wip(streaming): LOD rings tile exactly once, cache race, reconcile 104x -- gate stress FAILS 3/4

- Clipmap: finer rings snap to child-pair boundaries, so no two desired tiles of different
  levels overlap. Owner config 635 overlapping pairs -> 0; LOD0 ring 343 -> 512 tiles.
  New test sweeps 6,174 cases; fails on 7486c29 as intended, passes here.
- Shared room-graph cache: Entry->Cache read/written only under the mutex (race fix).
- ReconcileReadyTransitionVisibility indexed: moving p95 32.0 ms -> 0.31 ms.
- Block-vs-scalar density equivalence test: 5.1M samples bit-identical; catches an injected
  optimistic EffectOverBox (5,612 mismatches).

UNVALIDATED for merge: collision-gate stress passed 1 of 4 runs on this code (fails at 4.56 m,
support collision unready at start); it passed on 7486c29. No control run yet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Source/VoxelForge/Public/VoxelWorld.h

@@ -560,6 +560,7 @@ private:
     void MaybeFinishHeadlessStreamingTest();
     void UpdateVisualStalenessAudit();
     void LogVisualStalenessAudit();
+    void LogReadyTransitionVisibilityMeasure();
     void RecordTileHash(const FVoxelTileKey& Tile, const FIntVector& OriginVoxels,
                         int32 Step, int32 Cells, int32 BandChunkLo, int32 BandChunkHi,
                         bool bSheetTile, const FVoxelMeshData& MeshData);
@@ -989,10 +990,30 @@ public:
     bool bSampleStacksStarted = false;
     TArray<FVoxelTileKey> DesiredSorted;   // critical floor prefix, then true-pawn distance-first
     TArray<FVoxelTileKey> CriticalDesiredTiles; // occupied/support tile, then heading tile
+    // Ancestor -> desired descendants, rebuilt with DesiredSorted. Reconciliation uses this
+    // index to test transition coverage without rescanning the full desired set per old tile.
+    TMap<FVoxelTileKey, TArray<FVoxelTileKey>> DesiredTransitionDescendants;
+    int32 DesiredTransitionMaxLevel = 0;
     uint32 DesiredEpoch = 0;               // increments whenever DesiredStamped is rebuilt
     int32 ObsoleteTileAbortCount = 0;      // cumulative per-world moving-session cancellation count
     float PeakObservedPawnSpeedCmPerSecond = 0.0f;
 
+    struct FReadyTransitionVisibilitySample
+    {
+        uint64 Cycles = 0;
+        int32 TileComponentCount = 0;
+        int32 DesiredTileCount = 0;
+    };
+    struct FFarFieldSubmitSample
+    {
+        uint64 Cycles = 0;
+        int32 DesiredTileCount = 0;
+        int32 MaxDesiredLevel = 0;
+    };
+    bool bMeasureReadyTransitionVisibility = false;
+    TArray<FReadyTransitionVisibilitySample> ReadyTransitionVisibilitySamples;
+    TArray<FFarFieldSubmitSample> FarFieldSubmitSamples;
+
     // Clean performance accounting. LOD 0..8 covers every marching-cubes clip level; sheet tiles
     // above the configured MC range never enter the outer classifier.
     static constexpr int32 TrackedClassifierLODCount = 9;