+
+#echoControls label {
+    color: var(--color-text-muted);
+    display: flex;
+    flex-direction: column;
+    font-family: var(--font-mono);
+    font-size: 0.75rem;
+    gap: 0.3rem;
+    text-transform: lowercase;
+}
+
+#echoControls input {
+    background: var(--color-surface-raised);
+    border: 1px solid var(--color-border);
+    border-radius: 6px;
+    color: var(--color-heading);
+    font-family: var(--font-mono);
+    font-size: 1rem;
+    padding: 0.5rem 0.6rem;
+    width: 7rem;
+}
+
+#echoControls input:focus {
+    border-color: var(--color-accent-border);
+    outline: none;
+}
+
+#echoControls button {
+    background: transparent;
+    border: 1px solid var(--color-accent-border);
+    border-radius: 6px;
+    color: var(--color-accent);
+    cursor: pointer;
+    font-family: var(--font-mono);
+    font-size: 0.9rem;
+    padding: 0.6rem 1.1rem;
+    transition: background 0.15s ease, color 0.15s ease;
+}
+
+#echoControls button:hover:not(:disabled) {
+    background: var(--color-accent);
+    color: var(--color-bg);
+}
+
+#echoControls button:disabled {
+    border-color: var(--color-border);
+    color: var(--color-text-subtle);
+    cursor: default;
+}
+
+.echo-status,
+.echo-share {
+    font-family: var(--font-mono);
+    font-size: 0.8rem;
+    margin: 0 auto 0.4rem;
+    max-width: 46rem;
+}
+
+.echo-share a {
+    color: var(--color-accent);
+    text-decoration: none;
+    word-break: break-all;
+}
+
+#echoWarnings {
+    margin: 0 auto;
+    max-width: 46rem;
+}
+
+.echo-warning {
+    background: rgba(255, 170, 0, 0.08);
+    border: 1px solid rgba(255, 170, 0, 0.35);
+    border-radius: 6px;
+    color: #ffcc66;
+    font-size: 0.85rem;
+    line-height: 1.5;
+    margin: 0.5rem 0;
+    padding: 0.7rem 0.9rem;
+}
+
+.echo-readout {
+    align-items: baseline;
+    display: flex;
+    flex-direction: column;
+    gap: 0.4rem;
+    margin: 2rem auto;
+    max-width: 46rem;
+    min-height: 6rem;
+}
+
+.echo-metres {
+    color: var(--color-accent);
+    font-family: var(--font-mono);
+    font-size: clamp(3.5rem, 14vw, 7rem);
+    font-variant-numeric: tabular-nums;
+    line-height: 1;
+}
+
+.echo-metres small {
+    color: var(--color-text-subtle);
+    font-size: 0.28em;
+    margin-left: 0.2em;
+}
+
+.echo-readout-detail,
+.echo-readout-idle {
+    color: var(--color-text-subtle);
+    font-family: var(--font-mono);
+    font-size: 0.8rem;
+}
+
+#echoPanels {
+    display: grid;
+    gap: 1rem;
+    grid-template-columns: repeat(auto-fit, minmax(min(100%, 18rem), 1fr));
+    margin: 0 auto;
+    max-width: 46rem;
+}
+
+.echo-panel {
+    background: var(--color-surface);
+    border: 1px solid var(--color-border);
+    border-radius: 8px;
+    padding: 1rem 1.1rem;
+}
+
+.echo-panel-wide {
+    margin: 1rem auto 0;
+    max-width: 46rem;
+}
+
+.echo-panel h2 {
+    color: var(--color-heading-secondary);
+    font-family: var(--font-mono);
+    font-size: 0.8rem;
+    font-weight: 500;
+    letter-spacing: 0.08em;
+    margin: 0 0 0.75rem;
+    text-transform: uppercase;
+}
+
+.echo-hint {
+    color: var(--color-text-subtle);
+    font-size: 0.8rem;
+    margin: -0.4rem 0 0.75rem;
+}
+
+#echoRoster {
+    list-style: none;
+    margin: 0;
+    padding: 0;
+}
+
+.echo-device {
+    border-bottom: 1px solid var(--color-border);
+    font-family: var(--font-mono);
+    font-size: 0.85rem;
+    padding: 0.45rem 0;
+}
+
+.echo-device:last-child {
+    border-bottom: none;
+}
+
+.echo-device-self {
+    color: var(--color-accent);
+}
+
+#echoPairs {
+    overflow-x: auto;
+}
+
+#echoPairs table {
+    border-collapse: collapse;
+    font-family: var(--font-mono);
+    font-size: 0.85rem;
+    width: 100%;
+}
+
+#echoPairs th {
+    color: var(--color-text-subtle);
+    font-weight: 500;
+    padding: 0 0.6rem 0.4rem 0;
+    text-align: left;
+}
+
+#echoPairs td {
+    border-top: 1px solid var(--color-border);
+    color: var(--color-heading-secondary);
+    font-variant-numeric: tabular-nums;
+    padding: 0.4rem 0.6rem 0.4rem 0;
+}
+
+.echo-dropped td {
+    color: var(--color-text-subtle);
+    text-decoration: line-through;
+}
+
+.echo-slots {
+    list-style: none;
+    margin: 0 0 0.6rem;
+    padding: 0;
+}
+
+.echo-slots li {
+    color: var(--color-heading-secondary);
+    font-family: var(--font-mono);
+    font-size: 0.85rem;
+    font-variant-numeric: tabular-nums;
+    padding: 0.2rem 0;
+}
+
+.echo-slots .echo-missed {
+    color: #ff7676;
+}
+
+.echo-diag-line {
+    color: var(--color-text-subtle);
+    font-family: var(--font-mono);
+    font-size: 0.75rem;
+    line-height: 1.5;
+    margin: 0;
+}
+
+.echo-diag-line strong {
+    color: #ff7676;
+}
+
+#echoTrace {
+    display: block;
+    height: 160px;
+    width: 100%;
+}
+
+.echo-back {
+    color: var(--color-text-subtle);
+    display: block;
+    font-family: var(--font-mono);
+    font-size: 0.8rem;
+    margin: 2rem auto 0;
+    max-width: 46rem;
+    text-decoration: none;
+}
+
+.echo-back:hover {
+    color: var(--color-accent);
+}

JoshHeaps.Net/wwwroot/css/home/blog.css

@@ -0,0 +1,65 @@
+/* ── Blog Section ── */
+
+#BlogBox {
+    max-width: 1100px;
+    margin: clamp(4rem, 8vw, 8rem) auto;
+    padding: 0 clamp(1.5rem, 5vw, 4rem);
+}
+
+#blogPostsList {
+    display: flex;
+    flex-direction: column;
+    gap: 1rem;
+}
+
+.blog-teaser-item {
+    display: flex;
+    flex-direction: column;
+    gap: 0.3rem;
+    padding: 1.25rem 1.5rem;
+    border-left: 2px solid var(--color-accent-border);
+    background: var(--color-surface);
+    border-radius: 0 8px 8px 0;
+    transition: background 0.2s;
+}
+
+.blog-teaser-item:hover {
+    background: var(--color-surface-hover);
+}
+
+.blog-teaser-title {
+    font-size: clamp(1rem, 1.5vw, 1.15rem);
+    font-weight: 600;
+    color: var(--color-heading-secondary);
+    text-decoration: none;
+    transition: color 0.2s;
+}
+
+.blog-teaser-title:hover {
+    color: var(--color-accent);
+}
+
+.blog-teaser-date {
+    font-size: 0.75rem;
+    color: var(--color-text-subtle);
+}
+
+.blog-teaser-summary {
+    font-size: 0.85rem;
+    color: var(--color-text-muted);
+    margin: 0.25rem 0 0;
+    line-height: 1.6;
+}
+
+.blog-view-all {
+    display: inline-block;
+    margin-top: 1.5rem;
+    font-size: 0.85rem;
+    color: var(--color-accent);
+    text-decoration: none;
+    transition: color 0.2s;
+}
+
+.blog-view-all:hover {
+    color: var(--color-accent-hover);
+}

JoshHeaps.Net/wwwroot/css/home/footer.css

@@ -1,17 +1,25 @@
-#Contacts {
-    margin-top: 20vw;
+/* ── Footer / Contacts ── */
+
+#Contacts {
+    display: flex;
+    justify-content: center;
+    gap: 1.5rem;
+    padding: clamp(4rem, 8vw, 6rem) 0 clamp(3rem, 5vw, 4rem);
+}
+
+.social-link {
+    display: flex;
+    align-items: center;
+    text-decoration: none;
 }
 
 .social-icon {
     height: auto;
-    width: 3.5vw;
-    margin-bottom: 5vw;
-    margin-left: 3vw;
-    fill: rgb(212, 212, 212);
-    transition: fill 0.5s;
+    width: clamp(1.25rem, 2.5vw, 1.75rem);
+    fill: var(--color-text-subtle);
+    transition: fill 0.2s;
 }
 
-.social-icon:hover {
-    fill: white;
-    transition: fill 0.5s;
+.social-link:hover .social-icon {
+    fill: var(--color-heading-secondary);
 }

JoshHeaps.Net/wwwroot/css/home/imageLeftProject.css

@@ -1,36 +0,0 @@
-.diagonal-section-left {
-    position: absolute;
-    clip-path: polygon(0 0, 85vw 0, 60vw 100%, 0 100%);
-    background-color: rgb(104, 255, 0, 0.39);
-    transition: clip-path 0.5s ease;
-}
-
-.diagonal-section-left:has(.projectImage:hover) {
-    clip-path: polygon(0 0, 87vw 0, 58vw 100%, 0 100%);
-    transition: clip-path 0.5s ease;
-}
-
-.projectImageLeft {
-    width: 33vw;
-    height: auto;
-    margin: 3vw;
-}
-
-.projectTextRight {
-    position: relative;
-    z-index: 1;
-    margin-left: 50vw;
-}
-
-.projectHeaderRight {
-    margin: 0;
-    color: rgb(212, 212, 212);
-    font-size: 4vw;
-}
-
-.projectDescriptionRight {
-    margin: 0;
-    color: rgb(212, 212, 212);
-    font-size: 2vw;
-    width: 40vw;
-}

JoshHeaps.Net/wwwroot/css/home/imageRightProject.css

@@ -1,38 +0,0 @@
-.diagonal-section-right {
-    position: absolute;
-    clip-path: polygon(40vw 0, 100% 0, 100% 100%, 15vw 100%);
-    background-color: rgb(104, 255, 0, 0.39);
-    transition: clip-path 0.5s ease;
-}
-
-.diagonal-section-right:has(.projectImage:hover) {
-    clip-path: polygon(42vw 0, 100% 0, 100% 100%, 13vw 100%);
-    transition: clip-path 0.5s ease;
-}
-
-.projectImageRight {
-    width: 33vw;
-    height: auto;
-    margin: 3vw;
-    float: right;
-}
-
-.projectTextLeft {
-    position: relative;
-    z-index: 1;
-}
-
-.projectHeaderLeft {
-    margin: 0;
-    color: rgb(212, 212, 212);
-    font-size: 4vw;
-    margin-left: 10vw;
-}
-
-.projectDescriptionLeft {
-    margin: 0;
-    color: rgb(212, 212, 212);
-    font-size: 2vw;
-    width: 40vw;
-    margin-left: 10vw;
-}

JoshHeaps.Net/wwwroot/css/home/project.css

@@ -1,29 +1,90 @@
-#ProjectsBox {
+/* ── Projects Section ── */
+
+#ProjectsBox {
+    max-width: 1100px;
+    margin: 0 auto;
+    padding: 0 clamp(1.5rem, 5vw, 4rem);
+}
+
+.projects-grid {
     display: grid;
-    grid-auto-rows: 1fr;
-    gap: 20vw;
+    grid-template-columns: repeat(auto-fill, minmax(min(320px, 100%), 1fr));
+    gap: 1.5rem;
 }
 
-.projectContainer {
-    position: relative;
-    display: flex;
-    align-items: center;
+/* ── Card ── */
+
+.project-card {
+    border: 1px solid var(--color-border);
+    border-radius: 12px;
+    overflow: hidden;
+    background: var(--color-surface);
+    transition: border-color 0.25s, transform 0.25s;
 }
 
-.displayBox {
-    width: 100vw;
-    height: auto;
+.project-card:hover {
+    border-color: var(--color-border-hover);
+    transform: translateY(-2px);
 }
 
-a.projectContainer {
-    text-decoration: none;
+/* ── Image ── */
+
+.project-image-link {
+    display: block;
+    overflow: hidden;
 }
 
 .projectImage {
-    transition: width 0.5s ease;
+    width: 100%;
+    height: auto;
+    display: block;
+    transition: transform 0.4s ease;
 }
 
-.projectImage:hover {
-    width: 40vw;
-    transition: width 0.5s ease;
+.project-card:hover .projectImage {
+    transform: scale(1.03);
+}
+
+/* ── Info ── */
+
+.project-info {
+    padding: 1.25rem 1.5rem 1.5rem;
+}
+
+.project-title {
+    margin: 0 0 0.5rem;
+    font-size: 1.1rem;
+    font-weight: 600;
+    color: var(--color-heading);
+    letter-spacing: -0.01em;
+}
+
+.project-description {
+    margin: 0 0 1rem;
+    font-size: 0.85rem;
+    line-height: 1.65;
+    color: var(--color-text-muted);
+}
+
+.project-link {
+    font-size: 0.8rem;
+    color: var(--color-accent);
+    text-decoration: none;
+    transition: color 0.2s;
+}
+
+.project-link:hover {
+    color: var(--color-accent-hover);
+}
+
+/* ── Mobile ── */
+
+@media (max-width: 600px) {
+    .projects-grid {
+        grid-template-columns: 1fr;
+    }
+
+    .project-info {
+        padding: 1rem 1.25rem 1.25rem;
+    }
 }

JoshHeaps.Net/wwwroot/css/home/site.css

@@ -1,67 +1,134 @@
-body {
-    margin: 0px;
-    background-color: #2b2c30;
-    color: #09ff00;
-    overflow-x: hidden;
-    cursor: default;
+*, *::before, *::after {
+    box-sizing: border-box;
 }
 
+body {
+    margin: 0;
+    background-color: var(--color-bg);
+    color: var(--color-text);
+    overflow-x: hidden;
+    font-family: var(--font-body);
+    line-height: 1.6;
+}
+
+/* ── Navigation ── */
+
 #Header {
-    margin-top: 2vw;
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    max-width: 1100px;
+    margin: 0 auto;
+    padding: 2rem clamp(1.5rem, 5vw, 4rem);
 }
 
-.headerOption {
-    font: bold 2vw arial;
-    display: inline;
-    margin-left: 10vw;
+.site-name {
+    font-size: 1.05rem;
+    font-weight: 700;
+    color: var(--color-heading);
+    letter-spacing: -0.01em;
+}
+
+.nav-links {
+    display: flex;
+    gap: clamp(1.25rem, 3vw, 2.5rem);
+}
+
+.nav-link {
+    font-size: 0.875rem;
+    color: var(--color-text-subtle);
     cursor: pointer;
-    transition: color 0.5s ease, font 0.5s ease;
+    transition: color 0.2s;
+    text-decoration: none;
 }
 
-.headerOption:hover {
-    font: bold 2.3vw arial;
-    transition: color 0.5s ease, font 0.5s ease;
+.nav-link:hover {
+    color: var(--color-heading-secondary);
+}
+
+/* ── Hero / Welcome Message ── */
+
+#Hero {
+    max-width: 1100px;
+    margin: 0 auto;
+    padding: clamp(4rem, 10vw, 8rem) clamp(1.5rem, 5vw, 4rem) clamp(4rem, 8vw, 6rem);
 }
 
 #WelcomeMessage {
-    font: 3vw arial;
-    width: auto;
-    height: 40vw;
-    margin-top: 15vw;
-    text-align: left;
-    padding-left: 10vw;
-    padding-right: 10vw;
+    font-size: clamp(1.25rem, 2.2vw, 1.75rem);
+    max-width: 720px;
+    min-height: clamp(12rem, 28vw, 20rem);
+    line-height: 1.7;
+    color: var(--color-accent);
+    font-family: var(--font-mono);
 }
 
+/* ── Section Titles ── */
+
+.section-title {
+    font-size: clamp(1.3rem, 2.2vw, 1.75rem);
+    font-weight: 700;
+    color: var(--color-heading);
+    margin: 0 0 clamp(1.5rem, 3vw, 2.5rem);
+    letter-spacing: -0.02em;
+}
+
+/* ── Demos ── */
+
 #DemosBox {
-    margin: 10vw;
-    display: flex;
-    flex-direction: column;
-    justify-content: end;
-    width: 80%;
+    max-width: 1100px;
+    margin: clamp(4rem, 8vw, 8rem) auto;
+    padding: 0 clamp(1.5rem, 5vw, 4rem);
 }
 
-#DemoHeader {
-    margin: 0;
-    color: rgb(212, 212, 212);
-    font-size: 4vw;
+#buttonWrapper {
+    display: grid;
+    grid-template-columns: repeat(auto-fill, minmax(min(200px, 100%), 1fr));
+    gap: 0.75rem;
 }
 
 .demoButton {
-    margin-top: 5vw;
-    margin-right: 2vw;
-    padding-top: 0.5vw;
-    padding-bottom: 0.5vw;
+    padding: 0.875rem 1.25rem;
     text-align: center;
-    border: none;
-    border-radius: 5vw;
-    width: 20vw;
-    height: 8vw;
-    font-size: 2vw;
-    background-color: rgb(104, 255, 0, 0.39);
+    border: 1px solid var(--color-border);
+    border-radius: 8px;
+    font-size: 0.875rem;
+    font-family: inherit;
+    background: var(--color-surface);
+    color: var(--color-text);
     cursor: pointer;
+    transition: background 0.2s, border-color 0.2s, color 0.2s;
+}
+
+.demoButton:hover {
+    background: var(--color-surface-hover);
+    border-color: var(--color-border-hover);
+    color: var(--color-heading-secondary);
 }
 
 #MoreFiller {
     cursor: default;
+    opacity: 0.3;
+}
+
+#MoreFiller:hover {
+    background: var(--color-surface);
+    border-color: var(--color-border);
+    color: var(--color-text);
+}
+
+/* ── Mobile ── */
+
+@media (max-width: 600px) {
+    #Header {
+        padding: 1.25rem 1.25rem;
+    }
+
+    .site-name {
+        font-size: 0.95rem;
+    }
+
+    .nav-link {
+        font-size: 0.8rem;
+    }
 }

JoshHeaps.Net/wwwroot/css/variables.css

@@ -0,0 +1,28 @@
+:root {
+    /* Backgrounds */
+    --color-bg: #0a0a0a;
+    --color-surface: rgba(255, 255, 255, 0.02);
+    --color-surface-hover: rgba(255, 255, 255, 0.04);
+    --color-surface-raised: rgba(255, 255, 255, 0.05);
+    --color-surface-raised-hover: rgba(255, 255, 255, 0.08);
+
+    /* Text */
+    --color-heading: #fff;
+    --color-heading-secondary: #e0e0e0;
+    --color-text: #b0b0b0;
+    --color-text-muted: #aaa;
+    --color-text-subtle: #777;
+
+    /* Accent */
+    --color-accent: #09ff00;
+    --color-accent-hover: #5fff5f;
+
+    /* Borders */
+    --color-border: rgba(255, 255, 255, 0.07);
+    --color-border-hover: rgba(255, 255, 255, 0.15);
+    --color-accent-border: rgba(9, 255, 0, 0.4);
+
+    /* Typography */
+    --font-body: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+    --font-mono: 'SF Mono', 'Fira Code', 'Cascadia Code', 'Consolas', monospace;
+}

JoshHeaps.Net/wwwroot/js/ChessScripts/ChessAPI.js

@@ -4,8 +4,8 @@ const ChessAPI = {
         return await response.json();
     },
 
-    async createCPUGame(difficulty) {
-        const response = await fetch(`/api/chess/new/${difficulty}`);
+    async createCPUGame(difficulty, color = "random") {
+        const response = await fetch(`/api/chess/new/${difficulty}?color=${color}`);
         return await response.json();
     },
 
@@ -14,6 +14,20 @@ const ChessAPI = {
         return await response.json();
     },
 
+    async getPgn(gameId) {
+        const response = await fetch(`/api/chess/${gameId}/pgn`);
+        if (!response.ok) throw new Error("PGN unavailable");
+        return await response.text();
+    },
+
+    async forfeit(gameId, playerId) {
+        await fetch("/api/chess/forfeit", {
+            method: "POST",
+            headers: { "Content-Type": "application/json" },
+            body: JSON.stringify({ GameId: gameId, PlayerId: playerId })
+        });
+    },
+
     async getLegalMoves(pieceId) {
         const response = await fetch(`/api/chess/${GameState.currentGameId}/legalMoves/${pieceId}`);
         if (!response.ok) throw new Error("API failed");
@@ -32,13 +46,15 @@ const ChessAPI = {
             throw new Error(message || "Invalid move or not your turn.");
         }
 
-        const result = await response.json();
+        // The move endpoint returns both the move result and the full resulting
+        // board state, so the caller can render without a follow-up fetch.
+        const data = await response.json();
 
-        if (!result.success) {
-            throw new Error(result.message || "Invalid move or not your turn.");
+        if (!data.result.success) {
+            throw new Error(data.result.message || "Invalid move or not your turn.");
         }
 
-        return result;
+        return data;
     },
 
     async handleMove(targetRow, targetCol) {
@@ -71,16 +87,14 @@ const ChessAPI = {
         GameState.setPreviousMove([GameState.selectedPiece.row, GameState.selectedPiece.col], [targetRow, targetCol]);
 
         try {
-            const moveResult = await this.makeMove(moveDto);
+            const { result, state } = await this.makeMove(moveDto);
 
-            const updatedGame = await this.getGameState(GameState.currentGameId);
-            ChessBoard.renderPieces(updatedGame.pieces);
+            ChessBoard.renderState(state);
 
             GameState.clearSelection();
             ChessInteractions.clearHighlights();
 
