fix(rendering): bound portal resource lifetime

Separate logical ownership, render publication, and GPU retirement across live entities, landblocks, particles, textures, mesh arenas, portal/UI teardown, and per-frame scratch storage. Add bounded DAT/texture caches, upload budgets, three-frame fence retirement, exact-incarnation appearance reconciliation, frame pacing, and extensive lifetime conformance coverage.\n\nThe seven-destination connected route now cuts peak working/private memory roughly in half, returns Caul to 125-153 FPS locally, and produces no WER or AMD reset.\n\nCo-authored-by: OpenAI Codex <codex@openai.com>

tests/AcDream.App.Tests/UI/UiElementChildOrderTests.cs

@@ -0,0 +1,67 @@
+using AcDream.App.UI;
+
+namespace AcDream.App.Tests.UI;
+
+public sealed class UiElementChildOrderTests
+{
+    [Fact]
+    public void StableTree_ReusesBothTraversalSnapshots()
+    {
+        var parent = new TestElement();
+        parent.AddChild(new TestElement { ZOrder = 2 });
+        parent.AddChild(new TestElement { ZOrder = 1 });
+
+        UiElement[] drawFirst = parent.ChildrenBackToFrontSnapshot();
+        UiElement[] drawSecond = parent.ChildrenBackToFrontSnapshot();
+        UiElement[] hitFirst = parent.ChildrenFrontToBackSnapshot();
+        UiElement[] hitSecond = parent.ChildrenFrontToBackSnapshot();
+
+        Assert.Same(drawFirst, drawSecond);
+        Assert.Same(hitFirst, hitSecond);
+        Assert.Equal([1, 2], drawFirst.Select(child => child.ZOrder).ToArray());
+        Assert.Equal([2, 1], hitFirst.Select(child => child.ZOrder).ToArray());
+    }
+
+    [Fact]
+    public void ChildZOrderChange_InvalidatesBothTraversalSnapshots()
+    {
+        var parent = new TestElement();
+        var first = new TestElement { ZOrder = 1 };
+        var second = new TestElement { ZOrder = 2 };
+        parent.AddChild(first);
+        parent.AddChild(second);
+        UiElement[] oldDraw = parent.ChildrenBackToFrontSnapshot();
+        UiElement[] oldHit = parent.ChildrenFrontToBackSnapshot();
+
+        first.ZOrder = 3;
+        UiElement[] newDraw = parent.ChildrenBackToFrontSnapshot();
+        UiElement[] newHit = parent.ChildrenFrontToBackSnapshot();
+
+        Assert.NotSame(oldDraw, newDraw);
+        Assert.NotSame(oldHit, newHit);
+        Assert.Same(second, newDraw[0]);
+        Assert.Same(first, newDraw[1]);
+        Assert.Same(first, newHit[0]);
+        Assert.Same(second, newHit[1]);
+    }
+
+    [Fact]
+    public void MembershipChange_InvalidatesSnapshotsWithoutMutatingPriorWalk()
+    {
+        var parent = new TestElement();
+        var first = new TestElement { ZOrder = 1 };
+        var second = new TestElement { ZOrder = 2 };
+        parent.AddChild(first);
+        UiElement[] prior = parent.ChildrenBackToFrontSnapshot();
+
+        parent.AddChild(second);
+        UiElement[] current = parent.ChildrenBackToFrontSnapshot();
+
+        Assert.Single(prior);
+        Assert.Same(first, prior[0]);
+        Assert.Equal(2, current.Length);
+        Assert.NotSame(prior, current);
+    }
+
+    private sealed class TestElement : UiElement;
+}