perf(generation): spatial index default on; the 10 s question and the unknown bucket, answered

Measurement round (Codex; checked against its report):
- Per-tile identity for ab4bbe3's always-on LOD0 changes: a fresh 841-tile HEAD trace matches
  traces recorded before them (MemoStaticOn/Off), keyed by (x,y,z,level) with
  verdict/empty/triangles compared. 0 differences, 0 missing; LOD totals identical, 669,834 in all.
- The "missing 10 s" is not the spatial index: all six TileCacheWindow x SpatialIndex
  combinations are within ~1% for a given window setting. TileCacheWindow=0 at HEAD is not
  2990009's path. It still thrashes at L3/L4 (p95 ~250 ms). The default beats 2990009 on every
  metric: static worker 48 -> 34.4 s, moving 125 -> 101 s, LOD0 generation p50 73 -> 66 ms
  static and 70 -> 62 ms moving.
- voxel.SpatialIndex default -1 -> 1: forced-on was marginally best in every pair (within noise).
- The sampler's "unknown" ~13.8% LOD0 leaf is ucrtbase.dll!_finite (RVA 0x3C080), the non-inlined
  CRT call behind FMath::IsFinite, not Core.dll. Named by parsing Core's export table (no export at
  or below 0xC080) and aggregating callers: the tunnel chain, passage landing/floor checks,
  GetDensityWithParams, GetDensityAt, the spatial index range and EvaluateSDFCached.

Gates: export OBJ unchanged (b3e5f4c3..9b377), capability 20,830 / 10,909, determinism assertion
passed.

Next: an inline bit-test IsFinite (the same predicate for every input, so field-exact).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TaFdXhTdYMkW1xrV6ApT6Y

Source/VoxelForge/Private/VoxelGenerator.cpp

@@ -78,7 +78,7 @@ namespace
         GVoxelForgeTileCacheWindowOpStackMinLOD,
         TEXT("Minimum SampleStep LOD for the op-stack tile-sized room cache window."));
 
-    int32 GVoxelForgeSpatialIndex = -1;
+    int32 GVoxelForgeSpatialIndex = 1;
     FAutoConsoleVariableRef CVarVoxelForgeSpatialIndex(
         TEXT("voxel.SpatialIndex"),
         GVoxelForgeSpatialIndex,

WORK-NEXT.md

@@ -157,6 +157,19 @@ generation p50 is ~4% slower than at `2990009` (73 -> 77 ms static). Queued: att
 in-tree switches (first suspect: `voxel.SpatialIndex` auto-on at fused LOD1-2), never by running old
 commits.
 
+**Resolved 2026-09-13 (`ab4bbe3` + the switch sweep):** not the spatial index; every `SpatialIndex`
+setting is within ~1%. `TileCacheWindow=0` at HEAD is a different configuration from `2990009`, not
+the old path. It still thrashes at L3/L4 (p95 ~250 ms), now at 54 s. The DEFAULT beats `2990009` on
+every metric: static worker 48 -> 34 s, moving 125 -> 101 s, LOD0 generation p50 73 -> 66 ms static
+and 70 -> 62 ms moving. The "LOD0 ~4% slower" worry is gone. `SpatialIndex` now defaults to 1
+(marginally best, within noise). Per-tile identity: 0/841 tiles differ against traces recorded
+before the always-on LOD0 changes.
+
+**Next LOD0 target, found by the sampler's caller aggregation:** the "unknown" ~13.8% LOD0 leaf is
+`ucrtbase.dll!_finite`, the non-inlined CRT call behind `FMath::IsFinite`. Its callers are the tunnel
+chain, passage landing/floor checks and `GetDensityAt`. An inline bit test is exactly the same
+predicate, so it changes no field.
+
 ### Open design questions for the owner
 - All five strate slots resolve to `DA_Strate3`. Intended?
 - Should a composer roll be allowed to overwrite an explicitly authored value?