feat(node-modal): sanitize parent_id on type change and exclude descendants

- App.tsx: filter descendants of edited node from parentCandidates to
  prevent picking a child as parent (would create a cycle).
- NodeModal.tsx: clear parent_id when switching to a type with no valid
  parents, and revalidate parent_id on submit against the type's allowlist.
- Tests: cover getValidParentTypes for lxc/vm/docker_container and types
  that disallow parents.

ha-relevant: yes

frontend/src/App.tsx

@@ -561,7 +561,24 @@ export default function App() {
           onSubmit={handleUpdateNode}
           initial={editNode?.data}
           title="Edit Node"
-          parentCandidates={nodes.map((n) => ({ id: n.id, label: n.data.label ?? n.id, type: n.data.type }))}
+          parentCandidates={(() => {
+            const descendants = new Set<string>()
+            if (editNodeId) {
+              const queue = [editNodeId]
+              while (queue.length) {
+                const id = queue.shift()!
+                for (const n of nodes) {
+                  if (n.data.parent_id === id && !descendants.has(n.id)) {
+                    descendants.add(n.id)
+                    queue.push(n.id)
+                  }
+                }
+              }
+            }
+            return nodes
+              .filter((n) => !descendants.has(n.id))
+              .map((n) => ({ id: n.id, label: n.data.label ?? n.id, type: n.data.type }))
+          })()}
           currentNodeId={editNodeId ?? undefined}
         />
 

frontend/src/components/modals/NodeModal.tsx

@@ -95,8 +95,17 @@ export function NodeModal({ open, onClose, onSubmit, initial, title = 'Add Node'
     setLabelError(false)
     const selectedType = (form.type ?? 'generic') as NodeType
     const canUseContainerMode = CONTAINER_MODE_TYPES.includes(selectedType)
+    const validParentTypes = getValidParentTypes(selectedType)
+    let safeParentId = form.parent_id
+    if (validParentTypes.length === 0) {
+      safeParentId = undefined
+    } else if (safeParentId) {
+      const parent = parentCandidates.find((n) => n.id === safeParentId)
+      if (!parent || !validParentTypes.includes(parent.type)) safeParentId = undefined
+    }
     onSubmit({
       ...form,
+      parent_id: safeParentId,
       container_mode: canUseContainerMode ? !!form.container_mode : false,
     })
     onClose()
@@ -116,7 +125,12 @@ export function NodeModal({ open, onClose, onSubmit, initial, title = 'Add Node'
               <Label className="text-xs text-muted-foreground">Type</Label>
               <Select value={form.type} onValueChange={(v) => {
                 const t = v as NodeType
-                setForm((f) => ({ ...f, type: t, ...(ZIGBEE_TYPES.includes(t) ? { check_method: 'none' as CheckMethod } : {}) }))
+                setForm((f) => {
+                  const next: Partial<NodeData> = { ...f, type: t }
+                  if (ZIGBEE_TYPES.includes(t)) next.check_method = 'none' as CheckMethod
+                  if (getValidParentTypes(t).length === 0) next.parent_id = undefined
+                  return next
+                })
               }}>
                 <SelectTrigger className={`bg-[#21262d] border-[#30363d] text-sm h-8 w-full cursor-pointer ${modalStyles['modal-interactive']} ${modalStyles['modal-radius']}`} aria-label="Node type selector">
                   <SelectValue>{NODE_TYPE_LABELS[(form.type ?? 'server') as NodeType]}</SelectValue>

frontend/src/utils/__tests__/virtualEdgeParent.test.ts

@@ -1,5 +1,26 @@
 import { describe, it, expect } from 'vitest'
-import { resolveVirtualEdgeParent } from '../virtualEdgeParent'
+import { resolveVirtualEdgeParent, getValidParentTypes } from '../virtualEdgeParent'
+
+describe('getValidParentTypes', () => {
+  it('returns container-mode types for lxc', () => {
+    expect(getValidParentTypes('lxc')).toEqual(['proxmox', 'vm', 'lxc', 'docker_host'])
+  })
+
+  it('returns container-mode types for vm', () => {
+    expect(getValidParentTypes('vm')).toEqual(['proxmox', 'vm', 'lxc', 'docker_host'])
+  })
+
+  it('returns docker_host/lxc/vm/proxmox for docker_container', () => {
+    expect(getValidParentTypes('docker_container')).toEqual(['docker_host', 'lxc', 'vm', 'proxmox'])
+  })
+
+  it('returns empty list for types that cannot have a parent', () => {
+    expect(getValidParentTypes('server')).toEqual([])
+    expect(getValidParentTypes('router')).toEqual([])
+    expect(getValidParentTypes('proxmox')).toEqual([])
+    expect(getValidParentTypes('docker_host')).toEqual([])
+  })
+})
 
 describe('resolveVirtualEdgeParent', () => {
   it('nests lxc under proxmox (container-mode parent)', () => {