measure(step2c): setup once per chunk, still 1.6 us/sample -- exact per-sample density misses 600 ms

Editor-only, default off. 259^3 ring split into 1,000 aligned 32^3 chunks; cache/index builds
bounded by chunks (948 room/SDF caches, 800 active-op lists, 8,532 index tables); 800 block setups
+ 201,243 scalar fallback points (1.16%); no per-point GetDensityAt on supported routes.
Six workers: live 7.07 s wall / 1.678 us per sample; prepared 7.92 s / 1.595 us.
Candidate visits 21.2 -> 15.8 per sample, evaluations 6.31 -> 5.75; room / tunnel / tunnel-core
evaluations unchanged (48.1 M / 5.0 M / 38.4 M for 17.4 M samples). Passage evals 18.1 M -> 8.4 M.
Exact: 0 Q16/sign disagreements, five seeds, same hash on 1 and 6 workers, reach shrink caught.
Luna's verdict: 600 ms is not reachable while every lattice point evaluates the exact current
density; 27.7 worker-CPU seconds need >= 7.7x less work.

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

CODEMAP.md

@@ -117,10 +117,10 @@ 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|surface-fall|crossing|gate-stress|visual-edit|visual-lod|visual-gap-walk|visual-gap-inject|dig-motion|parity|horizon|horizon-render|determinism|region-eval`, optional `-Build`, `-Assets owner|default`, `-Cvars`, absolute `-Out`, `-Label`, `-HorizonLevel`, `-HorizonRenderDistanceChunks`, `-ParityExportSize=32|64|128`, `-ParityExportTile=x,y,z`, `-SharedDDC`, `-SampleDensityStacks`, `-StackSampleIntervalUs`, and `-RegionHashProbe -RegionWorkers N -RegionReferenceHash HASH`; stages the host/assets, isolates user/DDC/config state, serializes one Unreal launch at a time, enforces the 8 GiB/30-minute guards, waits for 6 GiB free RAM before launches, and emits compact `result.json`/`summary.txt` plus full logs. Parity can render its game leg with `-EnableRender` and compares the selected export region against the exact streamed tile hashes. `visual-gap-walk` records camera-frustum surface-point coverage at 6000 cm/s; `visual-gap-inject` proves an early component hide is detected; `dig-motion` logs per-frame vertical velocity, gate, support readiness, and movement mode. `-Cvars @{ 'voxel.TestGapAuditLegacyHandoff'=1 }` replays the old visibility handoff for A/B audit baselines. 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`; `region-eval` compares the live path with the default-off editor brick program on the 259³ lattice and five-seed probe set; `-RegionHashProbe -RegionWorkers N -RegionReferenceHash HASH` checks a full-ring hash at another partition count. `-SampleDensityStacks` captures profiles, and `-StackSampleIntervalUs` sets the sampling interval.
+| `Tools/VoxelForgeTest.ps1` | The single guarded test entry point. `-Scenario canonical|owner|probe|perf|tests|surface-fall|crossing|gate-stress|visual-edit|visual-lod|visual-gap-walk|visual-gap-inject|dig-motion|parity|horizon|horizon-render|determinism|region-eval`, optional `-Build`, `-Assets owner|default`, `-Cvars`, absolute `-Out`, `-Label`, `-HorizonLevel`, `-HorizonRenderDistanceChunks`, `-ParityExportSize=32|64|128`, `-ParityExportTile=x,y,z`, `-SharedDDC`, `-SampleDensityStacks`, `-StackSampleIntervalUs`, and `-RegionHashProbe -RegionWorkers N -RegionReferenceHash HASH`; stages the host/assets, isolates user/DDC/config state, serializes one Unreal launch at a time, enforces the 8 GiB/30-minute guards, waits for 6 GiB free RAM before launches, and emits compact `result.json`/`summary.txt` plus full logs. Parity can render its game leg with `-EnableRender` and compares the selected export region against the exact streamed tile hashes. `visual-gap-walk` records camera-frustum surface-point coverage at 6000 cm/s; `visual-gap-inject` proves an early component hide is detected; `dig-motion` logs per-frame vertical velocity, gate, support readiness, and movement mode. `-Cvars @{ 'voxel.TestGapAuditLegacyHandoff'=1 }` replays the old visibility handoff for A/B audit baselines. 