-            await ChessSignalR.notifyMoveMade(moveDto, moveResult);
-            this.alertGameStatusChange(moveResult);
+            this.alertGameStatusChange(result);
 
         } catch (error) {
             alert("❌ " + error.message);
@@ -101,9 +115,13 @@ const ChessAPI = {
             } else if (moveResult.isStalemate) {
                 alert("🤝 Stalemate!");
                 gameOver = true;
+            } else if (moveResult.isThreefoldRepetition) {
+                alert("🤝 Draw by threefold repetition!");
+                gameOver = true;
             }
 
             if (gameOver) {
+                showCopyPgn(GameState.currentGameId);
                 await ChessSignalR.leaveGame();
             }
         }, 500);

JoshHeaps.Net/wwwroot/js/ChessScripts/ChessBoard.js

@@ -1,4 +1,91 @@
+// Material value per piece type, indexed by PieceType (0=Pawn .. 5=King).
+const PIECE_VALUES = [1, 5, 3, 3, 9, 0];
+
 const ChessBoard = {
+    // Render from a full game-state payload (the shape returned by the move/state
+    // endpoints and pushed over SignalR). Ignores state older than what's already
+    // shown, so a slow initial fetch can't clobber a move that arrived first.
+    renderState(state) {
+        if (!state || !GameState.shouldApply(state.version)) return;
+        this.renderPieces(state.pieces);
+        this.renderCapturedTrays(state.pieces, state.capturedPieces);
+        this.renderMoveList(state.sanHistory);
+        this.renderStatus(state);
+        GameState.setVersion(state.version);
+    },
+
+    // Two-column numbered move list (white move, black move), latest highlighted.
+    renderMoveList(sanHistory) {
+        const list = document.getElementById("moveList");
+        if (!list) return;
+
+        const san = sanHistory ?? [];
+
+        if (san.length === 0) {
+            list.innerHTML = '<p class="movePlaceholder">Moves will appear here once a game begins.</p>';
+            return;
+        }
+
+        list.innerHTML = "";
+
+        for (let i = 0; i < san.length; i += 2) {
+            const row = document.createElement("div");
+            row.className = "moveRow";
+
+            const num = document.createElement("span");
+            num.className = "moveNum";
+            num.textContent = `${i / 2 + 1}.`;
+            row.appendChild(num);
+
+            row.appendChild(this.moveCell(san[i], i === san.length - 1));
+
+            if (i + 1 < san.length)
+                row.appendChild(this.moveCell(san[i + 1], i + 1 === san.length - 1));
+
+            list.appendChild(row);
+        }
+
+        list.scrollTop = list.scrollHeight;
+    },
+
+    moveCell(san, isLatest) {
+        const cell = document.createElement("span");
+        cell.className = isLatest ? "moveSan latest" : "moveSan";
+        cell.textContent = san;
+        return cell;
+    },
+
+    renderStatus(state) {
+        let text;
+        let alert = false;
+
+        if (state.isCheckmate) {
+            const winner = state.currentPlayer === "White" ? "Black" : "White";
+            text = `Checkmate — ${winner} wins`;
+            alert = true;
+        } else if (state.isStalemate) {
+            text = "Draw — stalemate";
+            alert = true;
+        } else if (state.isThreefoldRepetition) {
+            text = "Draw — threefold repetition";
+            alert = true;
+        } else {
+            text = `${state.currentPlayer} to move`;
+            if (state.isCheck) {
+                text += " — check";
+                alert = true;
+            }
+        }
+
+        // Mirror to both the desktop panel status and the mobile bar status.
+        ["statusLine", "mobileStatus"].forEach(id => {
+            const el = document.getElementById(id);
+            if (!el) return;
+            el.textContent = text;
+            el.classList.toggle("alert", alert);
+        });
+    },
+
     renderPieces(pieces) {
         this.clearAllSquares();
         this.renderCoordinateLabels();
@@ -7,6 +94,48 @@ const ChessBoard = {
         this.highlightPreviousMove();
     },
 
+    // Show each side's captured pieces and the leading side's material advantage,
+    // arranged so the current player's tray sits below the board.
+    renderCapturedTrays(activePieces, capturedPieces) {
+        const captured = capturedPieces ?? [];
+
+        // A captured piece's color is the side that lost it, so White's haul is the
+        // captured Black pieces, and vice versa.
+        const whiteCaptured = captured.filter(p => p.color === 1);
+        const blackCaptured = captured.filter(p => p.color === 0);
+
+        // Net material from pieces still on the board, so promotions count correctly.
+        const advantage = (activePieces ?? []).reduce(
+            (sum, p) => sum + (p.color === 0 ? PIECE_VALUES[p.type] : -PIECE_VALUES[p.type]), 0);
+
+        const white = { captured: whiteCaptured, advantage: Math.max(advantage, 0) };
+        const black = { captured: blackCaptured, advantage: Math.max(-advantage, 0) };
+
+        const isWhite = GameState.currentPlayerIsWhite !== false;
+        this.fillCapturedTray("bottom", isWhite ? white : black);
+        this.fillCapturedTray("top", isWhite ? black : white);
+    },
+
+    fillCapturedTray(position, side) {
+        const tray = document.getElementById(`captured-${position}`);
+        const badge = document.getElementById(`advantage-${position}`);
+        if (!tray || !badge) return;
+
+        tray.innerHTML = "";
+        [...side.captured]
+            .sort((a, b) => PIECE_VALUES[a.type] - PIECE_VALUES[b.type])
+            .forEach(piece => {
+                const img = document.createElement("img");
+                img.src = ChessUtils.getPieceImageUrl(piece);
+                img.alt = piece.type;
+                img.className = "capturedPiece";
+                img.draggable = false;
+                tray.appendChild(img);
+            });
+
+        badge.textContent = side.advantage > 0 ? `+${side.advantage}` : "";
+    },
+
     clearAllSquares() {
         for (let i = 0; i < 64; i++) {
             const square = document.getElementById(`square-${i}`);

JoshHeaps.Net/wwwroot/js/ChessScripts/ChessModals.js

@@ -23,6 +23,16 @@ const ChessModals = {
                 resolve(difficulty);
             };
         });
+    },
+
+    promptColor() {
+        return new Promise(resolve => {
+            document.getElementById("colorModal").style.display = "block";
+            window.selectColor = (color) => {
+                document.getElementById("colorModal").style.display = "none";
+                resolve(color);
+            };
+        });
     }
 };
 

JoshHeaps.Net/wwwroot/js/ChessScripts/ChessSignalR.js

@@ -11,8 +11,12 @@ const ChessSignalR = {
             console.error("❌ SignalR connection closed:", err?.message);
         });
 
-        this.connection.on("ReceiveMoveUpdate", async (gameId, moveDto, moveResultDto) => {
-            await this.handleMoveUpdate(gameId, moveDto, moveResultDto);
+        this.connection.on("ReceiveMoveUpdate", async (gameId, moveDto, moveResultDto, state) => {
+            await this.handleMoveUpdate(gameId, moveDto, moveResultDto, state);
+        });
+
+        this.connection.on("ReceiveGameOver", async (gameId, winner, reason) => {
+            await this.handleGameOver(gameId, winner, reason);
         });
 
         try {
@@ -24,20 +28,28 @@ const ChessSignalR = {
         }
     },
 
-    async handleMoveUpdate(gameId, moveDto, moveResultDto) {
+    async handleMoveUpdate(gameId, moveDto, moveResultDto, state) {
         if (gameId !== GameState.currentGameId) return;
 
-        const gameState = await ChessAPI.getGameState(gameId);
+        // Drop the echo of our own move and any out-of-order delivery.
+        if (!GameState.shouldApply(state?.version)) return;
+
         GameState.setPreviousMove([moveDto.sourceRow, moveDto.sourceCol], [moveDto.targetRow, moveDto.targetCol]);
-        ChessBoard.renderPieces(gameState.pieces);
+        ChessBoard.renderState(state);
 
         ChessAPI.alertGameStatusChange(moveResultDto);
     },
 
-    async notifyMoveMade(moveDto, moveResult) {
-        if (this.connection) {
-            await this.connection.invoke("MoveMade", GameState.currentGameId, moveDto, moveResult);
-        }
+    async handleGameOver(gameId, winner, reason) {
+        if (gameId !== GameState.currentGameId) return;
+
+        const youWon = (winner === "White") === GameState.currentPlayerIsWhite;
+
+        if (reason === "forfeit")
+            alert(youWon ? "🏳️ Your opponent forfeited — you win!" : "🏳️ You forfeited this game.");
+
+        showCopyPgn(gameId);
+        await this.leaveGame();
     },
 
     async leaveGame() {

JoshHeaps.Net/wwwroot/js/ChessScripts/GameState.js

@@ -6,6 +6,10 @@ const GameState = {
     legalMoves: [],
     previousMoveStart: null,
     previousMoveEnd: null,
+    // Highest ply (move count) already rendered. Lets us ignore stale or
+    // already-applied updates that arrive out of order, including the echo
+    // of our own move.
+    lastVersion: -1,
 
     reset() {
         this.currentGameId = null;
@@ -15,12 +19,22 @@ const GameState = {
         this.legalMoves = [];
         this.previousMoveStart = null;
         this.previousMoveEnd = null;
+        this.lastVersion = -1;
+    },
+
+    shouldApply(version) {
+        return typeof version !== "number" || version > this.lastVersion;
+    },
+
+    setVersion(version) {
+        if (typeof version === "number") this.lastVersion = version;
     },
 
     setGameInfo(gameId, playerId, isWhite) {
         this.currentGameId = gameId;
         this.currentPlayerId = playerId;
         this.currentPlayerIsWhite = isWhite;
+        this.lastVersion = -1;
     },
 
     setSelectedPiece(piece) {

JoshHeaps.Net/wwwroot/js/ChessScripts/Spectate.js

@@ -0,0 +1,341 @@
+const Spectate = {
+    connection: null,
+    games: new Map(),   // gameId -> { isVsComputer, isComputerVsComputer, result }
+    pgns: new Map(),    // gameId -> PGN text (prefetched when a game finishes)
+
+    pieceTypeNames: ["Pawn", "Rook", "Knight", "Bishop", "Queen", "King"],
+
+    async init() {
+        this.connection = new signalR.HubConnectionBuilder()
+            .withUrl("/chessHub")
+            .configureLogging(signalR.LogLevel.Warning)
+            .build();
+
+        this.connection.on("ReceiveMoveUpdate", (gameId, moveDto, _moveResult, state) =>
+            this.handleMoveUpdate(gameId, moveDto, state));
+
+        this.connection.on("ReceiveGameOver", (gameId) => this.removeGame(gameId));
+
+        try {
+            await this.connection.start();
+        } catch (err) {
+            console.error("❌ SignalR failed to start:", err);
+        }
+
+        await this.refreshGames();
+        await this.loadAutoTrainCount();
+        setInterval(() => this.refreshGames(), 5000);
+    },
+
+    // Auto-training runs server-side; show its target count and let it be changed here.
+    async loadAutoTrainCount() {
+        const input = document.getElementById("autoTrainCount");
+        if (!input) return;
+
+        try {
+            const response = await fetch("/api/chess/autotrain");
+            const data = await response.json();
+            input.max = data.max;
+            // Don't clobber the value while the user is editing it.
+            if (document.activeElement !== input)
+                input.value = data.count;
+        } catch {
+            // Leave the control as-is if auto-training status can't be read.
+        }
+    },
+
+    async setAutoTrainCount() {
+        const input = document.getElementById("autoTrainCount");
+        const count = Math.max(0, parseInt(input.value, 10) || 0);
+
+        try {
+            const response = await fetch(`/api/chess/autotrain?count=${count}`, { method: "POST" });
+            const data = await response.json();
+            input.value = data.count;
+        } catch (err) {
+            console.error("❌ Could not set the auto-training game count.", err);
+        }
+    },
+
+    async startCpuGame() {
+        const params = new URLSearchParams({
+            whiteEngine: document.getElementById("whiteEngine").value,
+            whiteSkill: document.getElementById("whiteSkill").value,
+            blackEngine: document.getElementById("blackEngine").value,
+            blackSkill: document.getElementById("blackSkill").value
+        });
+
+        try {
+            await fetch(`/api/chess/watch/cpu?${params}`);
+            await this.refreshGames();
+        } catch (err) {
+            console.error("❌ Could not start CPU vs CPU game.", err);
+        }
+    },
+
+    async refreshGames() {
+        let games;
+
+        try {
+            const response = await fetch("/api/chess/active");
+            games = await response.json();
+        } catch {
+            return;
+        }
+
+        const activeIds = new Set(games.map(g => g.gameId));
+
+        for (const gameId of [...this.games.keys()])
+            if (!activeIds.has(gameId))
+                await this.removeGame(gameId);
+
+        for (const game of games)
+            if (this.games.has(game.gameId))
+                this.updateHeader(game.gameId, game.currentPlayer, game.moveCount, game.isCheck);
+            else
+                await this.addGame(game);
+
+        const status = document.getElementById("watchStatus");
+        status.textContent = games.length === 0
+            ? "No games are being played right now."
+            : `${games.length} game${games.length === 1 ? "" : "s"} in progress`;
+    },
+
+    async addGame(game) {
+        this.games.set(game.gameId, {
+            isVsComputer: game.isVsComputer,
+            isComputerVsComputer: game.isComputerVsComputer,
+            whiteEngine: game.whiteEngine,
+            blackEngine: game.blackEngine
+        });
+
+        const card = document.createElement("div");
+        card.className = "gameCard";
+        card.id = `card-${game.gameId}`;
+        card.onclick = () => this.enterFullscreen(game.gameId);
+
+        const back = document.createElement("button");
+        back.className = "backButton";
+        back.textContent = "← Back";
+        back.onclick = (event) => this.exitFullscreen(game.gameId, event);
+        card.appendChild(back);
+
+        const header = document.createElement("div");
+        header.className = "gameCardHeader";
+        header.id = `header-${game.gameId}`;
+        header.textContent = this.headerText(this.games.get(game.gameId), game.currentPlayer, game.moveCount, game.isCheck);
+        card.appendChild(header);
+
+        const board = document.createElement("div");
+        board.className = "miniBoard";
+
+        for (let i = 0; i < 64; i++) {
+            const square = document.createElement("div");
+            square.id = `sq-${game.gameId}-${i}`;
+            square.className = `chessSquare ${(i + Math.floor(i / 8)) % 2 === 0 ? "light" : "dark"}`;
+            board.appendChild(square);
+        }
+
+        card.appendChild(board);
+        document.getElementById("gamesFeed").appendChild(card);
+
+        await this.connection.invoke("JoinWebsocketGroup", game.gameId).catch(() => { });
+        await this.renderGame(game.gameId);
+    },
+
+    async removeGame(gameId) {
+        this.games.delete(gameId);
+        this.pgns.delete(gameId);
+        document.getElementById(`card-${gameId}`)?.remove();
+        await this.connection.invoke("LeaveWebsocketGroup", gameId).catch(() => { });
+    },
+
+    async renderGame(gameId) {
+        const response = await fetch(`/api/chess/${gameId}`);
+
+        if (!response.ok) return;
+
+        this.renderFromState(gameId, await response.json());
+    },
+
+    renderFromState(gameId, state) {
+        const result = this.resultTextFromState(state);
+        const stored = this.games.get(gameId);
+
+        if (stored) stored.result = result;
+
+        this.renderPieces(gameId, state.pieces);
+        this.updateHeader(gameId, state.currentPlayer, state.moveHistory.length, state.isCheck);
+        this.setResult(gameId, result);
+    },
+
+    async handleMoveUpdate(gameId, moveDto, state) {
+        if (!this.games.has(gameId)) return;
+
+        // Render from the pushed state; fall back to a fetch only if it's missing.
+        if (state) this.renderFromState(gameId, state);
+        else await this.renderGame(gameId);
+
+        this.highlightMove(gameId, moveDto);
+    },
+
+    renderPieces(gameId, pieces) {
+        this.clearBoard(gameId);
+
+        pieces.forEach(piece => {
+            const square = document.getElementById(`sq-${gameId}-${piece.row * 8 + piece.col}`);
+
+            if (!square) return;
+
+            const img = document.createElement("img");
+            img.src = this.pieceImageUrl(piece);
+            img.alt = piece.type;
+            img.className = "chessPiece";
+            img.draggable = false;
+            square.appendChild(img);
+        });
+    },
+
+    clearBoard(gameId) {
+        for (let i = 0; i < 64; i++) {
+            const square = document.getElementById(`sq-${gameId}-${i}`);
+
+            if (!square) continue;
+
+            square.innerHTML = "";
+            square.classList.remove("previous-start", "previous-end");
+        }
+    },
+
+    highlightMove(gameId, moveDto) {
+        document.getElementById(`sq-${gameId}-${moveDto.sourceRow * 8 + moveDto.sourceCol}`)?.classList.add("previous-start");
+        document.getElementById(`sq-${gameId}-${moveDto.targetRow * 8 + moveDto.targetCol}`)?.classList.add("previous-end");
+    },
+
+    updateHeader(gameId, currentPlayer, moveCount, isCheck) {
+        const stored = this.games.get(gameId);
+        const header = document.getElementById(`header-${gameId}`);
+
+        if (stored && header)
+            header.textContent = this.headerText(stored, currentPlayer, moveCount, isCheck);
+    },
+
+    gameLabel(stored) {
+        if (stored.isComputerVsComputer)
+            return `${this.engineName(stored.whiteEngine)} (W) vs ${this.engineName(stored.blackEngine)} (B)`;
+        if (stored.isVsComputer) return "Vs CPU";
+        return "Player vs Player";
+    },
+
+    engineName(kind) {
+        switch (kind) {
+            case "CustomLearned": return "Learned";
+            case "Custom": return "Custom";
+            case "Stockfish": return "Stockfish";
+            default: return kind || "CPU";
+        }
+    },
+
+    headerText(stored, currentPlayer, moveCount, isCheck) {
+        if (stored.result)
+            return `${this.gameLabel(stored)} · move ${moveCount} · final`;
+
+        const check = isCheck ? " • check" : "";
+        return `${this.gameLabel(stored)} · move ${moveCount} · ${currentPlayer} to move${check}`;
+    },
+
+    resultTextFromState(state) {
+        if (state.isCheckmate)
+            return `${state.currentPlayer === "White" ? "Black" : "White"} wins by checkmate`;
+        if (state.isStalemate)
+            return "Draw — stalemate";
+        if (state.isThreefoldRepetition)
+            return "Draw — threefold repetition";
+        return null;
+    },
+
+    setResult(gameId, text) {
+        const card = document.getElementById(`card-${gameId}`);
+
+        if (!card) return;
+
+        let banner = card.querySelector(".gameResult");
+
+        if (!text) {
+            banner?.remove();
+            card.querySelector(".copyPgnBtn")?.remove();
+            card.classList.remove("over");
+            return;
+        }
+
+        if (!banner) {
+            banner = document.createElement("div");
+            banner.className = "gameResult";
+            card.appendChild(banner);
+        }
+
+        banner.textContent = text;
+        card.classList.add("over");
+        this.addCopyPgn(gameId, card);
+    },
+
+    addCopyPgn(gameId, card) {
+        if (card.querySelector(".copyPgnBtn")) return;
+
+        const btn = document.createElement("button");
+        btn.className = "copyPgnBtn";
+        btn.textContent = "Copy PGN";
+        btn.onclick = (event) => { event.stopPropagation(); this.copyPgn(gameId); };
+        card.appendChild(btn);
+
+        // Prefetch now (while the game is still in memory) so copy works during the
+        // brief window before the finished game is cleaned up.
+        fetch(`/api/chess/${gameId}/pgn`)
+            .then(r => r.ok ? r.text() : null)
+            .then(t => { if (t) this.pgns.set(gameId, t); })
+            .catch(() => { });
+    },
+
+    async copyPgn(gameId) {
+        let pgn = this.pgns.get(gameId);
+
+        if (!pgn) {
+            try {
+                const r = await fetch(`/api/chess/${gameId}/pgn`);
+                if (r.ok) pgn = await r.text();
+            } catch { /* ignore */ }
+        }
+
+        if (!pgn) {
+            alert("PGN is no longer available for this game.");
+            return;
+        }
+
+        try {
+            await navigator.clipboard.writeText(pgn);
+            alert("📋 PGN copied to clipboard!");
+        } catch {
+            alert("Couldn't access the clipboard. Here's the PGN:\n\n" + pgn);
+        }
+    },
+
+    enterFullscreen(gameId) {
+        document.getElementById(`card-${gameId}`)?.classList.add("fullscreen");
+        document.body.classList.add("fullscreen-open");
+    },
+
+    exitFullscreen(gameId, event) {
+        event?.stopPropagation();
+        document.getElementById(`card-${gameId}`)?.classList.remove("fullscreen");
+        document.body.classList.remove("fullscreen-open");
+    },
+
+    pieceImageUrl(piece) {
+        const color = piece.color === 0 ? "White" : "Black";
+        return `/images/Chess Images/${color}${this.pieceTypeNames[piece.type]}.svg`;
+    }
+};
+
+window.addEventListener("load", () => Spectate.init());
+
+console.log("Spectate.js loaded");

