[BUG] Undo functionality should support redo

[djsavvy]

Environment

• Platform (select one):
  • [x] Anthropic API
  • [ ] AWS Bedrock
  • [ ] Google Vertex AI
  • [ ] Other:
• Claude CLI version: 1.0.34 (Claude Code)
• Operating System: macos 15.3.1
• Terminal: ghostty

Bug Description

Right now ctrl+z does undo in the input box. I agree with https://github.com/anthropics/claude-code/issues/588 that ctrl+z should be respected to background the process, but separately — I have a habit of using ctrl+z to background applications, as is standard. That tic means that I am losing edits in the input box without the ability to ctrl+y or ctrl+r in vi mode to redo them.

Steps to Reproduce

1. undo
2. try to redo
3. it fails