[BUG] Korean input characters disappear on iOS mobile SSH

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?

Summary

When connecting via Termius on iOS and running Claude Code over SSH,
Korean input characters disappear at the moment a consonant and vowel are combined.

• Consonant only: works
• Vowel only: works
• Consonant + vowel (e.g. ㄱ + ㅏ → 가): character disappears

⚠️ In the same Termius environment:

• ✅ Android: works correctly
• ❌ iOS: issue occurs

Other CLI/TUI tools such as Gemini CLI and Codex CLI work correctly even on iOS.

Screen Recording

https://github.com/user-attachments/assets/5d2d9796-7ecd-435e-8eb1-0abf334a9f7c

Environment

• Client
• ❌ iOS + Termius (issue occurs)
• ✅ Android + Termius (works)
• Server
• MacOS (SSH)
• Affected application
• Claude Code
• Not affected
• MacOS Terminal / iTerm2
• Gemini CLI
• Codex CLI

Actual Behavior

• During Korean jamo composition, the input buffer deletes the character and the final composed character is not rendered

Technical Analysis (Important)

iOS Termius input behavior

When typing the Korean character 가 on iOS Termius, the actual byte stream received by the server (logged in raw TTY mode) is:

e3 84 b1 7f ea b0 80

Interpretation:

• e3 84 b1 → ㄱ (U+3131)
• 7f → DEL (backspace)
• ea b0 80 → 가 (U+AC00)

This means iOS Termius does not send IME preedit composition to the server.
Instead, it emulates composition using a delete + re-insert sequence:
ㄱ → delete → 가.

Claude Code appears to mis-handle this sequence:

1. Receives ㄱ → inserts into buffer
2. Receives DEL → deletes ㄱ
3. Receives final character 가 → insertion is dropped due to internal input state or cursor calculation

As a result, no character remains on screen.

Why this does not occur on Android

On Android Termius:

• Korean IME composition is completed on the client side
• SSH sends only the final composed UTF-8 characters

This matches the behavior of macOS terminals, so Claude Code never receives the delete + re-insert sequence and works correctly.

Why this does not occur on macOS

• macOS Terminal / iTerm2 complete IME composition locally
• SSH transmits only finalized UTF-8 characters
• Claude Code never encounters the problematic delete + insert sequence

Additional Notes

• Changing Termius backspace transmission from DEL (0x7f) to Ctrl-H (0x08):
• Does not fully resolve the issue in Claude Code
• Can introduce input issues in other terminal applications

Conclusion

• This is not a locale, UTF-8, or font configuration issue
• The issue reproduces only on iOS, while Android and macOS work correctly
• Claude Code’s raw TUI input handling does not correctly process

the delete + re-insert based IME composition sequence used by iOS Termius

• To support iOS mobile SSH environments, Claude Code needs:
• Safe handling of IME composition or delete + insert sequences
• Or an alternative line-based / IME-safe input mode

Impact

• Korean (and likely other CJK) input is effectively unusable in Claude Code on iOS
• Copy/paste is the only practical workaround

What Should Happen?

Expected Behavior

• Korean input should be composed and rendered correctly (가, 나, 다, etc.)

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce (100% on iOS)

1. Connect to a Linux server via SSH using Termius on iOS
2. Run claude code
3. Try to input Korean text in the prompt
4. Example: input 가

• Type ㄱ → briefly appears
• Type ㅏ → the character disappears

Test for checking text input

$ cat > /tmp/ttylog.py <<'PY'
import sys, tty, termios

fd = sys.stdin.fileno()
if not sys.stdin.isatty():
    print("stdin is not a TTY. Run this in an interactive SSH shell.", file=sys.stderr)
    sys.exit(1)

old = termios.tcgetattr(fd)
try:
    tty.setraw(fd)
    print("RAW tty logger started. (Press Ctrl-\\ to quit)")
    while True:
        b = sys.stdin.buffer.read(1)
        if not b:
            break
        sys.stdout.write(b.hex() + " ")
        sys.stdout.flush()
finally:
    termios.tcsetattr(fd, termios.TCSADRAIN, old)
PY

$ python3 /tmp/ttylog.py

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.76

Platform

Anthropic API

Operating System

Other

Terminal/Shell

Other

Additional Information

_No response_