REPL/node:readline: text insertion or paste at non-end cursor position results in scrambled character order #60624

Version

v24.11.0

Platform

Darwin mba-mandel59.local 25.0.0 Darwin Kernel Version 25.0.0: Wed Sep 17 21:41:39 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T8103 arm64

Subsystem

REPL, node:readline

What steps will reproduce the bug?

1. Launch Node.js REPL by running node.

2. Type two single quotes: ''

3. Press the Left Arrow once — now the cursor (caret) is between the quotes.

4. Switch your input method to Japanese IME (Input Method Editor).

   • On macOS, this can be done from the top menu bar (“A” icon).

   • Make sure the input source is switched to Japanese - Romaji. Switch to a Japanese input source on Mac

5. Type using Roman letters (ai or aiu) which will be converted by the IME into Japanese Hiragana characters:

   • Typing ai produces the composition string あい

   • Typing aiu produces あいう

6. Press Return to confirm the IME composition.

How often does it reproduce? Is there a required condition?

Always reproducible (100%)

What is the expected behavior? Why is that the expected behavior?

• When typing ai → the line should show 'あい'

• When typing aiu → the line should show 'あいう'

What do you see instead?

• When typing ai → the line becomes ''いあ

• When typing aiu → the line becomes ''あうい

The composed text appears in an incorrect order and is placed after the closing quote.

Additional information

• Occurs both in the REPL and in a standalone readline interface.
• The regression likely appeared between v24.8.0 and v24.9.0 — possibly related to readline changes.