fix: use deterministic positions for group membership check on header drag

The previous implementation called getNodes() in handlePointerUp which
could return stale pre-drag positions in React Flow's controlled mode,
causing nodes to remain in groups after being dragged out. Also only
checked the header node, not all selected nodes moved together.

Now calculates final positions from drag delta (startPos + clientDelta/zoom)
and iterates all entries in startPositions to check group membership for
every moved node.

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

src/components/nodes/FloatingNodeHeader.tsx

@@ -263,50 +263,56 @@ export function FloatingNodeHeader({
       }
     };
 
-    const handlePointerUp = () => {
+    const handlePointerUp = (e: PointerEvent) => {
       const wasDragging = isDraggingRef.current;
 
       document.removeEventListener('pointermove', handlePointerMove);
       document.removeEventListener('pointerup', handlePointerUp);
       isDraggingRef.current = false;
 
-      // Check group membership if the node was actually dragged
+      // Check group membership for ALL moved nodes
       if (wasDragging) {
         const store = useWorkflowStore.getState();
-        const allNodes = getNodes();
-        const draggedNode = allNodes.find(n => n.id === id);
-
-        if (!draggedNode) return;
-
-        // Get node dimensions (prefer measured, fallback to defaults)
-        const defaults = defaultNodeDimensions[type] || { width: 300, height: 280 };
-        const nodeWidth = draggedNode.measured?.width || (draggedNode.style?.width as number) || defaults.width;
-        const nodeHeight = draggedNode.measured?.height || (draggedNode.style?.height as number) || defaults.height;
-
-        // Calculate node center
-        const nodeCenterX = draggedNode.position.x + nodeWidth / 2;
-        const nodeCenterY = draggedNode.position.y + nodeHeight / 2;
-
-        // Check if node center is inside any group
-        let targetGroupId: string | undefined;
-
-        for (const group of Object.values(store.groups)) {
-          const inBoundsX = nodeCenterX >= group.position.x && nodeCenterX <= group.position.x + group.size.width;
-          const inBoundsY = nodeCenterY >= group.position.y && nodeCenterY <= group.position.y + group.size.height;
-
-          if (inBoundsX && inBoundsY) {
-            targetGroupId = group.id;
-            break;
+        const { zoom } = getViewport();
+        const dx = (e.clientX - startX) / zoom;
+        const dy = (e.clientY - startY) / zoom;
+
+        for (const [nodeId, startPos] of startPositions) {
+          // Calculate final position deterministically from drag delta
+          const finalX = startPos.x + dx;
+          const finalY = startPos.y + dy;
+
+          // Get node dimensions from store (always fresh)
+          const storeNode = store.nodes.find(n => n.id === nodeId);
+          if (!storeNode) continue;
+
+          const nodeType = storeNode.type as NodeType;
+          const defaults = defaultNodeDimensions[nodeType] || { width: 300, height: 280 };
+          const nodeWidth = storeNode.measured?.width || (storeNode.style?.width as number) || defaults.width;
+          const nodeHeight = storeNode.measured?.height || (storeNode.style?.height as number) || defaults.height;
+
+          // Calculate node center
+          const nodeCenterX = finalX + nodeWidth / 2;
+          const nodeCenterY = finalY + nodeHeight / 2;
+
+          // Check if node center is inside any group
+          let targetGroupId: string | undefined;
+
+          for (const group of Object.values(store.groups)) {
+            const inBoundsX = nodeCenterX >= group.position.x && nodeCenterX <= group.position.x + group.size.width;
+            const inBoundsY = nodeCenterY >= group.position.y && nodeCenterY <= group.position.y + group.size.height;
+
+            if (inBoundsX && inBoundsY) {
+              targetGroupId = group.id;
+              break;
+            }
           }
-        }
 
-        // Get the node's current groupId
-        const currentNode = store.nodes.find((n) => n.id === id);
-        const currentGroupId = currentNode?.groupId;
-
-        // Update groupId if it changed
-        if (targetGroupId !== currentGroupId) {
-          store.setNodeGroupId(id, targetGroupId);
+          // Update groupId if it changed
+          const currentGroupId = storeNode.groupId;
+          if (targetGroupId !== currentGroupId) {
+            store.setNodeGroupId(nodeId, targetGroupId);
+          }
         }
       }
     };