diff --git a/Backend.Tests/EndToEndSmokeTests.cs b/Backend.Tests/EndToEndSmokeTests.cs
new file mode 100644
index 0000000..1ce8b10
--- /dev/null
+++ b/Backend.Tests/EndToEndSmokeTests.cs
@@ -0,0 +1,95 @@
+using System.IO;
+using System.Net.WebSockets;
+using System.Text;
+using System.Text.Json;
+using Backend;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Testing;
+using Xunit;
+
+namespace Backend.Tests;
+
+public class EndToEndSmokeTests : IClassFixture<WebApplicationFactory<Program>>
+{
+    private readonly WebApplicationFactory<Program> _factory;
+
+    public EndToEndSmokeTests(WebApplicationFactory<Program> factory)
+    {
+        _factory = factory.WithWebHostBuilder(b =>
+        {
+            // Prevent MVC picking up assemblies; force env vars if needed.
+            b.UseEnvironment("Development");
+        });
+    }
+
+    [Fact]
+    public async Task WebSocket_ReceivesInitAndStateFrames()
+    {
+        // Prerequisites: publish/GameCli/GameCli and models/ppo_lander.onnx must exist.
+        var repoRoot = FindRepoRoot();
+        Assert.True(File.Exists(Path.Combine(repoRoot, "publish", "GameCli", "GameCli")),
+            "run `dotnet publish GameCli -c Release -o publish/GameCli` before this test");
+        Assert.True(File.Exists(Path.Combine(repoRoot, "models", "ppo_lander.onnx")),
+            "run `python Training/export_onnx.py ...` before this test");
+
+        var client = _factory.Server.CreateWebSocketClient();
+        var baseUri = _factory.Server.BaseAddress;
+        var wsUri = new UriBuilder(baseUri) { Scheme = "ws", Path = "/ws/game" }.Uri;
+
+        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(15));
+        using var ws = await client.ConnectAsync(wsUri, cts.Token);
+
+        var initText = await ReceiveTextAsync(ws, cts.Token);
+        using var initDoc = JsonDocument.Parse(initText);
+        Assert.Equal("init", initDoc.RootElement.GetProperty("type").GetString());
+
+        // Send a cursor and receive at least one state frame.
+        var cursorPayload = """{"type":"cursor","x":0.3,"y":0.7}""";
+        await ws.SendAsync(Encoding.UTF8.GetBytes(cursorPayload),
+            WebSocketMessageType.Text, true, cts.Token);
+
+        // Read up to N frames looking for a state frame; the ticker runs at 50 Hz.
+        for (int i = 0; i < 100; i++)
+        {
+            var text = await ReceiveTextAsync(ws, cts.Token);
+            using var doc = JsonDocument.Parse(text);
+            if (doc.RootElement.GetProperty("type").GetString() == "state")
+            {
+                Assert.True(doc.RootElement.TryGetProperty("x",      out _));
+                Assert.True(doc.RootElement.TryGetProperty("y",      out _));
+                Assert.True(doc.RootElement.TryGetProperty("angle",  out _));
+                Assert.True(doc.RootElement.TryGetProperty("engine", out _));
+                Assert.True(doc.RootElement.TryGetProperty("target", out _));
+                Assert.True(doc.RootElement.TryGetProperty("step",   out _));
+                return;
+            }
+        }
+        Assert.Fail("did not receive a state frame in 100 messages");
+    }
+
+    private static async Task<string> ReceiveTextAsync(WebSocket ws, CancellationToken ct)
+    {
+        var buffer = new byte[16 * 1024];
+        var sb = new StringBuilder();
+        WebSocketReceiveResult result;
+        do
+        {
+            result = await ws.ReceiveAsync(buffer, ct);
+            sb.Append(Encoding.UTF8.GetString(buffer, 0, result.Count));
+        } while (!result.EndOfMessage);
+        return sb.ToString();
+    }
+
+    private static string FindRepoRoot()
+    {
+        var dir = AppContext.BaseDirectory;
+        while (dir is not null)
+        {
+            if (File.Exists(Path.Combine(dir, "GameCli.sln"))) return dir;
+            var parent = Directory.GetParent(dir);
+            if (parent is null) break;
+            dir = parent.FullName;
+        }
+        throw new InvalidOperationException("repo root not found");
+    }
+}