diff --git a/src/plugin/operationHistory.ts b/src/plugin/operationHistory.ts
index 83366fb3..0c5ce3a6 100644
--- a/src/plugin/operationHistory.ts
+++ b/src/plugin/operationHistory.ts
@@ -88,6 +88,12 @@ export default function (mei: MindElixirInstance) {
       }
     }
   }
+  mei.clearHistory = function () {
+    history = []
+    currentIndex = -1
+    current = mei.getData()
+    mei.clearSelection()
+  }
   const handleOperation = function (operation: Operation) {
     if (operation.name === 'beginEdit') return
     history = history.slice(0, currentIndex + 1)
diff --git a/src/types/index.ts b/src/types/index.ts
index ef130cf7..4d7f57a9 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -121,6 +121,15 @@ export interface MindElixirInstance extends Omit<Required<Options>, 'markdown' |
   history: Operation[]
   undo: () => void
   redo: () => void
+  /**
+   * Reset the undo/redo stack and update the internal baseline snapshot to the
+   * current diagram state. Call this after loading new data into an existing
+   * instance (e.g. after `refresh()`) to prevent users from undoing back into
+   * a previously loaded diagram.
+   *
+   * Only available when `allowUndo` is `true` (the default).
+   */
+  clearHistory?: () => void
 
   selection: SelectionArea
   dragMoveHelper: ReturnType<typeof createDragMoveHelper>
diff --git a/tests/clear-history.spec.ts b/tests/clear-history.spec.ts
new file mode 100644
index 00000000..ca738df5
--- /dev/null
+++ b/tests/clear-history.spec.ts
@@ -0,0 +1,105 @@
+import { test, expect } from './mind-elixir-test'
+
+const diagramA = {
+  nodeData: {
+    id: 'root-a',
+    topic: 'Diagram A',
+    children: [{ id: 'child-a', topic: 'Child A' }],
+  },
+}
+
+const diagramB = {
+  nodeData: {
+    id: 'root-b',
+    topic: 'Diagram B',
+    children: [{ id: 'child-b', topic: 'Child B' }],
+  },
+}
+
+test.beforeEach(async ({ me }) => {
+  await me.init(diagramA)
+})
+
+test('clearHistory - undo cannot revert into pre-refresh diagram', async ({ page, me }) => {
+  // Perform an operation in Diagram A
+  await me.click('Child A')
+  await page.keyboard.press('Tab')
+  await page.keyboard.press('Enter')
+  await expect(me.getByText('New Node')).toBeVisible()
+
+  // Load Diagram B and clear the history stack
+  await page.evaluate((data: typeof diagramB) => {
+    const mind = (window as any)['#map']
+    mind.refresh(data)
+    mind.clearHistory()
+  }, diagramB)
+
+  await expect(me.getByText('Diagram B')).toBeVisible()
+  await expect(me.getByText('Diagram A')).toBeHidden()
+
+  // Undo should be a no-op — must not travel back into Diagram A
+  await page.keyboard.press('Control+z')
+  await expect(me.getByText('Diagram B')).toBeVisible()
+  await expect(me.getByText('Diagram A')).toBeHidden()
+
+  // Redo should also be a no-op
+  await page.keyboard.press('Control+y')
+  await expect(me.getByText('Diagram B')).toBeVisible()
+  await expect(me.getByText('Diagram A')).toBeHidden()
+})
+
+test('clearHistory - operations after clearHistory are undoable normally', async ({ page, me }) => {
+  // Perform an operation in Diagram A, then switch to Diagram B and clear history
+  await me.click('Child A')
+  await page.keyboard.press('Delete')
+  await expect(me.getByText('Child A')).toBeHidden()
+
+  await page.evaluate((data: typeof diagramB) => {
+    const mind = (window as any)['#map']
+    mind.refresh(data)
+    mind.clearHistory()
+  }, diagramB)
+
+  await expect(me.getByText('Diagram B')).toBeVisible()
+
+  // Add a node to Diagram B
+  await me.click('Child B')
+  await page.keyboard.press('Tab')
+  await page.keyboard.press('Enter')
+  await expect(me.getByText('New Node')).toBeVisible()
+
+  // Undo the add — should work
+  await page.keyboard.press('Control+z')
+  await expect(me.getByText('New Node')).toBeHidden()
+  await expect(me.getByText('Diagram B')).toBeVisible()
+
+  // Another undo should be a no-op — must not reach Diagram A
+  await page.keyboard.press('Control+z')
+  await expect(me.getByText('Diagram B')).toBeVisible()
+  await expect(me.getByText('Diagram A')).toBeHidden()
+
+  // Redo restores the added node
+  await page.keyboard.press('Control+y')
+  await expect(me.getByText('New Node')).toBeVisible()
+})
+
+test('clearHistory - first undo baseline is the refreshed diagram state', async ({ page, me }) => {
+  // Switch to Diagram B and clear history
+  await page.evaluate((data: typeof diagramB) => {
+    const mind = (window as any)['#map']
+    mind.refresh(data)
+    mind.clearHistory()
+  }, diagramB)
+
+  // Add a node to Diagram B
+  await me.click('Child B')
+  await page.keyboard.press('Tab')
+  await page.keyboard.press('Enter')
+  await expect(me.getByText('New Node')).toBeVisible()
+
+  // Undo should restore exactly to the post-refresh state of Diagram B
+  await page.keyboard.press('Control+z')
+  await expect(me.getByText('New Node')).toBeHidden()
+  await expect(me.getByText('Child B')).toBeVisible()
+  await expect(me.getByText('Diagram B')).toBeVisible()
+})