Visual Studio 2026 Extension: Korean (CJK) text rendering doubled and IME input reversion

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.