fix(launcher): close Campaign LA LA1 review findings

tests/AcDream.App.Tests/Rendering/LinuxPlatformBoundaryTests.cs

@@ -87,6 +87,27 @@ public sealed class LinuxPlatformBoundaryTests
         Assert.Empty(offenders);
     }
 
+    [Fact]
+    public void RuntimePlatformGuardHasOneDefinitionAndOneApprovedConsumer()
+    {
+        string app = AppSourceRoot();
+        string[] files = Directory
+            .EnumerateFiles(app, "*.cs", SearchOption.AllDirectories)
+            .Where(path => File.ReadAllText(path).Contains(
+                "RuntimePlatformGuard",
+                StringComparison.Ordinal))
+            .Select(path => Path.GetRelativePath(app, path).Replace('\\', '/'))
+            .OrderBy(static path => path, StringComparer.Ordinal)
+            .ToArray();
+
+        Assert.Equal(
+            [
+                "Credentials/AppCredentialResolver.cs",
+                "Platform/GraphicalHostPlatformServices.cs",
+            ],
+            files);
+    }
+
     [Fact]
     public void SmokePluginCopyUsesRidAwarePortableBuildAndPublishPaths()
     {