JoshHeaps.Net/wwwroot/js/ChessScripts/Weights.js

@@ -0,0 +1,158 @@
+const Weights = {
+    async init() {
+        await this.refresh();
+    },
+
+    async refresh() {
+        let data;
+
+        try {
+            const response = await fetch("/api/chess/weights");
+            data = await response.json();
+        } catch (err) {
+            console.error("❌ Could not load weights.", err);
+            document.getElementById("weightsStatus").textContent = "Could not load weights.";
+            return;
+        }
+
+        this.renderBoardSet(data.mg, "weightsGridMg");
+        this.renderBoardSet(data.eg, "weightsGridEg");
+        this.renderFeatures(data.features);
+
+        const trained = [...data.mg, ...data.eg].some(b => b.squares.some(v => v !== 0))
+            || data.features.some(f => f.value !== 0);
+
+        document.getElementById("weightsStatus").textContent = trained
+            ? "Where the learned engine thinks each piece belongs. Blue = preferred, red = avoided. Midgame vs endgame tables are blended by how much material is left."
+            : "No training yet — everything is neutral. Run some learned games on the Watch page.";
+    },
+
+    // pieces: [{ name, squares[64] }]. Prepends an "Overall" board summing the set.
+    renderBoardSet(pieces, containerId) {
+        const overall = new Array(64).fill(0);
+        for (const piece of pieces)
+            for (let sq = 0; sq < 64; sq++)
+                overall[sq] += piece.squares[sq];
+
+        const boards = [{ name: "Overall", squares: overall }, ...pieces];
+        const grid = document.getElementById(containerId);
+        grid.innerHTML = "";
+        boards.forEach(board => grid.appendChild(this.buildBoard(board)));
+    },
+
+    buildBoard(board) {
+        const wrapper = document.createElement("div");
+        wrapper.className = "weightBoard";
+
+        const maxAbs = board.squares.reduce((m, v) => Math.max(m, Math.abs(v)), 0);
+
+        const header = document.createElement("div");
+        header.className = "weightBoardHeader";
+        if (board.name !== "Overall") {
+            const icon = document.createElement("img");
+            icon.src = `/images/Chess Images/White${board.name}.svg`;
+            icon.alt = board.name;
+            icon.className = "weightBoardIcon";
+            header.appendChild(icon);
+        }
+        const title = document.createElement("span");
+        title.textContent = board.name;
+        header.appendChild(title);
+        const range = document.createElement("span");
+        range.className = "weightRange";
+        range.textContent = maxAbs === 0 ? "neutral" : `±${maxAbs}`;
+        header.appendChild(range);
+        wrapper.appendChild(header);
+
+        const heat = document.createElement("div");
+        heat.className = "miniHeat";
+
+        for (let row = 0; row < 8; row++) {
+            const rankLabel = document.createElement("div");
+            rankLabel.className = "heatLabel";
+            rankLabel.textContent = 8 - row;          // rank 8 at top, 1 at bottom
+            heat.appendChild(rankLabel);
+
+            for (let col = 0; col < 8; col++) {
+                const rank = 7 - row;                 // rank index, 0 = rank 1
+                const sq = rank * 8 + col;            // white-relative square (A1 = 0)
+                heat.appendChild(this.buildSquare(board.squares[sq], sq, maxAbs));
+            }
+        }
+
+        heat.appendChild(this.cornerSpacer());
+        for (let col = 0; col < 8; col++) {
+            const fileLabel = document.createElement("div");
+            fileLabel.className = "heatLabel";
+            fileLabel.textContent = String.fromCharCode(97 + col);
+            heat.appendChild(fileLabel);
+        }
+
+        wrapper.appendChild(heat);
+        return wrapper;
+    },
+
+    buildSquare(value, sq, maxAbs) {
+        const cell = document.createElement("div");
+        cell.className = "heatSquare";
+
+        if (value !== 0 && maxAbs > 0) {
+            const ratio = Math.abs(value) / maxAbs;
+            const alpha = (0.12 + 0.88 * ratio).toFixed(3);
+            cell.style.backgroundColor = value > 0
+                ? `rgba(74, 134, 232, ${alpha})`      // high -> blue
+                : `rgba(232, 74, 74, ${alpha})`;      // low  -> red
+            cell.textContent = value;
+        }
+
+        const file = String.fromCharCode(97 + (sq & 7));
+        const rank = (sq >> 3) + 1;
+        cell.title = `${file}${rank}: ${value}`;
+        return cell;
+    },
+
+    cornerSpacer() {
+        const spacer = document.createElement("div");
+        spacer.className = "heatLabel";
+        return spacer;
+    },
+
+    // features: [{ name, value }]
+    renderFeatures(features) {
+        const panel = document.getElementById("featureWeights");
+        panel.innerHTML = "";
+
+        const maxAbs = features.reduce((m, f) => Math.max(m, Math.abs(f.value)), 0);
+
+        features.forEach(feature => {
+            const row = document.createElement("div");
+            row.className = "featureRow";
+
+            const label = document.createElement("span");
+            label.className = "featureLabel";
+            label.textContent = feature.name;
+
+            const track = document.createElement("div");
+            track.className = "featureTrack";
+            const bar = document.createElement("div");
+            bar.className = "featureBar";
+            const ratio = maxAbs === 0 ? 0 : Math.abs(feature.value) / maxAbs;
+            bar.style.width = `${(ratio * 100).toFixed(1)}%`;
+            bar.style.backgroundColor = feature.value >= 0
+                ? "rgba(74, 134, 232, 0.85)"
+                : "rgba(232, 74, 74, 0.85)";
+            track.appendChild(bar);
+
+            const value = document.createElement("span");
+            value.className = "featureValue";
+            value.textContent = feature.value;
+
+            row.append(label, track, value);
+            panel.appendChild(row);
+        });
+    }
+};
+
+window.addEventListener("load", () => Weights.init());
+
+console.log("Weights.js loaded");

JoshHeaps.Net/wwwroot/js/ChessScripts/chessMain.js

@@ -1,5 +1,65 @@
+let lastPgn = null;
+
+async function showCopyPgn(gameId) {
+    try {
+        lastPgn = await ChessAPI.getPgn(gameId);
+        const btn = document.getElementById("copyPgnBtn");
+        if (btn) btn.style.display = "";
+    } catch (err) {
+        console.warn("Could not load PGN.", err);
+    }
+}
+
+async function copyPgn() {
+    if (!lastPgn) return;
+
+    try {
+        await navigator.clipboard.writeText(lastPgn);
+        alert("📋 PGN copied to clipboard!");
+    } catch {
+        alert("Couldn't access the clipboard. Here's the PGN:\n\n" + lastPgn);
+    }
+}
+
+function resetCopyPgn() {
+    lastPgn = null;
+    const btn = document.getElementById("copyPgnBtn");
+    if (btn) btn.style.display = "none";
+}
+
+window.copyPgn = copyPgn;
+window.showCopyPgn = showCopyPgn;
+
+// Mobile slide-up menu (move list + secondary actions).
+function toggleMenu() {
+    document.body.classList.toggle("menu-open");
+}
+
+function closeMenu() {
+    document.body.classList.remove("menu-open");
+}
+
+window.toggleMenu = toggleMenu;
+window.closeMenu = closeMenu;
+
+async function forfeitCurrentGame() {
+    const gameId = ChessUtils.getCookie("chessGameId");
+    const playerId = ChessUtils.getCookie("chessPlayerId");
+
+    if (!gameId || !playerId) return;
+
+    try {
+        await ChessAPI.forfeit(gameId, playerId);
+    } catch (err) {
+        console.warn("Could not forfeit previous game.", err);
+    }
+}
+
 async function startNewGame() {
+    closeMenu();
     await ChessSignalR.stopConnection();
+    await forfeitCurrentGame();
+    resetCopyPgn();
 
     try {
         const gameData = await ChessAPI.joinGame();
@@ -16,7 +76,7 @@ async function startNewGame() {
         await ChessSignalR.setupConnection();
 
         const gameState = await ChessAPI.getGameState(gameData.gameId);
-        ChessBoard.renderPieces(gameState.pieces);
+        ChessBoard.renderState(gameState);
 
     } catch (error) {
         console.error("Failed to start new game:", error);
@@ -24,11 +84,15 @@ async function startNewGame() {
 }
 
 async function startCPUGame() {
+    closeMenu();
     await ChessSignalR.stopConnection();
+    await forfeitCurrentGame();
+    resetCopyPgn();
 
     try {
         const difficulty = await ChessModals.promptDifficulty();
-        const gameData = await ChessAPI.createCPUGame(difficulty);
+        const color = await ChessModals.promptColor();
+        const gameData = await ChessAPI.createCPUGame(difficulty, color);
 
         GameState.setGameInfo(gameData.gameId, gameData.id, gameData.isWhite);
         GameState.clearPreviousMove();
@@ -42,7 +106,7 @@ async function startCPUGame() {
         await ChessSignalR.setupConnection();
 
         const gameState = await ChessAPI.getGameState(gameData.gameId);
-        ChessBoard.renderPieces(gameState.pieces);
+        ChessBoard.renderState(gameState);
 
     } catch (error) {
         console.error("Failed to start CPU game:", error);
@@ -62,7 +126,7 @@ async function resumeSavedGame() {
             GameState.setGameInfo(savedGameId, savedPlayerId, savedPlayerIsWhite === "true");
 
             await ChessSignalR.setupConnection();
-            ChessBoard.renderPieces(gameState.pieces);
+            ChessBoard.renderState(gameState);
 
         } catch (err) {
             console.warn("Saved game not found or expired.", err);

JoshHeaps.Net/wwwroot/js/EchoScripts/EchoAudio.js

@@ -0,0 +1,160 @@
+/*
+ * Microphone capture and chirp playback, both indexed by AudioContext frame.
+ *
+ * Frames, not wall-clock: currentTime * sampleRate is exactly the frame number, so a playback
+ * scheduled at an audio-clock time converts directly into a position in the recording. Nothing here
+ * depends on a timer firing on schedule, which matters because a hidden tab's timers are throttled
+ * to about once a second and its chirp would land in another device's slot.
+ */
+const EchoAudio = {
+    TARGET_SAMPLE_RATE: 48000,
+    RING_SECONDS: 20,
+    BLUETOOTH_HINTS: /bluetooth|airpod|hands-?free|headset|\bbt\b|wireless/i,
+
+    context: null,
+    stream: null,
+    capture: null,
+    ring: null,
+    highestFrame: 0,
+    peakAmplitude: 0,
+    warnings: [],
+    onSamples: null,
+
+    async start() {
+        if (this.context) return this.describe();
+
+        this.stream = await navigator.mediaDevices.getUserMedia({
+            // Echo cancellation exists to delete sounds this device just played, which is exactly
+            // the measurement. Gain control and noise suppression distort the chirp's envelope.
+            audio: {
+                echoCancellation: false,
+                noiseSuppression: false,
+                autoGainControl: false,
+                channelCount: 1
+            }
+        });
+
+        this.context = new AudioContext({ sampleRate: this.TARGET_SAMPLE_RATE, latencyHint: "interactive" });
+        await this.context.audioWorklet.addModule("/js/EchoScripts/EchoCaptureProcessor.js");
+        await this.context.resume();
+
+        this.ring = new Float32Array(Math.ceil(this.context.sampleRate * this.RING_SECONDS));
+        this.attachCapture();
+        this.warnings = this.inspectDevice();
+
+        return this.describe();
+    },
+
+    attachCapture() {
+        const source = this.context.createMediaStreamSource(this.stream);
+        this.capture = new AudioWorkletNode(this.context, "echo-capture", { numberOfOutputs: 0 });
+        this.capture.port.onmessage = ({ data }) => this.write(data.frame, data.samples);
+        source.connect(this.capture);
+        return this.capture;
+    },
+
+    write(frame, samples) {
+        const capacity = this.ring.length;
+        let loudest = 0;
+
+        for (let i = 0; i < samples.length; i++) {
+            this.ring[(frame + i) % capacity] = samples[i];
+            loudest = Math.max(loudest, Math.abs(samples[i]));
+        }
+
+        this.peakAmplitude = Math.max(this.peakAmplitude * 0.95, loudest);
+        this.highestFrame = Math.max(this.highestFrame, frame + samples.length);
+        this.onSamples?.(this.highestFrame);
+        return this.highestFrame;
+    },
+
+    /** The recording position for an AudioContext time. Exact: currentTime * sampleRate is a frame. */
+    frameAt(contextTime) {
+        return Math.round(contextTime * this.context.sampleRate);
+    },
+
+    /** Copy an absolute frame range out of the ring, or null if it is not (or no longer) held. */
+    read(startFrame, length) {
+        if (length <= 0) return null;
+        if (startFrame + length > this.highestFrame) return null;
+        if (startFrame < this.highestFrame - this.ring.length) return null;
+
+        const capacity = this.ring.length;
+        const window = new Float32Array(length);
+        for (let i = 0; i < length; i++) window[i] = this.ring[((startFrame + i) % capacity + capacity) % capacity];
+
+        return window;
+    },
+
+    /**
+     * Schedule a chirp on the audio clock and return the frame it was scheduled for. When it
+     * actually leaves the speaker is later by an unknown output latency and does not need to be
+     * known — it is recovered from the recording of it.
+     */
+    play(chirp, atContextTime, gain = 0.5) {
+        const when = Math.max(atContextTime, this.context.currentTime);
+        const buffer = this.context.createBuffer(1, chirp.length, this.context.sampleRate);
+        buffer.copyToChannel(chirp, 0);
+
+        const source = this.context.createBufferSource();
+        const volume = this.context.createGain();
+        volume.gain.value = gain;
+        source.buffer = buffer;
+        source.connect(volume).connect(this.context.destination);
+        source.start(when);
+
+        return this.frameAt(when);
+    },
+
+    /** How far behind the audio clock the main thread's view of the recording is running. */
+    captureLagSeconds() {
+        return this.context.currentTime - this.highestFrame / this.context.sampleRate;
+    },
+
+    /** Reported output latency, which bounds how late a scheduled chirp can reach the microphone. */
+    outputLatencySeconds() {
+        return (this.context.outputLatency || 0) + (this.context.baseLatency || 0);
+    },
+
+    inspectDevice() {
+        const warnings = [];
+        const track = this.stream.getAudioTracks()[0];
+        const settings = track?.getSettings() ?? {};
+
+        if (this.context.sampleRate !== this.TARGET_SAMPLE_RATE)
+            warnings.push(`Running at ${this.context.sampleRate}Hz instead of 48000Hz — ranges stay correct but resolution drops.`);
+
+        if (this.BLUETOOTH_HINTS.test(track?.label ?? ""))
+            warnings.push("This looks like a Bluetooth microphone. Bluetooth resamples and re-times the stream, which breaks the measurement — switch to the built-in speaker and microphone.");
+
+        for (const [name, label] of [["echoCancellation", "Echo cancellation"], ["autoGainControl", "Auto gain"], ["noiseSuppression", "Noise suppression"]])
+            if (settings[name] === true) warnings.push(`${label} could not be turned off on this device — the measurement will be unreliable.`);
+
+        return warnings;
+    },
+
+    describe() {
+        const track = this.stream.getAudioTracks()[0];
+
+        return {
+            sampleRate: this.context.sampleRate,
+            label: track?.label ?? "microphone",
+            outputLatencyMs: Math.round(this.outputLatencySeconds() * 1000),
+            warnings: this.warnings
+        };
+    },
+
+    async stop() {
+        this.stream?.getTracks().forEach(track => track.stop());
+        await this.context?.close();
+        this.context = null;
+        this.stream = null;
+        this.capture = null;
+        this.ring = null;
+        this.highestFrame = 0;
+        this.onSamples = null;
+        return true;
+    }
+};
+
+if (typeof window !== "undefined") window.EchoAudio = EchoAudio;

JoshHeaps.Net/wwwroot/js/EchoScripts/EchoCaptureProcessor.js

@@ -0,0 +1,39 @@
+/*
+ * Capture worklet. Every block is tagged with the AudioContext frame it started at, which makes the
+ * context's own clock the index for all captured audio: a scheduled playback time converts to a
+ * recording position exactly, with no dependence on when the main thread got round to noticing.
+ *
+ * A worklet rather than ScriptProcessorNode because a dropped buffer would break the continuity
+ * that the sample count depends on.
+ */
+const BLOCK_SAMPLES = 2048;
+
+class EchoCaptureProcessor extends AudioWorkletProcessor {
+    constructor() {
+        super();
+        this.block = new Float32Array(BLOCK_SAMPLES);
+        this.filled = 0;
+        this.blockStartFrame = 0;
+    }
+
+    process(inputs) {
+        const channel = inputs[0]?.[0];
+        if (!channel) return true;
+
+        for (let i = 0; i < channel.length; i++) {
+            if (this.filled === 0) this.blockStartFrame = currentFrame + i;
+            this.block[this.filled++] = channel[i];
+            if (this.filled === BLOCK_SAMPLES) this.flush();
+        }
+
+        return true;
+    }
+
+    flush() {
+        const samples = this.block.slice(0, this.filled);
+        this.port.postMessage({ frame: this.blockStartFrame, samples }, [samples.buffer]);
+        this.filled = 0;
+    }
+}
+
+registerProcessor("echo-capture", EchoCaptureProcessor);

