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/Streaming/WorldRevealCoordinatorTests.cs

@@ -1,4 +1,5 @@
 using AcDream.App.Streaming;
+using AcDream.Core.Selection;
 
 namespace AcDream.App.Tests.Streaming;
 
@@ -114,4 +115,46 @@ public sealed class WorldRevealCoordinatorTests
         Assert.Equal(default, coordinator.Snapshot.Readiness);
         Assert.Equal(0, coordinator.PortalMaterializationCount);
     }
+
+    [Fact]
+    public void RevealLifetime_QuiescesContinuouslyAndOnlyActiveGenerationReopens()
+    {
+        var availability = new WorldGenerationAvailabilityState();
+        var world = new GpuWorldState(availability: availability);
+        var audio = new RecordingAudioQuiescence();
+        var quiescence = new WorldGenerationQuiescence(
+            availability,
+            new SelectionState(),
+            world,
+            audio);
+        var coordinator = new WorldRevealCoordinator(
+            isRenderNeighborhoodReady: (_, _) => true,
+            isSpawnCellReady: _ => true,
+            isTerrainNeighborhoodReady: (_, _) => true,
+            areCompositeTexturesReady: () => true,
+            prepareCompositeTextures: (_, _) => { },
+            invalidateCompositeTextures: () => { },
+            isSpawnClaimUnhydratable: _ => false,
+            quiescence: quiescence);
+
+        Assert.Equal(1, coordinator.Begin(WorldRevealKind.Login));
+        Assert.Equal(2, coordinator.Begin(WorldRevealKind.Portal));
+        Assert.False(availability.IsWorldAvailable);
+        Assert.Equal(2, availability.QuiescedGeneration);
+        Assert.Equal(1, audio.SuspendCalls);
+
+        coordinator.Complete();
+
+        Assert.True(availability.IsWorldAvailable);
+        Assert.Equal(1, audio.ResumeCalls);
+    }
+
+    private sealed class RecordingAudioQuiescence : AcDream.App.Audio.IWorldAudioQuiescence
+    {
+        public int SuspendCalls { get; private set; }
+        public int ResumeCalls { get; private set; }
+
+        public void SuspendWorldAudio() => SuspendCalls++;
+        public void ResumeWorldAudio() => ResumeCalls++;
+    }
 }