Thai vowel characters not displaying correctly in Claude Code TUI on Windows

Root Cause Identified

The issue started in version 2.1.20. Version 2.1.19 works correctly.

The breaking change appears to be:

"Fixed wide character (emoji, CJK) rendering artifacts where trailing columns were not cleared when replaced by narrower characters"

This fix likely introduced a regression affecting Thai combining characters, specifically sara-aa (◌า U+0E32), which is a trailing character that needs special handling similar to CJK characters.

Versions Tested:

• v2.1.19: ✅ Thai rendering works correctly
• v2.1.20+: ❌ Sara-aa (◌า) disappears

Bug Description

Thai "sara-aa" vowel character (◌า - U+0E32) is not displaying in Claude Code TUI on Windows. When typing Thai text, the trailing vertical line vowel disappears, making text unreadable.
For example:

Expected: "ภาษาไทย"
Actual display in Claude Code: "ภาษไทย" (missing ◌า)

!Image

This issue occurs specifically within Claude Code's TUI interface, while the same text displays correctly in:

• Regular PowerShell/Terminal (outside Claude Code) ✓

!Image

This appears to be a Windows-specific rendering bug with Thai combining characters in the TUI library.

Environment Info

• Platform: win32
• Terminal: pycharm
• Version: 2.1.25
• Feedback ID: e519f403-5706-4925-ba73-92741fac31dc

Errors

No error messages displayed. The issue is purely visual - Thai sara-aa (◌า) characters are silently omitted from the rendered output in the Claude Code TUI.

Additional context:

• UTF-8 encoding is properly configured (chcp 65001)
• Issue persists across different terminal emulators
• Other Thai characters display correctly, only sara-aa (◌า) is affected