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

CODEMAP.md

@@ -114,7 +114,7 @@ remains `0`, and lateral regions remain gated off.
 |------|------|
 | `../../VoxelForge.uplugin` | Plugin manifest. Runtime module `VoxelForge` plus the Editor-only `VoxelForgeEditor` commandlet module. Beta. |
 | `VoxelForge.Build.cs` | Deps: Core, CoreUObject, Engine, **GameplayTags**, **RealtimeMeshComponent**. |
-| `Tools/VoxelForgeTest.ps1` | The single guarded test entry point. `-Scenario canonical|owner|probe|perf|tests|parity`, optional `-Build`, `-Assets owner|default`, `-Cvars`, absolute `-Out`, and `-Label`; stages the host/assets, isolates user/DDC/config state, serializes Unreal launches, and emits compact `result.json`/`summary.txt` plus full logs. |
+| `Tools/VoxelForgeTest.ps1` | The single guarded test entry point. `-Scenario canonical|owner|probe|perf|tests|parity|horizon|horizon-render|determinism`, optional `-Build`, `-Assets owner|default`, `-Cvars`, absolute `-Out`, `-Label`, `-HorizonLevel`, `-HorizonRenderDistanceChunks`, and `-SharedDDC`; stages the host/assets, isolates user/DDC/config state, serializes one Unreal launch at a time, enforces the 8 GiB/30-minute guards, and emits compact `result.json`/`summary.txt` plus full logs. Horizon traces report desired/loaded tiles, resident stream geometry, worker seconds, steady wall time, and peak private memory; `horizon-render` captures the owner view; `determinism` compares per-tile hashes across the default CRT path and `-voxel.CrtFma3=0`. |
 | `Public/VoxelForgeModule.h` / `Private/VoxelForgeModule.cpp` | `FVoxelForgeModule` boilerplate (Startup/Shutdown just log). |
 | `Source/VoxelForgeEditor/VoxelForgeEditor.Build.cs` / `Private/VoxelForgeExploreCommandlet.*` | Editor/commandlet-only `-run=VoxelForgeExplore`; owns bounded render/`VF_` walk/OBJ export orchestration and is not linked by Game/Shipping. |
 | `Public/VoxelGeometryHash.h` | Header-only geometry digest shared by commandlet export and runtime tile-hash dump; hashes mesh counts and the vertex/normal/UV/color/triangle arrays with the historical CRC order. |
@@ -260,7 +260,7 @@ redesign; tile identity lives in `FVoxelTileKey` (VoxelWorld.h).
 | Group | Fields (line) |
 |-------|---------------|
 | Streaming | `ViewDistanceXY=16`, `ViewDistanceUp/Down=5`, `MaxConcurrentTasks=16`, `MaxMeshAppliesPerFrame=4` (defaults — actual values live on the data asset) |
-| Clipmap | `ClipRadius`, `MaxClipLevel`, `FullResClipLevels`, `CoarseTileCells`, `RenderDistanceChunks` (custom horizontal reach: the outermost shell keeps generating until it covers this many chunks; 0 = off), `bFarSheetRing` + `FarSheetSpanLevels` (F18 — the render-distance ring streams per-surface SHEETS: level MaxClipLevel+span heightfield tiles instead of MC, see `GenerateSheetMesh`), skirts, `LODOctaveDrop` (T2.b octave drop on coarse tiles — 0 = off/byte-identical) (the old `LOD0/1Distance` + `ContentMaxLevel` were dead → removed) |
+| Clipmap | `ClipRadius`, `MaxClipLevel=5`, `FullResClipLevels`, `CoarseTileCells`, `RenderDistanceChunks=768` (measured ship defaults; custom horizontal reach: the outermost shell keeps generating until it covers this many chunks; 0 = off), `bFarSheetRing=false` by default, plus `FarSheetSpanLevels` (F18 — the optional render-distance ring streams per-surface SHEETS: level MaxClipLevel+span heightfield tiles instead of MC, see `GenerateSheetMesh`), skirts, `LODOctaveDrop` (T2.b octave drop on coarse tiles — 0 = off/byte-identical). Existing serialized data assets retain their authored values until deliberately migrated. |
 | World bounds | `WorldRadiusVoxels=8192` and `EdgeSealThickness=64` (actor-space XY radial shell; radius 0 = true legacy no-op) |
 | Lighting | `bEnableDensityVolume` + DensityVolume* tunables (§3.11 density clipmap / mini-sun shadows) |
 | Rendering | `VoxelMaterial` (61) |
@@ -270,7 +270,7 @@ redesign; tile identity lives in `FVoxelTileKey` (VoxelWorld.h).
 ### 3.5 World orchestrator — `Public/VoxelWorld.h` + `Private/VoxelWorld.cpp`
 `AVoxelWorld : AActor` — owns everything, drives streaming. Also `FChunkResult` struct
 (VoxelWorld.h:35) = async task payload (coord, chunk, meshdata, LOD, **Epoch**, request timing,
-desired-set epoch and obsolete/cancellation state).
+worker-built stream geometry counts/bytes, desired-set epoch and obsolete/cancellation state).
 
