Thai vowels (สระ อา, อำ) not rendering correctly in input/output

<img width="865" height="1293" alt="Image" src="https://github.com/user-attachments/assets/e3a0fd28-c989-4c0e-8ed5-8f409ccc480d" />

Description

Thai combining vowels like สระ อา (า - sara aa) and สระ อำ (ำ - sara am) are not rendering correctly in Claude Code CLI. This affects both:

1. Input: Users cannot type these characters
2. Output: Even Claude's responses have these characters stripped/missing

Evidence

Screenshot showing the issue - notice how Thai vowels are missing from Claude's own output:

• "สระ อ ()" instead of "สระ อา (า)"
• "ต้องกร" instead of "ต้องการ"

Environment

• OS: macOS (Darwin 25.2.0)
• Thai Keyboard Layout: Kedmanee
• Affected characters: า (sara aa), ำ (sara am), possibly other Thai combining characters

Expected Behavior

Thai text should render correctly with all vowels and tone marks intact, both in user input and Claude's output.

Actual Behavior

Thai combining characters (particularly sara aa and sara am) are being stripped or not displayed in the terminal output.

Notes

This appears to be a Unicode handling issue specific to Thai combining characters in the CLI's terminal rendering.