[BUG] Ctrl-G external editor invocation causes TTIN suspension and EINTR crash with emacs

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?

# Environment:

• Claude Code Version: 2.0.37
• OS: macOS (Darwin 25.0.0)
• Shell: zsh with oh-my-zsh
• EDITOR: emacs -nw (GNU Emacs 30.2)
• Installation method: Native installer (shell script, not npm)

# Description:

When attempting to use Ctrl-G to edit a long prompt in an external editor (as suggested by the CLI when lines exceed the terminal width), Claude Code suspends with a TTIN signal instead of launching the editor.

# Actual Behavior:

1. Claude Code process suspends immediately with:

zsh: suspended (tty input) claude --resume

1. The terminal shows TTIN status (terminal input while backgrounded)
2. Running fg to bring the process to the foreground results in a crash with the following error:
3. The stack trace shows an attempt to access a non-existent lock file:

Error: ENOENT: no such file or directory, stat '/Users/capehart/.local/state/claude/locks/2.0.35.lock'

1. (Note: The lock file references version 2.0.35, but I'm running 2.0.37)

Possible Root Cause (as identified by Claude):

The editor appears to be launched as a background process without proper TTY control, causing the OS to suspend it when it attempts to read from stdin. The subsequent lock file error suggests a state management issue when recovering from the suspension.

What Should Happen?

Emacs should launch in terminal mode (-nw) to edit the prompt, then return the edited text to Claude Code when exiting the editor.

Error Messages/Logs

EINTR: interrupted system call, read
      fd: 8,
    syscall: "read",
      errno: -4,
      code: "EINTR"

Steps to Reproduce

1. Start Claude Code CLI session
2. Begin typing a prompt that exceeds one line
3. Press Ctrl-G (as instructed by the "Press ^G to edit with emacs" message)
4. Observe the process suspension

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.37 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Additional Context:

• The ~/.local/state/claude/locks/ directory exists
• Multiple previous Ctrl-G attempts can be brought to foreground with successive fg commands, each resulting in the same crash
• After all suspended processes are exhausted with fg, Claude Code does not return to normal operation
• This appears to be a TTY handling issue where the editor subprocess is being spawned without proper terminal control

❯ echo ${EDITOR}
emacs -nw

❯ emacs --version
GNU Emacs 30.2

❯ which emacs
/opt/homebrew/bin/emacs

<img width="1290" height="813" alt="Image" src="https://github.com/user-attachments/assets/ce1efc5b-9bb8-44da-b33c-451b44a8e8a2" />