Summarized pasted text is corrupted around wide characters in TUI prompt #29707

Description

Bug Description

When the TUI prompt contains wide characters, such as Chinese text, around a summarized paste placeholder like [Pasted ~N lines], the submitted prompt can be corrupted.

The submitted text may keep a partial [Pas prefix from the placeholder and drop trailing characters after the pasted content.

Expected Behavior

The submitted prompt should contain:

• The Chinese text before the paste.
• The full pasted content.
• The Chinese text after the paste.
• No leftover placeholder text.

Actual Behavior

The submitted prompt can contain a leftover [Pas prefix before the pasted content and can lose trailing characters after the pasted content.

Example:

[Paspublic:

FDelegateHandle AttackFinishedDelegateHandle;斯顿法国红酒看来

Plugins

none

OpenCode version

1.15.11

Steps to reproduce

1. Open the TUI prompt.
2. Type Chinese text before the paste, for example 你好你好.
3. Paste a multi-line code snippet so it becomes [Pasted ~N lines].
4. Type Chinese text after the paste, for example 阿斯顿法国红酒看来.
5. Submit the prompt.
6. Check the actual message sent to the model.

Screenshot and/or share link

Operating System

Windows11

Terminal

Windows PowerShell