Fixes threejs-0002: StackNode build() uses nodes.indexOf() inside filter callback —
O(n²) during shader graph compilation per unique node set comparison.

--- a/src/nodes/core/StackNode.js
+++ b/src/nodes/core/StackNode.js
@@ -380,7 +380,8 @@ class StackNode extends Node {
     this._currentNode = null;

-    const newNodes = this.nodes.filter( ( node ) => nodes.indexOf( node ) === - 1 );
+    // FIX threejs-0002: nodes.indexOf() inside filter = O(n²) — CWE-407
+    const nodesSet = new Set( nodes );                                    // O(n) build once
+    const newNodes = this.nodes.filter( ( node ) => ! nodesSet.has( node ) ); // O(1) per check