fix: address 2nd-round adversarial review of PR #402 fixes

- core: decouple drag-follow from distributionRole — add
  portConnectivityFollow flag to NodeDefinition; pipe-trap opts out
  (portConnectivityFollow: false) so dragging a connected pipe endpoint
  stretches the trap arm instead of yanking the anchored trap fixture

- core: remove the module-level getLevelHeight cache entirely — it was
  keyed only by nodes-object identity, which could return stale heights
  for in-place mutations by pure/headless callers. The function is now
  fully pure and deterministic; viewer hot path recomputes per frame as
  before (the cache only ever skipped the resolver-free branch)

- test: harden port-connectivity-pipe.test.ts — real DuctSegmentNode
  cross-family isolation case (was waste-vs-vent), new pipe-trap anchor
  case (run drag doesn't move trap; trap drag still stretches run), and
  beforeEach/afterEach registry reset instead of leaky beforeAll

- nit: biome format/import-order on all touched files

packages/core/src/registry/types.ts

@@ -720,6 +720,20 @@ export type NodeDefinition<S extends ZodObject<any>> = {
    * Kinds outside any distribution system leave this unset.
    */
   distributionRole?: DistributionRole
+  /**
+   * When `distributionRole` is `'fitting'`, controls whether this fitting
+   * is dragged as a rigid follower when a connected run endpoint moves.
+   *
+   * - `true` (default for `distributionRole === 'fitting'`): the fitting
+   *   translates rigidly so its mated collar stays on the moved port — the
+   *   right behaviour for in-line fittings (elbows, tees, wyes, crosses).
+   * - `false`: the fitting is anchored in space; moving a connected run
+   *   endpoint stretches the run arm, not the fitting. Use this for
+   *   fixed-position fixtures like `pipe-trap`.
+   *
+   * Has no effect when `distributionRole` is not `'fitting'`.
+   */
+  portConnectivityFollow?: boolean
 
   defaults: () => Omit<z.infer<S>, 'id' | 'type'>
   migrate?: Record<number, (old: unknown) => unknown>

packages/core/src/services/level-height.ts

@@ -7,40 +7,18 @@ export const DEFAULT_LEVEL_HEIGHT = 2.5
  * Optional resolver for a wall's rendered base Y (mesh elevation).
  *
  * `packages/core` is pure domain logic and must not read viewer/Three.js
- * state (see AGENTS.md "Layer Boundaries"). Callers that legitimately have
+ * state (see AGENTS.md “Layer Boundaries”). Callers that legitimately have
  * registry access (viewer systems, node tools) may pass a resolver so the
  * mesh elevation is factored in; pure/headless callers (MCP, tests, server)
  * omit it and get a deterministic result from serialized node data alone.
  */
 export type WallBaseYResolver = (wallId: AnyNodeId) => number | undefined
 
-// Cache: levelId → computed height. Invalidated when the nodes reference changes.
-// Zustand produces a new `nodes` object on every mutation, so reference equality
-// is a zero-cost way to detect stale data without any subscription overhead.
-//
-// NOTE: the cache is keyed only by the `nodes` reference, so it is only safe to
-// reuse across calls that pass the same resolver semantics. When a resolver is
-// supplied (viewer path), mesh Y can change without a `nodes` reference change,
-// so the viewer caller must not rely on the cache for live values — it passes a
-// resolver and we recompute. We therefore only cache resolver-free (pure)
-// results, which are a deterministic function of `nodes`.
-const heightCache = new Map<string, number>()
-let lastNodesRef: object | null = null
-
 export function getLevelHeight(
   levelId: string,
   nodes: Record<AnyNodeId, AnyNode>,
   resolveWallBaseY?: WallBaseYResolver,
 ): number {
-  if (nodes !== lastNodesRef) {
-    heightCache.clear()
-    lastNodesRef = nodes
-  }
-
-  // Only the pure (resolver-free) computation is cacheable: with a resolver the
-  // result can depend on live mesh state that the `nodes` reference doesn't track.
-  if (!resolveWallBaseY && heightCache.has(levelId)) return heightCache.get(levelId)!
-
   const level = nodes[levelId as LevelNode['id']] as LevelNode | undefined
   if (!level) return DEFAULT_LEVEL_HEIGHT
 
