fix(editor): harden editor interactions and WebGPU rendering

Fix editor bug sweep regressions, WebGPU CSG/material crashes, Shift snap bypass behavior, arrow handle drag projection, and the wall preview null guard covered by the Sentry follow-up PRs.

packages/nodes/src/item/definition.ts

@@ -22,10 +22,10 @@ const ROTATE_RING_OFFSET = 0.06
 // Whole-item rotation handle — the two-headed curved arrow. `arc-resize`
 // does the angular drag math (raycasts a horizontal plane at the gizmo's
 // Y, measures cursor bearing around the item's local origin, returns the
-// delta). Holding Shift snaps to 15° increments (handled generically in
-// node-arrow-handles for any `shape: 'rotate'`), matching the R/T rotate
-// step for placed items. Item rotation is stored as `[x, y, z]`; only the
-// Y component turns.
+// delta). Rotation snaps to 15° increments by default; holding Shift
+// bypasses that snap (handled generically in node-arrow-handles for any
+// `shape: 'rotate'`), matching the R/T rotate step for placed items. Item
+// rotation is stored as `[x, y, z]`; only the Y component turns.
 function itemRotateHandle(): HandleDescriptor<ItemNodeType> {
   return {
     kind: 'arc-resize',

packages/nodes/src/item/floorplan-move.ts

@@ -211,16 +211,17 @@ function buildWallItemSession(
 
       // Figma-style along-wall alignment (edge-to-edge with other openings /
       // wall items / wall ends), winning over the 0.5m grid snap; falls back
-      // to grid when nothing aligns. Alt bypasses; Shift drops the grid snap.
-      const neighborX = modifiers.altKey
-        ? null
-        : snapLocalXToNeighbors({
-            wall: hit.wall,
-            localX: hit.localX,
-            width,
-            selfId: node.id as AnyNodeId,
-            nodes,
-          })
+      // to grid when nothing aligns. Alt bypasses alignment; Shift bypasses all snap.
+      const neighborX =
+        modifiers.altKey || modifiers.shiftKey
+          ? null
+          : snapLocalXToNeighbors({
+              wall: hit.wall,
+              localX: hit.localX,
+              width,
+              selfId: node.id as AnyNodeId,
+              nodes,
+            })
       const step = useEditor.getState().gridSnapStep
       const snappedLocalX =
         neighborX ?? (modifiers.shiftKey ? hit.localX : Math.round(hit.localX / step) * step)
@@ -286,7 +287,7 @@ function buildFloorItemSession(
           rotationY,
         ),
         candidates,
-        { bypass: modifiers.altKey },
+        { bypass: modifiers.altKey || modifiers.shiftKey },
       )
 
       const sourceY = node.position[1]