IME composition events not handled correctly in Agents panel chat input

[yamachu]

Select Topic Area

Bug

GitHub Feature Area

UI/UX

Body

Environment

• OS: macOS (or other environments with IME support)
• Browser: Chrome

Describe the bug

When using an Input Method Editor (IME) such as Japanese, Chinese, or Korean input methods in the Agents panel chat input field, the composition event is not properly handled. This causes the chat message to be submitted prematurely while the user is still composing text through IME conversion.

Steps to reproduce

1. Open the Agents panel in GitHub.com
2. Click on the chat input field
3. Enable IME (e.g., Japanese input method)
4. Start typing characters that need IME conversion
5. Press the conversion key to confirm the composition

Expected behavior

• The chat input should not submit while the user is composing text via IME
• The message should only be sent when the user explicitly triggers the send action (Enter key for send, not for confirming IME input)

Actual behavior

Messages are being sent prematurely when confirming IME compositions, interrupting the user's input workflow.

Suggested fix

Handle the compositionstart and compositionend events on the input field to prevent sending messages while composition is active.

[github-actions[bot]]

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