JoshHeaps.Net/wwwroot/js/EchoScripts/EchoDsp.js

@@ -0,0 +1,585 @@
+/*
+ * Pure signal-processing and geometry for acoustic ranging. No DOM, no Web Audio, no network:
+ * everything here is a function of its arguments so the simulator and the tests can drive the
+ * exact code the page runs.
+ */
+const EchoDsp = {
+    speedOfSound(temperatureCelsius = 20) {
+        return 331.3 + 0.606 * temperatureCelsius;
+    },
+
+    nextPowerOfTwo(value) {
+        let size = 1;
+        while (size < value) size <<= 1;
+        return size;
+    },
+
+    /**
+     * Linear frequency sweep, tapered at both ends. A sweep is used rather than a tone because a
+     * tone's autocorrelation peaks once per period, leaving no unambiguous arrival to measure.
+     */
+    makeChirp({ sampleRate, durationSeconds, startHz, endHz, taperFraction = 0.15 }) {
+        const length = Math.round(sampleRate * durationSeconds);
+        const sweepRate = (endHz - startHz) / durationSeconds;
+        const chirp = new Float32Array(length);
+
+        for (let i = 0; i < length; i++) {
+            const t = i / sampleRate;
+            chirp[i] = Math.sin(2 * Math.PI * (startHz * t + 0.5 * sweepRate * t * t));
+        }
+
+        return this.applyTaper(chirp, taperFraction);
+    },
+
+    applyTaper(signal, fraction) {
+        const edge = Math.max(1, Math.floor(signal.length * fraction));
+
+        for (let i = 0; i < edge; i++) {
+            const window = 0.5 - 0.5 * Math.cos((Math.PI * i) / edge);
+            signal[i] *= window;
+            signal[signal.length - 1 - i] *= window;
+        }
+
+        return signal;
+    },
+
+    twiddles(size) {
+        this._twiddleCache ??= new Map();
+        const cached = this._twiddleCache.get(size);
+        if (cached) return cached;
+
+        const half = size >> 1;
+        const table = { cos: new Float64Array(half), sin: new Float64Array(half) };
+
+        for (let i = 0; i < half; i++) {
+            const angle = (-2 * Math.PI * i) / size;
+            table.cos[i] = Math.cos(angle);
+            table.sin[i] = Math.sin(angle);
+        }
+
+        this._twiddleCache.set(size, table);
+        return table;
+    },
+
+    fft(real, imaginary, inverse = false) {
+        const size = real.length;
+        this.reverseBits(real, imaginary);
+        const { cos, sin } = this.twiddles(size);
+
+        for (let span = 2; span <= size; span <<= 1) {
+            const half = span >> 1;
+            const stride = size / span;
+
+            for (let base = 0; base < size; base += span) {
+                for (let k = 0; k < half; k++) {
+                    const twiddle = k * stride;
+                    const wReal = cos[twiddle];
+                    const wImaginary = inverse ? -sin[twiddle] : sin[twiddle];
+
+                    const lower = base + k;
+                    const upper = lower + half;
+                    const productReal = real[upper] * wReal - imaginary[upper] * wImaginary;
+                    const productImaginary = real[upper] * wImaginary + imaginary[upper] * wReal;
+
+                    real[upper] = real[lower] - productReal;
+                    imaginary[upper] = imaginary[lower] - productImaginary;
+                    real[lower] += productReal;
+                    imaginary[lower] += productImaginary;
+                }
+            }
+        }
+
+        if (!inverse) return { real, imaginary };
+
+        for (let i = 0; i < size; i++) {
+            real[i] /= size;
+            imaginary[i] /= size;
+        }
+
+        return { real, imaginary };
+    },
+
+    reverseBits(real, imaginary) {
+        const size = real.length;
+
+        for (let i = 1, j = 0; i < size; i++) {
+            let bit = size >> 1;
+            for (; j & bit; bit >>= 1) j ^= bit;
+            j ^= bit;
+            if (i >= j) continue;
+
+            [real[i], real[j]] = [real[j], real[i]];
+            [imaginary[i], imaginary[j]] = [imaginary[j], imaginary[i]];
+        }
+
+        return { real, imaginary };
+    },
+
+    /**
+     * Matched-filter envelope of a recording against a template, via FFT cross-correlation.
+     * Negative frequencies are dropped so the result is the analytic envelope rather than a burst
+     * oscillating at the sweep frequency — an oscillating peak defeats sub-sample interpolation
+     * and makes first-arrival detection jitter by half a carrier period.
+     */
+    matchedFilterEnvelope(recording, template) {
+        const size = this.nextPowerOfTwo(recording.length + template.length);
+        const recordingReal = new Float64Array(size);
+        const recordingImaginary = new Float64Array(size);
+        const templateReal = new Float64Array(size);
+        const templateImaginary = new Float64Array(size);
+
+        recordingReal.set(recording);
+        templateReal.set(template);
+        this.fft(recordingReal, recordingImaginary);
+        this.fft(templateReal, templateImaginary);
+
+        const analyticReal = new Float64Array(size);
+        const analyticImaginary = new Float64Array(size);
+        const half = size >> 1;
+
+        for (let i = 0; i <= half; i++) {
+            const gain = i === 0 || i === half ? 1 : 2;
+            analyticReal[i] = gain * (recordingReal[i] * templateReal[i] + recordingImaginary[i] * templateImaginary[i]);
+            analyticImaginary[i] = gain * (recordingImaginary[i] * templateReal[i] - recordingReal[i] * templateImaginary[i]);
+        }
+
+        this.fft(analyticReal, analyticImaginary, true);
+
+        const envelope = new Float32Array(recording.length);
+        for (let i = 0; i < envelope.length; i++)
+            envelope[i] = Math.sqrt(analyticReal[i] * analyticReal[i] + analyticImaginary[i] * analyticImaginary[i]);
+
+        return envelope;
+    },
+
+    maxInRange(values, start, end) {
+        let index = start;
+        let value = -Infinity;
+
+        for (let i = start; i < end; i++) {
+            if (values[i] <= value) continue;
+            value = values[i];
+            index = i;
+        }
+
+        return { index, value };
+    },
+
+    medianInRange(values, start, end, sampleLimit = 2048) {
+        const span = end - start;
+        if (span <= 0) return 0;
+
+        const stride = Math.max(1, Math.floor(span / sampleLimit));
+        const sampled = [];
+        for (let i = start; i < end; i += stride) sampled.push(values[i]);
+
+        sampled.sort((left, right) => left - right);
+        return sampled[sampled.length >> 1];
+    },
+
+    /**
+     * Sub-sample peak position by fitting a parabola through the peak and its neighbours. One
+     * tenth of a sample is 0.7mm of range at 48kHz, so this is most of the accuracy for free.
+     */
+    refinePeakIndex(envelope, index) {
+        if (index <= 0 || index >= envelope.length - 1) return index;
+
+        const before = envelope[index - 1];
+        const peak = envelope[index];
+        const after = envelope[index + 1];
+        const curvature = before - 2 * peak + after;
+        if (curvature === 0) return index;
+
+        const offset = (0.5 * (before - after)) / curvature;
+        return index + Math.max(-1, Math.min(1, offset));
+    },
+
+    /**
+     * First arrival in a window, not the loudest one. A reflection off a wall or table often
+     * comes back louder than the direct path, and only the direct path is the distance.
+     */
+    findFirstPeak(envelope, options = {}) {
+        const start = Math.max(0, Math.floor(options.start ?? 0));
+        const end = Math.min(envelope.length, Math.ceil(options.end ?? envelope.length));
+        if (end - start < 8) return null;
+
+        const loudest = this.maxInRange(envelope, start, end);
+        const noiseFloor = this.medianInRange(envelope, start, end);
+        const snr = noiseFloor > 0 ? loudest.value / noiseFloor : Infinity;
+        if (snr < (options.minSnr ?? 4)) return null;
+
+        // Held above the noise floor so sidelobes cannot trigger it, but well below the loudest
+        // arrival so that a reflection several times louder than the direct path cannot mask it.
+        const threshold = Math.max(
+            noiseFloor * (options.noiseMultiple ?? 6),
+            loudest.value * (options.relativeThreshold ?? 0.15)
+        );
+
+        let crossing = start;
+        while (crossing < end && envelope[crossing] < threshold) crossing++;
+        if (crossing >= end) return null;
+
+        const lobeEnd = Math.min(end, crossing + (options.lobeSamples ?? 64));
+        const arrival = this.maxInRange(envelope, crossing, lobeEnd);
+
+        return { index: this.refinePeakIndex(envelope, arrival.index), amplitude: arrival.value, snr };
+    },
+
+    /**
+     * Locate every chirp of one round in a single device's recording.
+     *
+     * The device's own chirp is the anchor: it is always present and always the loudest thing in
+     * the recording, and its position absorbs this device's own output and input latency. Every
+     * other slot is then searched relative to that anchor, so no clock agreement between devices
+     * is required — only that the chirps stay in their slots.
+     */
+    detectSlotPeaks({
+        envelope,
+        slotCount,
+        slotSamples,
+        ownSlot,
+        ownSearchStart,
+        ownSearchSamples,
+        slotHints = null,
+        peakOptions = {}
+    }) {
+        const own = this.findFirstPeak(envelope, {
+            ...peakOptions,
+            start: ownSearchStart,
+            end: ownSearchStart + ownSearchSamples
+        });
+
+        if (!own) return null;
+
+        const anchor = own.index - ownSlot * slotSamples;
+        const pad = Math.floor(slotSamples * 0.45);
+        const peaks = new Array(slotCount).fill(null);
+        peaks[ownSlot] = own;
+
+        for (let slot = 0; slot < slotCount; slot++) {
+            if (slot === ownSlot) continue;
+
+            const centre = anchor + slot * slotSamples + (slotHints?.[slot] ?? 0);
+            peaks[slot] = this.findFirstPeak(envelope, {
+                ...peakOptions,
+                start: centre - pad,
+                end: centre + pad
+            });
+        }
+
+        return { anchor, peaks };
+    },
+
+    /**
+     * Distance between two devices from four arrival indices, each measured inside the recording
+     * of the device that made it. Clock offset and audio-pipeline latency appear once with each
+     * sign and cancel; the devices' own speaker-to-microphone spacing does not, and is added back.
+     */
+    pairDistance({ a1, a2, b1, b2, sampleRate, sampleRateA, sampleRateB, speedOfSound, epsilonA = 0, epsilonB = 0 }) {
+        // Each interval is converted to seconds in its own device's sample rate before the two are
+        // subtracted: a device that hands back 44100 instead of 48000 would otherwise contribute
+        // its interval in the wrong unit.
+        const intervalA = (a2 - a1) / (sampleRateA ?? sampleRate);
+        const intervalB = (b2 - b1) / (sampleRateB ?? sampleRate);
+        return ((intervalA - intervalB) / 2) * speedOfSound + (epsilonA + epsilonB) / 2;
+    },
+
+    /**
+     * Symmetric distance matrix from one round of reports. Entries stay null where either device
+     * failed to hear one of the four chirps the pair needs.
+     */
+    buildDistanceMatrix(reports, { speedOfSound = 343, maxDistance = 40 } = {}) {
+        const count = reports.length;
+        const matrix = Array.from({ length: count }, () => new Array(count).fill(null));
+
+        for (let i = 0; i < count; i++) {
+            matrix[i][i] = 0;
+
+            for (let j = i + 1; j < count; j++) {
+                const distance = this.distanceBetween(reports[i], reports[j], speedOfSound);
+                if (distance === null || distance < -1 || distance > maxDistance) continue;
+
+                matrix[i][j] = Math.max(0, distance);
+                matrix[j][i] = matrix[i][j];
+            }
+        }
+
+        return matrix;
+    },
+
+    distanceBetween(deviceA, deviceB, speedOfSound) {
+        const a1 = deviceA.peaks[deviceA.slot];
+        const a2 = deviceA.peaks[deviceB.slot];
+        const b1 = deviceB.peaks[deviceA.slot];
+        const b2 = deviceB.peaks[deviceB.slot];
+        if (a1 === null || a2 === null || b1 === null || b2 === null) return null;
+
+        return this.pairDistance({
+            a1,
+            a2,
+            b1,
+            b2,
+            sampleRateA: deviceA.sampleRate,
+            sampleRateB: deviceB.sampleRate,
+            speedOfSound,
+            epsilonA: deviceA.epsilon ?? 0,
+            epsilonB: deviceB.epsilon ?? 0
+        });
+    },
+
+    /**
+     * Largest set of devices linked by measured distances. Anything outside it cannot be placed
+     * relative to the others, and leaving it in makes the completed matrix infinite.
+     */
+    largestConnectedComponent(matrix) {
+        const unvisited = new Set(matrix.map((_, index) => index));
+        let largest = [];
+
+        while (unvisited.size > 0) {
+            const component = [];
+            const queue = [unvisited.values().next().value];
+            unvisited.delete(queue[0]);
+
+            while (queue.length > 0) {
+                const current = queue.pop();
+                component.push(current);
+
+                for (const next of unvisited)
+                    if (matrix[current][next] !== null) {
+                        unvisited.delete(next);
+                        queue.push(next);
+                    }
+            }
+
+            if (component.length > largest.length) largest = component;
+        }
+
+        return largest.sort((left, right) => left - right);
+    },
+
+    /**
+     * Drop devices whose distances are geometrically impossible. One device reporting a bad peak
+     * distorts the whole layout, so the worst triangle-inequality offender is removed and the
+     * check repeated. Below four devices there is no redundancy left and nothing can be checked.
+     */
+    rejectOutliers(matrix, candidates, tolerance = 0.5) {
+        const keep = [...candidates];
+
+        while (keep.length > 3) {
+            const violations = this.countTriangleViolations(matrix, keep, tolerance);
+            const worst = violations.reduce((best, count, index) => (count > violations[best] ? index : best), 0);
+            if (violations[worst] === 0) break;
+
+            keep.splice(worst, 1);
+        }
+
+        return keep;
+    },
+
+    submatrix(matrix, indices) {
+        return indices.map(row => indices.map(column => matrix[row][column]));
+    },
+
+    countTriangleViolations(matrix, keep, tolerance) {
+        const violations = new Array(keep.length).fill(0);
+
+        for (let i = 0; i < keep.length; i++) {
+            for (let j = i + 1; j < keep.length; j++) {
+                for (let k = j + 1; k < keep.length; k++) {
+                    const sides = [matrix[keep[i]][keep[j]], matrix[keep[j]][keep[k]], matrix[keep[i]][keep[k]]];
+                    if (sides.some(side => side === null)) continue;
+
+                    const longest = Math.max(...sides);
+                    const perimeter = sides.reduce((sum, side) => sum + side, 0);
+                    if (longest <= perimeter - longest + tolerance) continue;
+
+                    violations[i]++;
+                    violations[j]++;
+                    violations[k]++;
+                }
+            }
+        }
+
+        return violations;
+    },
+
+    /** Fill gaps with the shortest known path between the two devices so MDS gets a full matrix. */
+    completeMatrix(matrix) {
+        const count = matrix.length;
+        const filled = matrix.map(row => row.map(value => (value === null ? Infinity : value)));
+
+        for (let via = 0; via < count; via++)
+            for (let i = 0; i < count; i++)
+                for (let j = 0; j < count; j++)
+                    filled[i][j] = Math.min(filled[i][j], filled[i][via] + filled[via][j]);
+
+        return filled;
+    },
+
+    /** Jacobi eigendecomposition of a symmetric matrix. Returns eigenvalues and column vectors. */
+    symmetricEigen(matrix, maxSweeps = 100, tolerance = 1e-14) {
+        const count = matrix.length;
+        const working = matrix.map(row => Float64Array.from(row));
+        const vectors = Array.from({ length: count }, (_, i) => {
+            const column = new Float64Array(count);
+            column[i] = 1;
+            return column;
+        });
+
+        for (let sweep = 0; sweep < maxSweeps; sweep++) {
+            if (this.offDiagonalMagnitude(working) < tolerance) break;
+
+            for (let p = 0; p < count - 1; p++)
+                for (let q = p + 1; q < count; q++)
+                    this.rotateOut(working, vectors, p, q);
+        }
+
+        return {
+            values: working.map((row, i) => row[i]),
+            vectors
+        };
+    },
+
+    offDiagonalMagnitude(matrix) {
+        let total = 0;
+
+        for (let i = 0; i < matrix.length; i++)
+            for (let j = i + 1; j < matrix.length; j++) total += matrix[i][j] * matrix[i][j];
+
+        return total;
+    },
+
+    rotateOut(matrix, vectors, p, q) {
+        if (Math.abs(matrix[p][q]) < 1e-300) return matrix;
+
+        const theta = (matrix[q][q] - matrix[p][p]) / (2 * matrix[p][q]);
+        const sign = theta >= 0 ? 1 : -1;
+        const tangent = sign / (Math.abs(theta) + Math.sqrt(theta * theta + 1));
+        const cosine = 1 / Math.sqrt(tangent * tangent + 1);
+        const sine = tangent * cosine;
+        const count = matrix.length;
+
+        for (let k = 0; k < count; k++) {
+            const left = matrix[k][p];
+            const right = matrix[k][q];
+            matrix[k][p] = cosine * left - sine * right;
+            matrix[k][q] = sine * left + cosine * right;
+        }
+
+        for (let k = 0; k < count; k++) {
+            const left = matrix[p][k];
+            const right = matrix[q][k];
+            matrix[p][k] = cosine * left - sine * right;
+            matrix[q][k] = sine * left + cosine * right;
+        }
+
+        for (let k = 0; k < count; k++) {
+            const left = vectors[k][p];
+            const right = vectors[k][q];
+            vectors[k][p] = cosine * left - sine * right;
+            vectors[k][q] = sine * left + cosine * right;
+        }
+
+        return matrix;
+    },
+
+    /**
+     * Classical multidimensional scaling: coordinates whose pairwise distances best reproduce the
+     * matrix. The result is only defined up to rotation, translation and mirroring.
+     */
+    classicalMds(distances, dimensions = 2) {
+        const count = distances.length;
+        const squared = distances.map(row => row.map(value => value * value));
+        const rowMeans = squared.map(row => row.reduce((sum, value) => sum + value, 0) / count);
+        const grandMean = rowMeans.reduce((sum, value) => sum + value, 0) / count;
+
+        const centred = squared.map((row, i) => row.map((value, j) => -0.5 * (value - rowMeans[i] - rowMeans[j] + grandMean)));
+        const { values, vectors } = this.symmetricEigen(centred);
+        const order = values
+            .map((value, index) => ({ value, index }))
+            .sort((left, right) => right.value - left.value)
+            .slice(0, dimensions);
+
+        return Array.from({ length: count }, (_, i) =>
+            order.map(({ value, index }) => vectors[i][index] * Math.sqrt(Math.max(0, value)))
+        );
+    },
+
+    /**
+     * Rotate, mirror and translate a constellation onto a reference layout. Without this, every
+     * solve returns an arbitrary orientation and the display spins and flips between updates.
+     */
+    alignToReference(points, reference) {
+        if (!reference || reference.length !== points.length || points.length === 0) return points;
+
+        const pointCentre = this.centroid(points);
+        const referenceCentre = this.centroid(reference);
+        let best = null;
+
+        for (const mirror of [1, -1]) {
+            const candidate = this.rotateOnto(points, reference, pointCentre, referenceCentre, mirror);
+            if (!best || candidate.residual < best.residual) best = candidate;
+        }
+
+        return best.points;
+    },
+
+    centroid(points) {
+        const sum = points.reduce((total, [x, y]) => [total[0] + x, total[1] + y], [0, 0]);
+        return [sum[0] / points.length, sum[1] / points.length];
+    },
+
+    rotateOnto(points, reference, pointCentre, referenceCentre, mirror) {
+        let sineTerm = 0;
+        let cosineTerm = 0;
+
+        for (let i = 0; i < points.length; i++) {
+            const px = (points[i][0] - pointCentre[0]) * mirror;
+            const py = points[i][1] - pointCentre[1];
+            const qx = reference[i][0] - referenceCentre[0];
+            const qy = reference[i][1] - referenceCentre[1];
+            sineTerm += px * qy - py * qx;
+            cosineTerm += px * qx + py * qy;
+        }
+
+        const angle = Math.atan2(sineTerm, cosineTerm);
+        const cosine = Math.cos(angle);
+        const sine = Math.sin(angle);
+        let residual = 0;
+
+        const aligned = points.map((point, i) => {
+            const px = (point[0] - pointCentre[0]) * mirror;
+            const py = point[1] - pointCentre[1];
+            const x = px * cosine - py * sine + referenceCentre[0];
+            const y = px * sine + py * cosine + referenceCentre[1];
+            residual += (x - reference[i][0]) ** 2 + (y - reference[i][1]) ** 2;
+            return [x, y];
+        });
+
+        return { points: aligned, residual };
+    },
+
+    /**
+     * Full solve for one round: distances, connectivity, outlier rejection, then a constellation
+     * aligned onto the previous frame.
+     *
+     * <c>previousPoints</c> is indexed by report position, with null for devices that were dropped
+     * last round, so alignment survives devices coming and going.
+     */
+    solveRound(reports, { speedOfSound = 343, previousPoints = null, tolerance = 0.5 } = {}) {
+        const matrix = this.buildDistanceMatrix(reports, { speedOfSound });
+        const connected = this.largestConnectedComponent(matrix);
+        const keep = this.rejectOutliers(matrix, connected, tolerance);
+        const points = keep.length >= 2 ? this.classicalMds(this.completeMatrix(this.submatrix(matrix, keep))) : [];
+        const reference = previousPoints ? keep.map(index => previousPoints[index]) : null;
+        const alignable = reference?.length === points.length && reference.every(Boolean);
+
+        return {
+            matrix,
+            keep,
+            points: alignable ? this.alignToReference(points, reference) : points
+        };
+    }
+};
+
+if (typeof window !== "undefined") window.EchoDsp = EchoDsp;

JoshHeaps.Net/wwwroot/js/EchoScripts/EchoSession.js

@@ -0,0 +1,269 @@
+/*
+ * Round lifecycle: join a room, chirp when told to, measure every chirp in our own recording, and
+ * report the frame indices. Peaks are reported relative to the analysis window rather than to an
+ * absolute frame — every measurement is a difference within one device's own recording, so a
+ * constant per-device origin cancels.
+ *
+ * Both the chirp and the analysis are driven by the audio clock rather than by timers: a hidden tab
+ * has its timers throttled to roughly once a second, which is long enough to put its chirp in
+ * another device's slot and turn the whole round into nonsense.
+ */
+const EchoSession = {
+    LEAD_IN_SECONDS: 0.25,
+    TEMPERATURE_CELSIUS: 20,
+    MAX_OUTPUT_LATENCY_SECONDS: 0.35,
+    CHIRP: { durationSeconds: 0.05, startHz: 2000, endHz: 8000 },
+
+    CLOCK_SAMPLES: 5,
+    LATE_TOLERANCE_SECONDS: 0.05,
+
+    connection: null,
+    deviceId: null,
+    roomCode: null,
+    serverOffsetMs: 0,
+    skippedRounds: 0,
+    devices: [],
+    chirp: null,
+    pending: null,
+    lastRound: null,
+    hintsByDevice: {},
+    previousPoints: null,
+    epsilon: 0.08,
+    onUpdate: () => {},
+
+    async join(roomCode, displayName, { onUpdate }) {
+        this.onUpdate = onUpdate ?? this.onUpdate;
+        const audio = await EchoAudio.start();
+        this.chirp = EchoDsp.makeChirp({ sampleRate: audio.sampleRate, ...this.CHIRP });
+        EchoAudio.onSamples = frame => this.analyseIfCaptured(frame);
+
+        this.connection = new signalR.HubConnectionBuilder().withUrl("/echoHub").withAutomaticReconnect().build();
+        this.connection.on("RoomChanged", room => this.handleRoomChanged(room));
+        this.connection.on("RoundStarting", schedule => this.handleRoundStarting(schedule));
+        this.connection.on("RoundComplete", result => this.handleRoundComplete(result));
+        await this.connection.start();
+
+        const joined = await this.connection.invoke("JoinRoom", roomCode, displayName, audio.sampleRate);
+        this.deviceId = joined.deviceId;
+        this.roomCode = joined.roomCode;
+        this.devices = joined.room.devices;
+        this.serverOffsetMs = await this.estimateServerOffset();
+
+        return { ...joined, audio, serverOffsetMs: this.serverOffsetMs };
+    },
+
+    /**
+     * Offset from the server clock, by the usual round-trip midpoint. Only needs to be good enough
+     * to identify which chirp belongs to which slot, which is tens of milliseconds — the ranging
+     * itself never uses a shared clock.
+     */
+    async estimateServerOffset() {
+        const offsets = [];
+
+        for (let attempt = 0; attempt < this.CLOCK_SAMPLES; attempt++) {
+            const sent = Date.now();
+            const serverNow = await this.connection.invoke("ServerTime");
+            const received = Date.now();
+            offsets.push(serverNow - (sent + received) / 2);
+        }
+
+        offsets.sort((left, right) => left - right);
+        return offsets[offsets.length >> 1];
+    },
+
+    serverNowMs() {
+        return Date.now() + this.serverOffsetMs;
+    },
+
+    handleRoomChanged(room) {
+        this.devices = room.devices;
+        this.previousPoints = null;
+        this.hintsByDevice = {};
+        this.onUpdate({ kind: "room", room });
+        return room;
+    },
+
+    /**
+     * Schedule our chirp for our slot on the audio clock, and record which frames this round will
+     * occupy so the analysis can start the moment that audio has actually been captured.
+     */
+    handleRoundStarting(schedule) {
+        const ownSlot = schedule.slotOrder.indexOf(this.deviceId);
+        if (ownSlot < 0 || !EchoAudio.context) return null;
+
+        const sampleRate = EchoAudio.context.sampleRate;
+        const slotSeconds = schedule.slotMilliseconds / 1000;
+        const secondsUntilStart = (schedule.startsAtUnixMs - this.serverNowMs()) / 1000;
+        const roundStartTime = EchoAudio.context.currentTime + secondsUntilStart;
+        const playAtTime = roundStartTime + ownSlot * slotSeconds;
+
+        // Sitting a round out is far better than chirping late: a chirp in the wrong slot is
+        // attributed to the wrong device and ruins the round for everyone, whereas a missing chirp
+        // costs only this pair, this round.
+        if (playAtTime < EchoAudio.context.currentTime - this.LATE_TOLERANCE_SECONDS) {
+            this.skippedRounds++;
+            this.onUpdate({ kind: "skipped", schedule, lateBySeconds: EchoAudio.context.currentTime - playAtTime });
+            return null;
+        }
+
+        const scheduledFrame = EchoAudio.play(this.chirp, playAtTime);
+
+        const round = {
+            schedule,
+            ownSlot,
+            sampleRate,
+            scheduledFrame,
+            slotSamples: Math.round(slotSeconds * sampleRate),
+            leadInSamples: Math.round(this.LEAD_IN_SECONDS * sampleRate),
+            startFrame: EchoAudio.frameAt(roundStartTime),
+            outputLatencyMs: Math.round(EchoAudio.outputLatencySeconds() * 1000),
+            captureLagMs: Math.round(EchoAudio.captureLagSeconds() * 1000)
+        };
+
+        round.windowStart = round.startFrame - round.leadInSamples;
+        round.windowLength =
+            round.leadInSamples +
+            schedule.slotOrder.length * round.slotSamples +
+            Math.round((schedule.tailMilliseconds / 1000) * sampleRate);
+
+        this.pending = round;
+        this.onUpdate({ kind: "roundStarting", round });
+        return round;
+    },
+
+    /**
+     * Run as soon as the round's audio exists in the ring. Driven by captured audio rather than a
+     * timer so a throttled tab still analyses on time.
+     */
+    analyseIfCaptured(highestFrame) {
+        const round = this.pending;
+        if (!round) return null;
+        if (highestFrame < round.windowStart + round.windowLength) return null;
+
+        this.pending = null;
+        return this.analyse(round);
+    },
+
+    analyse(round) {
+        this.lastRound = round;
+        const recording = EchoAudio.read(round.windowStart, round.windowLength);
+        if (!recording) return null;
+
+        const envelope = EchoDsp.matchedFilterEnvelope(recording, this.chirp);
+        const detected = EchoDsp.detectSlotPeaks({
+            envelope,
+            slotCount: round.schedule.slotOrder.length,
+            slotSamples: round.slotSamples,
+            ownSlot: round.ownSlot,
+            // Anchored on the frame the chirp was scheduled for, so the only unknown left is how
+            // long the speaker takes to actually emit it.
+            ownSearchStart: round.scheduledFrame - round.windowStart,
+            ownSearchSamples: Math.round((this.MAX_OUTPUT_LATENCY_SECONDS + this.CHIRP.durationSeconds) * round.sampleRate),
+            slotHints: this.hintsFor(round.schedule)
+        });
+
+        const diagnostics = this.describeRound(round, detected);
+        this.onUpdate({ kind: "envelope", envelope, detected, round, diagnostics });
+        if (!detected) return null;
+
+        this.rememberHints(round.schedule, detected, round.slotSamples);
+        return this.report(round, detected);
+    },
+
+    describeRound(round, detected) {
+        const millisecondsPer = 1000 / round.sampleRate;
+
+        return {
+            captureLagMs: round.captureLagMs,
+            outputLatencyMs: round.outputLatencyMs,
+            serverOffsetMs: Math.round(this.serverOffsetMs),
+            skippedRounds: this.skippedRounds,
+            clipping: EchoAudio.peakAmplitude >= 0.99,
+            inputPeak: Number(EchoAudio.peakAmplitude.toFixed(3)),
+            ownFound: Boolean(detected?.peaks[round.ownSlot]),
+            slots: round.schedule.slotOrder.map((deviceId, slot) => ({
+                deviceId,
+                own: slot === round.ownSlot,
+                residualMs: detected?.peaks[slot]
+                    ? Math.round((detected.peaks[slot].index - (detected.anchor + slot * round.slotSamples)) * millisecondsPer)
+                    : null,
+                snr: detected?.peaks[slot] ? Math.round(detected.peaks[slot].snr) : null
+            }))
+        };
+    },
+
+    report(round, detected) {
+        return this.connection.invoke("ReportRound", {
+            deviceId: this.deviceId,
+            roundId: round.schedule.roundId,
+            slot: round.ownSlot,
+            sampleRate: round.sampleRate,
+            epsilon: this.epsilon,
+            peaks: detected.peaks.map(peak => peak?.index ?? null)
+        });
+    },
+
+    /**
+     * Where each device's chirp actually landed last round, relative to where the slot said it
+     * would. Output latency differs by tens of milliseconds per device and is stable, so carrying
+     * the residual forward keeps the search windows centred instead of merely wide.
+     */
+    rememberHints(schedule, detected, slotSamples) {
+        schedule.slotOrder.forEach((deviceId, slot) => {
+            const peak = detected.peaks[slot];
+            if (!peak) return;
+            this.hintsByDevice[deviceId] = peak.index - (detected.anchor + slot * slotSamples);
+        });
+
+        return this.hintsByDevice;
+    },
+
+    hintsFor(schedule) {
+        return schedule.slotOrder.map(deviceId => this.hintsByDevice[deviceId] ?? 0);
+    },
+
+    handleRoundComplete(result) {
+        const reports = result.reports.map(report => ({ ...report, peaks: report.peaks ?? [] }));
+        const solved = EchoDsp.solveRound(reports, {
+            speedOfSound: EchoDsp.speedOfSound(this.TEMPERATURE_CELSIUS),
+            previousPoints: this.previousPoints
+        });
+
+        this.previousPoints = this.pointsByReportIndex(reports, solved);
+        this.onUpdate({ kind: "solved", result, reports, solved, deviceId: this.deviceId });
+        return solved;
+    },
+
+    pointsByReportIndex(reports, solved) {
+        const points = new Array(reports.length).fill(null);
+        solved.keep.forEach((reportIndex, i) => {
+            points[reportIndex] = solved.points[i];
+        });
+        return points;
+    },
+
+    setEpsilon(metres) {
+        this.epsilon = metres;
+        localStorage.setItem("echo.epsilon", String(metres));
+        return this.epsilon;
+    },
+
+    loadEpsilon() {
+        const stored = Number(localStorage.getItem("echo.epsilon"));
+        this.epsilon = Number.isFinite(stored) && stored > 0 ? stored : 0.08;
+        return this.epsilon;
+    },
+
+    async leave() {
+        await this.connection?.invoke("LeaveRoom").catch(() => {});
+        await this.connection?.stop();
+        await EchoAudio.stop();
+        this.connection = null;
+        this.pending = null;
+        this.previousPoints = null;
+        this.hintsByDevice = {};
+        return true;
+    }
+};
+
+if (typeof window !== "undefined") window.EchoSession = EchoSession;