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`; `region-eval` compares the live path with the default-off editor chunk program on the 259³ lattice and five-seed probe set, reporting whole-ring setup/candidate counters; `-RegionHashProbe -RegionWorkers N -RegionReferenceHash HASH` checks a full-ring hash at another partition count. `-SampleDensityStacks` captures profiles, and `-StackSampleIntervalUs` sets the sampling interval.
 | `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. Optional `-exporttilex/y/z` sets an exact L0 tile origin for controlled export/game parity; omitting all three preserves the existing center-derived origin. `-regioneval=1` runs the default-off step-2 research harness: full-ring and five-seed Q16 comparisons, repeat hashes, shrunk-reach falsification, cold timings, counted live fallbacks, and separate before/after stack captures when `-SampleDensityStacks` is set. `-RegionHashProbe` runs one full-ring brick evaluation and compares its raw float hash with a reference from another worker count. |
-| `Source/VoxelForgeEditor/Private/VoxelForgeRegionEvalExperiment.*` | Lattice driver with six workers by default for the commandlet-only region experiment. The live path calls `GetDensityAt` per point; the brick path groups the lattice into aligned 8³ regions and calls the editor-only `EvaluateDensityBrick` once per region, counts scalar fallback points, and compares the exact final field. The operator block uses prepared SDF candidate bins and retains canonical per-point post-stack writer order. The full-ring hash probe supports 1–32 fixed partitions to check determinism across worker counts. |
+| `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. Optional `-exporttilex/y/z` sets an exact L0 tile origin for controlled export/game parity; omitting all three preserves the existing center-derived origin. `-regioneval=1` runs the default-off step-2 research harness: full-ring and five-seed Q16 comparisons, repeat hashes, shrunk-reach falsification, cold timings, full-ring setup/candidate counters, counted live fallbacks, and separate before/after stack captures when `-SampleDensityStacks` is set. `-RegionHashProbe` runs one full-ring chunk evaluation and compares its raw float hash with a reference from another worker count. |
+| `Source/VoxelForgeEditor/Private/VoxelForgeRegionEvalExperiment.*` | Lattice driver with six workers by default for the commandlet-only region experiment. The live path calls `GetDensityAt` per point; the prepared path assigns each 32³ chunk once and calls editor-only `EvaluateDensityChunk`, which seeds one block evaluation and runs canonical final-field writers across that chunk. The prepared room/SDF cache window is aligned to that chunk; 8-voxel SDF candidate bins stay editor-only and default off. Unsupported routes use counted scalar fallbacks. Full-ring output reports room/SDF cache, active-op-list, and broad-phase/index builds; general-path entries and fallbacks; candidate visits/evaluations per point; and fresh sampled attribution. The full-ring hash probe supports 1–32 fixed partitions to check determinism across worker counts. |
 | `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. |
 | `Public/VoxelStats.h` / `Private/VoxelStats.cpp` | `stat VoxelForge` DWORD counters for tile classification, skipping, meshing, operator-stack verdicts, and cave-bail diagnosis. Each `Cave Bail *` counter names one guard; `Cave Bail No Stack` counts slots with no buildable stack (no definition, or a degenerate strate). |
 
