[Bug] CJK and wide emoji disappear behind translucent TUI dialog backdrops

Description

When a TUI dialog/overlay is opened, such as the command palette with Ctrl+P, CJK text and some wide emoji in the dimmed background become blank/invisible. ASCII text in the same background remains visible.

The text is restored immediately after closing the dialog.

This reproduces in both Windows Terminal and WezTerm, so it is not limited to one terminal emulator.

OpenCode version

1.18.15

Expected behavior

All text should remain readable, merely dimmed, while an overlay is open.

Actual behavior

Wide graphemes in the background are replaced by blank cells.

Related reports

• #7650
• #18088
• #29007
• https://github.com/anomalyco/opentui/issues/837
• https://github.com/anomalyco/opentui/pull/791

Plugins

oh-my-opencode 4.19.4 (Irrelevant)

OpenCode version

1.18.15

Steps to reproduce

1. Produce a response containing mixed ASCII, CJK, and emoji text.
2. Press Ctrl+P to open the command palette.
3. Observe the dimmed background:
   • Chinese/Japanese/Korean characters disappear.
   • Some emoji disappear.
   • ASCII text remains visible.
4. Close the palette; the missing text returns immediately.

Screenshot and/or share link

The first two screenshots show the same test text before opening the overlay.
The latter two show the failure after opening Ctrl+P, including reproduction in Windows Terminal and WezTerm.

Operating System

wsl for ubuntu 24.04 & windows 11

Terminal

windows terminal & wezterm