diff --git a/SVSim.BattleNode/Sessions/Participants/RealParticipant.cs b/SVSim.BattleNode/Sessions/Participants/RealParticipant.cs
new file mode 100644
index 0000000..d2ec4d9
--- /dev/null
+++ b/SVSim.BattleNode/Sessions/Participants/RealParticipant.cs
@@ -0,0 +1,262 @@
+using System.Net.WebSockets;
+using System.Security.Cryptography;
+using System.Text;
+using Microsoft.Extensions.Logging;
+using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Protocol;
+using SVSim.BattleNode.Protocol.Bodies;
+using SVSim.BattleNode.Reliability;
+using SVSim.BattleNode.Wire;
+
+namespace SVSim.BattleNode.Sessions.Participants;
+
+/// <summary>
+/// WS-backed participant. Owns the WS read loop, SIO encoding/decoding, per-WS
+/// <see cref="OutboundSequencer"/> + <see cref="InboundTracker"/>. Fires
+/// <see cref="FrameEmitted"/> on each deduplicated inbound <see cref="MsgEnvelope"/>.
+/// PushAsync encodes + sends; ordered pushes get a playSeq from the sequencer,
+/// no-stock control pushes bypass it.
+/// </summary>
+public sealed class RealParticipant : IBattleParticipant
+{
+    private readonly WebSocket _ws;
+    private readonly ILogger<RealParticipant> _log;
+    private CancellationToken _sessionCt;
+
+    public long ViewerId { get; }
+    public MatchContext Context { get; }
+    public InboundTracker Inbound { get; } = new();
+    public OutboundSequencer Outbound { get; } = new();
+
+    public event Func<MsgEnvelope, CancellationToken, Task>? FrameEmitted;
+
+    public RealParticipant(WebSocket ws, long viewerId, MatchContext context,
+        ILogger<RealParticipant> log)
+    {
+        _ws = ws;
+        _log = log;
+        ViewerId = viewerId;
+        Context = context;
+    }
+
+    public async Task RunAsync(CancellationToken cancellation)
+    {
+        _sessionCt = cancellation;
+        await SendEioOpenAsync(cancellation);
+
+        var buffer = new byte[8192];
+        var pendingAttachments = new List<byte[]>();
+        SocketIoFrame? pendingFrame = null;
+
+        while (_ws.State == WebSocketState.Open && !cancellation.IsCancellationRequested)
+        {
+            var msg = await ReadCompleteMessageAsync(buffer, cancellation);
+            if (msg is null) break;
+
+            if (msg.Value.IsText)
+            {
+                var text = Encoding.UTF8.GetString(msg.Value.Bytes);
+                if (text.Length == 0) continue;
+                var eio = EngineIoFrame.Parse(text);
+                if (eio.Type == EngineIoPacketType.Ping)
+                {
+                    await SendTextAsync("3", cancellation);
+                    continue;
+                }
+                if (eio.Type != EngineIoPacketType.Message) continue;
+
+                var sio = SocketIoFrame.Parse(eio.Payload);
+                if (sio.AttachmentCount > 0)
+                {
+                    pendingFrame = sio;
+                    pendingAttachments.Clear();
+                    continue;
+                }
+                await DispatchSocketIo(sio);
+            }
+            else
+            {
+                var bin = msg.Value.Bytes;
+                if (bin.Length > 0 && bin[0] == (byte)EngineIoPacketType.Message)
+                {
+                    bin = bin.AsSpan(1).ToArray();
+                }
+                pendingAttachments.Add(bin);
+                if (pendingFrame is not null && pendingAttachments.Count == pendingFrame.AttachmentCount)
+                {
+                    var assembled = pendingFrame.WithAttachments(pendingAttachments.ToArray());
+                    pendingFrame = null;
+                    await DispatchSocketIo(assembled);
+                }
+            }
+        }
+    }
+
+    public async Task PushAsync(MsgEnvelope envelope, bool noStock, CancellationToken ct)
+    {
+        var stamped = noStock ? Outbound.WrapNoStock(envelope) : Outbound.AssignAndArchive(envelope);
+        await EncodeAndSendAsync(stamped, WireConstants.SynchronizeEvent, ct);
+    }
+
+    public Task TerminateAsync(BattleFinishReason reason)
+    {
+        // WS will close via the read loop exiting; nothing to do here.
