feat(runtime): atomically replace collision generations

tests/AcDream.Runtime.Tests/Physics/RuntimePhysicsOwnershipBoundaryTests.cs

@@ -0,0 +1,44 @@
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using AcDream.Core.Physics;
+
+namespace AcDream.Runtime.Tests.Physics;
+
+public sealed class RuntimePhysicsOwnershipBoundaryTests
+{
+    [Fact]
+    public void PhysicsWorldRootMutatorsAreRuntimeOnlyProductionInternals()
+    {
+        string[] rootMutators =
+        [
+            nameof(PhysicsEngine.AddLandblock),
+            nameof(PhysicsEngine.RemoveLandblock),
+            nameof(PhysicsEngine.DemoteLandblockToTerrain),
+            nameof(PhysicsEngine.Clear),
+        ];
+        Type engine = typeof(PhysicsEngine);
+        MethodInfo[] publicMethods = engine.GetMethods(
+            BindingFlags.Instance | BindingFlags.Public);
+        MethodInfo[] internalMethods = engine.GetMethods(
+            BindingFlags.Instance | BindingFlags.NonPublic);
+        foreach (string name in rootMutators)
+        {
+            Assert.DoesNotContain(
+                publicMethods,
+                method => method.Name == name);
+            Assert.Contains(
+                internalMethods,
+                method => method.Name == name);
+        }
+
+        string[] friends = engine.Assembly
+            .GetCustomAttributes<InternalsVisibleToAttribute>()
+            .Select(attribute => attribute.AssemblyName.Split(',')[0])
+            .ToArray();
+        Assert.Contains("AcDream.Runtime", friends);
+        Assert.DoesNotContain("AcDream.App", friends);
+        Assert.DoesNotContain("acdream-headless", friends);
+        Assert.Contains("AcDream.App.Tests", friends);
+        Assert.Contains("AcDream.Headless.Tests", friends);
+    }
+}