Поправил логику проверки удаления узлов

src/DiagramEditor.tsx

@@ -259,17 +259,25 @@ function DiagramCanvas({ initialValue, onChange }: DiagramEditorProps) {
     setSelectedEdgeId(null);
   }, []);
 
-  const onNodesChange = useCallback(
-    (changes: NodeChange[]) => {
-      const withChildren = new Set(nodes.filter((n) => n.parentId).map((n) => n.parentId!));
-      const filteredChanges = changes.filter((change) => {
-        if (change.type !== 'remove' || !withChildren.has(change.id)) return true;
+  // Runs before React Flow computes any removal changes at all (for both
+  // nodes and their connected edges), so blocking here — unlike filtering
+  // inside onNodesChange — stops the connected edges from being deleted too.
+  const onBeforeDelete = useCallback(
+    async ({ nodes: nodesToDelete }: { nodes: Node[]; edges: Edge[] }) => {
+      const hasContainerNode = nodesToDelete.some((node) => nodes.some((n) => n.parentId === node.id));
+      if (hasContainerNode) {
         window.alert('Сначала удалите вложенные узлы — у этого узла есть под-процесс.');
         return false;
-      });
+      }
+      return true;
+    },
+    [nodes],
+  );
 
-      const positionChanges = filteredChanges.filter((c) => c.type === 'position' && c.position);
-      let adjustedChanges = filteredChanges;
+  const onNodesChange = useCallback(
+    (changes: NodeChange[]) => {
+      const positionChanges = changes.filter((c) => c.type === 'position' && c.position);
+      let adjustedChanges = changes;
       if (positionChanges.length === 1) {
         const change = positionChanges[0];
         const draggedNode = change.type === 'position' ? nodes.find((n) => n.id === change.id) : undefined;
@@ -286,7 +294,7 @@ function DiagramCanvas({ initialValue, onChange }: DiagramEditorProps) {
           };
           const snapped = computeSnapAndGuides(dragged, others);
           setAlignmentGuides(change.dragging === false ? [] : snapped.guides);
-          adjustedChanges = filteredChanges.map((c) =>
+          adjustedChanges = changes.map((c) =>
             c === change ? { ...c, position: { x: snapped.x, y: snapped.y } } : c,
           );
         }
@@ -294,7 +302,7 @@ function DiagramCanvas({ initialValue, onChange }: DiagramEditorProps) {
         setAlignmentGuides([]);
       }
 
-      const isHistoryWorthy = filteredChanges.some(
+      const isHistoryWorthy = changes.some(
         (change) =>
           change.type === 'remove' ||
           (change.type === 'position' && change.dragging === false) ||
@@ -308,7 +316,7 @@ function DiagramCanvas({ initialValue, onChange }: DiagramEditorProps) {
       // emitChange — filtering edges here too (redundantly with onEdgesChange)
       // guarantees a removed node never leaves a dangling edge behind.
       const removedIds = new Set(
-        filteredChanges.filter((change) => change.type === 'remove').map((change) => change.id),
+        changes.filter((change) => change.type === 'remove').map((change) => change.id),
       );
       const nextEdges = removedIds.size
         ? edges.filter((edge) => !removedIds.has(edge.source) && !removedIds.has(edge.target))
@@ -574,6 +582,7 @@ function DiagramCanvas({ initialValue, onChange }: DiagramEditorProps) {
             onEdgesChange={onEdgesChange}
             onConnect={onConnect}
             onReconnect={onReconnect}
+            onBeforeDelete={onBeforeDelete}
             edgesReconnectable={mode === 'edit'}
             onNodeClick={onNodeClick}
             onEdgeClick={onEdgeClick}