+        return Task.CompletedTask;
+    }
+
+    public ValueTask DisposeAsync()
+    {
+        if (_ws.State == WebSocketState.Open || _ws.State == WebSocketState.CloseReceived)
+        {
+            try { _ws.Abort(); } catch { /* best effort */ }
+        }
+        _ws.Dispose();
+        return ValueTask.CompletedTask;
+    }
+
+    private async Task DispatchSocketIo(SocketIoFrame frame)
+    {
+        if (frame.Type is SocketIoPacketType.Event or SocketIoPacketType.BinaryEvent)
+        {
+            switch (frame.EventName)
+            {
+                case WireConstants.MsgEvent when frame.BinaryAttachments.Count == 1:
+                    await HandleMsgEventAsync(frame);
+                    return;
+                case WireConstants.AliveEvent when frame.BinaryAttachments.Count == 1:
+                    await HandleAliveEventAsync(frame);
+                    return;
+            }
+        }
+        _log.LogDebug("RealParticipant viewer={Vid}: dropping SIO event={Event}", ViewerId, frame.EventName);
+    }
+
+    private async Task HandleMsgEventAsync(SocketIoFrame frame)
+    {
+        try
+        {
+            MsgEnvelope env;
+            try { env = MsgPayloadCodec.Decode(frame.BinaryAttachments[0]); }
+            catch (Exception ex)
+            {
+                _log.LogWarning(ex, "RealParticipant viewer={Vid}: failed to decode msg envelope", ViewerId);
+                return;
+            }
+
+            bool shouldDispatch = true;
+            if (env.PubSeq.HasValue)
+            {
+                shouldDispatch = Inbound.Observe(env.PubSeq.Value);
+                if (frame.AckId.HasValue)
+                {
+                    await SendSioAckAsync(frame.AckId.Value, env.PubSeq.Value);
+                }
+            }
+            if (!shouldDispatch) return;
+
+            if (FrameEmitted is not null)
+            {
+                await FrameEmitted.Invoke(env, _sessionCt);
+            }
+        }
+        catch (Exception ex)
+        {
+            _log.LogError(ex, "RealParticipant viewer={Vid}: unhandled in HandleMsgEventAsync", ViewerId);
+        }
+    }
+
+    private async Task HandleAliveEventAsync(SocketIoFrame frame)
+    {
+        try
+        {
+            if (frame.AckId.HasValue)
+            {
+                await SendSioAckAsync(frame.AckId.Value, 0);
+            }
+            var aliveEnv = new MsgEnvelope(
+                Uri: NetworkBattleUri.Gungnir,
+                ViewerId: SVSim.BattleNode.Lifecycle.ScriptedLifecycle.FakeOpponentViewerId,
+                Uuid: WireConstants.ServerUuid,
+                Bid: null,
+                Try: 0,
+                Cat: EmitCategory.General,
+                PubSeq: null,
+                PlaySeq: null,
+                Body: new AlivePushBody(Scs: WireConstants.OnlineStatus, Ocs: WireConstants.OnlineStatus));
+            var stamped = Outbound.WrapNoStock(aliveEnv);
+            await EncodeAndSendAsync(stamped, WireConstants.AliveEvent, _sessionCt);
+        }
+        catch (Exception ex)
+        {
+            _log.LogError(ex, "RealParticipant viewer={Vid}: unhandled in HandleAliveEventAsync", ViewerId);
+        }
+    }
+
+    private async Task EncodeAndSendAsync(MsgEnvelope env, string eventName, CancellationToken ct)
+    {
+        var key = NodeCrypto.GenerateKey(() => RandomNumberGenerator.GetInt32(0, 16));
+        var bytes = MsgPayloadCodec.Encode(env, key);
+        var sio = SocketIoFrame.BinaryEventWithAttachments(eventName, new[] { bytes });
+        var (text, bins) = sio.Encode();
+        var eioText = $"{(int)EngineIoPacketType.Message}{text}";
+        await SendTextAsync(eioText, ct);
+        foreach (var bin in bins)
+        {
+            var prefixed = new byte[bin.Length + 1];
+            prefixed[0] = (byte)EngineIoPacketType.Message;
+            Buffer.BlockCopy(bin, 0, prefixed, 1, bin.Length);
+            await _ws.SendAsync(prefixed, WebSocketMessageType.Binary, endOfMessage: true, ct);
+        }
+    }
+
+    internal static int ClipAckArg(long arg, ILogger log, long viewerId)
+    {
+        if (arg > int.MaxValue)
+        {
+            log.LogWarning("RealParticipant viewer={Vid}: pubSeq {Seq} exceeds int.MaxValue; clipping.", viewerId, arg);
+            return int.MaxValue;
+        }
+        if (arg < int.MinValue)
+        {
+            log.LogWarning("RealParticipant viewer={Vid}: pubSeq {Seq} below int.MinValue; clipping.", viewerId, arg);
+            return int.MinValue;
+        }
+        return (int)arg;
+    }
+
