fix(streaming): #138 — rescue persistent entities from the pending bucket on unload

GpuWorldState.RemoveLandblock rescued persistent entities (the player)
only from the _loaded list, silently dropping one sitting in the
_pendingByLandblock bucket. The player is re-injected via AppendLiveEntity
every frame; right after a teleport its destination landblock has not
streamed in yet, so the player lands in the pending bucket — and if that
landblock is then unloaded during the streaming churn, the persistent
entry was dropped, violating the "persistent therefore survives unload"
contract. Leading candidate for the #138 "own avatar vanishes after a
couple round-trips" symptom (cumulative; needs user visual confirm).

Fix: scan the pending bucket for persistent guids and rescue them too,
so DrainRescued re-parks them at the next valid landblock. Provable
correctness fix with a deterministic test (rescue-from-pending plus a
negative for non-persistent). Core tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Streaming/GpuWorldState.cs

@@ -315,6 +315,26 @@ public sealed class GpuWorldState
             }
         }
 
+        // #138 (secondary): rescue persistent entities sitting in the PENDING
+        // bucket too, not just the loaded list. The player is re-injected via
+        // AppendLiveEntity into its current landblock every frame
+        // (GameWindow's DrainRescued loop); right after a teleport that
+        // landblock often hasn't streamed in yet, so the player lands in
+        // _pendingByLandblock. If that same landblock is then unloaded (a
+        // streaming churn / re-teleport before it finishes loading), the
+        // pending entry was silently dropped here — violating the
+        // "persistent ⇒ survives unload" contract and making the avatar
+        // vanish after a couple round-trips. Rescue them so DrainRescued
+        // re-parks them at the next valid landblock.
+        if (_pendingByLandblock.TryGetValue(landblockId, out var pendingForLb))
+        {
+            foreach (var entity in pendingForLb)
+            {
+                if (entity.ServerGuid != 0 && _persistentGuids.Contains(entity.ServerGuid))
+                    _persistentRescued.Add(entity);
+            }
+        }
+
         _pendingByLandblock.Remove(landblockId);
         _aabbs.Remove(landblockId);