TUI: Option/Ctrl+Arrow word navigation is not CJK/Unicode-aware

What version of Codex CLI is running?

codex-cli 0.104.0

What subscription do you have?

ChatGPT Plus

Which model were you using?

GPT-5.3-codex

What platform is your computer?

Darwin 24.6.0 arm64 arm

What terminal emulator and version are you using (if applicable)?

Ghostty + fish

What issue are you seeing?

Word navigation via Option/Ctrl + Left/Right in TUI input is not CJK/Unicode-aware.

In mixed-language text, ASCII words behave mostly as expected, but CJK text is treated as one large segment (or has incorrect boundaries), making cursor movement inefficient and inconsistent with common CLI/editor behavior.

What steps can reproduce the bug?

1. Open Codex CLI and type:

• 你好世界
• Hello你好World

1. Put cursor at end of line.
2. Press word-navigation keys:

• macOS: Option + Left/Right
• Windows/Linux: Ctrl + Left/Right

1. Observe cursor movement around CJK text.

What is the expected behavior?

Word navigation should follow Unicode-aware word boundaries (UAX #29 / ICU-like behavior), not ASCII-only heuristics.

Examples:

• 你好世界 should navigate in multiple logical word steps (not as a single large token).
• Hello你好World should stop at mixed-language boundaries predictably.

Additional information

• Context from related Codex Unicode boundary issues:
• #3588
• #3261
• #5016
• Possibly related but not the same as #4341 (terminal key-sequence transport discussion).
• Competitor reference (public): Gemini CLI uses Intl.Segmenter for CJK word navigation:
• https://github.com/google-gemini/gemini-cli/pull/14475
• I have a local fix using icu_segmenter + tests and can provide patch details if maintainers are interested.
• Reproduction videos:

OpenAI Codex

https://github.com/user-attachments/assets/82ea499e-c2a7-494c-b080-5780aa8ba799

Claude Code

https://github.com/user-attachments/assets/a8e4aaab-073b-4045-a0d9-57311e2bb1af