[BUG] Arrow Down Doesn't Restore Original Prompt After Arrow Up

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?

When using command history navigation in Claude Code CLI, pressing Arrow Up replaces the current prompt with a previous command, but pressing Arrow Down does not return to the original unsent prompt. This results in loss of the user's typed text.

• Users cannot safely explore command history without losing their current work
• Violates standard terminal UX conventions (bash, zsh, fish all preserve current prompt)
• Forces users to avoid Arrow Up entirely or copy text before navigating history

What Should Happen?

Expected Behavior -> Standard CLI command history behavior:

1. User types: "my original prompt"
2. Press Arrow Up -> Shows previous command from history
3. Press Arrow Down -> Should restore "my original prompt"
4. Press Arrow Down again (at newest position) → Empty prompt or stay at current

Error Messages/Logs

n/a

Steps to Reproduce

1. Open Claude Code CLI
2. Type any text (don't press Enter)
3. Press Arrow Up key
4. Press Arrow Down key
5. Observe that original text is not restored

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

n/a

Claude Code Version

2.0.14

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

Preserve the "current unsent prompt" as the newest entry in the history stack, allowing Arrow Down to return to it before it's submitted.