@@ -60,7 +38,5 @@ export function getLevelHeight(
     }
   }
 
-  const height = maxTop > 0 ? maxTop : DEFAULT_LEVEL_HEIGHT
-  if (!resolveWallBaseY) heightCache.set(levelId, height)
-  return height
+  return maxTop > 0 ? maxTop : DEFAULT_LEVEL_HEIGHT
 }

packages/core/src/services/port-connectivity.ts

@@ -112,8 +112,12 @@ export function analyzePortConnectivity(
     // Generalised across every distribution family (HVAC duct + DWV pipe):
     // `run` partners stretch an endpoint, `fitting` partners follow rigidly.
     // Terminals/equipment mount to surfaces and are intentionally NOT dragged.
+    // Fittings that declare `portConnectivityFollow: false` are anchored
+    // fixtures (e.g. pipe-trap) — moving a connected run stretches the arm.
     const otherRole = roleOf(other)
     if (otherRole !== 'run' && otherRole !== 'fitting') continue
+    const otherDef = nodeRegistry.get(other.type)
+    if (otherRole === 'fitting' && otherDef?.portConnectivityFollow === false) continue
     const otherPorts = portsOf(other)
     if (!otherPorts) continue
 

packages/nodes/src/duct-segment/tool.tsx

@@ -552,8 +552,10 @@ const DuctSegmentTool = () => {
     // ceiling (centerline = ceiling height − radius).
     const resolveBaseY = (): number => {
       if (!ceilingModeRef.current) return 0
-      const ceiling = getLevelHeight(activeLevelId, useScene.getState().nodes, (wallId) =>
-        sceneRegistry.nodes.get(wallId)?.position.y,
+      const ceiling = getLevelHeight(
+        activeLevelId,
+        useScene.getState().nodes,
+        (wallId) => sceneRegistry.nodes.get(wallId)?.position.y,
       )
       const p = profileRef.current
       const verticalIn = p.shape === 'round' ? p.diameter : p.height

packages/nodes/src/pipe-trap/definition.ts

@@ -17,6 +17,7 @@ export const pipeTrapDefinition: NodeDefinition<typeof PipeTrapNode> = {
   schema: PipeTrapNode,
   category: 'utility',
   distributionRole: 'fitting',
+  portConnectivityFollow: false, // trap is anchored; dragging a connected run stretches the arm, not the trap
 
   defaults: () => ({
     object: 'node',

packages/nodes/src/shared/port-connectivity-pipe.test.ts

@@ -1,31 +1,25 @@
-import { beforeAll, describe, expect, test } from 'bun:test'
+import { afterEach, beforeEach, describe, expect, test } from 'bun:test'
 import {
-  analyzePortConnectivity,
   type AnyNode,
+  analyzePortConnectivity,
+  DuctSegmentNode,
   loadPlugin,
   nodeRegistry,
   PipeFittingNode,
   PipeSegmentNode,
+  PipeTrapNode,
   resolveConnectivityUpdates,
 } from '@pascal-app/core'
 import { builtinPlugin } from '../index'
 
-/**
- * Regression coverage for the generalized (HVAC duct + DWV pipe)
- * port-connectivity service. Before PR #402's follow-up fix the service
- * only tracked `duct-segment` / `duct-fitting`, so moving a `pipe-fitting`
- * left attached `pipe-segment` endpoints behind. These tests assert the
- * role-based generalization carries pipe runs along.
- */
-describe('port connectivity — DWV pipe family', () => {
-  beforeAll(async () => {
-    nodeRegistry._reset()
-    await loadPlugin(builtinPlugin)
-  })
+type Port = { id: string; position: [number, number, number] }
 
