Thai character Sara Am (ำ, U+0E33) causes cursor to jump one position in input

Description

When typing Thai character ำ (Sara Am, U+0E33) in the Claude Code CLI input, the cursor jumps forward by one extra position, causing incorrect display and making it difficult to edit Thai text.

Environment

• OS: macOS Darwin 25.5.0
• Terminal: Warp
• Shell: zsh

Steps to Reproduce

1. Open Claude Code CLI in Warp terminal
2. Type any Thai word containing ำ (e.g., ทำ, ทำงาน, ดำ)
3. Observe cursor position after typing ำ

Expected Behavior

Cursor stays at the correct position after ำ — treated as a single full-width character (width = 1).

Actual Behavior

Cursor jumps one extra position forward, making subsequent characters appear misaligned. The display is garbled when editing text containing ำ.

Notes

• ำ (U+0E33 THAI CHARACTER SARA AM) is a precomposed Unicode character, not a combining mark — it should have wcwidth = 1.
• The issue appears to be in Claude Code's own input/readline handling, since Thai characters render correctly in the same terminal outside of Claude Code.
• Other Thai characters appear unaffected; the issue is specific to ำ.