tui: diff viewer palette shows Open instead of Close and breaks exit after re-entry

Description

When the command palette is opened from the active Diff Viewer, it still shows Open diff viewer and does not provide Close diff viewer.

Besides presenting the wrong action, this permits a broken route transition. Selecting Open diff viewer again replaces the original return route with the Diff Viewer itself. After that, q or escape runs the close action but navigates back into the viewer, making it appear impossible to close.

Expected behavior:

• Outside the Diff Viewer, the palette shows Open diff viewer.
• Inside the Diff Viewer, the palette shows Close diff viewer and does not expose Open diff viewer.
• Closing returns to the route from which the viewer was originally opened.

Plugins

None required to reproduce.

OpenCode version

1.18.8

Steps to reproduce

1. Start OpenCode.
2. Press Ctrl+P and select Open diff viewer.
3. Press Ctrl+P again from inside the Diff Viewer.
4. Observe that Open diff viewer is still present and Close diff viewer is missing.
5. Select Open diff viewer again.
6. Press q or escape.
7. Observe that the Diff Viewer remains open instead of returning to the original session.

Screenshot and/or share link

https://github.com/user-attachments/assets/394e7a55-87fb-4c8a-96c8-fd23f629c232

Operating System

MacOS 26.4

Terminal

Ghostty