Vietnamese IME Input Rendering Issue in Copilot CLI Overlay #838

Describe the bug

When typing Vietnamese characters using an IME (Input Method Editor) such as Telex or VNI, the characters are not composed correctly within the Copilot CLI input field. Instead of combining marks to form a single accented character, the characters appear fragmented or duplicated (e.g., typing "ư" results in "u ư").

Affected version

Version: 0.0.372

Steps to reproduce the behavior

1. Launch the Copilot CLI.
2. Switch the system keyboard input to a Vietnamese IME (e.g., Telex or VNI).
3. Attempt to type words with diacritics (e.g., "ngưỡng", "tiếng", "chào").
4. Observe the text appearing in the input prompt.

Expected behavior

The CLI should support standard IME composition, allowing the characters to be combined into proper accented Vietnamese words (e.g., "ngưỡng").

Additional context

This issue makes it extremely difficult for Vietnamese developers to describe tasks or ask questions in their native language, forcing them to use English or copy-paste text from external editors.