feat(editor): placement & interaction overhaul — FSM spine, bug tracks, perf

Implements plans/editor-placement-interaction-overhaul.md: an authoritative
interaction-scope state machine plus the catalogued placement/interaction
fixes, and split-view floor-plan performance.

- Interaction-scope spine (lib/interaction/* + store/use-interaction-scope),
  driven from central useEditor setters; overlay scoping (zone labels,
  context badges, floating action menu) reads resolveOverlayPolicy.
- Bug tracks A/B/D/E/F/G/H: handle/cutout raycast, footprint validity,
  auto-slab loop, ceiling hosting, B-key tool desync, 2D drop offset,
  per-frame jank.
- Snapping modes (grid/lines/angles/off) + contextual HUD chips; modifier
  model (Shift=cycle, Alt=free place, Ctrl=grid step).
- Item move now tracks the cursor 1:1 (was a laggy per-frame lerp); handle
  rig hides during a whole-node move; rotate gizmo advertises Shift=free
  rotation in the HUD and hides the move cross while rotating.
- Floor-plan perf: pause live reactivity while in 3D-only view; per-node
  geometry cache so only changed nodes rebuild on a drag; hoist wall miters
  to a once-per-pass ctx.levelData (O(N^2) -> O(N) on wall/opening drags).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/nodes/src/wall/definition.ts

@@ -1,5 +1,5 @@
 import type { NodeDefinition } from '@pascal-app/core'
-import { buildWallFloorplan } from './floorplan'
+import { buildWallFloorplan, computeWallFloorplanLevelData } from './floorplan'
 import { wallCurveAffordance, wallMoveEndpointAffordance } from './floorplan-affordances'
 import { wallFloorplanMoveTarget } from './floorplan-move'
 import { wallFloorplanSiblingOverrides } from './floorplan-overrides'
@@ -18,7 +18,8 @@ import { wallSlots } from './slots'
  *   `renderer` + `system` keep wrap-exporting legacy WallRenderer +
  *   WallSystem + WallCutout.
  * Stage C: `def.floorplan` builder produces the mitered plan footprint
- *   polygon using `ctx.siblings` to assemble miter context.
+ *   polygon from shared floor-plan level data, with `ctx.siblings` as the
+ *   direct-caller fallback.
  *   floorplan-panel.tsx's `wallPolygons` short-circuits to [] when
  *   wall is registered.
  */
@@ -98,9 +99,11 @@ export const wallDefinition: NodeDefinition<typeof WallNode> = {
     // Priority 4 mirrors the legacy WallSystem's useFrame priority.
     priority: 4,
   },
-  // Stage C: floor-plan rendering. ctx.siblings provides other walls in
-  // the level so `calculateLevelMiters` can compute correct corner joins.
+  // Stage C: floor-plan rendering. Precomputes the level miter graph once
+  // per render pass, then the builder reads its own junctions by wall id.
+  computeFloorplanLevelData: computeWallFloorplanLevelData,
   floorplan: buildWallFloorplan,
+  floorplanDependsOnSiblings: true,
   // 2D drag affordances triggered by `endpoint-handle` primitives in
   // `def.floorplan`'s output. Sister to `affordanceTools` (3D) — the
   // same legacy `MoveWallEndpointTool` flow, reachable from both the
@@ -114,7 +117,6 @@ export const wallDefinition: NodeDefinition<typeof WallNode> = {
 
   toolHints: [
     { key: 'Left click', label: 'Set wall start / end' },
-    { key: 'Shift', label: 'Free angle (no 15° snap)' },
     { key: 'Esc', label: 'Cancel' },
   ],