Fix flaky TextInput and AutocompletePrompt tests under React 19

Replace async useEffect cursor clamping in TextInput with synchronous
clamping during render to eliminate stale cursorOffset race condition
exposed by React 19 scheduler changes. Also make AutocompletePrompt
DELETE tests wait for deterministic content instead of any frame change.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: tewson

packages/cli-kit/src/private/node/ui/components/AutocompletePrompt.test.tsx

@@ -448,7 +448,7 @@ describe('AutocompletePrompt', async () => {
       "
     `)
 
-    await sendInputAndWaitForChange(renderInstance, DELETE)
+    await sendInputAndWaitForContent(renderInstance, 'ype to search', DELETE)
 
     expect(renderInstance.lastFrame()).toMatchInlineSnapshot(`
       "?  Associate your project with the org Castile Ventures?   Type to search...
@@ -697,7 +697,7 @@ describe('AutocompletePrompt', async () => {
       "
     `)
 
-    await sendInputAndWaitForChange(renderInstance, DELETE)
+    await sendInputAndWaitForContent(renderInstance, 'ype to search', DELETE)
 
     expect(renderInstance.lastFrame()).toMatchInlineSnapshot(`
       "?  Associate your project with the org Castile Ventures?   Type to search...

packages/cli-kit/src/private/node/ui/components/TextInput.tsx

@@ -1,6 +1,6 @@
 /* eslint-disable no-nested-ternary */
 import {shouldDisplayColors} from '../../../../public/node/output.js'
-import React, {useEffect, useState} from 'react'
+import React, {useState} from 'react'
 import {Text, useInput} from 'ink'
 import chalk from 'chalk'
 import figures from 'figures'
@@ -29,18 +29,11 @@ const TextInput: FunctionComponent<TextInputProps> = ({
 }: TextInputProps) => {
   const [cursorOffset, setCursorOffset] = useState((originalValue || '').length)
 
-  // if the updated value is shorter than the last one we need to reset the cursor
-  useEffect(() => {
-    setCursorOffset((previousOffset) => {
-      const newValue = originalValue || ''
-
-      if (previousOffset > newValue.length - 1) {
-        return newValue.length
-      }
-
-      return previousOffset
-    })
-  }, [originalValue])
+  // Clamp cursor synchronously so useInput never sees a stale offset
+  const clampedCursorOffset = Math.min(cursorOffset, (originalValue || '').length)
+  if (clampedCursorOffset !== cursorOffset) {
+    setCursorOffset(clampedCursorOffset)
+  }
 
   const value = password ? '*'.repeat(originalValue.length) : originalValue
   let renderedValue
@@ -60,15 +53,15 @@ const TextInput: FunctionComponent<TextInputProps> = ({
   renderedValue = value
     .split('')
     .map((char, index) => {
-      if (index === cursorOffset) {
+      if (index === clampedCursorOffset) {
         return noColor ? cursorChar : chalk.inverse(char)
       } else {
         return char
       }
     })
     .join('')
 
-  if (cursorOffset === value.length) {
+  if (clampedCursorOffset === value.length) {
     renderedValue = (
       <Text>
         {renderedValue}
@@ -89,25 +82,29 @@ const TextInput: FunctionComponent<TextInputProps> = ({
         }
       }
 
-      let nextCursorOffset = cursorOffset
+      let nextCursorOffset = clampedCursorOffset
       let nextValue = originalValue
 
       if (key.leftArrow) {
-        if (cursorOffset > 0) {
+        if (clampedCursorOffset > 0) {
           nextCursorOffset--
         }
       } else if (key.rightArrow) {
-        if (cursorOffset < originalValue.length) {
+        if (clampedCursorOffset < originalValue.length) {
           nextCursorOffset++
         }
       } else if (key.backspace || key.delete) {
-        if (cursorOffset > 0) {
-          nextValue = originalValue.slice(0, cursorOffset - 1) + originalValue.slice(cursorOffset, originalValue.length)
+        if (clampedCursorOffset > 0) {
+          nextValue =
+            originalValue.slice(0, clampedCursorOffset - 1) +
+            originalValue.slice(clampedCursorOffset, originalValue.length)
           nextCursorOffset--
         }
       } else {
         nextValue =
-          originalValue.slice(0, cursorOffset) + input + originalValue.slice(cursorOffset, originalValue.length)
+          originalValue.slice(0, clampedCursorOffset) +
+          input +
+          originalValue.slice(clampedCursorOffset, originalValue.length)
         nextCursorOffset += input.length
       }