[BUG] Title: Korean IME (CapsLock) toggle inserts [57358u in VS Code extension input

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?

Description:
When using Claude Code VS Code extension on macOS with Korean IME, pressing the CapsLock key (used as
Korean/English toggle) inserts [57358u into the input field.

Environment:

• macOS (Darwin 25.0.0)
• VS Code with Claude Code extension
• Korean IME, CapsLock configured as language toggle
• terminal.integrated.enableKittyProtocol: false already set — issue persists

Root cause (suspected):
When Korean IME switches, macOS sends a synthetic CapsLock event (kitty keyboard protocol key code
57358) directly to the app's input pipeline, bypassing Karabiner-Elements remapping. Claude Code
extension does not suppress/consume this synthetic ESC[57358u sequence.

Expected: IME toggle silently switches language, no text inserted
Actual: [57358u appears in the input field on every IME toggle

What Should Happen?

Description:
When using Claude Code VS Code extension on macOS with Korean IME, pressing the CapsLock key (used as
Korean/English toggle) inserts [57358u into the input field.

Environment:

• macOS (Darwin 25.0.0)
• VS Code with Claude Code extension
• Korean IME, CapsLock configured as language toggle
• terminal.integrated.enableKittyProtocol: false already set — issue persists

Root cause (suspected):
When Korean IME switches, macOS sends a synthetic CapsLock event (kitty keyboard protocol key code
57358) directly to the app's input pipeline, bypassing Karabiner-Elements remapping. Claude Code
extension does not suppress/consume this synthetic ESC[57358u sequence.

Expected: IME toggle silently switches language, no text inserted
Actual: [57358u appears in the input field on every IME toggle

Error Messages/Logs

Steps to Reproduce

just click capslock

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.84 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_