perf(rendering): retain synchronous frame scratch

Reuse the PView frame input, publish mutation-invalidated landblock views, and avoid constructing optional shadow iterators while preserving title and lifecycle visibility facts.

tests/AcDream.App.Tests/Streaming/GpuWorldStateRenderTraversalTests.cs

@@ -68,6 +68,44 @@ public sealed class GpuWorldStateRenderTraversalTests
         Assert.False(state.TryGetRenderTraversalSortKey(pending, out _));
     }
 
+    [Fact]
+    public void StableRenderViews_AllocateOnlyWhenSpatialContentChanges()
+    {
+        var state = new GpuWorldState();
+        state.AddLandblock(Landblock(
+            FirstLandblock,
+            Entity(1, 0x80000001u)));
+        state.SetLandblockAabb(
+            FirstLandblock,
+            new Vector3(1f, 2f, 3f),
+            new Vector3(4f, 5f, 6f));
+
+        var entries = state.LandblockEntries;
+        var bounds = state.LandblockBounds;
+        _ = entries.Count;
+        _ = bounds.Count;
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        for (int iteration = 0; iteration < 1_000; iteration++)
+        {
+            _ = state.LandblockEntries.Count;
+            _ = state.LandblockBounds.Count;
+        }
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.Equal(0, allocated);
+        Assert.Same(entries, state.LandblockEntries);
+        Assert.Same(bounds, state.LandblockBounds);
+
+        state.AddLandblock(Landblock(
+            SecondLandblock,
+            Entity(2, 0x80000002u)));
+
+        Assert.Same(entries, state.LandblockEntries);
+        Assert.Same(bounds, state.LandblockBounds);
+        Assert.Equal(2, entries.Count);
+        Assert.Equal(2, bounds.Count);
+    }
+
     private static void AssertSort(
         GpuWorldState state,
         WorldEntity entity,