diff --git a/package.json b/package.json
index e793b7f..45299b3 100644
--- a/package.json
+++ b/package.json
@@ -28,7 +28,6 @@
     "react": "18.2.0",
     "react-dom": "18.2.0",
     "react-zoom-pan-pinch": "^3.7.0",
-    "reactflow": "^11.0.0",
     "tailwind-merge": "^3.5.0",
     "tailwindcss-animate": "^1.0.7"
   },
diff --git a/src/App.tsx b/src/App.tsx
index b8a9b1e..1e80c66 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -39,6 +39,7 @@ import {
   getDefaultStyle,
   isConnectionAllowed,
 } from './lib/nodeRegistry'
+import type { AppNode, AppEdge } from './lib/nodeTypes'
 
 const SNAP_GRID: [number, number] = [15, 15]
 const snapToGrid = (x: number, y: number): { x: number; y: number } => ({
@@ -46,7 +47,7 @@ const snapToGrid = (x: number, y: number): { x: number; y: number } => ({
   y: Math.round(y / SNAP_GRID[1]) * SNAP_GRID[1],
 })
 
-const initialNodes: Node[] = [
+const initialNodes: AppNode[] = [
   {
     id: 'cfg_001',
     position: { x: 50, y: 50 },
@@ -63,11 +64,14 @@ const initialNodes: Node[] = [
   },
 ]
 
-const initialEdges: Edge[] = [
+const initialEdges: AppEdge[] = [
   { id: 'e-cfg_001-rnd_001', source: 'cfg_001', target: 'rnd_001', type: 'animated' },
 ]
 
 const PROJECT_FILE_EXT = '.zui.json'
+const PROJECT_VERSION = 1
+
+export type ProjectMessage = { type: 'success' | 'error'; text: string }
 
 export default function App() {
   const { theme } = useTheme()
@@ -91,6 +95,7 @@ export default function App() {
   const [rfInstance, setRfInstance] = React.useState<any | null>(null)
   const [renamingNodeId, setRenamingNodeId] = React.useState<string | null>(null)
   const [connectionFrom, setConnectionFrom] = React.useState<{ nodeId: string; sourceHandle?: string } | null>(null)
+  const [projectMessage, setProjectMessage] = React.useState<ProjectMessage | null>(null)
 
   const wrapperRef = React.useRef<HTMLDivElement | null>(null)
   const lastClickRef = React.useRef<{ clientX: number; clientY: number } | null>(null)
@@ -184,6 +189,12 @@ export default function App() {
     setRfInstance(instance)
   }, [])
 
+  React.useEffect(() => {
+    if (!projectMessage) return
+    const t = setTimeout(() => setProjectMessage(null), 3000)
+    return () => clearTimeout(t)
+  }, [projectMessage])
+
   const onNodeDragStart = useCallback(() => {
     saveForDragEnd()
   }, [saveForDragEnd])
@@ -193,7 +204,7 @@ export default function App() {
   }, [commitDragEnd])
 
   const handleExportProject = useCallback(() => {
-    const state = { nodes, edges }
+    const state = { version: PROJECT_VERSION, nodes, edges }
     const blob = new Blob([JSON.stringify(state, null, 2)], { type: 'application/json' })
     const url = URL.createObjectURL(blob)
     const a = document.createElement('a')
@@ -201,6 +212,7 @@ export default function App() {
     a.download = `project${PROJECT_FILE_EXT}`
     a.click()
     URL.revokeObjectURL(url)
+    setProjectMessage({ type: 'success', text: 'Project exported' })
   }, [nodes, edges])
 
   const handleImportProject = useCallback(() => {
@@ -216,11 +228,19 @@ export default function App() {
       reader.onload = () => {
         try {
           const text = reader.result as string
-          const state = JSON.parse(text) as { nodes?: Node[]; edges?: Edge[] }
-          if (!state || !Array.isArray(state.nodes) || !Array.isArray(state.edges)) return
-          setStateImmediate({ nodes: state.nodes, edges: state.edges })
+          const state = JSON.parse(text) as { version?: number; nodes?: unknown[]; edges?: unknown[] }
+          if (!state || !Array.isArray(state.nodes) || !Array.isArray(state.edges)) {
+            setProjectMessage({ type: 'error', text: 'Invalid file: expected nodes and edges arrays' })
+            return
+          }
+          setStateImmediate({ nodes: state.nodes as AppNode[], edges: state.edges as AppEdge[] })
+          setProjectMessage(
+            state.version != null && state.version > PROJECT_VERSION
+              ? { type: 'error', text: 'Project was created with a newer app version' }
+              : { type: 'success', text: 'Project loaded' }
+          )
         } catch {
-          // Invalid JSON
+          setProjectMessage({ type: 'error', text: 'Invalid file: not valid JSON' })
         }
       }
       reader.readAsText(file)
@@ -383,6 +403,18 @@ export default function App() {
         canUndo={canUndo}
         canRedo={canRedo}
       />
+      {projectMessage && (
+        <div
+          role="status"
+          className={`shrink-0 px-3 py-2 text-sm ${
+            projectMessage.type === 'success'
+              ? 'bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-200'
+              : 'bg-red-100 text-red-800 dark:bg-red-900/30 dark:text-red-200'
+          }`}
+        >
+          {projectMessage.text}
+        </div>
+      )}
       <div className="flex-1 min-h-0 relative flex flex-col">
         <div className="flex-1 min-h-0 flex flex-col">
           <FlowContext.Provider value={flowContextValue}>
diff --git a/src/hooks/useGraphStateWithHistory.ts b/src/hooks/useGraphStateWithHistory.ts
index 8276f79..2f4f9fb 100644
--- a/src/hooks/useGraphStateWithHistory.ts
+++ b/src/hooks/useGraphStateWithHistory.ts
@@ -1,7 +1,7 @@
 import { useCallback, useRef, useState } from 'react'
-import type { Node, Edge } from '@xyflow/react'
+import type { AppNode, AppEdge } from '@/lib/nodeTypes'
 
