perf(streaming): outer tile classifier off by default; delete mode 2

Owner-approved, on the A/B measured in 83a0e4d: the classifier plus exact validation cost more
than it saved on the game path. With it off, ready p95 is 182 vs 190-195 ms, generation p95 is
125-127 vs 139-141 ms, and density calls drop 18%.

- GVoxelForgeOuterClassifierMode defaults to 0. Mode 1 stays reachable via
  voxel.OuterClassifierMode=1 as an A/B instrument; the clamp is now 0..1.
- Mode 2 (validation samples reused as the mesher core grid) is deleted: the reuse grid,
  FVoxelMesherCoreDensityGrid, GenerateMesh's ReusableCoreGrid parameter, bValidationCoreReused,
  TotalValidationCoreReuseTiles and its log field. It could not fire: it reused the grid only
  when validation disproved a uniform verdict, which never happened, and Mixed tiles never
  validate. The mode-1 validation loop exits early again on the first disagreeing sample.
- All three GenerateMesh call sites checked; the density-count pointer binds after BandVoxHi.

Verified by Codex, checked by me against the logs:
- build ok; the measured process loaded the staged DLL, SHA-256 1024D8CF..04D
- export OBJ SHA-256 unchanged: b3e5f4c3..9b377
- a run WITHOUT the override prints outer_classifier_mode=0 validation_density_calls=0,
  proving the new default took effect
- 841/841 tiles have identical triangle counts between mode 0 and mode 1. The 394 tiles mode 1
  skipped as uniform produce 0 triangles in mode 0, so the strate band cut (applied by the
  mesher, not by validation) was not hiding geometry.

Docs: ARCHITECTURE 8.10, CODEMAP (GenerateTileResult, ClassifyTile) and fable-idea T1.d record
that streaming no longer classifies by default. WORK-NEXT item 1 records the owner's playtest:
he can no longer fall through the world.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VZS94UH8bSsBeg5sZaxe2Y

CODEMAP.md

@@ -301,7 +301,7 @@ casse cette arithmetique *structurellement* — `BeginPlay` loggue une **Error**
 | `GetPlayerPosition` | 231 | Pawn position or zero. (`GetLODForChunk`/`LODToStep`/`IsChunkInRange` removed — dead since the clipmap.) |
 | `ProcessPendingChunks` | 301 | Drains ProcessQueue under per-frame budget; reads the per-request cancellation token before removing its map entry, drops obsolete/aborted results, then applies each live result via `ApplyTileResult`. |
 | `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). |
-| `GenerateTileResult` | — | **Shared worker-side gen** for one tile (async `LoadTile` task + sync `SyncRemeshTile`): ClassifyTile (T1.d) → `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`. Reads Generator/Mesher only → safe on a worker or the game thread; fills `FChunkResult`, no enqueue. |
 | `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. |
 | `BuildDesiredTiles` | ~722 | Builds `DesiredSorted`+`DesiredStamped` (player clipmap shells + F18 sheet ring) then `AddAnchorDesiredTiles()` before the leaver sweep; it orders from the true local pawn position and builds `CriticalDesiredTiles` for the occupied/support and heading tiles. |
@@ -344,7 +344,7 @@ This is **where terrain shape lives.**
 | `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` / `GetSurfaceDensity` | — | SurfaceWorld heightfield → terrain Z, then density; 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/sheets/ClassifyTile/deco/BP bridge). **Phase 2 OVERHANG** (volumetric — real jutting shelves): in `SurfaceDensityFromColumn`, 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. §8.14. |
 | `VF_BuildOpStackForChunk` (file-static) | — | **The archetype → stack mapping, written down once.** `GetDensityAt` and `ClassifyTile` both call it; params are passed in, never fetched here. A second copy would be the worst bug available in this file — a tile skipped on the verdict of a stack that is not the one producing its density is a hole. Returns false (⇒ caller falls back to the `switch`) for an unported archetype, missing params, or a **degenerate strate**, since five archetype functions early-out to air there and the stack deliberately has no such early-out. `Refs.Surface == nullptr` makes it refuse SurfaceWorld, which is how `ClassifyTile` keeps its own exact-lattice proof. |
-| `ClassifyTile` | — | **T1.d trivial-tile reject.** Cooked/editor recipes now build the exact recipe stack and call its proved `ClassifyBox`; a tile crossing a slot/gap, any diff, or any disturbance returns `Mixed`. This replaces the old global `HasComposerRecipeOverride()` force-to-Mixed. Native cave/surface/gap proofs and all §8.10 caches remain unchanged. |
+| `ClassifyTile` | — | **T1.d trivial-tile reject. ⛔ Not called by streaming by default since 2026-09-13** (`voxel.OuterClassifierMode=0`; net-negative in game, see ARCHITECTURE §8.10). Cooked/editor recipes now build the exact recipe stack and call its proved `ClassifyBox`; a tile crossing a slot/gap, any diff, or any disturbance returns `Mixed`. This replaces the old global `HasComposerRecipeOverride()` force-to-Mixed. Native cave/surface/gap proofs and all §8.10 caches remain unchanged. |
 | `SampleRelief` / `SampleMoisture` | — | Climate fields (pure XY, [0,1]). Relief = shared source of truth for the relief map M. §8.14. |
 | `SampleBiomeAt` | — | Warped-Voronoi + climate biome query (dominant + neighbour + weight). Reference used by the preview bake + `GetDominantBiomeAt`. §8.14. |
 | `ResolveBiomeSampleAt` / `RebuildBiomeGrid` | — | Hot-path biome resolve (FBiomeSample) via a box-validated per-chunk cell-grid cache. Bit-identical to `SampleBiomeAt`. §8.14, §8.10. |