Korean (CJK) text rendering doubled and IME input reversion on Windows 11 #12
Description
Bug Description
When using the Claude Code Extension in Visual Studio 2026 on Windows 11 with Korean IME, two rendering issues occur:
1. Korean text appears doubled/overlapped vertically
Korean (CJK double-width) characters render as if they are single-width, causing lines to overlap or display twice vertically in the extension's output panel.
2. IME input reversion during typing pauses
When the extension is idle (e.g., waiting for a response or between outputs), typing Korean text in the input box causes characters to revert/jump back. The IME composition seems to conflict with the extension's input handling — composed characters get reset when the extension refreshes its output.
Environment
- IDE: Visual Studio 2026 (latest)
- OS: Windows 11 Pro (Build 26200)
- Language/IME: Korean (Microsoft IME)
- Display: Standard DPI
Expected Behavior
- Korean text should render correctly with proper double-width character spacing
- IME composition should not be interrupted by extension output updates
Suggested Fix Areas
- Terminal/text renderer: CJK character width calculation (wcwidth)
- Input handler: IME composition event handling (preserve composition state during output updates)
Workaround
Using the claude CLI directly in Windows Terminal works correctly for Korean text.