 **Owned objects (UPROPERTY):** `Settings`, `Generator`, `Mesher`, `StrateManager`,
 `DiffLayer` (VoxelWorld.h:55-78). **Storage:** `Chunks` map, `ChunkMeshes` map,
@@ -307,7 +307,7 @@ casse cette arithmetique *structurellement* — `BeginPlay` loggue une **Error**
 | `ApplyTileResult` | — | **Shared game-thread apply** for one `FChunkResult` (async drain + sync carve): discards stale generation epochs and keys no longer desired, marks loaded, ingests capture, EMPTY releases the tile's existing component (a re-gen can flip content→empty on band change — old geometry must not linger), else `ApplyMeshToTile`. Returns true iff a visible mesh uploaded (counts the budget). Doesn't touch `PendingTiles` (caller's). |
 | `FVoxelStackSampler` / `FScopedVoxelStackRegistration` (`VoxelStackSampler.h/.cpp`) | — | **Diagnostic raw stack sampler, off by default.** A sampler thread captures registered generation workers' stacks (`CaptureThreadStackBackTrace`) every N µs and tags each with the tile's LOD. It writes bounded raw PCs to CSV plus a symbolization-free summary under `Saved/`; symbol resolution is deferred until after process exit so the measured process never initializes/calls DbgHelp for this diagnostic. Lifecycle teardown is serialized and registration TLS is session-tagged. Registration is per tile TASK in `LoadTile` (and the export's tasks), never per sample; disabled costs one relaxed atomic load. Game `-voxel.SampleStacks=<us>`, commandlet `-samplestacks[=us]`. |
 | Room-cache performance (2026-09-13): `VF_FindPlayerFitPointForRoomMemoized` / `GPlayerFitMemo` (`VoxelCaveMorphology.cpp`), `voxel.TileCacheWindow` + `VoxelGenLOD::TileOriginVoxels/TileCellsPerAxis` (`VoxelGenerator.h`), `FChunkSDFSpatialIndex` | — | **Player-fit memo:** exact 97-word key, process-wide, `voxel.PlayerFitMemo`. **Tile cache window:** the room cache covers the requesting tile's footprint plus a fixed collect margin. It is set via `TGuardValue` in `GenerateMesh`/classify, and is window-invariant by construction (the margin does not grow with the tile). **LOD-gated:** fused path at LOD ≥ `voxel.TileCacheWindowMinLOD` (3), op-stack at LOD ≥ `voxel.TileCacheWindowOpStackMinLOD` (4); lower LODs keep the 4-chunk worker window, because the tile window slowed LOD0 evaluation ~6%. Strates whose authored terrain ops exceed the proven 256-voxel extent (or are malformed/unloaded) fall back to the legacy window (`VF_ComputeTerrainOpEnvelope`). `voxel.SpatialIndex` is -1 auto (off at fused LOD0, on elsewhere), 0 or 1. **Spatial index:** ordered XY buckets over cache primitives, exact rejection. The `static_assert` in `VoxelStrateTypes.h` ties `VF_STRATE_PARAM_FIELDS` to `FStrateGenerationParams` (83 fields + 8 B padding). |
-| `GenerateTileResult` | — | **Shared worker-side gen** for one tile (async `LoadTile` task + sync `SyncRemeshTile`): [ClassifyTile (T1.d) + exact validation, only when `voxel.OuterClassifierMode=1`; **default 0 since 2026-09-13**] → `GenerateMesh`/`GenerateSheetMesh` → `BuildTileStreamSet`. Reads Generator/Mesher only → safe on a worker or the game thread; fills `FChunkResult`, no enqueue. |
+| `GenerateTileResult` | — | **Shared worker-side gen** for one tile (async `LoadTile` task + sync `SyncRemeshTile`): [ClassifyTile (T1.d) + exact validation, only when `voxel.OuterClassifierMode=1`; **default 0 since 2026-09-13**] → `GenerateMesh`/`GenerateSheetMesh` → `BuildTileStreamSet`; records vertex count and resident stream allocation bytes for the horizon trace. Reads Generator/Mesher only → safe on a worker or the game thread; fills `FChunkResult`, no enqueue. |
 | `RecordTileHash` / `WriteTileHashDump` | — | Headless `-voxel.TileHashDump=<absolute path>` parity instrument. Records the exact `FVoxelMeshData` used by the streaming result, including empty/classified tiles, then writes sorted absolute tile keys, LOD step/cells, content-band limits, settings digest context, and the shared `VoxelGeometryHash` at `EndPlay`. |
 | `SyncRemeshTile` | — | **INSTANT DIG**: level-0 same-frame re-mesh on the game thread (`GenerateTileResult` + `ApplyTileResult` inline, Cells=CHUNK_SIZE/Step=1 + strate band, no capture). Used for the tile under the brush centre so a carve is visible THIS frame; one full-res gen on the game thread. |
 | `UpdateChunksAroundPosition` | 362 | Builds desired set, cancels pending keys that left it, sorts from the **true pawn position**, submits the occupied/support LOD0 tile and the next tile along the pawn heading as an absolute `BackgroundHigh` prefix, then loads/unloads and handles LOD changes. **Delta cull**: `BuildDesiredTiles` returns the LEAVERS (stamped `DesiredStamped` map, one sweep) — only those + `TransitionHold` are considered per crossing, not every loaded tile. `BuildDesiredTiles` also applies `RenderDistanceChunks`: the outermost shell widens to cover the distance — as level-MaxClipLevel MC tiles, or (F18 `bFarSheetRing`) as a SHEET ring at level MaxClipLevel+span (covered-check vs the MaxClipLevel box; `VF_OuterShell` shared with `IsTileInClipRange` so the cull sees the same horizon), dz pre-clamped to the vertical band. **§9.3 anchors:** also prunes dead `StreamingAnchors` + detects their chunk crossings → rebuilds the desired set when an anchor moves/(un)registers (`bAnchorsMoved`/`bForceDesiredRebuild`), same cadence as player movement. §8.10. |