JoshHeaps.Net/wwwroot/js/EchoScripts/EchoSim.js

@@ -0,0 +1,213 @@
+/*
+ * Virtual room for exercising the real ranging pipeline without microphones. Synthesizes what
+ * each device would have recorded — propagation delay, reflections, noise, per-device clock offset
+ * and unknown output latency — then runs the same EchoDsp code the page runs.
+ */
+const EchoSim = {
+    DEFAULTS: {
+        sampleRate: 48000,
+        slotSeconds: 0.4,
+        tailSeconds: 0.5,
+        speedOfSound: 343,
+        noiseAmplitude: 0.01,
+        referenceGain: 0.5,
+        minimumPathMetres: 0.25,
+        maximumOutputLatencySeconds: 0.2,
+        chirp: { durationSeconds: 0.05, startHz: 2000, endHz: 8000 },
+        reflectionsPerPath: 2,
+        reflectionExtraRange: [0.4, 4.0],
+        reflectionGainRange: [0.2, 0.8],
+        seed: 20260730
+    },
+
+    randomGenerator(seed) {
+        let state = seed >>> 0;
+
+        return () => {
+            state = (state + 0x6d2b79f5) >>> 0;
+            let mixed = Math.imul(state ^ (state >>> 15), 1 | state);
+            mixed = (mixed + Math.imul(mixed ^ (mixed >>> 7), 61 | mixed)) ^ mixed;
+            return ((mixed ^ (mixed >>> 14)) >>> 0) / 4294967296;
+        };
+    },
+
+    separation(first, second) {
+        return Math.hypot(first[0] - second[0], first[1] - second[1]);
+    },
+
+    buildConfiguration(overrides = {}) {
+        const config = { ...this.DEFAULTS, ...overrides };
+        const count = config.positions.length;
+
+        config.chirp = { ...this.DEFAULTS.chirp, ...(overrides.chirp ?? {}) };
+        config.epsilon ??= new Array(count).fill(0.05);
+        config.clockOffsets ??= config.positions.map((_, i) => i * 7919);
+        config.outputLatencies ??= config.positions.map((_, i) => 0.02 + 0.03 * i);
+        config.scheduleJitter ??= config.positions.map((_, i) => 0.004 * i);
+        config.reflections ??= this.buildReflectionTable(config);
+        return config;
+    },
+
+    /**
+     * Multipath for every source-to-listener path independently. Giving every path the same echo
+     * would be worthless as a test: an identical bias on all four arrivals cancels out of the
+     * range formula, so a uniform echo model hides exactly the error it is supposed to expose.
+     */
+    buildReflectionTable(config) {
+        const random = this.randomGenerator(config.seed ^ 0x5f3759df);
+        const spread = (range, value) => range[0] + value * (range[1] - range[0]);
+
+        return config.positions.map(() =>
+            config.positions.map(() =>
+                Array.from({ length: config.reflectionsPerPath }, () => ({
+                    extraMetres: spread(config.reflectionExtraRange, random()),
+                    gain: spread(config.reflectionGainRange, random())
+                }))
+            )
+        );
+    },
+
+    reflectionsFor(config, source, listener) {
+        return Array.isArray(config.reflections[0]) ? config.reflections[source][listener] : config.reflections;
+    },
+
+    /** One recording per device, plus the index each device believes it started playing at. */
+    synthesizeRound(config) {
+        const { positions, sampleRate, slotSeconds, tailSeconds } = config;
+        const random = this.randomGenerator(config.seed);
+        const template = EchoDsp.makeChirp({ sampleRate, ...config.chirp });
+        const maximumOffset = Math.max(...config.clockOffsets);
+        const length = Math.ceil((positions.length * slotSeconds + tailSeconds) * sampleRate) + maximumOffset;
+
+        const devices = positions.map((_, index) => ({
+            recording: this.noiseBuffer(length, config.noiseAmplitude, random),
+            ownSearchStart: Math.round((index * slotSeconds + config.scheduleJitter[index]) * sampleRate) + config.clockOffsets[index]
+        }));
+
+        for (let source = 0; source < positions.length; source++)
+            for (let listener = 0; listener < positions.length; listener++)
+                this.mixArrivals(devices[listener].recording, template, config, source, listener);
+
+        return { devices, template };
+    },
+
+    noiseBuffer(length, amplitude, random) {
+        const buffer = new Float32Array(length);
+        for (let i = 0; i < length; i++) buffer[i] = (random() * 2 - 1) * amplitude;
+        return buffer;
+    },
+
+    mixArrivals(recording, template, config, source, listener) {
+        const emissionSeconds =
+            source * config.slotSeconds + config.scheduleJitter[source] + config.outputLatencies[source];
+        const directMetres =
+            source === listener ? config.epsilon[source] : this.separation(config.positions[source], config.positions[listener]);
+
+        const paths = [
+            { metres: directMetres, gain: 1 },
+            ...this.reflectionsFor(config, source, listener).map(({ extraMetres, gain }) => ({
+                metres: directMetres + extraMetres,
+                gain
+            }))
+        ];
+
+        for (const path of paths) {
+            const arrival = emissionSeconds + path.metres / config.speedOfSound;
+            const amplitude =
+                (config.referenceGain / Math.max(path.metres, config.minimumPathMetres)) * path.gain;
+            this.addAt(recording, template, Math.round(arrival * config.sampleRate) + config.clockOffsets[listener], amplitude);
+        }
+
+        return recording;
+    },
+
+    addAt(recording, template, offset, amplitude) {
+        const start = Math.max(0, offset);
+        const end = Math.min(recording.length, offset + template.length);
+
+        for (let i = start; i < end; i++) recording[i] += template[i - offset] * amplitude;
+
+        return recording;
+    },
+
+    /** Run every device's recording through detection and return one report per device. */
+    detectAll({ devices, template }, config) {
+        const slotSamples = Math.round(config.slotSeconds * config.sampleRate);
+        const searchSamples = Math.round(
+            (config.maximumOutputLatencySeconds + config.chirp.durationSeconds + 0.05) * config.sampleRate
+        );
+
+        return devices.map((device, slot) => {
+            const envelope = EchoDsp.matchedFilterEnvelope(device.recording, template);
+            const detected = EchoDsp.detectSlotPeaks({
+                envelope,
+                slotCount: devices.length,
+                slotSamples,
+                ownSlot: slot,
+                ownSearchStart: device.ownSearchStart,
+                ownSearchSamples: searchSamples,
+                peakOptions: config.peakOptions ?? {}
+            });
+
+            return {
+                deviceId: `sim-${slot}`,
+                slot,
+                sampleRate: config.sampleRate,
+                epsilon: config.epsilon[slot],
+                peaks: (detected?.peaks ?? new Array(devices.length).fill(null)).map(peak => peak?.index ?? null)
+            };
+        });
+    },
+
+    /** Synthesize, detect and solve, reporting recovered geometry against the ground truth. */
+    runRound(overrides = {}) {
+        const config = this.buildConfiguration(overrides);
+        const round = this.synthesizeRound(config);
+        const reports = this.detectAll(round, config);
+        const solved = EchoDsp.solveRound(reports, { speedOfSound: config.speedOfSound });
+
+        return {
+            config,
+            reports,
+            ...solved,
+            distanceErrors: this.distanceErrors(solved.matrix, config),
+            positionErrors: this.positionErrors(solved, config)
+        };
+    },
+
+    distanceErrors(matrix, config) {
+        const errors = [];
+
+        for (let i = 0; i < matrix.length; i++)
+            for (let j = i + 1; j < matrix.length; j++) {
+                const truth = this.separation(config.positions[i], config.positions[j]);
+                errors.push({
+                    pair: [i, j],
+                    truth,
+                    measured: matrix[i][j],
+                    error: matrix[i][j] === null ? null : matrix[i][j] - truth
+                });
+            }
+
+        return errors;
+    },
+
+    positionErrors({ keep, points }, config) {
+        if (points.length !== keep.length || points.length < 2) return [];
+
+        const truth = keep.map(index => config.positions[index]);
+        const aligned = EchoDsp.alignToReference(points, truth);
+        return aligned.map((point, i) => this.separation(point, truth[i]));
+    },
+
+    worstDistanceError(result) {
+        const magnitudes = result.distanceErrors.map(({ error }) => (error === null ? Infinity : Math.abs(error)));
+        return magnitudes.length === 0 ? 0 : Math.max(...magnitudes);
+    },
+
+    worstPositionError(result) {
+        return result.positionErrors.length === 0 ? Infinity : Math.max(...result.positionErrors);
+    }
+};
+
+if (typeof window !== "undefined") window.EchoSim = EchoSim;

JoshHeaps.Net/wwwroot/js/EchoScripts/echoMain.js

@@ -0,0 +1,282 @@
+/*
+ * Page wiring for /echo. Renders what the session measures: the matched-filter trace with the
+ * arrivals it picked, the pairwise ranges, and — while only two devices are present — one large
+ * number, because that number is the whole measurement.
+ */
+const EchoPage = {
+    HISTORY_LENGTH: 12,
+
+    elements: {},
+    lastSolved: null,
+    lastDiagnostics: null,
+    history: [],
+    roundsSeen: 0,
+
+    start() {
+        this.elements = {
+            room: document.getElementById("echoRoom"),
+            name: document.getElementById("echoName"),
+            join: document.getElementById("echoJoin"),
+            leave: document.getElementById("echoLeave"),
+            status: document.getElementById("echoStatus"),
+            warnings: document.getElementById("echoWarnings"),
+            readout: document.getElementById("echoReadout"),
+            pairs: document.getElementById("echoPairs"),
+            roster: document.getElementById("echoRoster"),
+            trace: document.getElementById("echoTrace"),
+            epsilon: document.getElementById("echoEpsilon"),
+            shareLink: document.getElementById("echoShareLink"),
+            diagnostics: document.getElementById("echoDiagnostics")
+        };
+
+        this.elements.room.value = new URLSearchParams(location.search).get("room") ?? this.randomCode();
+        this.elements.epsilon.value = EchoSession.loadEpsilon();
+        this.elements.epsilon.addEventListener("change", () => this.applyEpsilon());
+        this.elements.join.addEventListener("click", () => this.join());
+        this.elements.leave.addEventListener("click", () => this.leave());
+
+        return this;
+    },
+
+    randomCode() {
+        const alphabet = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789";
+        return Array.from({ length: 4 }, () => alphabet[Math.floor(Math.random() * alphabet.length)]).join("");
+    },
+
+    applyEpsilon() {
+        const metres = Number(this.elements.epsilon.value);
+        if (!Number.isFinite(metres) || metres < 0) return null;
+
+        EchoSession.setEpsilon(metres);
+        return metres;
+    },
+
+    async join() {
+        const roomCode = this.elements.room.value.trim().toUpperCase();
+        if (!roomCode) return null;
+
+        this.setStatus("Requesting the microphone…");
+        this.elements.join.disabled = true;
+
+        try {
+            const joined = await EchoSession.join(roomCode, this.deviceName(), { onUpdate: update => this.handle(update) });
+            this.showJoined(joined);
+            return joined;
+        } catch (error) {
+            this.setStatus(`Could not start: ${error.message}`);
+            this.elements.join.disabled = false;
+            return null;
+        }
+    },
+
+    deviceName() {
+        const typed = this.elements.name.value.trim();
+        if (typed) return typed;
+
+        return /android|iphone|ipad|mobile/i.test(navigator.userAgent) ? "phone" : "laptop";
+    },
+
+    showJoined(joined) {
+        this.elements.leave.hidden = false;
+        this.elements.room.disabled = true;
+        this.elements.name.disabled = true;
+        this.elements.shareLink.textContent = `${location.origin}/echo?room=${joined.roomCode}`;
+        this.elements.shareLink.href = `/echo?room=${joined.roomCode}`;
+        this.renderWarnings(joined.audio);
+        this.renderRoster(joined.room.devices);
+        this.setStatus(`Listening at ${joined.audio.sampleRate}Hz. Open the same room on another device.`);
+        return joined;
+    },
+
+    async leave() {
+        await EchoSession.leave();
+        this.elements.leave.hidden = true;
+        this.elements.join.disabled = false;
+        this.elements.room.disabled = false;
+        this.elements.name.disabled = false;
+        this.setStatus("Left the room.");
+        return true;
+    },
+
+    handle(update) {
+        if (update.kind === "room") return this.renderRoster(update.room.devices);
+        if (update.kind === "envelope") {
+            this.renderDiagnostics(update.diagnostics);
+            return this.renderTrace(update);
+        }
+        if (update.kind === "solved") return this.renderSolved(update);
+        return null;
+    },
+
+    /**
+     * Per-slot residual is the diagnostic that matters: it is how far each chirp landed from where
+     * its slot said it would. Steady residuals mean the arrivals are being attributed correctly;
+     * residuals jumping by more than a slot mean they are not, and every range is then meaningless.
+     */
+    renderDiagnostics(diagnostics) {
+        if (!diagnostics) return null;
+        this.lastDiagnostics = diagnostics;
+
+        const slots = diagnostics.slots
+            .map(slot => {
+                const label = slot.own ? "self" : slot.deviceId;
+                const residual = slot.residualMs === null ? "missed" : `${slot.residualMs > 0 ? "+" : ""}${slot.residualMs}ms`;
+                return `<li class="${slot.residualMs === null ? "echo-missed" : ""}">${label} · ${residual}${slot.snr === null ? "" : ` · snr ${slot.snr}`}</li>`;
+            })
+            .join("");
+
+        this.elements.diagnostics.innerHTML = `
+            <ul class="echo-slots">${slots}</ul>
+            <p class="echo-diag-line">
+                capture lag ${diagnostics.captureLagMs}ms · output latency ${diagnostics.outputLatencyMs}ms ·
+                clock offset ${diagnostics.serverOffsetMs}ms · rounds sat out ${diagnostics.skippedRounds} ·
+                input peak ${diagnostics.inputPeak}${diagnostics.clipping ? " <strong>CLIPPING</strong>" : ""}
+            </p>`;
+
+        return diagnostics;
+    },
+
+    recordHistory(metres) {
+        this.history.push(metres);
+        if (this.history.length > this.HISTORY_LENGTH) this.history.shift();
+
+        const spread = Math.max(...this.history) - Math.min(...this.history);
+        return { spread, count: this.history.length };
+    },
+
+    setStatus(message) {
+        this.elements.status.textContent = message;
+        return message;
+    },
+
+    renderWarnings(audio) {
+        this.elements.warnings.innerHTML = "";
+
+        for (const warning of audio.warnings) {
+            const item = document.createElement("p");
+            item.className = "echo-warning";
+            item.textContent = warning;
+            this.elements.warnings.appendChild(item);
+        }
+
+        return audio.warnings.length;
+    },
+
+    renderRoster(devices) {
+        this.elements.roster.innerHTML = "";
+
+        for (const device of devices) {
+            const row = document.createElement("li");
+            row.className = device.deviceId === EchoSession.deviceId ? "echo-device echo-device-self" : "echo-device";
+            row.textContent = `${device.displayName} · ${device.sampleRate}Hz`;
+            this.elements.roster.appendChild(row);
+        }
+
+        if (devices.length < 2) this.setStatus("Waiting for a second device to join this room.");
+        return devices.length;
+    },
+
+    renderSolved({ result, reports, solved }) {
+        this.roundsSeen++;
+        const raw = EchoDsp.buildDistanceMatrix(
+            reports.map(report => ({ ...report, epsilon: 0 })),
+            { speedOfSound: EchoDsp.speedOfSound(EchoSession.TEMPERATURE_CELSIUS) }
+        );
+
+        this.lastSolved = { result, reports, solved, raw };
+        this.renderReadout(reports, solved, raw);
+        this.renderPairs(reports, solved, raw);
+        this.setStatus(`Round ${this.roundsSeen} · ${reports.length} of ${EchoSession.devices.length} devices reported`);
+        return solved;
+    },
+
+    renderReadout(reports, solved, raw) {
+        const readout = this.elements.readout;
+
+        if (reports.length !== 2 || solved.matrix[0][1] === null) {
+            readout.innerHTML = `<span class="echo-readout-idle">${reports.length < 2 ? "waiting for a pair" : "measuring…"}</span>`;
+            return null;
+        }
+
+        const corrected = solved.matrix[0][1];
+        const { spread, count } = this.recordHistory(corrected);
+        readout.innerHTML = `
+            <span class="echo-metres">${corrected.toFixed(2)}<small>m</small></span>
+            <span class="echo-readout-detail">
+                raw ${raw[0][1].toFixed(3)}m · calibration +${(corrected - raw[0][1]).toFixed(3)}m ·
+                spread over last ${count} ${spread.toFixed(2)}m
+            </span>`;
+
+        return corrected;
+    },
+
+    renderPairs(reports, solved, raw) {
+        const rows = [];
+
+        for (let i = 0; i < reports.length; i++)
+            for (let j = i + 1; j < reports.length; j++) {
+                const dropped = !solved.keep.includes(i) || !solved.keep.includes(j);
+                const measured = solved.matrix[i][j];
+                rows.push(`<tr class="${dropped ? "echo-dropped" : ""}">
+                    <td>${reports[i].deviceId} ↔ ${reports[j].deviceId}</td>
+                    <td>${measured === null ? "—" : measured.toFixed(3) + " m"}</td>
+                    <td>${raw[i][j] === null ? "—" : raw[i][j].toFixed(3) + " m"}</td>
+                </tr>`);
+            }
+
+        this.elements.pairs.innerHTML = rows.length
+            ? `<table><thead><tr><th>pair</th><th>range</th><th>raw</th></tr></thead><tbody>${rows.join("")}</tbody></table>`
+            : "";
+
+        return rows.length;
+    },
+
+    /** The matched-filter trace, with a marker on each arrival the detector accepted. */
+    renderTrace({ envelope, detected, round }) {
+        const canvas = this.elements.trace;
+        const context = canvas.getContext("2d");
+        const width = (canvas.width = canvas.clientWidth);
+        const height = (canvas.height = 160);
+        const peak = EchoDsp.maxInRange(envelope, 0, envelope.length).value || 1;
+
+        context.clearRect(0, 0, width, height);
+        context.strokeStyle = "rgba(9, 255, 0, 0.75)";
+        context.beginPath();
+
+        const bucket = envelope.length / width;
+        for (let x = 0; x < width; x++) {
+            const start = Math.floor(x * bucket);
+            const highest = EchoDsp.maxInRange(envelope, start, Math.min(envelope.length, Math.floor(start + bucket))).value;
+            const y = height - (highest / peak) * (height - 8) - 4;
+            x === 0 ? context.moveTo(x, y) : context.lineTo(x, y);
+        }
+
+        context.stroke();
+        this.drawMarkers(context, detected, round, envelope.length, width, height);
+        return canvas;
+    },
+
+    drawMarkers(context, detected, round, envelopeLength, width, height) {
+        if (!detected) return null;
+
+        context.font = "11px 'Cascadia Code', monospace";
+
+        detected.peaks.forEach((peak, slot) => {
+            if (!peak) return;
+
+            const x = (peak.index / envelopeLength) * width;
+            const own = slot === round.ownSlot;
+            context.strokeStyle = own ? "#5fff5f" : "rgba(255, 255, 255, 0.55)";
+            context.fillStyle = context.strokeStyle;
+            context.beginPath();
+            context.moveTo(x, 0);
+            context.lineTo(x, height);
+            context.stroke();
+            context.fillText(own ? `self (${slot})` : `slot ${slot}`, x + 4, 14 + slot * 13);
+        });
+
+        return detected.peaks.length;
+    }
+};
+
+document.addEventListener("DOMContentLoaded", () => EchoPage.start());

