test(installer): prove RegisterMcpStep still resolves from the DI container

tests/ClaudeDo.Installer.Tests/StepDiRegistrationTests.cs

@@ -0,0 +1,21 @@
+using ClaudeDo.Installer.Steps;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace ClaudeDo.Installer.Tests;
+
+public sealed class StepDiRegistrationTests
+{
+    // RegisterMcpStep is registered type-based (App.xaml.cs) and has an optional
+    // Func<InstallerWorkerConfig> constructor parameter. A compile-time build proves
+    // nothing here — if the container refused to honour the default value, the
+    // installer would only blow up at runtime, where it cannot be smoke-tested.
+    [Fact]
+    public void RegisterMcpStep_resolves_from_the_container_without_a_config_loader()
+    {
+        var sp = new ServiceCollection()
+            .AddSingleton<RegisterMcpStep>()
+            .BuildServiceProvider();
+
+        Assert.NotNull(sp.GetRequiredService<RegisterMcpStep>());
+    }
+}