Ctrl+B (Emacs cursor-left) stops working after ~3 presses in Chat input

Description

When using Ctrl+B (Emacs backward-char) in the Chat input to move the cursor left, it works for approximately 1-3 key presses but then stops responding. The cursor no longer moves backward on subsequent Ctrl+B presses.

Environment

• macOS (Darwin 25.2.0, Apple Silicon)
• Claude Code CLI (latest)
• Shell: zsh

Steps to Reproduce

1. Type a long line of text in the Chat input
2. Press Ctrl+B repeatedly to move the cursor backward
3. After ~3 presses, the cursor stops moving

Expected Behavior

Ctrl+B should consistently move the cursor one character to the left on every press, matching standard Emacs/readline keybinding behavior.

Notes

• ctrl+b is only bound to task:background in the Task context by default. There is no binding in the Chat context, so it should pass through to the underlying terminal input handler as Emacs cursor-left.
• Unbinding ctrl+b in Task context via ~/.claude/keybindings.json does not resolve the issue (since the problem occurs in Chat context).
• This may be related to how the Ink-based TUI handles repeated modifier key presses.