Initialize nodePositions structure before nested access

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/stores/cytoscapeStore.ts

@@ -45,6 +45,12 @@ export const useCytoscapeStore = defineStore('cytoscapeStore', {
      * @param {string} direction - Layout direction ('TB' or 'LR').
      */
     saveNodePosition(nodeId: string, position: Position, direction: string) {
+      if (!this.nodePositions[this.currentGraphId]) {
+        this.nodePositions[this.currentGraphId] = {};
+      }
+      if (!this.nodePositions[this.currentGraphId][direction]) {
+        this.nodePositions[this.currentGraphId][direction] = [];
+      }
       // 若是資訊曾經存在這張圖於localStorage中
       if (localStorage.getItem(SAVE_KEY_NAME)) {
         const nodeToSave = this.nodePositions[this.currentGraphId][direction]
@@ -56,7 +62,6 @@ export const useCytoscapeStore = defineStore('cytoscapeStore', {
             .push({ id: nodeId, position: position });
         }
       } else {
-        this.nodePositions[this.currentGraphId][direction] = [];
         this.nodePositions[this.currentGraphId][direction]
           .push({ id: nodeId, position: position });
         localStorage.setItem(SAVE_KEY_NAME, JSON.stringify(this.nodePositions));