Default MarchingCubesV1 unchanged (W1/W8/W16 = round-6 hashes). Hybrid DC only in LOD0 interior cells with tagged features; tile-border cells and LOD1+ stay MC. BuildHost: fixtures repeat exactly, cooked collision bounds = render bounds, same-LOD borders pass, sampled SurfaceWorld cliff bit-identical to MC. Open: tagged tiles cost 5.7-6.7x MC; corner-top field contact error 20 cm; 5 MC doorway LOD cases. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