fix(rack-planner): resolve infinite re-render loop in ConnectionLayer and add null-safety for VLAN tooltips

client/src/components/rack/ConnectionLayer.tsx

@@ -40,11 +40,17 @@ export function ConnectionLayer() {
     // Also re-calculate if the user scrolls (though ideally lines are pinned to the canvas)
     // Actually, if SVG is INSIDE the scrollable container, we don't need scroll adjustment.
     
-    // We'll use a MutationObserver to detect DOM changes (like modules being added/moved)
-    const observer = new MutationObserver(updateCoords);
+    // Use a MutationObserver to detect DOM changes (like modules being added/moved)
+    const observer = new MutationObserver(() => {
+      // Small debounce or check if it was our OWN SVG that changed
+      updateCoords();
+    });
+
     const canvas = document.querySelector('.rack-planner-canvas');
     if (canvas) {
-      observer.observe(canvas, { childList: true, subtree: true, attributes: true });
+      // DO NOT observe the entire subtree with attributes if it includes the ConnectionLayer
+      // Instead, just watch for module layout changes
+      observer.observe(canvas, { childList: true, subtree: true });
     }
 
     return () => {