fix(portal): synchronize destination presentation state

src/AcDream.App/Streaming/StreamingRegion.cs

@@ -171,6 +171,25 @@ public sealed class StreamingRegion
     internal static uint EncodeLandblockIdForTest(int lbX, int lbY)
         => EncodeLandblockId(lbX, lbY);
 
+    /// <summary>
+    /// Returns the tier currently owned by this region after bootstrap/recenter
+    /// hysteresis has been applied. Late worker completions use this to avoid
+    /// resurrecting a Near layer after the region has demoted it to Far.
+    /// </summary>
+    internal bool TryGetDesiredTier(uint landblockId, out LandblockStreamTier tier)
+    {
+        if (_tierResidence.TryGetValue(landblockId, out var residence))
+        {
+            tier = residence == TierResidence.Near
+                ? LandblockStreamTier.Near
+                : LandblockStreamTier.Far;
+            return true;
+        }
+
+        tier = default;
+        return false;
+    }
+
     /// <summary>
     /// Two-tier recenter: computes the 5-list diff per Phase A.5 spec §4.2.
     /// Hysteresis: NearRadius+2 for Near→Far demote; FarRadius+2 for Far→null