# UNDF: UNDF-2026-000000752
# UNDF: (leave blank)
--- a/src/nodes/core/NodeBuilder.js
+++ b/src/nodes/core/NodeBuilder.js
@@ -137,6 +137,13 @@ class NodeBuilder {
 		 * @type {Array<Node>}
 		 */
 		this.nodes = [];
+
+		// O(1) membership guard for this.nodes and this.sequentialNodes.
+		// this.nodes.includes(node) is O(N) and is called once per node during
+		// the shader build traversal, making addNode() O(N²) for graphs with N
+		// nodes.  A Set<Node> reduces each membership test to O(1), giving O(N)
+		// total build cost.  CWE-407.
+		this._nodesSet = new Set();
+		this._sequentialNodesSet = new Set();

 		/**
 		 * A list of all nodes the builder is processing in sequential order.
@@ -762,8 +762,8 @@ class NodeBuilder {
 	addNode( node ) {

-		if ( this.nodes.includes( node ) === false ) {
+		if ( this._nodesSet.has( node ) === false ) {

 			this.nodes.push( node );
+			this._nodesSet.add( node );

 			this.setHashNode( node, node.getHash( this ) );

@@ -785,8 +785,8 @@ class NodeBuilder {
 			if ( updateBeforeType !== NodeUpdateType.NONE || updateAfterType !== NodeUpdateType.NONE ) {

-			if ( this.sequentialNodes.includes( node ) === false ) {
+			if ( this._sequentialNodesSet.has( node ) === false ) {

 				this.sequentialNodes.push( node );
+				this._sequentialNodesSet.add( node );

 			}

--- a/src/nodes/core/StackNode.js
+++ b/src/nodes/core/StackNode.js
@@ -382,7 +382,9 @@ class StackNode extends Node {
 		this._currentNode = null;

-		const newNodes = this.nodes.filter( ( node ) => nodes.indexOf( node ) === - 1 );
+		// nodes.indexOf(node) is O(N) inside filter → O(N²) overall.
+		// Use a Set for O(N) total.  CWE-407.
+		const nodesSnapshot = new Set( nodes );
+		const newNodes = this.nodes.filter( ( node ) => nodesSnapshot.has( node ) === false );

 		for ( const node of newNodes ) {