feat(streaming): horizon distance with real tiles only -- sheets off by default

The sheet system models terrain as one ground and one cap height per column, which cannot express this world's overhangs, floating islands and open sky; three attempts to fix the MC/sheet seam produced holes, then caps over the void, then both. Measured alternative: cover the render distance with real marching-cubes tiles and switch the far-sheet ring off.

Benchmarks at RenderDistanceChunks=768, all tiles loaded at steady state: L4 57,473 tiles / 30.1M tris / 837 MiB / 2,514 s worker / 296 s to settle; L5 10,841 / 8.1M / 226 MiB / 375 s / 108 s; L6 3,281 / 2.9M / 82 MiB / 127 s / 77 s. Defaults now MaxClipLevel=5, bFarSheetRing=false. Invariants: strate crossing PASS, gate stress PASS (140.06 m, 0 full stops), determinism PASS with 10,841 tile hashes identical vs -voxel.CrtFma3=0. Peak memory ~4.2 GiB in all three.

Owner action required: his DA_Settings still serializes MaxClipLevel=3 (asset edits are out of scope for Codex), so his world needs that value raised to 5 to use the new far field. At twice the distance the estimate is ~39.5k tiles / 29-30M tris / ~0.8 GiB / ~1,500 worker-seconds, which would want L6 rather than L5.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Source/VoxelForge/Public/VoxelWorld.h

@@ -109,6 +109,8 @@ struct FChunkResult
     uint64 GenerationEndCycles = 0;
     uint64 ApplyStartCycles = 0;
     int32 ClassifyVerdict = -1; double ClassifySeconds = 0.0; double MeshSeconds = 0.0; double StreamSeconds = 0.0; int32 NumTriangles = 0; int32 NumCeilingTriangles = 0;
+    int32 NumVertices = 0;
+    uint64 GeometryBytes = 0;
     bool bSealedSolidProof = false; // true when the cheap gap/seal proof skipped meshing
     bool bOutOfLayoutAirProof = false; // true when the exact constant-air guard skipped meshing
     // Clean, low-overhead work counters. These are carried with the result so the worker can
@@ -154,6 +156,14 @@ struct FVoxelTileHashDumpRecord
     FString GeometryHash;
 };
 
+/** Resident CPU geometry payload associated with one currently loaded tile. */
+struct FLoadedTileGeometryStats
+{
+    uint64 Vertices = 0;
+    uint64 Triangles = 0;
+    uint64 GeometryBytes = 0;
+};
+
 UCLASS()
 class VOXELFORGE_API AVoxelWorld : public AActor
 {
@@ -985,6 +995,7 @@ public:
     uint64 AppliedVisibleTileCountByLevel[TrackedClassifierLODCount]{};
     uint64 AppliedTriangleCountByLevel[TrackedClassifierLODCount]{};
     uint64 AppliedBandTileCountByLevel[TrackedClassifierLODCount]{};
+    TMap<FVoxelTileKey, FLoadedTileGeometryStats> LoadedTileGeometry;
 
     struct FStreamingLatencySample
     {
@@ -998,6 +1009,7 @@ public:
     // Headless validation hook. These are intentionally non-UPROPERTY state and are enabled only
     // by explicit command-line switches; they do not alter ordinary player movement or streaming.
     bool bHeadlessStreamingTestMovement = false;
+    bool bHeadlessStreamingTestExitOnSteady = false;
     bool bHeadlessStreamingTestExitRequested = false;
     bool bStartupTraceThroughCrossing = false;
     bool bHeadlessStreamingTestCenterOverride = false;