perf(rendering): reconcile only changed attachments

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

@@ -257,6 +257,67 @@ public sealed class EquippedChildProjectionWithdrawalTests
         Assert.True(record.IsSpatiallyProjected);
     }
 
+    [Fact]
+    public void PostNetworkReconcile_SkipsStableTree_AndUpdatesChangedBranchParentFirst()
+    {
+        using var fixture = new ControllerFixture((_, _, _) =>
+            new(
+                ExactProjectionWithdrawalDisposition.Completed,
+                Failure: null));
+        LiveEntityRecord root = fixture.Spawn(0x70000241u, generation: 1);
+        LiveEntityRecord child = fixture.Spawn(
+            0x70000242u,
+            generation: 1,
+            LiveEntityProjectionKind.Attached);
+        LiveEntityRecord grandchild = fixture.Spawn(
+            0x70000243u,
+            generation: 1,
+            LiveEntityProjectionKind.Attached);
+        fixture.InstallAttached(root, child);
+        fixture.InstallAttached(child, grandchild);
+        fixture.Poses.Publish(root.WorldEntity!, Array.Empty<Matrix4x4>());
+
+        fixture.Controller.Tick();
+        Assert.Equal(2, fixture.Controller.LastFullPoseCompositionVisits);
+
+        fixture.Controller.ReconcileSpatialMutations();
+        Assert.Equal(0, fixture.Controller.LastReconcilePoseCompositionVisits);
+
+        root.WorldEntity!.SetPosition(new Vector3(7f, 8f, 9f));
+        Assert.True(fixture.Poses.UpdateRoot(root.WorldEntity));
+        fixture.Controller.ReconcileSpatialMutations();
+
+        Assert.Equal(2, fixture.Controller.LastReconcilePoseCompositionVisits);
+        Assert.Equal(root.WorldEntity.Position, child.WorldEntity!.Position);
+        Assert.Equal(child.WorldEntity.Position, grandchild.WorldEntity!.Position);
+    }
+
+    [Fact]
+    public void StablePostNetworkReconcile_AllocatesNoTransitionSnapshots()
+    {
+        using var fixture = new ControllerFixture((_, _, _) =>
+            new(
+                ExactProjectionWithdrawalDisposition.Completed,
+                Failure: null));
+        LiveEntityRecord root = fixture.Spawn(0x70000244u, generation: 1);
+        LiveEntityRecord child = fixture.Spawn(
+            0x70000245u,
+            generation: 1,
+            LiveEntityProjectionKind.Attached);
+        fixture.InstallAttached(root, child);
+        fixture.Poses.Publish(root.WorldEntity!, Array.Empty<Matrix4x4>());
+        fixture.Controller.Tick();
+        fixture.Controller.ReconcileSpatialMutations();
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        for (int i = 0; i < 1_000; i++)
+            fixture.Controller.ReconcileSpatialMutations();
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.Equal(0L, allocated);
+        Assert.Equal(0, fixture.Controller.LastReconcilePoseCompositionVisits);
+    }
+
     [Fact]
     public void AcceptedValidParent_WithdrawsWorldProjectionBeforePosePrerequisitesExist()
     {

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

@@ -356,7 +356,7 @@ public sealed class UpdateFrameOrchestratorTests
             source,
             "public void Reconcile()",
             "_entityEffects.RefreshLiveOwnerPoses",
-            "_equippedChildren.Tick",
+            "_equippedChildren.ReconcileSpatialMutations",
             "_particleSink.RefreshAttachedEmitters",
             "_lights.Refresh");