Desktop: session switch shortcuts (Alt+↑/↓) do nothing in the new tab layout #48603

Description

In OpenCode Desktop with the new tab-based layout (settings → General → new layout design enabled, session tabs in the title bar), the documented/expected shortcuts for switching between session tabs — Alt+↑ (previous) / Alt+↓ (next) — have no effect.

These keybinds are registered only in the legacy sidebar layout (packages/app/src/pages/layout.tsx, commands session.previous / session.next). The new layout (packages/app/src/pages/layout-new.tsx + Titlebar in packages/app/src/components/titlebar.tsx) registers only tab.new, tab.close, and tab.reopenClosed — there is no command to move to the previous/next tab, so nothing handles Alt+↑/Alt+↓.

Additionally, the "Go" menu still lists "Previous Session" / "Next Session" entries with the Alt+↑/Alt+↓ keybinds shown, but the commands are not registered in this layout, which is misleading (menu items are effectively dead and the displayed shortcut suggests it should work).

Plugins

No response

OpenCode version

1.18.30

Steps to reproduce

1. Open OpenCode Desktop and enable the new layout design (tabs in the title bar).
2. Open two or more session tabs.
3. Press Alt+↑ / Alt+↓ (macOS: Option+↑ / Option+↓).
4. Observe: no tab switch happens.
5. Open the command palette (Ctrl/⌘+K) and search for "next session"/"previous session" — the commands are missing/disabled.

Screenshot and/or share link

No response

Operating System

windows10

Terminal

No response