[BUG] Inconsistent `alt+backspace` behavior

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?

alt+backspace/alt+delete have inconsistent behavior: sometimes it deletes a single word from the prompt, but sometimes it deletes a whole line. (This seems to happen sometimes when the cursor is in the middle of a prompt).

What Should Happen?

alt+backspace and alt+delete should always either delete a single word, or delete the whole line (if ctrl+backspace is used to delete single words).

Error Messages/Logs

Steps to Reproduce

1. Type a multi-line prompt.
2. Navigate to the middle of the third line.
3. Hit alt+backspace or alt+delete.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.20 (Claude Code)

Platform

Anthropic API

Operating System

Linux

Terminal/Shell

Other

Additional Information

_No response_