Ctrl+B stops working after first prompt execution

Environment

• Claude Code version: 2.1.31
• OS: macOS 15.6.1 (Build 24G90)
• Terminal: xterm-256color
• Shell: /bin/zsh
• Note: CPU lacks AVX support warning present

Steps to reproduce

1. Start Claude Code (new session)
2. In the input field, Ctrl+B works to move cursor back one character ✓
3. Execute any prompt (send a message)
4. In the next input prompt, Ctrl+B no longer works ✗
5. Ctrl+A (beginning of line) and Ctrl+E (end of line) still work
6. Restart Claude Code → Ctrl+B works again (until next prompt execution)

Expected behavior

Ctrl+B should consistently move the cursor back one character (standard readline/emacs keybinding)

Actual behavior

Ctrl+B stops working immediately after the first prompt execution. Other readline shortcuts (Ctrl+A, Ctrl+E) continue to function normally.

Additional context

• Vim mode is NOT enabled
• Not running inside tmux/screen
• Custom keybindings.json was tested both with and without entries - issue persists
• The issue is 100% reproducible with the steps above