arch(runtime): establish presentation-independent boundary

Create the dependency-only Runtime project before moving any gameplay owner, enforce its direct, transitive, source, and load-time closure, and pin coherent lifetime-group extraction plus retryable teardown ordering. No production behavior changes in J0.

Validated by the four focused Runtime boundary tests, a zero-error Release solution build, and 8,406 passing Release tests with five pre-existing skips.

Co-authored-by: Codex <codex@openai.com>

tests/AcDream.Runtime.Tests/RuntimeDependencyBoundaryTests.cs

@@ -0,0 +1,127 @@
+using System.Text.Json;
+using System.Xml.Linq;
+
+namespace AcDream.Runtime.Tests;
+
+public sealed class RuntimeDependencyBoundaryTests
+{
+    private static readonly string[] ForbiddenDependencyPrefixes =
+    [
+        "AcDream.App",
+        "AcDream.UI.",
+        "Silk.NET",
+        "OpenAL",
+        "Arch",
+        "ImGui",
+    ];
+
+    [Fact]
+    public void RuntimeAssemblyHasNoDirectPresentationOrBackendReferences()
+    {
+        var references = typeof(RuntimeAssemblyMarker).Assembly
+            .GetReferencedAssemblies()
+            .Select(static reference => reference.Name ?? string.Empty)
+            .ToArray();
+
+        Assert.DoesNotContain(references, IsForbidden);
+    }
+
+    [Fact]
+    public void RuntimeDependencyClosureHasNoPresentationOrBackendLibraries()
+    {
+        var depsPath = Path.ChangeExtension(
+            typeof(RuntimeDependencyBoundaryTests).Assembly.Location,
+            ".deps.json");
+
+        using var document = JsonDocument.Parse(File.ReadAllText(depsPath));
+        var libraries = document.RootElement
+            .GetProperty("libraries")
+            .EnumerateObject()
+            .Select(static library => LibraryName(library.Name))
+            .ToArray();
+
+        Assert.DoesNotContain(libraries, IsForbidden);
+    }
+
+    [Fact]
+    public void RuntimeProjectDeclaresOnlyApprovedProjectDependencies()
+    {
+        var repositoryRoot = FindRepositoryRoot();
+        var projectPath = Path.Combine(
+            repositoryRoot,
+            "src",
+            "AcDream.Runtime",
+            "AcDream.Runtime.csproj");
+        var project = XDocument.Load(projectPath);
+        var projectDirectory = Path.GetDirectoryName(projectPath)!;
+
+        var actualReferences = project
+            .Descendants("ProjectReference")
+            .Select(reference => reference.Attribute("Include")?.Value)
+            .Where(static include => !string.IsNullOrWhiteSpace(include))
+            .Select(include => Path.GetFullPath(Path.Combine(projectDirectory, include!)))
+            .Order(StringComparer.OrdinalIgnoreCase)
+            .ToArray();
+        var expectedReferences = new[]
+            {
+                "AcDream.Content",
+                "AcDream.Core",
+                "AcDream.Core.Net",
+                "AcDream.Plugin.Abstractions",
+            }
+            .Select(projectName => Path.Combine(
+                repositoryRoot,
+                "src",
+                projectName,
+                $"{projectName}.csproj"))
+            .Order(StringComparer.OrdinalIgnoreCase)
+            .ToArray();
+
+        Assert.Equal(expectedReferences, actualReferences);
+        Assert.Empty(project.Descendants("PackageReference"));
+    }
+
+    [Fact]
+    public void LoadingRuntimeMarkerDoesNotLoadPresentationOrBackendAssemblies()
+    {
+        _ = typeof(RuntimeAssemblyMarker).Assembly;
+
+        var loadedAssemblies = AppDomain.CurrentDomain
+            .GetAssemblies()
+            .Select(static assembly => assembly.GetName().Name ?? string.Empty)
+            .ToArray();
+
+        Assert.DoesNotContain(loadedAssemblies, IsForbidden);
+    }
+
+    private static string FindRepositoryRoot()
+    {
+        var directory = new DirectoryInfo(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            if (File.Exists(Path.Combine(directory.FullName, "AcDream.slnx")))
+            {
+                return directory.FullName;
+            }
+
+            directory = directory.Parent;
+        }
+
+        throw new DirectoryNotFoundException(
+            $"Could not find AcDream.slnx above {AppContext.BaseDirectory}.");
+    }
+
+    private static string LibraryName(string libraryIdentity)
+    {
+        var separatorIndex = libraryIdentity.IndexOf('/');
+        return separatorIndex < 0
+            ? libraryIdentity
+            : libraryIdentity[..separatorIndex];
+    }
+
+    private static bool IsForbidden(string assemblyName)
+    {
+        return ForbiddenDependencyPrefixes.Any(prefix =>
+            assemblyName.StartsWith(prefix, StringComparison.OrdinalIgnoreCase));
+    }
+}