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/VoxelSettings.h

@@ -148,8 +148,9 @@ public:
 
 	// Coarsest LOD level. 0 = full-res only (no clipmap). Each level up doubles tile size &
 	// reach at ~constant cost — raise this to see much farther for cheap. (Level L step = 2^L.)
+	// Ship default: level 5, the measured horizon-distance balance at 768 chunks.
 	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Voxel|Clipmap", meta = (ClampMin = "0", ClampMax = "8"))
-	int32 MaxClipLevel = 4;
+	int32 MaxClipLevel = 5;
 
 	// How many near levels mesh at FULL resolution (CHUNK_SIZE cells). Levels at or above this
 	// use the cheaper CoarseTileCells → MUCH faster gen for the far field (it's far, so the
@@ -171,9 +172,9 @@ public:
 	// cell must fit inside a strate band — level ≥7 blanks via the too-coarse skip) and buy the
 	// remaining horizon here. Cost: the extra ring is all same-level tiles — tile/draw/gen count
 	// grows with (distance / 2^MaxClipLevel)², so each MaxClipLevel step down quadruples the ring.
-	// 0 = off (natural reach, byte-identical streaming).
+	// Ship default: 768 chunks (about 6.1 km at 8 m/chunk). 0 = off (natural reach).
 	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Voxel|Clipmap", meta = (ClampMin = "0"))
-	int32 RenderDistanceChunks = 0;
+	int32 RenderDistanceChunks = 768;
 
 	// F18 — the render-distance ring streams per-surface SHEETS instead of MC tiles: in an open
 	// strate the far field is exactly two heightfields (TerrainZ + sky-cap CeilSurf, both already
@@ -182,10 +183,11 @@ public:
 	// sheet spans 2^FarSheetSpanLevels MC-tile footprints per axis). Non-open strates produce
 	// empty sheets (their far ring was enclosed rock anyway). Carved features (passages, chasms,
 	// spine) don't show at sheet distance. Needs the strate band armed (StrateContentCutMinLevel
-	// active); in the inter-strate gap the sheet ring blanks until you land. Off = the ring stays
-	// MC tiles at level MaxClipLevel (pre-F18 behaviour). Only matters when RenderDistanceChunks > 0.
+	// active); in the inter-strate gap the sheet ring blanks until you land. The ship default is OFF:
+	// the ring stays real MC tiles at level MaxClipLevel (pre-F18 behaviour). Only matters when
+	// RenderDistanceChunks > 0.
 	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Voxel|Clipmap")
-	bool bFarSheetRing = true;
+	bool bFarSheetRing = false;
 
 	// Sheet tile size = MaxClipLevel + this many levels (2 → one sheet covers 4×4 MC-tile
 	// footprints → ~16× fewer far components). Sampling density stays that of the MaxClipLevel