wip(assembler): round L37 -- FI mouth carve-fade fix, no raised bridge (style 0); research R1

The passage mouth fade multiplied the signed carve distance by zero, which turned native rock into an
open surface (the reason earlier rounds stamped walk pads at mouths); it now blends between the
uncarved field and the full signed carve. The FI style-0 route followed a lifted grade envelope over
the crater (the "bridge"); it now runs on the rim and follows the native surface. New built-shape and
crease audits with thresholds frozen before the fix (L36 and box controls fail). 24/24 passage rows,
30/30 determinism, 16/16 invariants, 18/18 interface/ring. Unreal: one recipe setter (uncompiled).
Research R1 (read-only, web): ranked proposals for natural walkable mouths, floor-limited carve first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Source/VoxelForge/Private/VoxelForgeCoreAdapter.cpp

@@ -486,6 +486,7 @@ bool BuildFloatingIslandStratumPlan(const UVoxelStrateManager* StrateManager,
     IslandPlan.bottomChunkZ = Slot.BottomChunkZ;
     auto& Recipe = IslandPlan.manifest.recipe;
     Recipe.geometryVersion = 8;
+    Recipe.terrainFollowingRoute = static_cast<std::uint32_t>(Passage.Style) == 0;
     Recipe.layoutChunkWidthSubvoxels = LayoutChunkWidthSubvoxels;
     Recipe.seed = static_cast<std::uint32_t>(StrateManager->GetWorldSeed());
     Recipe.ownerVoxelSizeMicrons = static_cast<std::uint32_t>(std::llround(OwnerVoxelSizeCm * 10000.0));