perf(streaming): quiesce retired generations and budget teardown

Publish the retail blocking-for-cells edge before deferred recenter work, freeze old-world presentation/simulation/audio, and advance full-window retirement from exact metered entity and owner cursors. This removes synchronous portal teardown without allowing retained owners to remain observable.

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

@@ -3,6 +3,7 @@ using System.Reflection;
 using AcDream.App.Rendering;
 using AcDream.App.Rendering.Selection;
 using AcDream.App.Rendering.Vfx;
+using AcDream.App.Streaming;
 using AcDream.Core.Rendering;
 using AcDream.Core.World;
 
@@ -21,6 +22,23 @@ public sealed class WorldSceneRendererTests
         Assert.Equal(["selection:begin", "selection:complete"], rig.Calls);
     }
 
+    [Fact]
+    public void QuiescedGeneration_PublishesEmptySelectionFrameAndSkipsEveryWorldOwner()
+    {
+        var availability = new WorldGenerationAvailabilityState();
+        availability.Begin(4);
+        var rig = new Rig(
+            portalVisible: false,
+            waitingForLogin: false,
+            clipRoot: null,
+            availability: availability);
+
+        WorldRenderFrameOutcome result = rig.Renderer.Render(default);
+
+        Assert.Equal(default, result);
+        Assert.Equal(["selection:begin", "selection:complete"], rig.Calls);
+    }
+
     [Fact]
     public void LoginWait_DrawsFlatSkyThenCompletesFrameWithoutWorldGeometry()
     {
@@ -332,7 +350,8 @@ public sealed class WorldSceneRendererTests
             bool waitingForLogin,
             LoadedCell? clipRoot,
             bool? playerSeenOutside = null,
-            EnvironOverride environOverride = EnvironOverride.None)
+            EnvironOverride environOverride = EnvironOverride.None,
+            IWorldGenerationAvailability? availability = null)
         {
             Calls = [];
             DayGroup = new DayGroupData { Name = "sentinel-day-group" };
@@ -385,7 +404,8 @@ public sealed class WorldSceneRendererTests
                 new PViewCells(),
                 Passes,
                 new WorldRenderRangeState(4, 12),
-                diagnostics);
+                diagnostics,
+                availability);
         }
 
         public List<string> Calls { get; }