-  test('moving a pipe-fitting stretches the connected pipe-segment endpoint', () => {
-    // A sanitary tee at the origin; its run ports sit on ±X at the hub legs.
-    const fitting = PipeFittingNode.parse({
+function portsOf(kind: string, node: AnyNode): ReadonlyArray<Port> {
+  return nodeRegistry.get(kind)!.ports!(node) as ReadonlyArray<Port>
+}
+
+function wasteTee(): PipeFittingNode {
+  return PipeFittingNode.parse({
     object: 'node',
     parentId: null,
     visible: true,
@@ -38,27 +32,46 @@ describe('port connectivity — DWV pipe family', () => {
     position: [0, 0, 0],
     rotation: [0, 0, 0],
   })
+}
 
-    const fittingPorts = nodeRegistry.get('pipe-fitting')!.ports!(fitting) as ReadonlyArray<{
-      id: string
-      position: [number, number, number]
-    }>
-    const outlet = fittingPorts.find((p) => p.id === 'outlet')!
-
-    // A pipe run whose START port coincides with the fitting's outlet collar.
-    const run = PipeSegmentNode.parse({
+function pipeRunFrom(point: [number, number, number], system: 'waste' | 'vent' = 'waste') {
+  return PipeSegmentNode.parse({
     object: 'node',
     parentId: null,
     visible: true,
     metadata: {},
     diameter: 2,
     pipeMaterial: 'pvc',
-      system: 'waste',
-      path: [
-        [outlet.position[0], outlet.position[1], outlet.position[2]],
-        [outlet.position[0] + 3, outlet.position[1], outlet.position[2]],
-      ],
+    system,
+    path: [point, [point[0] + 3, point[1], point[2]]],
   })
+}
+
+/**
+ * Regression coverage for the generalized (HVAC duct + DWV pipe)
+ * port-connectivity service. Before PR #402's follow-up fix the service
+ * only tracked `duct-segment` / `duct-fitting`, so moving a `pipe-fitting`
+ * left attached `pipe-segment` endpoints behind. These tests assert the
+ * role-based generalization carries pipe runs along without fusing unrelated
+ * systems or anchored trap fixtures.
+ */
+describe('port connectivity — DWV pipe family', () => {
+  beforeEach(async () => {
+    nodeRegistry._reset()
+    await loadPlugin(builtinPlugin)
+  })
+
+  afterEach(() => {
+    nodeRegistry._reset()
+  })
+
+  test('moving a pipe-fitting stretches the connected pipe-segment endpoint', () => {
+    // A sanitary tee at the origin; its run ports sit on ±X at the hub legs.
+    const fitting = wasteTee()
+    const outlet = portsOf('pipe-fitting', fitting as AnyNode).find((p) => p.id === 'outlet')!
+
+    // A pipe run whose START port coincides with the fitting's outlet collar.
+    const run = pipeRunFrom(outlet.position)
 
     const nodes: Record<string, AnyNode> = {
       [fitting.id]: fitting as AnyNode,
@@ -84,45 +97,55 @@ describe('port connectivity — DWV pipe family', () => {
   })
 
   test('incompatible systems do not fuse (a supply duct is not dragged by a waste fitting)', () => {
-    const fitting = PipeFittingNode.parse({
-      object: 'node',
-      parentId: null,
-      visible: true,
-      metadata: {},
-      fittingType: 'sanitary-tee',
-      diameter: 2,
-      diameter2: 2,
-      pipeMaterial: 'pvc',
-      system: 'waste',
-      position: [0, 0, 0],
-      rotation: [0, 0, 0],
-    })
-    const fittingPorts = nodeRegistry.get('pipe-fitting')!.ports!(fitting) as ReadonlyArray<{
-      id: string
-      position: [number, number, number]
-    }>
-    const outlet = fittingPorts.find((p) => p.id === 'outlet')!
+    const fitting = wasteTee()
+    const outlet = portsOf('pipe-fitting', fitting as AnyNode).find((p) => p.id === 'outlet')!
 
