User-reported regressions after the previous Stage D move ports:
1. Slab/ceiling moves were sluggish because the actions wrote
scene.update(polygon) every grid:move tick → React re-render +
CSG-with-holes geometry rebuild per frame.
Apply the live-drag exception (same recipe fence move already used):
visual translation via `sceneRegistry.nodes.get(id).position` +
`useLiveTransforms`; scene.polygon is only written on commit. Polygon
center precomputed in ctx, mesh-offset clears on commit/cancel.
2. Cursor sphere sat at the polygon center (offset from the user's
actual cursor by `originalCenter - first_cursor`). Move wrappers
now subscribe to `grid:move` and set `cursorRef.current.position`
directly — no React state, no per-tick reconcile. Cursor lands on
the user's pointer.
3. Fence move had the same React-reconcile-per-tick cost via its
`useLiveTransforms` subscription. Switched to the same direct
ref-mutation pattern.
Adds a "REAL bend" test pinning that one Ctrl-Z after a real curve
drag undoes only the bend, not the create. The previously reported
"first undo does nothing" outcome reproduces only for no-op bends
(drags within `normalizeWallCurveOffset`'s straight-snap threshold,
≈1.5cm on a 3m fence). For visible bends the dance pushes a real
pastState entry and one undo step rolls back the bend.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
