diff --git a/src/e2e/iOS/__tests__/caret.ts b/src/e2e/iOS/__tests__/caret.ts
index 29e773dc8f0..d7b5fd26bbe 100644
--- a/src/e2e/iOS/__tests__/caret.ts
+++ b/src/e2e/iOS/__tests__/caret.ts
@@ -4,6 +4,7 @@
  */
 import gestures from '../../../test-helpers/gestures'
 import clickThought from '../helpers/clickThought'
+import doubleTap from '../helpers/doubleTap'
 import editThought from '../helpers/editThought'
 import gesture from '../helpers/gesture'
 import getEditable from '../helpers/getEditable'
@@ -251,4 +252,29 @@ describe('Caret', () => {
     expect(selectionTextContent).toBe('new')
     expect(childrenTexts).toEqual(['foo', 'bar'])
   })
+
+  it('Set caret on adjacent thought within 1 second (#4173)', async () => {
+    // Reproduces https://github.com/cybersemics/em/issues/4173: tapping an adjacent thought within
+    // ~1 second of a previous tap fails to move the cursor. doubleTap fires two real touch taps with
+    // a deterministic sub-second interval, which a hand-driven repro cannot reliably achieve. The
+    // interval is overridable via TAP_INTERVAL_MS to probe the threshold.
+    const intervalMs = process.env.TAP_INTERVAL_MS ? parseInt(process.env.TAP_INTERVAL_MS, 10) : 300
+
+    const importText = `
+    - a
+    - b
+    - c`
+    await paste(importText)
+    await waitForEditable('c')
+
+    const a = await waitForEditable('a')
+    const b = await waitForEditable('b')
+
+    // Tap a to set the caret, then within intervalMs tap the adjacent thought b.
+    await doubleTap(a, b, { intervalMs })
+
+    // Give the app a moment to dispatch setCursor and re-render, then assert the cursor moved to b.
+    await browser.pause(1000)
+    expect(await getEditingText()).toBe('b')
+  })
 })
diff --git a/src/e2e/iOS/helpers/doubleTap.ts b/src/e2e/iOS/helpers/doubleTap.ts
new file mode 100644
index 00000000000..ac706b6079e
--- /dev/null
+++ b/src/e2e/iOS/helpers/doubleTap.ts
@@ -0,0 +1,60 @@
+import type { Element } from 'webdriverio'
+import getElementRectByScreen from './getElementRectByScreen.js'
+
+interface Options {
+  // Milliseconds to pause between the release of the first tap and the press of the second tap.
+  intervalMs?: number
+  // Milliseconds each tap is held down before release.
+  holdMs?: number
+}
+
+/**
+ * Computes the center point of an element in native screen coordinates.
+ * Touch pointer actions on iOS Safari (XCUITest) are interpreted in screen coordinates, unlike the
+ * mouse pointer used by the `tap` helper which uses web viewport coordinates. The screen rect
+ * adds the native Safari content offset so the touch lands on the element.
+ */
+const centerOf = async (nodeHandle: Element) => {
+  const exists = await nodeHandle.isExisting()
+  if (!exists) throw new Error('Element does not exist in the DOM.')
+  const rect = await getElementRectByScreen(nodeHandle)
+  if (!rect) throw new Error('Bounding box of element not found.')
+  return {
+    x: Math.round(rect.x + rect.width / 2),
+    y: Math.round(rect.y + rect.height / 2),
+  }
+}
+
+/**
+ * Taps two elements in quick succession with a single touch pointer, with a precisely controlled
+ * interval between the two taps. Both element coordinates are resolved up front so that the gap
+ * between the taps is exactly intervalMs rather than incidental round-trip latency (which can exceed
+ * a second and is the reason a hand-driven repro of #4173 is unreliable). Uses a real touch pointer
+ * (pointerType: 'touch') so WebKit's rapid-tap gesture recognition is exercised the same way a
+ * physical double tap would exercise it. See https://github.com/cybersemics/em/issues/4173.
+ */
+const doubleTap = async (first: Element, second: Element, { intervalMs = 300, holdMs = 60 }: Options = {}) => {
+  const firstPoint = await centerOf(first)
+  const secondPoint = await centerOf(second)
+
+  await browser.performActions([
+    {
+      type: 'pointer',
+      id: 'finger1',
+      parameters: { pointerType: 'touch' },
+      actions: [
+        { type: 'pointerMove', duration: 0, x: firstPoint.x, y: firstPoint.y, origin: 'viewport' },
+        { type: 'pointerDown', button: 0 },
+        { type: 'pause', duration: holdMs },
+        { type: 'pointerUp', button: 0 },
+        { type: 'pause', duration: intervalMs },
+        { type: 'pointerMove', duration: 0, x: secondPoint.x, y: secondPoint.y, origin: 'viewport' },
+        { type: 'pointerDown', button: 0 },
+        { type: 'pause', duration: holdMs },
+        { type: 'pointerUp', button: 0 },
+      ],
+    },
+  ])
+}
+
+export default doubleTap