fix(editor): preserve grab offset when moving items (no teleport-to-cursor)

[Aymericr]

What does this PR do?

Fixes the move-grab "teleport": grabbing an already-placed item to move it (the move-cross handle, or the Move affordance) snapped the item's origin to the cursor instead of preserving the offset between where you grabbed it and the item's origin. Grabbing a sofa by its left edge and nudging it shouldn't recenter it under the pointer.

Root cause was two distinct problems:

• Floor items — a regression. The grab-offset correction rewrote event.localPosition, but floorStrategy.move reads event.position (the raw world cursor) for its world-grid snap on the default (non-Shift) path — that read was introduced when world-grid alignment landed (editor: building rotation, alt-click single wall, world-grid alignment, tap-to-engage move #388), after the offset fix (be0f491b). So the correction was silently bypassed and the item snapped its origin to the grid-snapped cursor. The correction now also rewrites event.position, derived from the corrected building-local point via a new buildingLocalToWorld (the exact inverse of the transform that produced localPosition; buildings rotate only about Y, so the affine identity holds exactly).

• Wall / ceiling / item-surface / shelf items — pre-existing. The shared surface strategies snap the item's origin straight to the cursor hit with no grab offset. Added per-surface grab anchors (seeded on the first move per host, reset on leave/detach) that offset every move by start + (raw − anchor) in the surface's own frame — mirroring the floor path and the existing door/window move tools, with the world point re-derived so the visual cursor stays synced with the mesh. Items resting on a table/shelf now start in their host surface so the first move preserves the offset instead of snapping via enter(), and the level-reparent effect skips intentionally-hosted items so the dragged mesh stays on its host.

Renamed the coordinator's preserveFloorDragOffset → preserveDragOffset (it now governs all surfaces).

2D parity: the 2D move paths already preserve the grab offset (relative-mode resolvePlanarCursorPosition), so no 2D sibling change is needed — this brings 3D into parity with 2D.

Out of scope: roof-wall-mounted items (rare; the face-UV frame needs separate handling). 2D door/window keep mode:'absolute' on purpose (a wall opening snaps to the wall nearest the cursor — documented).

How to test

1. Place an item on the floor. Grab its move-cross handle (or use Move) at a point offset from its center and drag — it should follow the grabbed point, not jump its origin under the cursor. (Previously it teleported on the first move.)
2. Repeat for a wall-mounted item (art / light), a ceiling fixture, and an item resting on a table or shelf — all should preserve the grab offset and stay on their surface.
3. Hold Shift while dragging a floor item (free / off-grid) — offset still preserved.
4. Press R / T to rotate mid-drag — the item stays at the grab-offset position.
5. On a rotated building, floor moves should still track the cursor by the grabbed point.

Notes for reviewers

Diagnosed and adversarially reviewed with an independent multi-agent review and Codex; both converged. The floor world↔local math was verified correct; one host-reparent issue (host-resting items being ejected to the level mid-drag) was found by both reviewers and fixed by gating the reparent effect.

Checklist

• My code follows the existing code style (bun check clean on the changed files)
• Typechecks (@pascal-app/editor + @pascal-app/nodes)
• Manual verification in the running editor (author will verify)
• This PR targets the main branch

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Project	Status	Preview	Updated (UTC)
pascal	🔴 Failed	–	Jun 16, 2026, 7:13 PM

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