fix(classify): use the public GetStrateChunkZBounds; the index accessor is protected

VoxelGenerator.cpp(2796): C2248 -- FindSlotIndexForChunkZ is protected.

I claimed it was public "verified" in the previous commit. The grep printed the
declaration line, not the access specifier above it. Same shape as the partial
read that produced a false accusation earlier today.

GetStrateChunkZBounds is public (VoxelStrateManager.h:177), returns false for
exactly the no-slot case, and ClassifyTile already calls it three times for the
same question. Wrapped in a VF_ChunkZHasSlot lambda so the condition reads as
the predicate it is. No accessor promoted, no API widened.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

OPSTACK-PROGRESS.md

@@ -4402,3 +4402,18 @@ flight, and it is a class of tile T1.d has never once been able to prove.
 Compile-risk spots: `FindSlotIndexForChunkZ` is public (`VoxelStrateManager.h:351`, verified);
 `FStrateDisturbanceParams` is already used later in the same function; the new `else if` sits before
 the surface `else`, so `Slots[MemoSlotIdx]` is never dereferenced for the new category.
+
+## 2026-08-16 (t) — build break: `FindSlotIndexForChunkZ` is protected, not public
+
+`VoxelGenerator.cpp(2796): C2248 — cannot access protected member`.
+
+I wrote "`FindSlotIndexForChunkZ` is public (`VoxelStrateManager.h:351`, verified)" in the previous
+entry. **It is `protected`.** The grep I called verification printed the declaration line and not the
+access specifier above it — I checked that the symbol existed and reported it as checked for
+something else. Exactly the "assert a negative from a partial read" mistake made earlier today with
+the test fixture, in the same shape.
+
+**Fixed without widening the API:** `GetStrateChunkZBounds` is `public:` (line 177), returns false
+for precisely the no-slot case, and this same function already calls it three times for the same
+question. A small `VF_ChunkZHasSlot` lambda wraps it so the `else if` reads as the predicate it is.
+No accessor promoted, no new surface.

Source/VoxelForge/Private/VoxelGenerator.cpp

@@ -2762,8 +2762,16 @@ EVoxelTileClass UVoxelGenerator::ClassifyTile(const FIntVector& OriginVoxels, in
     bool  bAnyNonCave   = false;       // gap ou SurfaceWorld dans la même tuile ⇒ on abandonne
 
     int32 MemoChunkZ  = INT32_MAX;
-    int32 MemoCat     = -1;            // 0 = gap, 1 = surface, 2 = cave (pile d'opérateurs)
+    int32 MemoCat     = -1;            // 0 = gap, 1 = surface, 2 = cave (pile), 3 = hors layout
     int32 MemoSlotIdx = -1;
+
+    // « Ce chunk Z appartient-il à une strate ? » sous forme publique : `FindSlotIndexForChunkZ`
+    // est `protected`, `GetStrateChunkZBounds` rend false pour exactement le même cas.
+    auto VF_ChunkZHasSlot = [&](int32 Z) -> bool
+    {
+        int32 UnusedTopCZ = 0, UnusedBotCZ = 0;
+        return StrateManager->GetStrateChunkZBounds(Z, UnusedTopCZ, UnusedBotCZ);
+    };
     for (int32 g = -1; g <= GridDim; ++g)
     {
         const int32 Zi = OriginVoxels.Z + g * Step;
@@ -2793,7 +2801,12 @@ EVoxelTileClass UVoxelGenerator::ClassifyTile(const FIntVector& OriginVoxels, in
             //
             // Out-of-layout is a CONSTANT AIR field, not a cave archetype. Every tile touching the
             // open air above the world was being routed into the cave branch and bailing there.
-            else if (StrateManager->FindSlotIndexForChunkZ(ChunkZ) < 0)
+            // `GetStrateChunkZBounds` (PUBLIC) rend false exactement quand `FindSlotIndexForChunkZ`
+            // rend -1 — ce dernier est `protected`, et cette fonction l'utilise déjà deux fois pour
+            // la même question. Pas de nouvelle surface d'API pour un prédicat qui existe.
+            // GetStrateChunkZBounds is the public form of "has a layout slot"; the index accessor
+            // is protected and this function already uses the bounds call twice for the same test.
+            else if (!VF_ChunkZHasSlot(ChunkZ))
             {
                 MemoCat = 3;
                 bAnyNonCave = true;   // n'entre JAMAIS dans la branche de cave