refactor(runtime): own canonical entity identity and incarnations

Introduce the presentation-free RuntimeEntityDirectory and RuntimeEntityRecord as the sole owners of server GUIDs, INSTANCE_TS incarnations, accepted snapshots, authority versions, retryable tombstones, session epochs, and local-ID allocation. Convert LiveEntityRuntime into an App projection sidecar host resolved through canonical record identity without a second GUID map.

Preserve the existing synchronous and reentrant projection lifecycle, including retryable registration/delete/session teardown. Add Runtime-only identity/lifetime tests and App ownership guards.

Validated by the Release solution build and 8,441 complete Release tests with five existing skips.

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

tests/AcDream.App.Tests/World/RuntimeEntityOwnershipTests.cs

@@ -0,0 +1,76 @@
+using System.Reflection;
+using AcDream.App.World;
+using AcDream.Runtime.Entities;
+
+namespace AcDream.App.Tests.World;
+
+public sealed class RuntimeEntityOwnershipTests
+{
+    [Fact]
+    public void LiveEntityRuntime_ComposesCanonicalRuntimeDirectory()
+    {
+        FieldInfo directory = typeof(LiveEntityRuntime).GetField(
+            "_directory",
+            BindingFlags.Instance | BindingFlags.NonPublic)
+            ?? throw new InvalidOperationException("Missing canonical entity directory.");
+        FieldInfo sidecars = typeof(LiveEntityRuntime).GetField(
+            "_activeRecords",
+            BindingFlags.Instance | BindingFlags.NonPublic)
+            ?? throw new InvalidOperationException("Missing App projection sidecar store.");
+
+        Assert.Equal(typeof(RuntimeEntityDirectory), directory.FieldType);
+        Assert.Equal(typeof(RuntimeEntityRecord), sidecars.FieldType.GetGenericArguments()[0]);
+        Assert.Equal(typeof(LiveEntityRecord), sidecars.FieldType.GetGenericArguments()[1]);
+    }
+
+    [Fact]
+    public void AppCompatibilityLookup_IsNotASecondGuidDictionary()
+    {
+        FieldInfo compatibilityView = typeof(LiveEntityRuntime).GetField(
+            "_recordsByGuid",
+            BindingFlags.Instance | BindingFlags.NonPublic)
+            ?? throw new InvalidOperationException("Missing migration compatibility view.");
+
+        Assert.False(compatibilityView.FieldType.IsGenericType);
+        Assert.DoesNotContain(
+            compatibilityView.FieldType.GetInterfaces(),
+            type => type.IsGenericType
+                && type.GetGenericTypeDefinition() == typeof(IDictionary<,>));
+    }
+
+    [Fact]
+    public void CanonicalRuntimeRecord_HasNoProjectionOrBackendSurface()
+    {
+        string[] forbiddenPropertyNames =
+        [
+            "WorldEntity",
+            "AnimationRuntime",
+            "RemoteMotionRuntime",
+            "ProjectileRuntime",
+            "EffectProfile",
+            "ResourcesRegistered",
+            "IsSpatiallyProjected",
+            "IsSpatiallyVisible",
+        ];
+        PropertyInfo[] properties = typeof(RuntimeEntityRecord).GetProperties(
+            BindingFlags.Instance | BindingFlags.Public);
+
+        Assert.DoesNotContain(
+            properties,
+            property => forbiddenPropertyNames.Contains(
+                property.Name,
+                StringComparer.Ordinal));
+        Assert.DoesNotContain(
+            properties,
+            property => IsPresentationType(property.PropertyType));
+    }
+
+    private static bool IsPresentationType(Type type)
+    {
+        string? ns = type.Namespace;
+        return ns?.StartsWith("AcDream.App", StringComparison.Ordinal) == true
+            || ns?.StartsWith("AcDream.UI", StringComparison.Ordinal) == true
+            || ns?.StartsWith("Silk.NET", StringComparison.Ordinal) == true
+            || ns?.StartsWith("ImGuiNET", StringComparison.Ordinal) == true;
+    }
+}