diff --git a/src/App.tsx b/src/App.tsx
index e10384d..e0aa2b7 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback, useRef } from 'react';
+import { useState, useEffect, useCallback, useRef, useReducer } from 'react';
 import { addEdge, applyNodeChanges, applyEdgeChanges, type Node, type Edge, type Connection, type NodeChange, type EdgeChange } from '@xyflow/react';
 import TitleBar from './components/TitleBar';
 import ActivityBar from './components/ActivityBar';
@@ -66,44 +66,68 @@ export default function App() {
     }));
   }, [activeTransactionId]);
 
-  // Undo/redo
-  const [history, setHistory] = useState<HistoryEntry[]>([{ nodes: [], edges: [] }]);
-  const [historyIndex, setHistoryIndex] = useState(0);
+  // Undo/redo — combined into single state to prevent index/entries divergence
+  type HistoryState = { entries: HistoryEntry[]; index: number };
+  type HistoryAction =
+    | { type: 'push'; nodes: Node[]; edges: Edge[] }
+    | { type: 'undo' }
+    | { type: 'redo' }
+    | { type: 'reset' };
+
+  const historyReducer = useCallback((state: HistoryState, action: HistoryAction): HistoryState => {
+    switch (action.type) {
+      case 'push': {
+        const trimmed = state.entries.slice(0, state.index + 1);
+        const entry = { nodes: JSON.parse(JSON.stringify(action.nodes)), edges: JSON.parse(JSON.stringify(action.edges)) };
+        const next = [...trimmed, entry];
+        let newIndex = trimmed.length;
+        if (next.length > 50) {
+          next.shift();
+          newIndex = next.length - 1;
+        }
+        return { entries: next, index: newIndex };
+      }
+      case 'undo': {
+        if (state.index <= 0) return state;
+        return { ...state, index: state.index - 1 };
+      }
+      case 'redo': {
+        if (state.index >= state.entries.length - 1) return state;
+        return { ...state, index: state.index + 1 };
+      }
+      case 'reset': {
+        return { entries: [{ nodes: [], edges: [] }], index: 0 };
+      }
+    }
+  }, []);
+
+  const [historyState, dispatchHistory] = useReducer(historyReducer, { entries: [{ nodes: [], edges: [] }], index: 0 });
+  const history = historyState.entries;
+  const historyIndex = historyState.index;
   const skipHistoryRef = useRef(false);
 
   const pushHistory = useCallback((n: Node[], e: Edge[]) => {
     if (skipHistoryRef.current) { skipHistoryRef.current = false; return; }
-    setHistory(prev => {
-      const trimmed = prev.slice(0, historyIndex + 1);
-      const entry = { nodes: JSON.parse(JSON.stringify(n)), edges: JSON.parse(JSON.stringify(e)) };
-      const next = [...trimmed, entry];
-      if (next.length > 50) next.shift();
-      return next;
-    });
-    setHistoryIndex(prev => Math.min(prev + 1, 50));
-  }, [historyIndex]);
+    dispatchHistory({ type: 'push', nodes: n, edges: e });
+  }, []);
 
   const undo = useCallback(() => {
-    if (historyIndex <= 0) return;
-    const newIndex = historyIndex - 1;
-    const entry = history[newIndex];
-    if (!entry) return;
+    const entry = historyState.entries[historyState.index - 1];
+    if (!entry || historyState.index <= 0) return;
     skipHistoryRef.current = true;
-    setHistoryIndex(newIndex);
+    dispatchHistory({ type: 'undo' });
     setNodes(JSON.parse(JSON.stringify(entry.nodes)));
     setEdges(JSON.parse(JSON.stringify(entry.edges)));
-  }, [historyIndex, history, setNodes, setEdges]);
+  }, [historyState, setNodes, setEdges]);
 
   const redo = useCallback(() => {
-    if (historyIndex >= history.length - 1) return;
-    const newIndex = historyIndex + 1;
-    const entry = history[newIndex];
-    if (!entry) return;
+    const entry = historyState.entries[historyState.index + 1];
+    if (!entry || historyState.index >= historyState.entries.length - 1) return;
     skipHistoryRef.current = true;
-    setHistoryIndex(newIndex);
+    dispatchHistory({ type: 'redo' });
     setNodes(JSON.parse(JSON.stringify(entry.nodes)));
     setEdges(JSON.parse(JSON.stringify(entry.edges)));
-  }, [historyIndex, history, setNodes, setEdges]);
+  }, [historyState, setNodes, setEdges]);
 
   // Selected nodes
   const [selectedNodeIds, setSelectedNodeIds] = useState<Set<string>>(new Set());
@@ -359,8 +383,7 @@ export default function App() {
     const id = `tx-${Date.now()}`;
     setTransactionTabs(prev => [...prev, { id, name: `Transaction ${prev.length + 1}`, nodes: [], edges: [] }]);
     setActiveTransactionId(id);
-    setHistory([{ nodes: [], edges: [] }]);
-    setHistoryIndex(0);
+    dispatchHistory({ type: 'reset' });
     addTerminalEntry('info', 'system', 'New transaction tab created');
   }, [addTerminalEntry]);