Stray DECRPM response printed on tmux window focus after resuming conversation

Description

When resuming a specific conversation with claude --resume, switching away from the tmux window containing Claude Code and switching back (via an fzf-based tmux picker) prints a stray terminal escape sequence to the visible output:

[?997;1n

This is a DECRPM (DEC Private Mode Report) response for mode 997 (modifyOtherKeys/extended keyboard protocol).

Reproduction

1. Have a Claude Code session running inside tmux
2. End the session
3. Resume the conversation with claude --resume
4. Switch to a different tmux window using an fzf-based tmux picker
5. Switch back to the Claude Code window
6. [?997;1n is printed in the terminal

Key observations

• Only affects the resumed conversation — other Claude Code sessions in the same tmux server are unaffected
• Starting a fresh claude session does not exhibit the issue
• Persists across restarts: closing and resuming the same conversation brings the issue back
• Other conversations resumed with --resume do not have this issue — it appears to be specific to certain conversation states

Environment

• Claude Code CLI
• tmux 3.6a with extended-keys always and extkeys terminal feature
• Ghostty terminal
• macOS 26.3.1 (Darwin 25.3.0)