@@ -363,7 +363,7 @@ This is **where terrain shape lives.**
 | `ApplyBoundarySeal` (static) | 996 | Solidifies strate top/bottom shells. |
 | `InitializeSettings` | 2691 | Copies the effective seed, spine radius, and global XY world-bound settings from `UVoxelSettings` (the season owns all three when assigned); radius 0 preserves the unbounded field. |
 | **`GetDensityAt`** | 2712 | **Entry point.** Picks strate + generator type and, on the per-chunk refetch, builds the chunk's operator stack (editor composer → cooked-season recipe → native archetype stack); evaluates it (TunnelNetwork/Underwater through the fused `GetDensityWithParams`), then adds disturbances and structural posts. Optional `OutPreEditDensity` receives the exact final procedural field immediately before the player DiffLayer tail, allowing the near-player dig cache to replay edits without regenerating the operator stack. Its ordinary one-argument behavior is unchanged. A degenerate strate has no stack and is air; `CP_*` state remains keyed by `(DensityCacheOwnerId, ChunkCoord, LayoutVersion)`. |
-| **`EvaluateDensityBrick`** | 2728 | **Editor-only, default-off research API.** Accepts a lattice region contained by one 8-voxel bin and one 32-voxel chunk. Routes once, reuses `FVoxelDensityBlockSession::FillChunk` / `EvalBlock` for supported TunnelNetwork and Underwater operator stacks, and applies the existing post-stack writers across all brick points before returning. Unsupported routes use scalar `GetDensityAt` and return their fallback count. The API is absent from non-editor builds; streaming and gameplay continue through the original scalar API. |
+| **`EvaluateDensityChunk`** | 2728 | **Editor-only, default-off research API.** Accepts a lattice region contained by one 32-voxel chunk. Routes once, reuses `FVoxelDensityBlockSession::FillChunk` / `EvalBlock` for supported TunnelNetwork and Underwater operator stacks, and applies the existing post-stack writers across all chunk points before returning. Unsupported routes use scalar `GetDensityAt` and return both fallback and general-path entry counts. The region evaluator prepares bounded cache/index state once per region or chunk. The API is absent from non-editor builds; streaming and gameplay continue through the original scalar API. |
 | **`GetDensityWithParams`** | 3749 | TunnelNetwork pipeline (~1000 lines) — the fused evaluator of the TunnelNetwork/Underwater stack in `GetDensityAt`. See §4. ⚠️ Takes **required** `ParamsFingerprint` + `LayoutVersion` since the AUDIT §C2 fix (2026-07-28) — they go into the SDF cache key so a chunk can no longer be evaluated against a neighbour's rooms. Callers compute the CRC **once per chunk** (`CP_TunnelFP`), never per voxel. The optional `voxel.WormBlockSkip` path (default 0) uses `VF_TryGetWormBlockSkip` + a worker-local 4³ lattice-block cache to prove `|N1| >= WormThreshold` and remove both worm noise calls only; it never changes `NetworkMask` or the fallback field path. |
 | `SampleSurfaceStructuralZ` | — | **F20:** the RAW SurfaceWorld heightfield (continents+mountains+detail), BEFORE any terrain op; returns terrain Z + relief M. Cliff re-samples it at an XY offset for a cheap analytic slope. |
 | `ComputeSurfaceTerrainZ` / `ComputeSurfaceColumn` | — | SurfaceWorld heightfield → terrain Z (+ sky-cap ceiling and overhang gate per column); biome **output-blend** lerps dominant/neighbour heights (`ParamsD`/`ParamsN`/weight). **F20 surface ops** (`FSurfaceGenerationParams`, biome-selected + slope/relief-conditioned, all default off): Cliff (slope-gated STEEPENING — push height from local mean where steep ⇒ sheer walls; 4 structural resamples only when on), Terrace (relief-gated + `TerraceHardness`), LayerLines (sedimentary shelves) — pure per-column height REMAPS applied here so the single height oracle stays consistent (MC/ClassifyTile/deco/BP bridge). **Phase 2 OVERHANG** (volumetric — real jutting shelves): in the stack's `FOverhangShelfMod`, for AIR voxels in a window `(TerrainZ, TerrainZ+OverhangHeight]` above a steep slope, the heightfield is re-sampled UPHILL (toward the cliff) by a reach that GROWS with height (tiny low ⇒ air over the void, full high ⇒ borrows the far cliff rock) and unioned in ⇒ a shelf attached to the cliff, tapering out over the void with air beneath (the sketch). Per-column `OverhangAmp`(=strength·slope-gate) + unit uphill `(DirX,DirY)` resolved once in `ComputeSurfaceColumn` (gradient sampled at the REACH scale so a spot over the void can see the cliff), cached on `FSurfaceColumn`. Genuine 3D (per-voxel structural re-eval, gated to steep overhang columns). Off ⇒ byte-identical. The field-preserving LOD0 pass removes only needless temporaries/default construction; every output remains bit-identical. §8.14. |