fix(desktop): mark the File Browser setting session-only in Simple mode

Simple mode shadows fileBrowserOpen, so a flip on this row lands in the
session reveal layer and never persists. Show the same Simple-mode note the
other shadowed Appearance rows carry, so the row doesn't promise a standing
default it can't keep.

apps/desktop/src/app/settings/appearance-settings.tsx

@@ -432,6 +432,7 @@ export function AppearanceSettings({ subpage }: AppearanceSettingsProps = {}) {
   const embedAllowed = useStore($embedAllowed)
   const composerPopoutGesturesEnabled = useStore($composerPopoutGesturesEnabled)
   const fileBrowserOpen = useStore($fileBrowserOpen)
+  const fileBrowserShadowed = useStore($modeShadowed('fileBrowserOpen'))
   const translucency = useStore($translucency)
   const glassMode = translucency.mode === 'glass' && GLASS_SUPPORTED
   const userBubbleTransparency = useStore($userBubbleTransparency)
@@ -927,11 +928,12 @@ export function AppearanceSettings({ subpage }: AppearanceSettingsProps = {}) {
           )}
 
           {/* The same state as the titlebar toggle / ⌘J, which persists across
-              launches — so this is the file browser's standing default. */}
+              launches — so this is the file browser's standing default. Simple
+              mode shadows it; a flip there only lasts the session, so say so. */}
           {show('window-layout') && (
             <ToggleRow
               checked={fileBrowserOpen}
-              description={a.fileBrowserDesc}
+              description={withModeNote(a.fileBrowserDesc, fileBrowserShadowed)}
               id={settingElementId(ids.fileBrowser)}
               label={a.fileBrowserTitle}
               onChange={setFileBrowserOpen}

apps/desktop/src/app/settings/file-browser-setting.test.tsx

@@ -3,6 +3,8 @@ import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
 import { act, cleanup, fireEvent, render, screen } from '@testing-library/react'
 import { afterEach, describe, expect, it } from 'vitest'
 
+import { en } from '@/i18n/en'
+import { $interfaceMode } from '@/store/interface-mode'
 import { $fileBrowserOpen, FILE_BROWSER_PANE_ID, setFileBrowserOpen, toggleFileBrowserOpen } from '@/store/layout'
 import { $paneStates } from '@/store/panes'
 
@@ -14,7 +16,10 @@ import { AppearanceSettings } from './appearance-settings'
 
 afterEach(() => {
   cleanup()
-  act(() => setFileBrowserOpen(false))
+  act(() => {
+    $interfaceMode.set('advanced')
+    setFileBrowserOpen(false)
+  })
 })
 
 function fileBrowserSwitch() {
@@ -51,4 +56,21 @@ describe('File Browser setting', () => {
 
     expect(toggle.getAttribute('aria-checked')).toBe('true')
   })
+
+  it('says a flip is session-only while Simple mode decides the value', () => {
+    const note = en.interfaceMode.sessionNote
+
+    act(() => $interfaceMode.set('simple'))
+    const toggle = fileBrowserSwitch()
+
+    expect(screen.getByText(content => content.includes(note))).toBeTruthy()
+
+    // Simple shadows the preference: the click is a session reveal, not a new default.
+    fireEvent.click(toggle)
+    expect(toggle.getAttribute('aria-checked')).toBe('true')
+
+    act(() => $interfaceMode.set('advanced'))
+    expect(screen.queryByText(content => content.includes(note))).toBeNull()
+    expect(toggle.getAttribute('aria-checked')).toBe('false')
+  })
 })