-export type GraphState = { nodes: Node[]; edges: Edge[] }
+export type GraphState = { nodes: AppNode[]; edges: AppEdge[] }
 
 function cloneState(state: GraphState): GraphState {
   return {
@@ -12,9 +12,9 @@ function cloneState(state: GraphState): GraphState {
 
 const MAX_HISTORY = 100
 
-export function useGraphStateWithHistory(initialNodes: Node[], initialEdges: Edge[]) {
-  const [nodes, setNodesState] = useState<Node[]>(initialNodes)
-  const [edges, setEdgesState] = useState<Edge[]>(initialEdges)
+export function useGraphStateWithHistory(initialNodes: AppNode[], initialEdges: AppEdge[]) {
+  const [nodes, setNodesState] = useState<AppNode[]>(initialNodes)
+  const [edges, setEdgesState] = useState<AppEdge[]>(initialEdges)
   const [historySizes, setHistorySizes] = useState({ past: 0, future: 0 })
 
   const pastRef = useRef<GraphState[]>([])
@@ -32,21 +32,21 @@ export function useGraphStateWithHistory(initialNodes: Node[], initialEdges: Edg
     setHistorySizes({ past: pastRef.current.length, future: 0 })
   }, [])
 
-  const setNodes = useCallback((updater: Node[] | ((prev: Node[]) => Node[])) => {
+  const setNodes = useCallback((updater: AppNode[] | ((prev: AppNode[]) => AppNode[])) => {
     pushToPast({ nodes: nodesRef.current, edges: edgesRef.current })
     setNodesState(typeof updater === 'function' ? updater : () => updater)
   }, [pushToPast])
 
-  const setEdges = useCallback((updater: Edge[] | ((prev: Edge[]) => Edge[])) => {
+  const setEdges = useCallback((updater: AppEdge[] | ((prev: AppEdge[]) => AppEdge[])) => {
     pushToPast({ nodes: nodesRef.current, edges: edgesRef.current })
     setEdgesState(typeof updater === 'function' ? updater : () => updater)
   }, [pushToPast])
 
-  const setNodesSilent = useCallback((updater: Node[] | ((prev: Node[]) => Node[])) => {
+  const setNodesSilent = useCallback((updater: AppNode[] | ((prev: AppNode[]) => AppNode[])) => {
     setNodesState(typeof updater === 'function' ? updater : () => updater)
   }, [])
 
-  const setEdgesSilent = useCallback((updater: Edge[] | ((prev: Edge[]) => Edge[])) => {
+  const setEdgesSilent = useCallback((updater: AppEdge[] | ((prev: AppEdge[]) => AppEdge[])) => {
     setEdgesState(typeof updater === 'function' ? updater : () => updater)
   }, [])
 
diff --git a/src/lib/flowContext.tsx b/src/lib/flowContext.tsx
index 9b5b0ee..4eaaf15 100644
--- a/src/lib/flowContext.tsx
+++ b/src/lib/flowContext.tsx
@@ -1,13 +1,14 @@
 import React from 'react'
 import type { Connection } from '@xyflow/react'
+import type { AppNode, AppEdge } from '@/lib/nodeTypes'
 
 export type ConnectionFrom = { nodeId: string; sourceHandle?: string } | null
 
 export type FlowContextValue = {
-    nodes: any[]
-    setNodes: (updater: any) => void
-    edges: any[]
-    setEdges: (updater: any) => void
+    nodes: AppNode[]
+    setNodes: (updater: AppNode[] | ((prev: AppNode[]) => AppNode[])) => void
+    edges: AppEdge[]
+    setEdges: (updater: AppEdge[] | ((prev: AppEdge[]) => AppEdge[])) => void
     renamingNodeId: string | null
     setRenamingNodeId: (id: string | null) => void
     /** Set when user starts dragging from an output handle; cleared on connect end. Used to highlight valid targets. */
diff --git a/src/lib/nodeTypes.ts b/src/lib/nodeTypes.ts
new file mode 100644
index 0000000..942c370
--- /dev/null
+++ b/src/lib/nodeTypes.ts
@@ -0,0 +1,13 @@
+/**
+ * Central node and edge types for the app. Use AppNode / AppEdge in graph state and context.
+ */
+
+import type { Node, Edge } from '@xyflow/react'
+import type { ConfigNodeData } from '@/components/nodes/ConfigNode'
+import type { RenderingNodeData } from '@/components/nodes/RenderingNode'
+import type { VariableNodeData } from '@/components/nodes/VariableNode'
+import type { FunctionNodeData } from '@/components/nodes/FunctionNode'
+
+export type AppNodeData = ConfigNodeData | RenderingNodeData | VariableNodeData | FunctionNodeData
+export type AppNode = Node<AppNodeData>
+export type AppEdge = Edge