+    private async Task SendSioAckAsync(int ackId, long arg)
+    {
+        var ack = SocketIoFrame.AckResponse(ackId, ClipAckArg(arg, _log, ViewerId));
+        var (text, _) = ack.Encode();
+        var eioText = $"{(int)EngineIoPacketType.Message}{text}";
+        await SendTextAsync(eioText, _sessionCt);
+    }
+
+    private async Task SendEioOpenAsync(CancellationToken ct)
+    {
+        var sid = Guid.NewGuid().ToString("N").Substring(0, 16);
+        var handshake = new EngineIoHandshake(sid, Array.Empty<string>(), 25000, 60000).ToJson();
+        await SendTextAsync($"0{handshake}", ct);
+    }
+
+    private Task SendTextAsync(string text, CancellationToken ct)
+    {
+        var bytes = Encoding.UTF8.GetBytes(text);
+        return _ws.SendAsync(bytes, WebSocketMessageType.Text, endOfMessage: true, ct);
+    }
+
+    private async Task<(byte[] Bytes, bool IsText)?> ReadCompleteMessageAsync(byte[] buffer, CancellationToken ct)
+    {
+        using var ms = new MemoryStream();
+        WebSocketReceiveResult result;
+        do
+        {
+            try { result = await _ws.ReceiveAsync(buffer, ct); }
+            catch (OperationCanceledException) { return null; }
+            catch (WebSocketException) { return null; }
+            if (result.MessageType == WebSocketMessageType.Close) return null;
+            ms.Write(buffer, 0, result.Count);
+        } while (!result.EndOfMessage);
+        return (ms.ToArray(), result.MessageType == WebSocketMessageType.Text);
+    }
+}
diff --git a/SVSim.UnitTests/BattleNode/Sessions/Participants/RealParticipantTests.cs b/SVSim.UnitTests/BattleNode/Sessions/Participants/RealParticipantTests.cs
new file mode 100644
index 0000000..cd39373
--- /dev/null
+++ b/SVSim.UnitTests/BattleNode/Sessions/Participants/RealParticipantTests.cs
@@ -0,0 +1,69 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using NUnit.Framework;
+using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Protocol;
+using SVSim.BattleNode.Protocol.Bodies;
+using SVSim.BattleNode.Sessions;
+using SVSim.BattleNode.Sessions.Participants;
+using SVSim.UnitTests.BattleNode.Infrastructure;
+
+namespace SVSim.UnitTests.BattleNode.Sessions.Participants;
+
+[TestFixture]
+public class RealParticipantTests
+{
+    [Test]
+    public void PushAsync_ordered_assigns_playSeq_via_OutboundSequencer()
+    {
+        var ws = new TestWebSocket();
+        var p = new RealParticipant(ws, viewerId: 1, FixtureCtx(),
+            NullLogger<RealParticipant>.Instance);
+
+        // First ordered push gets playSeq = 1; second = 2; etc.
+        // Inspect the participant's outbound sequencer state via its public Archive.
+        var env = NewEnvelope(NetworkBattleUri.Matched);
+        p.PushAsync(env, noStock: false, CancellationToken.None).Wait();
+        p.PushAsync(env, noStock: false, CancellationToken.None).Wait();
+
+        Assert.That(p.Outbound.Archive.Count, Is.EqualTo(2));
+        Assert.That(p.Outbound.Archive[1].PlaySeq, Is.EqualTo(1));
+        Assert.That(p.Outbound.Archive[2].PlaySeq, Is.EqualTo(2));
+    }
+
+    [Test]
+    public void PushAsync_noStock_omits_playSeq()
+    {
+        var ws = new TestWebSocket();
+        var p = new RealParticipant(ws, viewerId: 1, FixtureCtx(),
+            NullLogger<RealParticipant>.Instance);
+
+        p.PushAsync(NewEnvelope(NetworkBattleUri.BattleFinish), noStock: true, CancellationToken.None).Wait();
+
+        // No playSeq archive entry for no-stock pushes.
+        Assert.That(p.Outbound.Archive.Count, Is.EqualTo(0));
+    }
+
+    [Test]
+    public void ViewerId_and_Context_are_exposed()
+    {
+        var ws = new TestWebSocket();
+        var ctx = FixtureCtx();
+        var p = new RealParticipant(ws, viewerId: 906243102L, ctx,
+            NullLogger<RealParticipant>.Instance);
+
+        Assert.That(p.ViewerId, Is.EqualTo(906243102L));
+        Assert.That(p.Context, Is.SameAs(ctx));
+    }
+
+    private static MatchContext FixtureCtx() => new(
+        SelfDeckCardIds: Enumerable.Range(1, 30).Select(_ => 100_011_010L).ToList(),
+        ClassId: "1", CharaId: "1", CardMasterName: "card_master_node_10015",
+        CountryCode: "KOR", UserName: "Player", SleeveId: "3000011",
+        EmblemId: "701441011", DegreeId: "300003", FieldId: 43, IsOfficial: 0,
+        BattleType: 11);
+
+    private static MsgEnvelope NewEnvelope(NetworkBattleUri uri) =>
+        new(uri, ViewerId: 1, Uuid: "u", Bid: null, Try: 0,
+            Cat: EmitCategory.Battle, PubSeq: null, PlaySeq: null,
+            Body: new ResultCodeOnlyBody());
+}