TUI freezes when switching themes repeatedly via theme menu (desktop app)

Description

Switching themes from the theme menu repeatedly causes the TUI to freeze. After the first successful theme change, a second consecutive theme change hangs the app — no keystrokes or UI updates are processed. The app only recovers if you tab out to another section (e.g. away from the theme menu) and tab back; then a theme change works once before it hangs again.

Reproduction

1. Launch the opencode desktop app (OpenCode.app) and open the theme menu.
2. Select a theme — it applies fine.
3. Open the theme menu again and select another theme.
4. The TUI freezes: no response to input, new theme never renders.
5. Tab out to another section and tab back to the theme menu.
6. Select a theme — works once. Repeat step 3 and the hang returns.

Expected behavior

Themes should switch repeatedly without hanging; the TUI should stay responsive.

Actual behavior

Every second consecutive theme switch freezes the TUI until you leave the section and return.

Environment

• opencode 1.18.16 (desktop app, OpenCode.app)
• macOS (darwin)
• Related: #24475 covers a TUI hang from theme detection after the opentui upgrade — this may be the same underlying theme-detection/render stall but triggered by repeated theme changes rather than tmux.

Notes

Willing to capture logs / a trace if maintainers point me at the right flags.