wip(assembler): M3 round 2 -- islands get real mass: deep crust, separate tapered roots, arched spans

Pinch cause: SmoothStep taper drove the underside radius to zero at one point. Version 2: depth 0.75x
diameter (thin-pad control at 0.30 fails), 3-4 seeded roots, bounded contour warp + roughness, one
off-route side island, 3 m rock spans. Bounds/route/W1-W8-W16 pass. Open: legacy probe metadata says
25 cm but production legacy is 12.5 cm -- round 3 must fix the import scale contract.

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

CODEMAP.md

@@ -150,6 +150,7 @@ remains `0`, and lateral regions remain gated off.
 | `../../VoxelForgeCore/Private/Manifest/VFCore_*.cpp` | Eighteen one-source UBT shims that include canonical files under `Standalone/`; they do not copy Core implementation. The API-boundary row includes `Core/src/VoxelForgeCore.cpp` directly. |
 | `../../VoxelForgeCore/Private/ModuleEntry/` | Unreal module entry and an isolated `CoreMinimal.h` shim for the actual engine header. |
 | `../../Standalone/Core/include/VoxelForgeCore/VoxelForgeCore.h` | Standard-library-only public Core API. `VOXELFORGECORE_API` exports the API from the Unreal module and is empty for standalone builds. |
+| `../../Standalone/Core/src/FloatingIslandsInternal.h` | Canonical standalone/Core floating-island planner, geometry-versioned field, manifest serializer, influence bounds, capsule-route checks, and thickness audit. |
 | `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|step2d|step2e|step2f|step2f-capture|step3-scale|step3-game`, optional `-Build`, `-Assets owner|default`, `-Cvars`, absolute `-Out`, `-Label`, `-HorizonLevel`, `-HorizonRenderDistanceChunks`, `-Step2fProfile=0..7`, `-Step2fCaptureView=inside|wall-closeup`, `-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; `step2f-capture` selects one of eight parameter sets, finds a positive-density camera point and aims at a sampled rock wall for an inside or wall-closeup view, then saves it under `Saved/Research/step2f/captures` (pass the persistent render DDC with `-SharedDDC`); `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; `step2d` retains the earlier independent field; `step2e` retains its earlier benchmark; `step2f` compares frozen step 2e and the coherent field for all eight profiles on the same 259³ ring, applies geometry gates, and checks sound bounds, seams, and 1-vs-6-worker hashes. `-RegionHashProbe -RegionWorkers N -RegionReferenceHash HASH` checks a full-ring hash at another partition count. `-SampleDensityStacks` captures profiles, and `-StackSampleIntervalUs` sets the sampling interval.
 | Step-3 scale and game validation | `step3-scale` measures the same 519³ and 259³ six-worker lattices at 12.5 cm. The cached medians are 7.347496 s and 1.169567 s respectively; determinism and brick sound-proof audits pass. `step3-game` routes in-game generation through the brick evaluator and records tile timings, spawn fill, moving frames, and profile-switch rebuilds. The visible D3D12 run measured tile generation p50/p95/max 3.326/31.045/169.867 ms, full-detail L0 fill 12.369 s for 2,765 tiles, and moving-frame p50/p95/p99/max 4.856/8.922/13.090/80.575 ms. Switching profiles rebuilt 5,815 loaded tiles. Both high-resolution screenshot requests were logged, but the harness found only one fresh PNG and it is a blank pale viewport; no lit comparison capture is accepted. Raw output: `Saved/TestHarness/step3_game_visible_final`; scale output: `Saved/Research/step3/scale/step3_scale_cacheperf_v1`. |
 | `Public/VoxelForgeModule.h` / `Private/VoxelForgeModule.cpp` | `FVoxelForgeModule` boilerplate (Startup/Shutdown just log). |
@@ -833,6 +834,15 @@ World assembler field types and `AuditHeightfieldBounds`, `AuditHeightfieldShelf
 `AuditHeightfieldRoute` are declared in
 [`Standalone/Core/include/VoxelForgeCore/VoxelForgeCore.h`](Standalone/Core/include/VoxelForgeCore/VoxelForgeCore.h)
 and implemented in [`Standalone/Core/src/WorldAssemblerInternal.h`](Standalone/Core/src/WorldAssemblerInternal.h).
+`FloatingIslandRecipeV1`, `FloatingIslandManifestV1`, `FloatingIslandFieldV1`,
+`AuditFloatingIslandBounds`, `AuditFloatingIslandRoute`, and `AuditFloatingIslandThickness` are in the
+same public header; their canonical implementation is
+[`Standalone/Core/src/FloatingIslandsInternal.h`](Standalone/Core/src/FloatingIslandsInternal.h).
+M3 round 2 added geometry version 2's thick crust, lobed roots, bounded detail and arched spans while
+preserving version-1 field and hash behavior. The standalone audit driver remains under
+[`Standalone/Research/WorldAssemblerM3/Round1/FloatingIslandsAudit.cpp`](Standalone/Research/WorldAssemblerM3/Round1/FloatingIslandsAudit.cpp);
+round-2 matched capture source and results are under
+[`Standalone/Research/WorldAssemblerM3/Round2/`](Standalone/Research/WorldAssemblerM3/Round2/).
 `RefineLod8NativeCap` in [`Standalone/Core/src/VoxelForgeCore.cpp`](Standalone/Core/src/VoxelForgeCore.cpp)
 replaces coarse LOD8 ceiling surfaces with the planned 2D cap field while retaining ceiling skirts.
 The standalone SurfaceWorld plan composer and capture/audit entry point live in