MeshTransform: Slice H — TRELLIS localized edits (VoxHammer/Nano3D) — stretch, gated on #818 C5

[fernandotonon]

Part of #845 · Design: docs/MESH_TRANSFORM_DESIGN.md §5 · Stretch — DO NOT START before #818's C5 (TRELLIS.2 spike) memo lands.

Training-free localized editing of an existing mesh ("change only the goblin's head") via TRELLIS-latent inversion + masked re-denoise:

• VoxHammer (3DV 2026 oral, MIT, on MIT TRELLIS weights) — latent-cache unedited regions, re-denoise the masked region.
• Nano3D (ICLR 2026, MIT) — FlowEdit-style mask-free instruction editing; ships a 100k edit-pair dataset.

Strictly stronger than global SDEdit variants, but requires the TRELLIS(.2) runtime — whose ONNX feasibility (structured-latent custom ops, 4B params) is exactly what #818-C5 decides. If C5 adopts TRELLIS.2 as a generation tier, this slice rides the same graphs + a region-mask UI (Edit-mode face selection already provides masks).

• Blocked-on marker: revisit when the C5 decision memo is filed
• If TRELLIS.2 lands: scope VoxHammer-style edit mode (mask from face selection → voxelized latent mask), CLI/MCP/GUI parity per epic rules