fix(canvas): allow undo after Auto Layout and YAML import

Auto Layout and YAML import routed through loadCanvas, which wipes
past/future history and clears the unsaved flag (design-switch
semantics). Undo was therefore impossible after either action (#280).

Add an in-place applyLayout store action that snapshots history, marks
the canvas unsaved and re-fits the view without discarding undo history,
and wire both Auto Layout and YAML import to it.

ha-relevant: yes

frontend/src/App.tsx

@@ -53,7 +53,7 @@ import { buildProxmoxClusterEdges } from '@/components/proxmox/clusterEdges'
 const STANDALONE = import.meta.env.VITE_STANDALONE === 'true'
 
 export default function App() {
-  const { loadCanvas, markSaved, markUnsaved, selectedNodeId, selectedNodeIds, addNode, updateNode, deleteNode, onConnect, updateEdge, deleteEdge, setProxmoxContainerMode, setNodeZIndex, editingGroupRectId, setEditingGroupRectId, editingTextId, setEditingTextId, nodes, edges, snapshotHistory, undo, redo, addToGroup, addToContainer, floorMap, setFloorMap } = useCanvasStore()
+  const { loadCanvas, applyLayout, markSaved, markUnsaved, selectedNodeId, selectedNodeIds, addNode, updateNode, deleteNode, onConnect, updateEdge, deleteEdge, setProxmoxContainerMode, setNodeZIndex, editingGroupRectId, setEditingGroupRectId, editingTextId, setEditingTextId, nodes, edges, snapshotHistory, undo, redo, addToGroup, addToContainer, floorMap, setFloorMap } = useCanvasStore()
   const canvasRef = useRef<HTMLDivElement>(null)
   const { isAuthenticated } = useAuthStore()
   const { activeTheme, setTheme, customStyle, setCustomStyle } = useThemeStore()
@@ -498,9 +498,11 @@ export default function App() {
 
   const handleAutoLayout = useCallback(() => {
     const laid = applyDagreLayout(nodes, edges)
-    loadCanvas(laid, edges)
+    // applyLayout keeps undo history so the user can revert an accidental
+    // Auto Layout (#280); loadCanvas would wipe it.
+    applyLayout(laid, edges)
     toast.success('Canvas auto-arranged')
-  }, [nodes, edges, loadCanvas])
+  }, [nodes, edges, applyLayout])
 
   const handleExportMd = useCallback(async () => {
     const md = generateMarkdownTable(nodes)
@@ -522,14 +524,14 @@ export default function App() {
   const handleImportYaml = useCallback((content: string) => {
     try {
       const { nodes: merged, edges: mergedEdges, imported } = parseYamlToCanvas(content, nodes, edges)
-      snapshotHistory()
-      loadCanvas(merged, mergedEdges)
-      markUnsaved()
+      // applyLayout keeps undo history so an import can be reverted; loadCanvas
+      // would wipe it (#280).
+      applyLayout(merged, mergedEdges)
       toast.success(`Imported ${imported} node${imported !== 1 ? 's' : ''}`)
     } catch (err) {
       toast.error(`Import failed: ${err instanceof Error ? err.message : String(err)}`)
     }
-  }, [nodes, edges, snapshotHistory, loadCanvas, markUnsaved])
+  }, [nodes, edges, applyLayout])
 
   // Open the read-only live view of the currently active design in a new tab.
   // Standalone has no backend/key — it reads localStorage, so just open /view.

frontend/src/stores/__tests__/canvasStore/history.test.ts

@@ -85,4 +85,31 @@ describe('canvasStore — history', () => {
     addNode(makeNode('n3'))
     expect(useCanvasStore.getState().future).toHaveLength(0)
   })
+
+  // --- Auto Layout keeps history so it can be undone (#280) ---
+
+  it('applyLayout snapshots history and can be undone', () => {
+    const { addNode, applyLayout, undo } = useCanvasStore.getState()
+    addNode(makeNode('n1'))
+    const before = useCanvasStore.getState().nodes
+    // simulate an auto-layout that moves the node
+    applyLayout([{ ...before[0], position: { x: 500, y: 500 } }], [])
+    expect(useCanvasStore.getState().nodes[0].position).toEqual({ x: 500, y: 500 })
+    expect(useCanvasStore.getState().past).toHaveLength(1)
+    undo()
+    expect(useCanvasStore.getState().nodes[0].position).toEqual({ x: 0, y: 0 })
+  })
+
+  it('applyLayout marks the canvas unsaved and clears future', () => {
+    const { addNode, snapshotHistory, undo, applyLayout } = useCanvasStore.getState()
+    addNode(makeNode('n1'))
+    snapshotHistory()
+    addNode(makeNode('n2'))
+    undo() // creates a future entry
+    expect(useCanvasStore.getState().future).toHaveLength(1)
+    applyLayout(useCanvasStore.getState().nodes, [])
+    const s = useCanvasStore.getState()
+    expect(s.hasUnsavedChanges).toBe(true)
+    expect(s.future).toHaveLength(0)
+  })
 })

frontend/src/stores/canvasStore.ts

@@ -147,6 +147,10 @@ interface CanvasState {
   markSaved: () => void
   markUnsaved: () => void
   loadCanvas: (nodes: Node<NodeData>[], edges: Edge<EdgeData>[]) => void
+  /** In-place canvas replacement (e.g. Auto Layout) that KEEPS undo history and
+   *  marks the canvas unsaved. Unlike loadCanvas, it does not wipe past/future —
+   *  loadCanvas is for switching designs, this is for transforming the current one. */
+  applyLayout: (nodes: Node<NodeData>[], edges: Edge<EdgeData>[]) => void
   fitViewPending: boolean
   clearFitViewPending: () => void
   notifyScanDeviceFound: () => void
@@ -870,6 +874,22 @@ export const useCanvasStore = create<CanvasState>((set) => ({
     set({ nodes: [...parents, ...children], edges, hasUnsavedChanges: false, selectedNodeId: null, past: [], future: [], fitViewPending: true })
   },
 
+  applyLayout: (nodes, edges) =>
+    set((state) => {
+      // React Flow requires parents before children in the array
+      const parents = nodes.filter((n) => !n.parentId)
+      const children = nodes.filter((n) => !!n.parentId)
+      return {
+        nodes: [...parents, ...children],
+        edges,
+        past: [...state.past.slice(-49), { nodes: state.nodes, edges: state.edges }],
+        future: [],
+        hasUnsavedChanges: true,
+        selectedNodeId: null,
+        fitViewPending: true,
+      }
+    }),
+
   clearFitViewPending: () => set({ fitViewPending: false }),
 
   applyTypeNodeStyle: (nodeType, style) =>