JoshHeaps.Net/wwwroot/js/utils.js

@@ -45,9 +45,9 @@ function simulateTyping(element, text, speed = 50) {
 
 function showClickedContents(option) {
     if (option === 'projects') {
-        document.querySelector("#ChessProject > div.diagonal-section-left").scrollIntoView({
+        document.querySelector("#ProjectsBox").scrollIntoView({
             behavior: "smooth",
-            block: "center",
+            block: "start",
             inline: "nearest"
         });
     }
@@ -68,4 +68,11 @@ function showClickedContents(option) {
             inline: "nearest"
         });
     }
+    else if (option === 'blog') {
+        document.querySelector("#BlogBox").scrollIntoView({
+            behavior: "smooth",
+            block: "start",
+            inline: "nearest"
+        });
+    }
 }

docs/custom-chess-engine-rnd.md

@@ -0,0 +1,759 @@
+# R&D Findings: Swappable C++ Chess Engine via P/Invoke
+
+**Team:** Architect, Backend Engineer, Performance Engineer, DevOps Engineer (orchestrated by team lead)
+**Date:** 2026-05-28
+**Status:** Complete — engine *infrastructure* design only; the C++ search logic is intentionally left as an empty, compilable stub for the user to implement.
+
+---
+
+## Executive Summary
+
+We investigated how to host a custom chess engine written in C++ (compiled to `chess_engine.dll` for local Windows debugging and `libchess_engine.so` for the Linux server) behind a C# "middleman" wrapper that shares an interface with the existing `Stockfish.cs`, so the two are swappable by config. The key conclusion: the existing engine already uses a **string contract (FEN in → UCI move out)**, so the cleanest design mirrors it exactly — an opaque-handle `extern "C"` ABI, a `[LibraryImport]` P/Invoke wrapper, and a new `IChessEngine` interface that both `Stockfish` and the new `CustomChessEngine` implement, selected by a factory reading `appsettings`. The recommended next step is to land the **infrastructure** (interface, factory, P/Invoke wrapper, CMake project, empty C++ stub, build/packaging) and verify the round trip end-to-end with the stub returning a placeholder move — *before* any chess logic is written.
+
+> **Naming reconciliation:** the specialists used varying names for the native lib (`ChessEngine`, `chessengine`, `chess_engine`). This document standardizes on **logical name `chess_engine`** → `chess_engine.dll` (Windows) / `libchess_engine.so` (Linux), matching the Backend and DevOps proposals. Adjust the snippets from the Architect/Performance sections accordingly.
+
+### High-Level Architecture
+
+```mermaid
+graph TD
+    subgraph Managed["C# / .NET 8"]
+        CTRL[ChessController] --> FAC[IChessEngineFactory]
+        FAC -->|reads appsettings| OPT[ChessEngineOptions]
+        FAC -->|Stockfish| SF[Stockfish : IChessEngine]
+        FAC -->|Custom| CE[CustomChessEngine : IChessEngine]
+        CTRL --> ORCH[IComputerMoveOrchestrator]
+        ORCH -->|GetBestMoveAsync fen| IFACE[/IChessEngine/]
+        SF -.implements.-> IFACE
+        CE -.implements.-> IFACE
+        ORCH --> RULES[IChessService rules]
+        ORCH --> HUB[ChessHub SignalR]
+    end
+    subgraph Native["C++ shared library"]
+        CE -->|P/Invoke once per move| ABI["extern C ABI<br/>engine_best_move(fen, out)"]
+        ABI --> SEARCH["self-contained search<br/>bitboards, zero managed callbacks"]
+    end
+    SF -->|child process stdio| SFEXE[stockfish-*.exe]
+```
+
+---
+
+## Findings by Area
+
+### Architect: Engine Abstraction & Swap Mechanism
+
+#### Current State
+
+Two distinct concerns are easy to confuse:
+
+- **`IChessService` / `ChessService`** — the *rules engine* (move legality, check/mate). NOT the thing being swapped. `JoshHeaps.Net\Services\Interfaces\IChessService.cs:5-11`, `ChessService.cs:6`.
+- **`Stockfish`** — the *AI move-selection engine* (the thing being swapped). `Services\Implementations\Stockfish.cs:13`.
+
+`Stockfish` is a concrete `sealed` class with **no interface**, carrying three mixed responsibilities:
+
+1. **Engine lifecycle/IO** — spawns a child process, UCI handshake, `GetBestMoveAsync(fen)`. `Stockfish.cs:13-111`.
+2. **Orchestration** — `MakeMove(GameState, IHubContext<ChessHub>, IChessService)` gets a move, converts it, calls the rules service, broadcasts over SignalR. `Stockfish.cs:113-126`. Engine-agnostic glue.
+3. **FEN/UCI translation** — `StockfishHelpers.ToFen(...)` / `ToMoveDto(...)`. `Stockfish.cs:129-253`. Also engine-agnostic.
+
+Coupling points where the concrete type leaks:
+
+- `GameState.Computer` typed as concrete `Stockfish?` — domain model → implementation (inverted dependency). `Models\GameState.cs:46`, `using ...Implementations;` at `GameState.cs:1`.
+- Controller hand-constructs the engine: `gameState.Computer = new(difficulty);` `Controllers\ChessController.cs:45`. No DI, no abstraction.
+- Orchestration via concrete instance: `gameState.Computer.MakeMove(...)` at `ChessController.cs:60` and `:192`.
+- Disposal via concrete type: `await game.Computer.DisposeAsync();` `ChessController.cs:248`.
+- `Stockfish` is **not** registered in DI; `Program.cs:21-23` registers other services but the engine is `new`-ed inline per game.
+
+```mermaid
+classDiagram
+    class GameState {
+        +Stockfish? Computer
+        +bool IsVsComputer
+    }
+    class ChessController
+    class Stockfish {
+        +GetBestMoveAsync(fen) Task~string~
+        +MakeMove(state, hub, chessService) Task
+        +DisposeAsync() ValueTask
+    }
+    class StockfishHelpers {
+        +ToFen(GameState)$ string
+        +ToMoveDto(uci, state, playerId)$ MoveDto
+    }
+    class IChessService { <<interface>> }
+    class ChessService
+
+    IChessService <|.. ChessService
+    ChessController --> GameState : new()s Stockfish into
+    GameState *-- Stockfish : owns concrete
+    ChessController ..> Stockfish : MakeMove() / DisposeAsync()
+    Stockfish ..> StockfishHelpers
+    Stockfish ..> IChessService
+    Stockfish ..> ChessHub : broadcasts
+    note for GameState "Models depends on\nServices.Implementations — inverted"
+    note for Stockfish "Orchestration lives inside engine —\nwould duplicate across 2 engines"
+```
+
+#### Findings
+
+1. **No interface → cannot swap.** `Stockfish` is `sealed`, concrete-only (`Stockfish.cs:13`). Adding `CustomChessEngine` today means touching `GameState`, the controller, and disposal. *Impact:* an `IChessEngine` abstraction is the core requirement.
+2. **Domain model depends on a concrete service.** `GameState.cs:46` + `using ...Implementations` at `GameState.cs:1`. *Impact:* must become `IChessEngine?` (or leave the model entirely).
+3. **Engine hand-constructed in controller, no DI.** `ChessController.cs:45`. *Impact:* engine selection can't be config-driven; this is the seam for a factory.
+4. **Orchestration lives in the engine.** `Stockfish.MakeMove(...)` (`Stockfish.cs:113-126`) is not Stockfish-specific. *Impact:* copying it into `CustomChessEngine` duplicates rules-call + broadcast wiring; lift it to an orchestrator.
+5. **FEN/UCI translation is engine-agnostic** (`Stockfish.cs:169`, `:131`). *Impact:* keep shared (rename to `ChessEngineHelpers`), don't duplicate.
+6. **Engine lifecycle is game-scoped, not DI-scoped.** Created in `CreateGame` (`ChessController.cs:45`), disposed in the game-removal timer (`ChessController.cs:247-248`); the constructor spawns a process and blocks on UCI handshake (`Stockfish.cs:54,72,77`). *Impact:* a plain singleton won't fit — use a **per-game factory** producing disposable instances.
+7. **`MakeMove` is fire-and-forget returning non-generic `Task`** (`Stockfish.cs:113`). *Impact:* when lifted, the orchestrator should return the `(MoveDto, MoveResultDto)` it produced (per CodingStyle "Void Avoidance").
+
+#### Suggested Approach
+
+Three roles: `IChessEngine` (swappable contract), `IChessEngineFactory` (per-game creation from config), `IComputerMoveOrchestrator` (lifted glue).
+
+```csharp
+// Services/Interfaces/IChessEngine.cs
+public interface IChessEngine : IAsyncDisposable
+{
+    int Skill { get; }
+    // UCI long-algebraic, e.g. "e2e4", "e7e8q"
+    Task<string> GetBestMoveAsync(string fen, CancellationToken cancellationToken = default);
+}
+```
+
+```csharp
+// Services/Implementations/Stockfish.cs  (minimal change)
+public sealed class Stockfish : IChessEngine   // was: IAsyncDisposable
+{
+    public int Skill => _skill;
+    public Task<string> GetBestMoveAsync(string fen, CancellationToken ct = default) { /* existing body */ }
+    public ValueTask DisposeAsync() { /* unchanged */ }
+    // DELETE MakeMove(...) -> moves to IComputerMoveOrchestrator
+}
+// StockfishHelpers -> rename to ChessEngineHelpers in Services/Implementations/ChessEngineHelpers.cs (body unchanged)
+```
+
+```csharp
+// Services/Interfaces/IChessEngineFactory.cs
+public interface IChessEngineFactory { IChessEngine Create(int skill); }
+
+// Services/Implementations/ChessEngineFactory.cs
+public sealed class ChessEngineFactory(IOptions<ChessEngineOptions> options) : IChessEngineFactory
+{
+    private readonly ChessEngineKind _kind = options.Value.Engine;
+    public IChessEngine Create(int skill) => _kind switch
+    {
+        ChessEngineKind.Custom    => new CustomChessEngine(skill),
+        ChessEngineKind.Stockfish => new Stockfish(skill),
+        _ => throw new InvalidOperationException($"Unknown engine '{_kind}'.")
+    };
+}
+public enum ChessEngineKind { Stockfish, Custom }
+public sealed class ChessEngineOptions
+{
+    public const string SectionName = "ChessEngine";
+    public ChessEngineKind Engine { get; set; } = ChessEngineKind.Stockfish;
+}
+```
+
+```csharp
+// Program.cs (near :21-23)
+builder.Services.Configure<ChessEngineOptions>(configuration.GetSection(ChessEngineOptions.SectionName));
+builder.Services.AddSingleton<IChessEngineFactory, ChessEngineFactory>();
+builder.Services.AddSingleton<IComputerMoveOrchestrator, ComputerMoveOrchestrator>();
+```
+
+```jsonc
+// appsettings.json  — flip to "Custom" to swap (override per-env in appsettings.Development.json)
+{ "ChessEngine": { "Engine": "Stockfish" } }
+```
+
+```csharp
+// Services/Implementations/ComputerMoveOrchestrator.cs  (lifted from Stockfish.MakeMove, engine-agnostic)
+public interface IComputerMoveOrchestrator
+{
+    Task<(MoveDto move, MoveResultDto result)> PlayAsync(GameState state, IChessEngine engine, CancellationToken ct = default);
+}
+public sealed class ComputerMoveOrchestrator(IHubContext<ChessHub> chessHub, IChessService chessService) : IComputerMoveOrchestrator
+{
+    public async Task<(MoveDto, MoveResultDto)> PlayAsync(GameState state, IChessEngine engine, CancellationToken ct = default)
+    {
+        var uci = await engine.GetBestMoveAsync(state.ToFen(), ct);
+        var move = uci.ToMoveDto(state, state.CurrentPlayer == PieceColor.White ? state.WhitePlayerId : state.BlackPlayerId);
+        var result = chessService.MakeMove(state, move);
+        await chessHub.Clients.Group(state.GameId.ToString())
+            .SendAsync("ReceiveMoveUpdate", state.GameId.ToString(), move, result, ct);
+        return (move, result);
+    }
+}
+```
+
+**`GameState.Computer` recommendation:** keep the reference on `GameState` but retype to `IChessEngine?` (fixes Finding 2) — do *not* go full service-injection. Rationale: the engine is a stateful, per-game, disposable resource whose lifetime is managed by `ScheduleRemoveGame` (`ChessController.cs:247-248`); live games live in the controller's static `ConcurrentDictionary` (`ChessController.cs:20`), not DI. Only the engine's *construction* (factory) and *orchestration* (orchestrator) move out.
+
+```csharp
+// ChessController changes (inject factory + orchestrator into the primary ctor at :12-15)
+gameState.Computer = engineFactory.Create(difficulty);            // was :45 new(difficulty)
+await orchestrator.PlayAsync(gameState, gameState.Computer);       // was :60
+if (gameState.IsVsComputer && gameState.Computer is not null)      // was :192
+    queue.Queue(() => orchestrator.PlayAsync(gameState, gameState.Computer!));
+await game.Computer.DisposeAsync();                                // :248 unchanged (IChessEngine : IAsyncDisposable)
+```
+
+```mermaid
+classDiagram
+    class IChessEngine {
+        <<interface>>
+        +int Skill
+        +GetBestMoveAsync(fen, ct) Task~string~
+        +DisposeAsync() ValueTask
+    }
+    class Stockfish
+    class CustomChessEngine { -P/Invoke chess_engine (.dll/.so) }
+    class IChessEngineFactory { <<interface>> +Create(skill) IChessEngine }
+    class ChessEngineFactory
+    class ChessEngineOptions { +ChessEngineKind Engine }
+    class IComputerMoveOrchestrator { <<interface>> +PlayAsync(state, engine, ct) }
+    class ComputerMoveOrchestrator
+    class GameState { +IChessEngine? Computer }
+    class ChessController
+    class ChessEngineHelpers
+
+    IChessEngine <|.. Stockfish
+    IChessEngine <|.. CustomChessEngine
+    IChessEngineFactory <|.. ChessEngineFactory
+    IComputerMoveOrchestrator <|.. ComputerMoveOrchestrator
+    ChessEngineFactory ..> ChessEngineOptions : reads config
+    ChessEngineFactory ..> Stockfish : creates
+    ChessEngineFactory ..> CustomChessEngine : creates
+    ChessController ..> IChessEngineFactory
+    ChessController ..> IComputerMoveOrchestrator
+    GameState o-- IChessEngine : holds abstraction
+    ComputerMoveOrchestrator ..> IChessEngine
+    ComputerMoveOrchestrator ..> ChessEngineHelpers
+    ComputerMoveOrchestrator ..> IChessService
+    note for GameState "Now depends on Interfaces (DIP fixed)"
+    note for CustomChessEngine "C++ body empty; P/Invoke contract only"
+```
+
+#### Open Questions
+
+1. Does the custom engine speak FEN-in / UCI-out? (Assumed yes — confirm before locking the interface.)
+2. Per-game instance vs shared singleton for the in-process native engine (a `.dll`/`.so` may be cheap enough to share, unlike a Stockfish process).
+3. Skill/options surface — `int skill` vs an `EngineOptions` object if tunables diverge from Stockfish's `(skill, hash)` (`Stockfish.cs:20`).
+4. Cancellation/timeout — interface has a `CancellationToken` but nothing wires it today (`BackgroundTaskQueue.cs:11` fire-and-forgets).
+5. Concurrency — `GetBestMoveAsync` is not re-entrant per instance (single stdout `Channel`, `Stockfish.cs:17`); per-game instances make this moot today.
+
+---
+
+### Backend Engineer: Native Interop & I/O Contract
+
+#### Current State
+
+The load-bearing method is `GetBestMoveAsync(string fen)` at `Stockfish.cs:80-95`: writes `position fen <fen>` + `go depth N` to stdin (`:82-83`), reads stdout until a line starts with `bestmove` (`:88`), returns the second token — a raw UCI string like `e2e4` / `e7e8q` (`:90`). Input is produced by `ToFen()` (`Stockfish.cs:169-214`); output is consumed by `ToMoveDto()` (`Stockfish.cs:131-162`, parses chars `uci[0..4]` into `MoveDto`, `MoveDto.cs:3-20`). Consumer: `ChessController.cs:191-192` queues `gameState.Computer.MakeMove(...)`.
+
+**There is no native interop today.** A repo-wide grep for `DllImport|LibraryImport|NativeLibrary|Marshal|extern` returns only an unrelated hit in vendored `jquery.js`. Project targets `net8.0`, `Nullable=enable`, `ImplicitUsings=enable` (`JoshHeaps.Net.csproj:3-7`).
+
+```mermaid
+sequenceDiagram
+    participant C as ChessController
+    participant SF as Stockfish (C#)
+    participant P as stockfish.exe (subprocess)
+    C->>SF: MakeMove(state) / GetBestMoveAsync(fen)
+    Note over SF: state.ToFen() builds FEN
+    SF->>P: stdin "position fen <FEN>"
+    SF->>P: stdin "go depth N"
+    P-->>SF: stdout "info ..."
+    P-->>SF: stdout "bestmove e2e4"
+    Note over SF: Split(' ')[1] => "e2e4"
+    SF-->>C: "e2e4" (UCI)
+    Note over C: uci.ToMoveDto(state) => MoveDto
+```
+
+#### Findings
+
+1. **The boundary is already a pure string pair** (`Stockfish.cs:80,90`). *Impact:* the native ABI should mirror it exactly — `const char* fen` in, `char*` UCI out. No struct marshalling needed.
+2. **No `IChessEngine` abstraction; consumers bind the concrete type** (`GameState.cs:46`, `ChessController.cs:191-192`). *Impact:* the middleman implements the Architect's interface; the `GameState` retype is a cross-cutting dependency.
+3. **`MakeMove` mixes engine + SignalR/board concerns** (`Stockfish.cs:113-126`). *Impact:* keep it shared (orchestrator), not per-engine. The native-specific surface of `CustomChessEngine` is only `GetBestMoveAsync`.
+4. **The UCI string is the contract anchor.** As long as the native engine emits a 4-or-5-char UCI move, the whole downstream pipeline (`MoveDto` → `IChessService.MakeMove` → SignalR) is unchanged (`Stockfish.cs:131,169`).
+5. **Resource-shipping pattern is established** (`csproj:14-18` copies `Resources/**`). *Impact:* the `.dll`/`.so` ship the same way.
+
+#### Suggested Approach
+
+**Contract: strings (FEN in / UCI out), not a binary struct.** It is byte-identical to today's contract (so `ToFen`/`ToMoveDto` are untouched); FEN/UCI are stable ASCII (no layout/packing/endianness/enum-width to keep in sync); the user only writes string parsing in C++; per-move data is tiny. **Buffer-ownership rule:** the C# caller owns the output buffer; the engine only writes into it and never allocates returned strings — sidesteps cross-allocator free bugs.
+
+```c
+// native/chess_engine/include/chess_engine.h
+#ifndef CHESS_ENGINE_H
+#define CHESS_ENGINE_H
+#include <stddef.h>
+
+#if defined(_WIN32)
+  #ifdef CHESS_ENGINE_BUILD
+    #define CHESS_API __declspec(dllexport)
+  #else
+    #define CHESS_API __declspec(dllimport)
+  #endif
+  #define CHESS_CALL __cdecl
+#else
+  #define CHESS_API __attribute__((visibility("default")))
+  #define CHESS_CALL
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct ChessEngine* EngineHandle;   // opaque; host never dereferences
+
+enum {
+    CHESS_OK = 0, CHESS_ERR_NULL_HANDLE = -1, CHESS_ERR_BAD_FEN = -2,
+    CHESS_ERR_NO_MOVE = -3, CHESS_ERR_BUFFER = -4, CHESS_ERR_INTERNAL = -5
+};
+
+CHESS_API EngineHandle CHESS_CALL engine_create(const char* options);            // options e.g. "skill=20;hash=256" or NULL
+CHESS_API int          CHESS_CALL engine_set_option(EngineHandle, const char* name, const char* value);
+CHESS_API int          CHESS_CALL engine_best_move(EngineHandle, const char* fen, char* out_buf, int out_len); // writes "e2e4\0"
+CHESS_API int          CHESS_CALL engine_version(char* out_buf, int out_len);
+CHESS_API void         CHESS_CALL engine_destroy(EngineHandle);                  // safe with NULL
+
+#ifdef __cplusplus
+}
+#endif
+#endif
+```
+
+```cpp
+// native/chess_engine/src/chess_engine.cpp  — EMPTY stub; compiles, returns placeholder
+#define CHESS_ENGINE_BUILD
+#include "chess_engine.h"
+#include <cstring>
+#include <string>
+
+struct ChessEngine { std::string options; };   // put TT, tables, etc. here later
+
+static int copy_out(const char* src, char* out, int cap) {
+    if (!out || cap <= 0) return CHESS_ERR_BUFFER;
+    const size_t need = std::strlen(src) + 1;
+    if (need > (size_t)cap) return CHESS_ERR_BUFFER;
+    std::memcpy(out, src, need);
+    return CHESS_OK;
+}
+
+extern "C" {
+CHESS_API EngineHandle CHESS_CALL engine_create(const char* options) {
+    auto* e = new (std::nothrow) ChessEngine();
+    if (e && options) e->options = options;
+    return e;
+}
+CHESS_API int CHESS_CALL engine_set_option(EngineHandle e, const char*, const char*) {
+    return e ? CHESS_OK : CHESS_ERR_NULL_HANDLE;
+}
+CHESS_API int CHESS_CALL engine_best_move(EngineHandle e, const char* fen, char* out, int cap) {
+    if (!e)            return CHESS_ERR_NULL_HANDLE;
+    if (!fen || !*fen) return CHESS_ERR_BAD_FEN;
+    // TODO: parse fen, search, produce a real UCI move.
+    return copy_out("e2e4", out, cap);          // placeholder
+}
+CHESS_API int CHESS_CALL engine_version(char* out, int cap) { return copy_out("custom-engine 0.0.1-stub", out, cap); }
+CHESS_API void CHESS_CALL engine_destroy(EngineHandle e) { delete e; }
+}
+```
+
+**ABI notes:** `extern "C"` kills name mangling; `CHESS_API` = `__declspec(dllexport)` (MSVC, when `CHESS_ENGINE_BUILD` defined) or `__attribute__((visibility("default")))` (GCC/Clang, pair with `-fvisibility=hidden`); `CHESS_CALL` pins `__cdecl` on Windows, empty (SysV default) on Linux.
+
+```csharp
+// Services/Implementations/CustomChessEngine.cs
+public sealed class CustomChessEngine : IChessEngine   // IAsyncDisposable via IChessEngine
+{
+    private readonly EngineSafeHandle _handle;
+
+    public int Skill { get; }
+    public CustomChessEngine(int skill = 20)
+    {
+        Skill = skill;
+        var raw = NativeMethods.engine_create($"skill={skill}");
+        if (raw == IntPtr.Zero) throw new InvalidOperationException("engine_create returned null.");
+        _handle = new EngineSafeHandle(raw);
+    }
+
+    public Task<string> GetBestMoveAsync(string fen, CancellationToken ct = default)
+        => Task.Run(() => BestMove(fen), ct);      // native call is sync + CPU-bound; offload off request thread
+
+    private string BestMove(string fen)
+    {
+        Span<byte> outBuf = stackalloc byte[16];   // UCI <= 5 chars + NUL
+        bool added = false;
+        try
+        {
+            _handle.DangerousAddRef(ref added);
+            int rc;
+            unsafe { fixed (byte* p = outBuf) rc = NativeMethods.engine_best_move(_handle.DangerousGetHandle(), fen, p, outBuf.Length); }
+            ThrowIfError(rc);
+            int nul = outBuf.IndexOf((byte)0);
+            return System.Text.Encoding.ASCII.GetString(outBuf[..(nul < 0 ? outBuf.Length : nul)]);
+        }
+        finally { if (added) _handle.DangerousRelease(); }
+    }
+
+    private static void ThrowIfError(int rc) { if (rc != 0) throw rc switch {
+        -2 => new ArgumentException("CHESS_ERR_BAD_FEN"),
+        -3 => new InvalidOperationException("No move (mate/stalemate)"),
+        -4 => new InvalidOperationException("Output buffer too small"),
+        _  => new InvalidOperationException($"Native engine error {rc}") }; }
+
+    public ValueTask DisposeAsync() { _handle.Dispose(); return ValueTask.CompletedTask; }
+
+    private sealed class EngineSafeHandle : SafeHandle
+    {
+        public EngineSafeHandle(IntPtr h) : base(IntPtr.Zero, true) => SetHandle(h);
+        public override bool IsInvalid => handle == IntPtr.Zero;
+        protected override bool ReleaseHandle() { NativeMethods.engine_destroy(handle); return true; }
+    }
+
+    private static partial class NativeMethods
+    {
+        private const string Lib = "chess_engine";   // -> chess_engine.dll / libchess_engine.so
+        static NativeMethods() => NativeLibrary.SetDllImportResolver(typeof(NativeMethods).Assembly, Resolve);
+        private static IntPtr Resolve(string name, Assembly asm, DllImportSearchPath? path)
+        {
+            if (name != Lib) return IntPtr.Zero;
+            string file = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "chess_engine.dll" : "libchess_engine.so";
+            string probe = Path.Combine(AppContext.BaseDirectory, "Resources", file);
+            return File.Exists(probe) && NativeLibrary.TryLoad(probe, out var h) ? h : NativeLibrary.Load(name, asm, path);
+        }
+
+        [LibraryImport(Lib, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = new[] { typeof(CallConvCdecl) })]
+        internal static partial IntPtr engine_create(string? options);
+
+        [LibraryImport(Lib, StringMarshalling = StringMarshalling.Utf8)]
+        [UnmanagedCallConv(CallConvs = new[] { typeof(CallConvCdecl) })]
+        internal static unsafe partial int engine_best_move(IntPtr engine, string fen, byte* outBuf, int outLen);
+
+        [LibraryImport(Lib)]
+        [UnmanagedCallConv(CallConvs = new[] { typeof(CallConvCdecl) })]
+        internal static partial void engine_destroy(IntPtr engine);
+    }
+}
+```
+
+**Why these C# choices:** `[LibraryImport]` (source-generated, AOT/trim-safe, no runtime IL stub, compile-time diagnostics) over `[DllImport]`; `StringMarshalling.Utf8` matches `const char*`; a `DllImportResolver` probes `Resources/` first then falls back to default search; `SafeHandle` guarantees `engine_destroy` runs exactly once; return codes map to typed exceptions; `Task.Run` adapts the sync native call to the async interface (for a real long search, prefer one dedicated long-running thread per instance over thread-pool churn).
+
+```mermaid
+sequenceDiagram
+    participant C as ChessController
+    participant CE as CustomChessEngine (C#)
+    participant TP as Task.Run (threadpool)
+    participant N as chess_engine.dll/.so
+    C->>CE: GetBestMoveAsync(state.ToFen())
+    CE->>TP: offload sync native call
+    Note over TP: stackalloc byte[16] out_buf (host-owned)
+    TP->>N: engine_best_move(handle, fen, out_buf, 16)
+    Note over N: parse FEN, search, write "e2e4\0"
