fix(app): advanced settings toggles for desktop toolbar buttons do nothing in new layout #29951

Describe the bug

In the desktop app's new layout design (newLayoutDesigns enabled), the advanced settings toggles for File tree, Command palette, Terminal, and Server status (Settings → General → Advanced) have no visible effect. Enabling them does not make the corresponding buttons appear in the titlebar.

Steps to reproduce

1. Open the OpenCode desktop app
2. Open Settings → General
3. Enable New layout designs (if not already on)
4. Scroll to the Advanced section
5. Toggle on File tree, Command palette, Terminal, or Server status

Expected: The corresponding icon buttons appear in the titlebar's right-hand area.
Actual: Nothing changes — no buttons appear regardless of toggle state.

Root cause

Commit e1581183f ("feat(app): allow toggling tabs layout") changed isDesktopV2 in packages/app/src/components/session/session-header.tsx from a plain boolean constant to a reactive createMemo():

// Before (boolean constant — using it directly in JSX was correct)
const isDesktopV2 = platform.platform === "desktop" && USE_V2_TITLEBAR

// After (reactive memo — must be called as isDesktopV2() in JSX)
const isDesktopV2 = createMemo(() => platform.platform === "desktop" && settings.general.newLayoutDesigns())

The commit correctly updated the search, tree, term, and status memos to call isDesktopV2(), but missed updating the <Show> gate in the JSX:

// Bug: passes the memo function reference (always truthy!) instead of its value
<Show when={isDesktopV2} fallback={<OldLayoutButtons />}>
  <SessionHeaderV2Actions />
</Show>

Because a non-null function reference is always truthy in JavaScript, \<SessionHeaderV2Actions\> is rendered unconditionally — the fallback containing the old layout buttons (which the settings control) is never shown.

A secondary issue is that SessionHeaderV2Actions itself had no code to render search, file-tree, or terminal buttons even when their settings are enabled, so those toggles were wired up to memos that were never consumed in the V2 path.

Possible fixes

1. JSX fix (required): Change when={isDesktopV2} to when={isDesktopV2()} on the <Show> component so the branch is evaluated reactively.
2. V2 actions fix (required for full feature parity): Extend SessionHeaderV2ActionsState and SessionHeaderV2Actions to render compact icon buttons for search/terminal/file-tree when their respective settings are true, and add terminal and file-tree icons to the V2 icon sprite (packages/ui/src/v2/components/icon.tsx).

Environment

• Desktop app (new layout designs active)
• Regression introduced in commit e1581183f (PR feat(app): allow toggling tabs layout #29526 "feat(app): allow toggling tabs layout")