diff --git a/desktop/src/components/controls/PermissionModeSelector.test.tsx b/desktop/src/components/controls/PermissionModeSelector.test.tsx
index 98d2bfba..fe242066 100644
--- a/desktop/src/components/controls/PermissionModeSelector.test.tsx
+++ b/desktop/src/components/controls/PermissionModeSelector.test.tsx
@@ -38,6 +38,7 @@ vi.mock('../../i18n', () => ({
     'permMode.permShell': 'Run shell commands',
     'permMode.permPackages': 'Install packages',
     'permMode.enableBypassBtn': 'Enable bypass',
+    'permMode.disabledDuringTurn': 'Cannot switch permissions while session is active',
     'common.cancel': 'Cancel',
     'tabs.close': 'Close',
   }[key] ?? key),
@@ -159,4 +160,46 @@ describe('PermissionModeSelector', () => {
     expect(screen.getByText('C:\\Users\\LinTan\\MyScript\\test5')).toBeInTheDocument()
     expect(screen.queryByText('C:\\Users\\LinTan')).not.toBeInTheDocument()
   })
+
+  it('disables the trigger button when the session turn is active', () => {
+    const setSessionPermissionMode = vi.fn()
+    useChatStore.setState({
+      setSessionPermissionMode,
+      sessions: {
+        'current-tab': { chatState: 'thinking' },
+      },
+    } as Partial<ReturnType<typeof useChatStore.getState>>)
+    useSessionStore.setState({
+      activeSessionId: 'current-tab',
+      sessions: [
+        {
+          id: 'current-tab',
+          title: 'Current',
+          createdAt: '2026-05-24T00:00:00.000Z',
+          modifiedAt: '2026-05-24T00:00:00.000Z',
+          messageCount: 1,
+          projectPath: '/repo',
+          projectRoot: '/repo',
+          workDir: '/repo',
+          workDirExists: true,
+          permissionMode: 'default',
+        },
+      ],
+    })
+    useTabStore.setState({
+      activeTabId: 'current-tab',
+      tabs: [{ sessionId: 'current-tab', title: 'Current', type: 'session', status: 'idle' }],
+    })
+
+    render(<PermissionModeSelector />)
+
+    const trigger = screen.getByRole('button', { name: 'Ask permissions' })
+    expect(trigger).toBeDisabled()
+    expect(trigger).toHaveAttribute('title', 'Cannot switch permissions while session is active')
+
+    fireEvent.click(trigger)
+    // Menu should not open when disabled
+    expect(screen.queryByRole('menu')).not.toBeInTheDocument()
+    expect(setSessionPermissionMode).not.toHaveBeenCalled()
+  })
 })
diff --git a/desktop/src/components/controls/PermissionModeSelector.tsx b/desktop/src/components/controls/PermissionModeSelector.tsx
index f7d094ac..50da59ef 100644
--- a/desktop/src/components/controls/PermissionModeSelector.tsx
+++ b/desktop/src/components/controls/PermissionModeSelector.tsx
@@ -36,6 +36,10 @@ export function PermissionModeSelector({ workDir: workDirProp, compact = false,
   const setSessionPermissionMode = useChatStore((s) => s.setSessionPermissionMode)
   const activeTabId = useTabStore((s) => s.activeTabId)
   const sessions = useSessionStore((s) => s.sessions)
+  const chatState = useChatStore((s) =>
+    activeTabId ? s.sessions[activeTabId]?.chatState ?? 'idle' : 'idle',
+  )
+  const isTurnActive = chatState !== 'idle'
   const [open, setOpen] = useState(false)
   const [confirmDialog, setConfirmDialog] = useState(false)
   const ref = useRef<HTMLDivElement>(null)
@@ -179,15 +183,16 @@ export function PermissionModeSelector({ workDir: workDirProp, compact = false,
   return (
     <div ref={ref} className="relative">
       <button
-        onClick={() => setOpen(!open)}
+        onClick={() => { if (!isTurnActive) setOpen(!open) }}
+        disabled={isTurnActive}
         aria-label={MODE_LABELS[currentMode]}
         aria-haspopup="menu"
         aria-expanded={open}
         aria-controls={open ? menuId : undefined}
-        title={compact ? MODE_LABELS[currentMode] : undefined}
-        className={`flex items-center bg-[var(--color-surface-container-low)] font-medium text-[var(--color-text-secondary)] transition-colors hover:bg-[var(--color-surface-hover)] ${
-          compactButtonClass
-        }`}
+        title={isTurnActive ? t('permMode.disabledDuringTurn') : (compact ? MODE_LABELS[currentMode] : undefined)}
+        className={`flex items-center bg-[var(--color-surface-container-low)] font-medium text-[var(--color-text-secondary)] transition-colors ${
+          isTurnActive ? 'opacity-50 cursor-not-allowed' : 'hover:bg-[var(--color-surface-hover)]'
+        } ${compactButtonClass}`}
       >
         <span className="material-symbols-outlined text-[14px]">{MODE_ICONS[currentMode]}</span>
         {!compact && (