-    // A vent pipe sharing the same point but a different system.
-    const ventRun = PipeSegmentNode.parse({
+    // A supply duct sharing the same point but a different distribution system.
+    const duct = DuctSegmentNode.parse({
       object: 'node',
       parentId: null,
       visible: true,
       metadata: {},
-      diameter: 2,
-      pipeMaterial: 'pvc',
-      system: 'vent',
-      path: [
-        [outlet.position[0], outlet.position[1], outlet.position[2]],
-        [outlet.position[0] + 3, outlet.position[1], outlet.position[2]],
-      ],
+      diameter: 6,
+      ductMaterial: 'flex',
+      system: 'supply',
+      path: [outlet.position, [outlet.position[0] + 3, outlet.position[1], outlet.position[2]]],
     })
 
     const nodes: Record<string, AnyNode> = {
       [fitting.id]: fitting as AnyNode,
-      [ventRun.id]: ventRun as AnyNode,
+      [duct.id]: duct as AnyNode,
     }
     const connectivity = analyzePortConnectivity(fitting as AnyNode, nodes)
-    expect(connectivity.connections.find((c) => c.nodeId === ventRun.id)).toBeUndefined()
+    expect(connectivity.connections.find((c) => c.nodeId === duct.id)).toBeUndefined()
+  })
+
+  test('pipe-trap is anchored when a connected pipe endpoint moves', () => {
+    const trap = PipeTrapNode.parse({
+      object: 'node',
+      parentId: null,
+      visible: true,
+      metadata: {},
+      position: [0, 0, 0],
+      rotation: 0,
+      diameter: 1.5,
+      pipeMaterial: 'pvc',
+      armLengthM: 0,
+    })
+    const outlet = portsOf('pipe-trap', trap as AnyNode).find((p) => p.id === 'outlet')!
+    const run = pipeRunFrom(outlet.position)
+
+    const nodes: Record<string, AnyNode> = {
+      [trap.id]: trap as AnyNode,
+      [run.id]: run as AnyNode,
+    }
+
+    // Moving the run endpoint must not translate the fixed-position trap.
+    const runConnectivity = analyzePortConnectivity(run as AnyNode, nodes)
+    expect(runConnectivity.connections.find((c) => c.nodeId === trap.id)).toBeUndefined()
+
+    // Moving the trap itself still stretches the connected run endpoint.
+    const trapConnectivity = analyzePortConnectivity(trap as AnyNode, nodes)
+    expect(trapConnectivity.connections.find((c) => c.nodeId === run.id)).toBeDefined()
   })
 })

packages/viewer/src/systems/level/level-system.tsx

@@ -39,8 +39,10 @@ export const LevelSystem = () => {
       obj.position.y = lerp(obj.position.y, targetY, delta * 12) // Smoothly animate to new Y position
       obj.visible = levelMode !== 'solo' || level?.id === selectedLevel || !selectedLevel
 
-      cumulativeY += getLevelHeight(levelId, nodes, (wallId) =>
-        sceneRegistry.nodes.get(wallId)?.position.y,
+      cumulativeY += getLevelHeight(
+        levelId,
+        nodes,
+        (wallId) => sceneRegistry.nodes.get(wallId)?.position.y,
       )
     }
   }, 5) // Using a lower priority so it runs after transforms from other systems have settled

packages/viewer/src/systems/level/level-utils.ts

@@ -41,8 +41,10 @@ export function snapLevelsToTruePositions(): () => void {
   for (const { levelId, obj } of entries) {
     obj.position.y = cumulativeY
     obj.visible = true
-    cumulativeY += getLevelHeight(levelId, nodes, (wallId) =>
-      sceneRegistry.nodes.get(wallId)?.position.y,
+    cumulativeY += getLevelHeight(
+      levelId,
+      nodes,
+      (wallId) => sceneRegistry.nodes.get(wallId)?.position.y,
     )
   }