diff --git a/GameCli.Tests/ProgramSmokeTests.cs b/GameCli.Tests/ProgramSmokeTests.cs
new file mode 100644
index 0000000..a3f6a2e
--- /dev/null
+++ b/GameCli.Tests/ProgramSmokeTests.cs
@@ -0,0 +1,139 @@
+using System.Diagnostics;
+using System.Text.Json;
+using GameCli;
+using Xunit;
+
+namespace GameCli.Tests;
+
+public class ProgramSmokeTests
+{
+    private static string GetProjectPath()
+    {
+        // Locate the GameCli binary relative to the test binary's output dir.
+        // Tests run from GameCli.Tests/bin/<Config>/net8.0/, so ../../../.. gets to repo root.
+        var testDir = AppContext.BaseDirectory;
+        var repoRoot = Path.GetFullPath(Path.Combine(testDir, "..", "..", "..", ".."));
+        var projectPath = Path.Combine(repoRoot, "GameCli", "GameCli.csproj");
+        Assert.True(File.Exists(projectPath),
+            $"could not find GameCli.csproj at {projectPath}");
+        return projectPath;
+    }
+
+    private static Process StartGameCli()
+    {
+        var projectPath = GetProjectPath();
+
+        var psi = new ProcessStartInfo
+        {
+            FileName = "dotnet",
+            ArgumentList = { "run", "--project", projectPath, "-c", "Release", "--no-build" },
+            RedirectStandardInput = true,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+        };
+        var p = Process.Start(psi)
+                ?? throw new InvalidOperationException("failed to start GameCli");
+        return p;
+    }
+
+    [Fact]
+    public void FirstOutputLine_IsInitHandshake()
+    {
+        // Ensure release build exists so --no-build works reliably.
+        RunOrFail("dotnet", $"build -c Release \"{GetProjectPath()}\"");
+
+        using var p = StartGameCli();
+        try
+        {
+            var line = p.StandardOutput.ReadLine();
+            Assert.NotNull(line);
+            var init = JsonSerializer.Deserialize(line!, ProtocolJsonContext.Default.InitMessage);
+            Assert.NotNull(init?.Init);
+            Assert.Equal(Physics.Dt,       init!.Init.Dt);
+            Assert.Equal(Observation.Dim,  init.Init.ObsDim);
+            Assert.Equal(4,                init.Init.NActions);
+        }
+        finally
+        {
+            p.StandardInput.Close();
+            p.WaitForExit(3000);
+        }
+    }
+
+    [Fact]
+    public void StepRoundTrip_ReturnsSevenDimObservation()
+    {
+        RunOrFail("dotnet", $"build -c Release \"{GetProjectPath()}\"");
+
+        using var p = StartGameCli();
+        try
+        {
+            _ = p.StandardOutput.ReadLine(); // skip init
+
+            p.StandardInput.WriteLine("""{"action":0,"target":[0.5,0.5]}""");
+            p.StandardInput.Flush();
+
+            var line = p.StandardOutput.ReadLine();
+            Assert.NotNull(line);
+            var output = JsonSerializer.Deserialize(line!, ProtocolJsonContext.Default.StepOutput);
+            Assert.NotNull(output);
+            Assert.Equal(7, output!.Obs.Length);
+            Assert.Equal(1, output.Step);
+        }
+        finally
+        {
+            p.StandardInput.Close();
+            p.WaitForExit(3000);
+        }
+    }
+
+    [Fact]
+    public void ResetCommand_ResetsStepCounter()
+    {
+        RunOrFail("dotnet", $"build -c Release \"{GetProjectPath()}\"");
+
+        using var p = StartGameCli();
+        try
+        {
+            _ = p.StandardOutput.ReadLine(); // init
+
+            // Take three steps.
+            for (int i = 0; i < 3; i++)
+            {
+                p.StandardInput.WriteLine("""{"action":0,"target":[0.5,0.5]}""");
+            }
+            p.StandardInput.Flush();
+            string? last = null;
+            for (int i = 0; i < 3; i++) last = p.StandardOutput.ReadLine();
+            var afterThree = JsonSerializer.Deserialize(last!, ProtocolJsonContext.Default.StepOutput);
+            Assert.Equal(3, afterThree!.Step);
+
+            // Reset. Expect step=0 on the next output line.
+            p.StandardInput.WriteLine("""{"cmd":"reset","seed":42}""");
+            p.StandardInput.Flush();
+            var afterReset = JsonSerializer.Deserialize(
+                p.StandardOutput.ReadLine()!, ProtocolJsonContext.Default.StepOutput);
+            Assert.Equal(0, afterReset!.Step);
+        }
+        finally
+        {
+            p.StandardInput.Close();
+            p.WaitForExit(3000);
+        }
+    }
+
+    private static void RunOrFail(string file, string args)
+    {
+        var psi = new ProcessStartInfo(file, args)
+        {
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+        };
+        using var p = Process.Start(psi)!;
+        p.WaitForExit(120_000);
+        if (p.ExitCode != 0)
+            throw new Exception($"{file} {args} exited {p.ExitCode}\nstderr:\n{p.StandardError.ReadToEnd()}");
+    }
+}