+    N-->>TP: CHESS_OK; out_buf filled
+    TP-->>CE: "e2e4"
+    CE-->>C: "e2e4" (same UCI as Stockfish)
+    Note over C: uci.ToMoveDto(state) => MoveDto (unchanged)
+```
+
+#### Open Questions
+
+1. Should `MakeMove`/orchestration be on the interface or shared via the orchestrator? (Recommend orchestrator — aligns with Architect.)
+2. Who owns the `GameState.Computer` retype (Architect vs Backend)? Cross-cutting.
+3. Build/packaging: CMake + MSBuild copy vs commit binaries (see DevOps).
+4. Search timeout/cancellation: add `engine_stop(handle)` + token-aware wrapper, or fixed-depth like Stockfish's `go depth N` (`Stockfish.cs:83`)?
+5. `options` string format (`"key=value;..."`) vs per-option `engine_set_option`?
+6. Concurrency model — one move per instance at a time (current queue suggests yes)?
+
+---
+
+### Performance Engineer: Interop Boundary & Hot-Path Strategy
+
+#### Current State
+
+Two distinct things are being conflated:
+
+1. **The Stockfish path is already fast and well-structured** — one warm process (`Stockfish.cs:40-54`), two text commands per move, block on stdout (`:82-93`). The cost is the *search* (`go depth {_skill}`, `:83`), not the pipe. **Stockfish is not slow.** It is also already a self-contained native search — the model to preserve.
+2. **The C# `ChessService` is the genuinely slow thing** and the real motivation:
+   - **Object-graph board:** `GameState.Board` is `ChessPiece?[,]` (`GameState.cs:11`) of heap `ChessPiece` objects each with a `string Id` (`ChessPiece.cs:5`) — pointer chase / cache miss per square touch.
+   - **Allocation per pseudo-move:** legality calls `CloneGameState` (`ChessService.cs:319,453-483`) allocating a new `GameState`, `ChessPiece[8,8]`, `List<string>`, and a `ChessPiece` per piece — *every candidate move*.
+   - **LINQ in the inner loop:** `IsSquareAttacked` does `.Where(...).ToList()` + regenerates enemy moves (`ChessService.cs:396-407`); lookups by string id via `FirstOrDefault` (`:110,126`).
+   - Fine for validating one human move; orders of magnitude away from a search loop. Correct thing to move to C++.
+
+```mermaid
+flowchart TD
+    A["ChessController.MakeMove :192"] --> B["queue.Queue (IBackgroundTaskQueue)"]
+    B --> C["Stockfish.MakeMove :113"]
+    C --> D["state.ToFen() ~70B :169"]
+    D --> E["stdin 'position fen' + 'go depth N' :82-83"]
+    E --> F["stdin pipe -> stockfish.exe"]
+    F --> G["NATIVE SEARCH (seconds)<br/>millions of nodes, zero managed calls"]
+    G --> H["stdout 'bestmove e2e4' :86-92"]
+    H --> I["parse ~5B UCI -> MoveDto :117,136"]
+    style G fill:#2d6a2d,color:#fff
+    style F fill:#7a5c00,color:#fff
+    style H fill:#7a5c00,color:#fff
+```
+
+#### Findings
+
+1. **The move boundary is provably not the hot path.** Per move: ~70-byte FEN in, ~5-byte UCI out — sub-microsecond marshalling vs a multi-second search; the boundary is ~6+ orders of magnitude cheaper than the work it gates. The string contract is correct and will never bottleneck. Production already proves it via a *heavier* transport (OS pipes).
+2. **Forbidden anti-pattern: a chatty per-node boundary.** A `LibraryImport` P/Invoke transition is ~1–2 ns, but a search visits millions of nodes/sec. A managed callback per node (move-gen/eval) adds a GC-tracked frame, write-barrier exposure, and loss of native inlining on the hottest loop — defeating the whole point. **Rule: the native search owns move-gen, make/unmake, and eval; zero managed callbacks below the once-per-move boundary.**
+3. **Board representation is native-internal, not a marshalling concern.** Use **bitboards** inside C++ (~12 `uint64_t` + occupancy/flags); make/unmake and attacks become `&`/`|`/shifts/`popcnt`/`tzcnt` instead of pointer-chasing + LINQ (`ChessService.cs:392-410`). None of it crosses the boundary — C# keeps its `GameState` graph for rendering/human-move validation; the engine rebuilds bitboards from the FEN.
+4. **Threading/async.** The search is CPU-bound/synchronous; the controller already enqueues on a background queue (`ChessController.cs:192`) so the SignalR thread isn't blocked. Wrap the blocking P/Invoke in `Task.Run`; results push back over `IHubContext<ChessHub>` as today (`Stockfish.cs:125`). **Parallel search (Lazy SMP) stays 100% native.** **Cancellation = one atomic flag:** `engine_stop()` sets `std::atomic<bool>` polled between nodes — crosses the boundary once on cancel, never per node.
+
+| Operation | Approx. cost | Frequency |
+|---|---|---|
+| P/Invoke transition (blittable, `LibraryImport`) | ~1–2 ns | once per move |
+| Marshal ~70B FEN in + ~5B UCI out | < 1 µs | once per move |
+| `ToFen()` string build (`Stockfish.cs:169`) | low µs | once per move |
+| **Native search (`go depth N`)** | **~0.1–several s** | **once per move** |
+| Hypothetical managed eval callback **per node** | ~tens of ns × millions/sec | ❌ never — forbidden |
+
+#### Suggested Approach
+
+Cross the boundary **once per move**; keep the loop fully native.
+
+```cpp
+// RECOMMENDED: self-contained native search
+extern "C" int engine_best_move(ChessEngine* e, const char* fen, char* out, int cap) {
+    Position pos = parse_fen(fen);        // build bitboards ONCE
+    g_stop.store(false);
+    Move best = search(pos, e->depth);    // millions of nodes, NO callbacks out
+    return write_uci(best, out, cap);     // ~5 bytes back
+}
+```
+```cpp
+// FORBIDDEN: chatty boundary — do NOT do this
+int search(Position& pos, int depth) {
+    for (Move m : managed_generate_moves(pos))  // P/Invoke OUT per node
+        eval += managed_eval_callback(pos);      // managed frame per node — death
+}
+```
+
+**Optional blittable-struct contract — recommend DEFER.** If profiling ever showed FEN parse dominating (it won't at one call/move), you *could* pass a `[StructLayout(LayoutKind.Sequential)]` `NativePosition` (12 bitboards + flags) by `in`/`ref` (fully blittable, no marshalling). But it adds a second board-layout source-of-truth and couples C# to the engine's internals. **Ship the FEN/UCI string contract; don't build the struct path until a profiler proves it's needed.**
+
+```mermaid
+flowchart TD
+    A["ChessController.MakeMove :192"] --> B["queue.Queue -> Task.Run (SignalR thread freed)"]
+    B --> C["state.ToFen() ~70B"]
+    C --> D{{"engine_best_move(handle, fen, buf)<br/>ONE P/Invoke crossing (~1-2ns + <1us marshal)"}}
+    D --> E["NATIVE: parse_fen -> bitboards (x12 ulong)"]
+    E --> F["NATIVE SEARCH LOOP<br/>make/unmake on bitboards, native eval<br/>Lazy SMP threads, poll atomic g_stop<br/>ZERO managed callbacks"]
+    F --> G{{"return ~5B UCI move<br/>ONE crossing back"}}
+    G --> H["parse UCI -> MoveDto -> SignalR (Stockfish.cs:117-125)"]
+    I["engine_stop(handle)"] -. "once on cancel, NOT per node" .-> F
+    style D fill:#1f4e79,color:#fff
+    style G fill:#1f4e79,color:#fff
+    style E fill:#2d6a2d,color:#fff
+    style F fill:#2d6a2d,color:#fff
+```
+
+**Build flags (coordinate with DevOps):** MSVC `/O2 /GL` + `/LTCG`, `/arch:AVX2` (matches the shipped AVX2 Stockfish, `Stockfish.cs:25`); GCC/Clang `-O3 -flto` with a baseline `-march` the server supports (the Linux Stockfish targets `sse41-popcnt`, `Stockfish.cs:28`) — avoid `-march=native` on a build host differing from the server.
+
+#### Open Questions
+
+1. **Deploy CPU baseline** — server's CPU floor dictates safe `-march`/`/arch` and whether `popcnt`/AVX2 bitboard intrinsics are guaranteed (Stockfish picks `avx2` Win / `sse41-popcnt` Linux, `Stockfish.cs:24-28`).
+2. Will the native engine fully replace or coexist with Stockfish? (Recommend a shared `IChessEngine`.)
+3. Engine lifetime/concurrency — one handle per game (like Stockfish today) vs reused across games (needs re-entrancy)?
+4. Search termination — fixed depth, nodes, or wall-clock (time-based makes `engine_stop` most useful)?
+5. Move-legality ownership — human moves validated by `ChessService.MakeMove` (`ChessController.cs:179`); two move generators risk divergence.
+
+---
+
+### DevOps Engineer: Cross-Platform Native Build & Packaging
+
+#### Current State
+
+- **Packaging:** `JoshHeaps.Net.csproj:14-18` copies the whole Resources folder as `Content` with `CopyToOutputDirectory=PreserveNewest` → lands in `bin\<cfg>\net8.0\Resources\` and `publish\Resources\`. Binaries are **committed** (`Resources\stockfish-windows-x86-64-avx2.exe`, `Resources\stockfish-ubuntu-x86-64-sse41-popcnt`).
+- **Runtime load:** `Stockfish.cs:23` `AppContext.BaseDirectory`; `:24-28` OS filename switch; `:30` `Path.Combine(baseDir,"Resources",fileName)`; `:32-36` existence check. Stockfish is a **child process** (`:40-54`), so there is no native-library load path today.
+- **CI/deploy is Linux-only:** `.github\workflows\deploy.yml:17` `runs-on: ubuntu-latest`, `dotnet publish -c Release` (`:29`), `rsync -az --delete publish/` to the server (`:55-58`), systemd restart (`:60-64`). PR build also `ubuntu-latest` (`dotnet.yml:13`). **A Windows `.dll` can never be produced on the runner — it must be committed.**
+
+```mermaid
+flowchart TD
+    A["Resources/stockfish-windows-*.exe (committed)"] --> C
+    B["Resources/stockfish-ubuntu-* (committed)"] --> C
+    C["csproj Content Resources/** PreserveNewest (csproj:14-18)"]
+    C --> D["dotnet publish (ubuntu-latest) deploy.yml:29"]
+    D --> E["publish/Resources/*"]
+    E --> F["rsync to Linux server deploy.yml:55-58"]
+    F --> G["Runtime Stockfish.cs:23,30 BaseDirectory + Resources/fileName"]
+    G --> H["Process.Start(exePath) — child process, not P/Invoke :40-54"]
+```
+
+#### Findings
+
+1. **The existing Content glob already covers new Resources files** (`csproj:14-18`) — dropping the native libs in `Resources/` flows them to output/publish with zero csproj change required (explicit items optional for clarity).
+2. **Build host is Linux-only** (`deploy.yml:17`, `dotnet.yml:13`) — the Windows `.dll` MUST be committed; an MSBuild→CMake target only helps on a developer's Windows box.
+3. **Stockfish uses a child process, not P/Invoke** (`Stockfish.cs:40-54`) — no existing `DllImport`/`NativeLibrary` precedent; the resolver story is net-new.
+4. **Resources path is hardcoded `Path.Combine(baseDir,"Resources",...)`** (`Stockfish.cs:30`), but P/Invoke's default search does NOT look in a `Resources` subfolder. *Impact:* register a `DllImportResolver` pointing at `Resources/` **or** place the lib at the output root. Biggest divergence from the Stockfish pattern.
+5. **No CMake/C++ scaffolding exists** — greenfield; recommend `native/chess_engine/` at repo root, outside the csproj compile globs.
+6. **glibc/libstdc++ ABI risk** — the committed `.so` is built on a dev/CI machine but runs on the rsync'd server (`deploy.yml:55`); a newer build-host libstdc++/glibc → runtime load failure. Build against a server-matching baseline or static-link libstdc++.
+
+#### Suggested Approach
+
+**Recommendation: build natively per-platform and commit both artifacts into `Resources/`, mirroring Stockfish.** The repo already commits platform binaries, the build host is Linux-only, and committing keeps deploy a pure `dotnet publish`. An optional opt-in MSBuild target can rebuild the matching-platform artifact locally, but must never be the deploy's source of truth.
+
+```cmake
+# native/chess_engine/CMakeLists.txt
+cmake_minimum_required(VERSION 3.20)
+project(chess_engine LANGUAGES CXX)
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+add_library(chess_engine SHARED src/chess_engine.cpp)
+target_include_directories(chess_engine PUBLIC include)
+target_compile_definitions(chess_engine PRIVATE CHESS_ENGINE_BUILD)
+
+# Windows -> chess_engine.dll ; Linux -> libchess_engine.so
+set_target_properties(chess_engine PROPERTIES OUTPUT_NAME chess_engine POSITION_INDEPENDENT_CODE ON)
+set(CMAKE_CXX_VISIBILITY_PRESET hidden)
+set(CMAKE_VISIBILITY_INLINES_HIDDEN ON)
+
+if (MSVC)
+    target_compile_options(chess_engine PRIVATE
+        $<$<CONFIG:Release>:/O2 /GL /DNDEBUG /arch:AVX2>
+        $<$<CONFIG:Debug>:/Od /Zi>)             # /Zi => .pdb for mixed-mode debugging
+    target_link_options(chess_engine PRIVATE $<$<CONFIG:Release>:/LTCG> $<$<CONFIG:Debug>:/DEBUG>)
+else()
+    # Portable server baseline; do NOT use -march=native (build host may differ -> SIGILL).
+    target_compile_options(chess_engine PRIVATE
+        $<$<CONFIG:Release>:-O3 -flto -DNDEBUG -march=x86-64-v2>   # ~SSE4.2; confirm server floor
+        $<$<CONFIG:Debug>:-O0 -g>)
+endif()
+```
+
+The export macro (`CHESS_API`, defined under `CHESS_ENGINE_BUILD`) and `extern "C"` live in the Backend Engineer's `chess_engine.h`.
+
+```bash
+# Windows (Developer PowerShell, MSVC)
+cmake -S native/chess_engine -B native/chess_engine/build -A x64
+cmake --build native/chess_engine/build --config Release   # -> build/Release/chess_engine.dll (+ .pdb)
+# Linux (ideally in an ubuntu:22.04 container matching the server)
+cmake -S native/chess_engine -B native/chess_engine/build -DCMAKE_BUILD_TYPE=Release
+cmake --build native/chess_engine/build                    # -> build/libchess_engine.so
+```
+Copy each artifact into `JoshHeaps.Net/Resources/` and commit — same lifecycle as the Stockfish binaries.
+
+**Optional local-only CMake build target** (gated `BuildNativeEngine=true`, off by default, OS-conditioned, never gates deploy):
+```xml
+<Target Name="BuildNativeWindows" BeforeTargets="BeforeBuild"
+        Condition="'$(BuildNativeEngine)'=='true' AND '$(OS)'=='Windows_NT'">
+  <Exec Command="cmake -S native\chess_engine -B native\chess_engine\build -A x64" />
+  <Exec Command="cmake --build native\chess_engine\build --config $(Configuration)" />
+  <Copy SourceFiles="native\chess_engine\build\$(Configuration)\chess_engine.dll" DestinationFolder="Resources\" SkipUnchangedFiles="true" />
+</Target>
+<Target Name="BuildNativeLinux" BeforeTargets="BeforeBuild"
+        Condition="'$(BuildNativeEngine)'=='true' AND '$(OS)'!='Windows_NT'">
+  <Exec Command="cmake -S native/chess_engine -B native/chess_engine/build -DCMAKE_BUILD_TYPE=Release" />
+  <Exec Command="cmake --build native/chess_engine/build" />
+  <Copy SourceFiles="native/chess_engine/build/libchess_engine.so" DestinationFolder="Resources/" SkipUnchangedFiles="true" />
+</Target>
+```
+
+**Runtime load — recommendation: `DllImportResolver` pointing at `Resources/`** (co-locates with Stockfish, survives single-file publish). This matches the Backend Engineer's `NativeMethods` resolver. Keep the native libs **only** in `Resources/` (rely on the existing `Content` glob) — do not also `<Link>` them to the output root, to avoid two copies that drift.
+
+**Local debugging (mixed-mode):** CMake `Debug` emits `/Zi` + `/DEBUG` → `chess_engine.pdb`; ship it next to the `.dll` for local debug builds only (Debug-only `None` item, never committed/deployed). In Visual Studio enable **Project Properties → Debug → Enable native code debugging** to step from C# P/Invoke into C++.
+
+**Linux deployment:** `libchess_engine.so` ships via `Resources/**` → `publish/` → rsync automatically. It's `dlopen`'d (no `chmod +x` needed) but must be world-readable. It links `libstdc++`/`glibc` — build against a baseline ≤ the server's, or **static-link** (`-static-libstdc++ -static-libgcc`) to remove the version coupling (safest for a committed binary).
+
+```mermaid
+flowchart TD
+    subgraph Build["Build (per-platform)"]
+        W["Windows dev: cmake --build Release<br/>=> chess_engine.dll (+pdb in Debug)"]
+        L["Linux (ubuntu:22.04 container): cmake --build Release<br/>=> libchess_engine.so (-static-libstdc++)"]
+    end
+    W --> R["Commit into JoshHeaps.Net/Resources/ (as stockfish-* today)"]
+    L --> R
+    R --> CSP["csproj Content Resources/** (csproj:14-18) -> output/Resources/"]
+    CSP --> PUB["dotnet publish (ubuntu-latest) deploy.yml:29 — pure, no toolchain"]
+    PUB --> RS["rsync publish/ to server deploy.yml:55-58"]
+    RS --> RES["DllImportResolver: BaseDirectory + Resources/ + OS filename switch (mirrors Stockfish.cs:23-30)"]
+    RES --> PI["P/Invoke [LibraryImport(chess_engine)] -> NativeLibrary.Load"]
+    style W fill:#1d4ed8,color:#fff
+    style L fill:#15803d,color:#fff
+    style PI fill:#92400e,color:#fff
+```
+
+#### Open Questions
+
+1. **Server glibc/libstdc++ version unknown** — need `ldd --version` + `strings libstdc++.so.6 | grep GLIBCXX`; otherwise build in `ubuntu:22.04` or static-link libstdc++.
+2. **Commit binaries vs build `.so` in CI?** Recommend commit both (consistent, pure deploy); alternative is a Linux native-build step in `deploy.yml` for a reproducible/ABI-correct `.so`.
+3. **Target CPU baseline** — assumed `-march=x86-64-v2` to match `sse41-popcnt`; confirm the server floor; `-march=native` unsafe for committed/CI binaries.
+4. **`IChessEngine` doesn't exist yet** — prerequisite from the Architect (out of scope for build, flagged).
+5. **`.pdb` policy** — local-only Debug symbols recommended; confirm.
+
+---
+
+## Cross-Cutting Concerns
+
+```mermaid
+graph TD
+    subgraph Arch["Architect: abstraction"]
+        IFACE[/IChessEngine/] --> FAC[Factory + appsettings]
+    end
+    subgraph Backend["Backend: contract"]
+        ABI["extern C ABI<br/>FEN -> UCI"]
+    end
+    subgraph Perf["Performance"]
+        ONCE["once-per-move boundary<br/>native search"]
+    end
+    subgraph DevOps["DevOps"]
+        PKG["commit .dll/.so in Resources<br/>DllImportResolver"]
+    end
+    IFACE -.->|"GetBestMoveAsync(fen) shape<br/>must match ABI"| ABI
+    ABI -.->|"string contract = thin boundary"| ONCE
+    ONCE -.->|"build flags -O3/AVX2/LTO"| PKG
+    PKG -.->|"resolver finds lib for CustomChessEngine"| IFACE
+```
+
+1. **The string contract ties all four areas together.** `IChessEngine.GetBestMoveAsync(string fen) → string` (Architect) is the exact shape of `engine_best_move(const char* fen, char* out)` (Backend), which is what makes the boundary thin (Performance) and keeps `ToFen`/`ToMoveDto` untouched. If anyone changes to a struct contract, all four must change. Evidence: `Stockfish.cs:80,90,131,169`.
+2. **`GameState.Computer` retype is owned by the Architect but unblocks Backend.** `GameState.cs:46` must become `IChessEngine?` before `CustomChessEngine` can be slotted in. Both specialists flagged it.
+3. **Native-lib naming must be consistent end to end.** The logical name `chess_engine` (C# `[LibraryImport]`/resolver), the CMake `OUTPUT_NAME chess_engine`, and the committed filenames `chess_engine.dll` / `libchess_engine.so` must all agree. The specialists used different names — standardized here.
+4. **`Resources/` placement + resolver is the load contract.** DevOps's `DllImportResolver` (probing `BaseDirectory/Resources`) and Backend's `NativeMethods.Resolve` are the same mechanism and must be written once (in `CustomChessEngine`/`NativeMethods`). Evidence: `Stockfish.cs:23,30`, `csproj:14-18`.
+5. **Build optimization is a shared Performance/DevOps concern.** `-O3 -flto` / `/O2 /GL /LTCG`, `/arch:AVX2`, and a safe Linux `-march` baseline live in the CMakeLists (DevOps) but are motivated by the hot-loop requirement (Performance).
+6. **Move-generation single-source-of-truth.** Human moves stay validated by C# `ChessService` (`ChessController.cs:179`); the native engine has its own generator. Two generators risk divergence — consider exposing native `perft` later for cross-validation.
+
+## Risk Assessment
+
+| Risk | Severity | Likelihood | Mitigation | Related Files |
+|---|---|---|---|---|
+| Linux `.so` fails to load (glibc/libstdc++ mismatch) | High | Med | Build in `ubuntu:22.04` container or static-link libstdc++; capture server `ldd --version` | `deploy.yml:55-58`, CMakeLists |
+| Native crash takes down the ASP.NET process | High | Med | The empty stub returns codes, never throws across the boundary; validate FEN in C# first; consider process isolation if instability appears | `chess_engine.cpp`, `CustomChessEngine.cs` |
+| Windows `.dll` can't be built in CI (Linux runner) | Med | High (by design) | Commit the `.dll` like the Stockfish `.exe`; optional opt-in local MSBuild target | `deploy.yml:17`, `csproj:14-18` |
+| `-march`/`/arch` too aggressive → SIGILL on server | Med | Med | Use a confirmed server baseline; never `-march=native` for committed/CI binaries | CMakeLists, `Stockfish.cs:24-28` |
+| P/Invoke can't find the lib (Resources subfolder not searched) | Med | High without resolver | `DllImportResolver` probing `BaseDirectory/Resources` | `CustomChessEngine.cs`, `Stockfish.cs:30` |
+| Handle leak / double-free across boundary | Med | Low | `SafeHandle` + caller-owned out buffers + `delete nullptr`-safe `engine_destroy` | `CustomChessEngine.cs`, `chess_engine.cpp` |
+| Concurrent `GetBestMoveAsync` on one non-reentrant handle | Low | Low | One handle per game (as today); document non-reentrancy | `GameState.cs:46`, `ChessController.cs:192` |
+| Two move generators (C# rules vs native) diverge | Med | Med | Keep C# as legality authority; add native `perft` for cross-check later | `ChessService.cs`, native |
+
+## Recommendations
+
+Ordered by priority:
+
+1. **Introduce `IChessEngine` and retrofit `Stockfish`** (Architect §). Add the interface, make `Stockfish` implement it, rename `StockfishHelpers` → `ChessEngineHelpers`, retype `GameState.Computer` to `IChessEngine?`. Low effort, unblocks everything. *Supported by Findings A1–A2, B2.*
+2. **Lift orchestration out of the engine** into `IComputerMoveOrchestrator` (Architect §; Backend Finding 3). Removes duplication before a second engine exists. Low effort.
+3. **Add the factory + `appsettings` swap** (Architect §). `IChessEngineFactory` + `ChessEngineOptions`, registered in `Program.cs`. The swap mechanism the mission asks for. Low effort.
+4. **Stand up the native project + empty stub** (Backend + DevOps §). `native/chess_engine/` with `chess_engine.h`, the compilable `chess_engine.cpp` placeholder, and `CMakeLists.txt`. Medium effort (build setup, not logic).
+5. **Write `CustomChessEngine` P/Invoke wrapper** (Backend §) implementing `IChessEngine`, with `[LibraryImport]`, `DllImportResolver` → `Resources/`, `SafeHandle`, and `Task.Run` async adaptation. Medium effort.
+6. **Build + commit both artifacts; verify the round trip** (DevOps §). Build `.dll` on Windows / `.so` on Linux (container), commit to `Resources/`, flip `appsettings` to `Custom`, confirm the stub's `e2e4` flows through `ToMoveDto` → SignalR end to end. Medium effort. **Do this before writing any chess logic.**
+7. **Then implement the C++ engine** (user) — bitboards, search, eval, all native, honoring the "zero managed callbacks per node" rule (Performance §). The infrastructure above makes this a pure C++ task behind a stable contract.
+
+## Appendix: All Referenced Files
+
+| File | Referenced By | Context |
+|---|---|---|
+| `Services/Implementations/Stockfish.cs` | Architect, Backend, Performance, DevOps | The engine to mirror; `GetBestMoveAsync`/`MakeMove`/`ToFen`/`ToMoveDto`, process launch, Resources path |
+| `Services/Interfaces/IChessService.cs` | Architect, Backend | Rules engine (separate concern, not swapped) |
+| `Services/Implementations/ChessService.cs` | Architect, Performance | C# move-gen/legality — the genuinely slow code being replaced |
+| `Models/GameState.cs` | Architect, Backend, Performance | `Computer` coupling (`:46`), board model (`:11`) |
+| `Models/ChessPiece.cs`, `Position.cs`, `MoveDto.cs`, `Enums.cs` | Backend, Performance | Data shapes; UCI→`MoveDto` parsing |
+| `Controllers/ChessController.cs` | Architect, Backend, Performance | Engine construction (`:45`), invocation (`:60,192`), disposal (`:248`), game registry (`:20`) |
+| `Program.cs` | Architect | DI registration site (`:21-23`) |
+| `appsettings.json` | Architect | Swap config section |
+| `Services/Interfaces/IBackgroundTaskQueue.cs` | Performance | Background move execution |
+| `JoshHeaps.Net.csproj` | Backend, DevOps | `Content Resources/**` copy (`:14-18`), TFM/Nullable (`:3-7`) |
+| `Resources/stockfish-*` | DevOps | Committed-binary precedent for `.dll`/`.so` |
+| `.github/workflows/deploy.yml`, `dotnet.yml` | DevOps | Linux-only CI, publish + rsync deploy |
+| `native/chess_engine/include/chess_engine.h` (new) | Backend, DevOps | extern "C" ABI + export macro |
+| `native/chess_engine/src/chess_engine.cpp` (new) | Backend | Empty compilable stub |
+| `native/chess_engine/CMakeLists.txt` (new) | DevOps, Performance | Shared-lib build + optimization flags |
+| `Services/Implementations/CustomChessEngine.cs` (new) | Backend, Architect | P/Invoke middleman implementing `IChessEngine` |
+| `Services/Interfaces/IChessEngine.cs` + `IChessEngineFactory.cs` (new) | Architect | Swappable contract + factory |
+| `Services/Implementations/ChessEngineFactory.cs` + `ComputerMoveOrchestrator.cs` (new) | Architect | Config-driven selection + lifted orchestration |

