[BUG] Arrow down key moves cursor inside prompt instead of navigating history

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Steps to reproduce:

1. Press ↑ twice to navigate to a previous command in history
2. Press ↓ to go forward in history
3. ↓ moves cursor inside the multi-line prompt instead of navigating history
4. Pressing Enter executes malformed/wrong command

Actual result: ↓ moves cursor within the prompt text
Expected result: ↓ should navigate forward in command history

What Should Happen?

Steps to reproduce:

1. Press ↑ twice to navigate to a previous command in history
2. Press ↓ to go forward in history
3. ↓ moves cursor inside the multi-line prompt instead of navigating history
4. Pressing Enter executes malformed/wrong command

Actual result: ↓ moves cursor within the prompt text
Expected result: ↓ should navigate forward in command history

Error Messages/Logs

Steps to Reproduce

Steps to reproduce:

1. Press ↑ twice to navigate to a previous command in history
2. Press ↓ to go forward in history
3. ↓ moves cursor inside the multi-line prompt instead of navigating history
4. Pressing Enter executes malformed/wrong command

Actual result: ↓ moves cursor within the prompt text
Expected result: ↓ should navigate forward in command history

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.9 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_