[client] Add a UI setting to stay connected after quitting (#7078)

Quitting the GUI from the tray always sent a Down RPC, dropping the VPN
connection with it. Some users want the connection to survive the UI.

client/ui/preferences/store.go

@@ -58,6 +58,10 @@ type UIPreferences struct {
 	// decision has run for this OS user. It only ever transitions to true
 	// and is never reset, so the default-on flow runs at most once, ever.
 	AutostartInitialized bool `json:"autostartInitialized"`
+	// KeepConnectedOnQuit leaves the daemon connected when the GUI quits.
+	// Its false zero value preserves the historical disconnect-on-quit
+	// behaviour for preference files written before the field existed.
+	KeepConnectedOnQuit bool `json:"keepConnectedOnQuit"`
 }
 
 // LanguageValidator rejects SetLanguage inputs with no shipped bundle.
@@ -183,6 +187,26 @@ func (s *Store) SetAutostartInitialized(done bool) error {
 	return nil
 }
 
+// SetKeepConnectedOnQuit persists the disconnect-on-quit opt-out. No-op if unchanged.
+func (s *Store) SetKeepConnectedOnQuit(keep bool) error {
+	s.mu.Lock()
+	if s.current.KeepConnectedOnQuit == keep {
+		s.mu.Unlock()
+		return nil
+	}
+	next := s.current
+	next.KeepConnectedOnQuit = keep
+	if err := s.persistLocked(next); err != nil {
+		s.mu.Unlock()
+		return fmt.Errorf("persist preferences: %w", err)
+	}
+	s.current = next
+	s.mu.Unlock()
+
+	s.broadcast(next)
+	return nil
+}
+
 // SetLanguage validates, persists, and broadcasts. No-op if unchanged.
 func (s *Store) SetLanguage(lang i18n.LanguageCode) error {
 	if lang == "" {

client/ui/preferences/store_test.go

@@ -238,6 +238,42 @@ func TestStore_SetAutostartInitializedPersistsAcrossReload(t *testing.T) {
 	assert.True(t, reloaded.Get().AutostartInitialized, "marker must survive a reload from disk")
 }
 
+func TestStore_SetKeepConnectedOnQuitPersistsAcrossReload(t *testing.T) {
+	withTempConfigDir(t)
+	emitter := &recordingEmitter{}
+	s, err := NewStore(nil, emitter)
+	require.NoError(t, err)
+
+	assert.False(t, s.Get().KeepConnectedOnQuit, "quitting must disconnect by default")
+
+	require.NoError(t, s.SetKeepConnectedOnQuit(true))
+	assert.True(t, s.Get().KeepConnectedOnQuit, "Get should reflect the persisted opt-out")
+	require.Len(t, emitter.calledWith(EventPreferencesChanged), 1, "first write should broadcast")
+
+	require.NoError(t, s.SetKeepConnectedOnQuit(true))
+	assert.Len(t, emitter.calledWith(EventPreferencesChanged), 1, "idempotent write should not broadcast again")
+
+	reloaded, err := NewStore(nil, nil)
+	require.NoError(t, err)
+	assert.True(t, reloaded.Get().KeepConnectedOnQuit, "opt-out must survive a reload from disk")
+}
+
+func TestStore_KeepConnectedOnQuitDefaultsFalseForPreExistingFile(t *testing.T) {
+	withTempConfigDir(t)
+
+	// A preferences file written before the field existed must keep the
+	// historical disconnect-on-quit behaviour rather than silently opting out.
+	path, err := preferencesPath()
+	require.NoError(t, err)
+	require.NoError(t, os.MkdirAll(filepath.Dir(path), 0o755))
+	require.NoError(t, os.WriteFile(path, []byte(`{"language":"en","viewMode":"default"}`), 0o600))
+
+	s, err := NewStore(nil, nil)
+	require.NoError(t, err)
+	assert.False(t, s.Get().KeepConnectedOnQuit, "a file predating the field must not opt out of disconnect-on-quit")
+	assert.True(t, s.ExistedAtLoad(), "the pre-existing file must be seen on disk")
+}
+
 func TestStore_ExistedAtLoad(t *testing.T) {
 	withTempConfigDir(t)