native/chess_engine/CMakeLists.txt

@@ -0,0 +1,42 @@
+cmake_minimum_required(VERSION 3.20)
+project(chess_engine LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+# Shared library: chess_engine.dll (Windows) / libchess_engine.so (Linux).
+add_library(chess_engine SHARED
+    src/chess_engine.cpp
+    src/bitboard.cpp
+    src/zobrist.cpp
+    src/position.cpp
+    src/movegen.cpp
+    src/uci.cpp
+    src/perft.cpp)
+target_include_directories(chess_engine PUBLIC include)
+target_compile_definitions(chess_engine PRIVATE CHESS_ENGINE_BUILD)
+
+set_target_properties(chess_engine PROPERTIES
+    OUTPUT_NAME chess_engine
+    POSITION_INDEPENDENT_CODE ON)        # -fPIC on Linux (required for .so)
+
+# Export only the symbols marked with the CHESS_API macro.
+set(CMAKE_CXX_VISIBILITY_PRESET hidden)
+set(CMAKE_VISIBILITY_INLINES_HIDDEN ON)
+
+if (MSVC)
+    target_compile_options(chess_engine PRIVATE
+        $<$<CONFIG:Release>:/O2 /GL /DNDEBUG /arch:AVX2>
+        $<$<CONFIG:Debug>:/Od /Zi>)          # /Zi => .pdb for mixed-mode debugging
+    target_link_options(chess_engine PRIVATE
+        $<$<CONFIG:Release>:/LTCG>
+        $<$<CONFIG:Debug>:/DEBUG>)
+else()
+    # Portable server baseline. Do NOT use -march=native: the build host may have
+    # instructions the server lacks (SIGILL at runtime). Bump only once the server
+    # CPU floor is confirmed.
+    target_compile_options(chess_engine PRIVATE
+        $<$<CONFIG:Release>:-O3 -flto -DNDEBUG -march=x86-64-v2>
+        $<$<CONFIG:Debug>:-O0 -g>)
+endif()

native/chess_engine/bench.ps1

@@ -0,0 +1,115 @@
+<#
+.SYNOPSIS
+    Times the search before vs after killer-move ordering.
+
+.DESCRIPTION
+    Compiles two standalone bench binaries from the current engine source — one with killer
+    ordering disabled (the pre-killer baseline, via /DBENCH_DISABLE_KILLERS) and one with it
+    on — then runs each benchmark position in its own process (cold transposition table) and
+    reports wall-clock search time for both, plus the speedup. Timing is measured inside the
+    engine around engine_best_move, so process startup isn't counted. Each position is run
+    -Reps times and the fastest run is kept, to cut scheduling noise.
+
+.PARAMETER Skill
+    Search difficulty / max depth. Default 8.
+
+.PARAMETER Positions
+    Which position indices to run (0=kiwipete, 1=ruy, 2=sicilian). Default: all.
+
+.PARAMETER Reps
+    Runs per position per variant; the minimum time is reported. Default 3.
+
+.PARAMETER ShowDepths
+    Also print every per-depth line the engine emits.
+
+.EXAMPLE
+    .\bench.ps1
+    .\bench.ps1 -Skill 9 -Reps 5 -Positions 0,2
+#>
+[CmdletBinding()]
+param(
+    [int]$Skill = 8,
+    [int[]]$Positions,
+    [int]$Reps = 3,
+    [switch]$ShowDepths
+)
+
+$ErrorActionPreference = 'Stop'
+
+$root  = $PSScriptRoot
+$src   = Join-Path $root 'src'
+$inc   = Join-Path $root 'include'
+$build = Join-Path $root 'build'
+if (-not (Test-Path $build)) { New-Item -ItemType Directory -Path $build | Out-Null }
+
+# --- enter a VS dev shell so cl is on PATH ---
+$devShell = "D:\Program Files\Visual Studio 2026\Common7\Tools\Launch-VsDevShell.ps1"
+if (-not (Test-Path $devShell)) { throw "VS dev shell not found at $devShell" }
+& $devShell -Arch amd64 -HostArch amd64 -SkipAutomaticLocation | Out-Null
+
+$engineSources = 'chess_engine.cpp','bitboard.cpp','zobrist.cpp','position.cpp','movegen.cpp','uci.cpp' |
+    ForEach-Object { Join-Path $src $_ }
+$benchMain = Join-Path $root 'test\bench_main.cpp'
+
+function Build-Variant([string]$exe, [string[]]$extraDefs) {
+    $clArgs = @('/nologo','/std:c++17','/O2','/EHsc','/arch:AVX2','/DCHESS_ENGINE_BUILD','/DNDEBUG') +
+              $extraDefs + @("/I$inc","/I$src", $benchMain) + $engineSources + @("/Fe:$exe", "/Fo:$build\")
+    & cl @clArgs | Out-Null
+    if (-not (Test-Path $exe)) { throw "compile failed: $exe" }
+}
+
+$exeBefore = Join-Path $build 'bench_before.exe'   # killers disabled (pre-killer baseline)
+$exeAfter  = Join-Path $build 'bench_after.exe'    # killers enabled (current)
+
+Write-Host "Compiling both variants..." -ForegroundColor Cyan
+Build-Variant $exeBefore @('/DBENCH_DISABLE_KILLERS')
+Build-Variant $exeAfter  @()
+
+$nodePattern = '^depth (\d+) nodes (\d+) best (\S+) score (-?\d+)$'
+$timePattern = 'time_ms=(\d+)'
+
+function Run-One([string]$exe, [int]$pos) {
+    $nodes = 0; $best = '?'; $bestMs = [long]::MaxValue
+    for ($r = 0; $r -lt $Reps; $r++) {
+        $err = [System.IO.Path]::GetTempFileName()
+        $out = [System.IO.Path]::GetTempFileName()
+        Start-Process -FilePath $exe -ArgumentList $pos,$Skill -NoNewWindow -Wait `
+            -RedirectStandardError $err -RedirectStandardOutput $out | Out-Null
+        $lines = Get-Content $err
+        Remove-Item $err,$out -Force -ErrorAction SilentlyContinue
+        if ($ShowDepths) { $lines | ForEach-Object { Write-Host "  $_" -ForegroundColor DarkGray } }
+
+        $deepest = $lines | Select-String $nodePattern | Select-Object -Last 1
+        if ($deepest) { $nodes = [long]$deepest.Matches.Groups[2].Value; $best = $deepest.Matches.Groups[3].Value }
+        $tm = $lines | Select-String $timePattern | Select-Object -Last 1
+        if ($tm) { $ms = [long]$tm.Matches.Groups[1].Value; if ($ms -lt $bestMs) { $bestMs = $ms } }
+    }
+    return [pscustomobject]@{ Nodes = $nodes; Best = $best; Ms = $bestMs }
+}
+
+if (-not $Positions) { $Positions = 0,1,2 }
+$names = @('kiwipete','ruy','sicilian')
+$rows = @()
+
+foreach ($i in $Positions) {
+    $b = Run-One $exeBefore $i
+    $a = Run-One $exeAfter  $i
+    $speedup = if ($a.Ms -gt 0) { [math]::Round($b.Ms / $a.Ms, 2) } else { 0 }
+    $rows += [pscustomobject]@{
+        Position       = $names[$i]
+        'ms (before)'  = $b.Ms
+        'ms (after)'   = $a.Ms
+        Speedup        = "${speedup}x"
+        'nodes before' = $b.Nodes
+        'nodes after'  = $a.Nodes
+    }
+}
+
+Write-Host ""
+Write-Host "Skill $Skill, best of $Reps runs   (before = no killers, after = killers)" -ForegroundColor Cyan
+$rows | Format-Table -AutoSize
+
+$tb = ($rows | Measure-Object -Property 'ms (before)' -Sum).Sum
+$ta = ($rows | Measure-Object -Property 'ms (after)'  -Sum).Sum
+$tot = if ($ta -gt 0) { [math]::Round($tb / $ta, 2) } else { 0 }
+Write-Host ("TOTAL   {0} ms  ->  {1} ms   ({2}x faster)" -f $tb, $ta, $tot)

native/chess_engine/chess_engine/chess_engine.vcxproj

@@ -0,0 +1,179 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <VCProjectVersion>18.0</VCProjectVersion>
+    <Keyword>Win32Proj</Keyword>
+    <ProjectGuid>{2579bbbc-1830-4342-bc10-0a4182dc84c7}</ProjectGuid>
+    <RootNamespace>chessengine</RootNamespace>
+    <WindowsTargetPlatformVersion>10.0</WindowsTargetPlatformVersion>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v145</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v145</PlatformToolset>
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