[BUG] Focus reporting escape sequences ([I[O) appear in input when using mouse/modifiers

[ree-see]

Bug Description

When using Claude Code in WezTerm (and likely other terminals), focus reporting escape sequences [I and [O are being injected into the input interface when clicking with the mouse or using modifier keys. These escape sequences should be filtered by Claude Code's input handler.

Environment

• Terminal: WezTerm
• Platform: macOS (Darwin 25.0.0)
• Claude Code Version: Latest (2025-10-26)

Root Cause

Terminal applications can enable focus reporting mode (ANSI mode 1004) which causes the terminal to send:

• ESC[I (or [I) when the terminal gains focus
• ESC[O (or [O) when the terminal loses focus

These escape sequences are leaking into Claude Code's input interface instead of being filtered out.

Steps to Reproduce

1. Launch Claude Code in WezTerm
2. Click in the input area with mouse
3. Use modifier keys (Cmd, Shift, etc.)
4. Observe [I or [O characters appearing in the input

Expected Behavior

Claude Code should filter focus reporting escape sequences (CSI I and CSI O) from user input, similar to how other terminal applications handle these sequences.

Actual Behavior

The raw escape sequence characters appear in the input field, interfering with normal typing and command input.

Technical Details

Focus Reporting Overview:

• Enabled by: ESC[?1004h
• Disabled by: ESC[?1004l
• Focus gained sends: ESC[I
• Focus lost sends: ESC[O

Applications like Vim may enable this mode and sometimes fail to disable it on exit, leaving the terminal in focus reporting mode.

Workarounds

Temporary fix (run in terminal):

printf '\e[?1004l'

Permanent fix (add to shell RC file):

# Disable focus reporting on shell startup
printf '\e[?1004l'

Related Issues

• Similar issue in iTerm2: https://superuser.com/questions/931873/o-and-i-appearing-on-iterm2-when-focus-lost
• Vim focus reporting fix: Remove mode 1004 (focus reporting) from XM termcap vim/vim#13440
• htop bug with focus events: Applications that support mouse but not focus events incorrectly process I/O as key events

Proposed Solution

Claude Code's input handler should filter the following escape sequences:

• \x1b[I (focus in)
• \x1b[O (focus out)
• Potentially other CSI sequences that shouldn't appear in user input

Impact

This affects users who:

• Use WezTerm or terminals with focus reporting enabled
• Have applications (vim, etc.) that leave focus reporting enabled after exit
• Frequently use mouse or keyboard modifiers while interacting with Claude Code

Thank you for looking into this!

[github-actions]

Found 3 possible duplicate issues:

1. [Bug] Control characters [I and [O[I appear in prompt after VS Code editor return on macOS #10202
2. [Bug] Unintended iTerm2 Session Spawning with Claude Code #9494
3. [Bug] Terminal Escape Sequences Incorrectly Rendered in Prompt #9249

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🤖 Generated with Claude Code

[lanej]

Also happens in Kitty.

[leoauri]

Also experiencing this issue in iTerm2...

[zeenix]

Also on Ptyxis on Linux (#10735).

[coreymaher]

Also seeing this with ghostty