[client] Debug: create GUI windows on demand and destroy them on close

Experiment on top of the memory profiler: the main and Settings windows are no
longer created at startup or kept alive hidden, so an idle tray holds no webview
process. The WindowManager owns creation, rebuilds the main window on the next
show, and defers every show until the frontend reports it has rendered, which
keeps an empty webview off screen.

Measured on macOS: idle footprint drops from ~160 MB to ~74 MB, at the cost of
~150-250 ms per window open.

client/ui/services/windowmanager.go

@@ -8,6 +8,7 @@ import (
 	"sync"
 	"time"
 
+	log "github.com/sirupsen/logrus"
 	"github.com/wailsapp/wails/v3/pkg/application"
 	"github.com/wailsapp/wails/v3/pkg/events"
 
@@ -29,6 +30,10 @@ const EventBrowserLoginCancel = "browser-login:cancel"
 // EventSettingsOpen tells the mounted settings window which tab to show.
 const EventSettingsOpen = "netbird:settings:open"
 
+const EventWindowPainted = "netbird:window-painted"
+
+const paintedFallback = 2 * time.Second
+
 var WindowBackgroundColour = application.NewRGB(24, 26, 29) // bg-nb-gray-950
 
 // WindowHeight is shared by the main and Settings windows.
@@ -94,9 +99,6 @@ func DialogWindowOptions(name, title, url string, linuxIcon []byte) application.
 	}
 }
 
-// WindowManager owns the auxiliary windows (main is created in main.go). Settings is created
-// eagerly and hidden on close to keep React state; the rest are created on open, destroyed on
-// close, so the macOS dock-reopen handler finds no hidden window to resurrect.
 type WindowManager struct {
 	app               *application.App
 	mainWindow        *application.WebviewWindow
@@ -112,15 +114,31 @@ type WindowManager struct {
 	// hiddenForLogin holds windows hidden while the BrowserLogin popup is open, restored on close.
 	hiddenForLogin []application.Window
 	mu             sync.Mutex
+	newMain        func() *application.WebviewWindow
+	ready          map[uint]bool
+	showPending    map[uint]bool
+	showAsked      map[uint]time.Time
+	pendingTab     map[uint]string
+	fallbackTimers map[uint]*time.Timer
 	// recenterOnShow is set only on the minimal-WM/XEmbed path, where the WM neither centers nor
 	// restores position; nil on full desktops so re-centering can't fight a user-moved window.
 	recenterOnShow func() bool
 }
 
-// NewWindowManager wires the manager to the main app; translator/prefs may be nil (tests). The
-// Settings window is created here (hidden) so the first OpenSettings is instant.
 func NewWindowManager(app *application.App, mainWindow *application.WebviewWindow, translator ErrorTranslator, prefs LanguagePreference, linuxIcon []byte) *WindowManager {
-	s := &WindowManager{app: app, mainWindow: mainWindow, translator: translator, prefs: prefs, linuxIcon: linuxIcon}
+	s := &WindowManager{
+		app:            app,
+		mainWindow:     mainWindow,
+		translator:     translator,
+		prefs:          prefs,
+		linuxIcon:      linuxIcon,
+		ready:          map[uint]bool{},
+		showPending:    map[uint]bool{},
+		showAsked:      map[uint]time.Time{},
+		pendingTab:     map[uint]string{},
+		fallbackTimers: map[uint]*time.Timer{},
+	}
+	s.watchPainted()
 	// Re-title live windows on language flip. Wired internally so the binding generator
 	// doesn't try to expose the interface param.
 	if sub, ok := prefs.(LanguageSubscriber); ok && sub != nil {
@@ -136,7 +154,11 @@ func NewWindowManager(app *application.App, mainWindow *application.WebviewWindo
 			}
 		}()
 	}
-	s.settings = app.Window.NewWithOptions(application.WebviewWindowOptions{
+	return s
+}
+
+func (s *WindowManager) newSettingsWindow() *application.WebviewWindow {
+	w := s.app.Window.NewWithOptions(application.WebviewWindowOptions{
 		Name:                "settings",
 		Title:               s.title("window.title.settings"),
 		Width:               900,
@@ -150,18 +172,15 @@ func NewWindowManager(app *application.App, mainWindow *application.WebviewWindo
 		URL:                 "/#/settings",
 		Mac:                 AppleMacOSAppearanceOptions(),
 		Windows:             MicrosoftWindowsAppearanceOptions(),
-		Linux:               LinuxAppearanceOptions(linuxIcon),
+		Linux:               LinuxAppearanceOptions(s.linuxIcon),
 	})
-	// Hide (not destroy) on close to keep React state; reset to General for a flash-free reopen.
-	s.settings.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
-		if ShuttingDown() {
-			return
-		}
-		e.Cancel()
-		s.app.Event.Emit(EventSettingsOpen, "general")
-		s.settings.Hide()
+	w.RegisterHook(events.Common.WindowClosing, func(_ *application.WindowEvent) {
+		s.mu.Lock()
+		s.settings = nil
+		s.forgetWindowLocked(w)
+		s.mu.Unlock()
 	})
-	return s
+	return w
 }
 
 // OpenSettings shows the settings window on tab (empty → General), switching tab via
@@ -171,11 +190,23 @@ func (s *WindowManager) OpenSettings(tab string) {
 	if target == "" {
 		target = "general"
 	}
-	s.app.Event.Emit(EventSettingsOpen, target)
-	s.settings.Show()
-	s.settings.Focus()
-	// Re-center (minimal-WM only; see centerWhenReady).
-	s.centerWhenReady(s.settings)
+
+	s.mu.Lock()
+	fresh := s.settings == nil
+	if fresh {
+		s.settings = s.newSettingsWindow()
+		s.armReady(s.settings)
+	}
+	w := s.settings
+	if fresh {
+		s.pendingTab[w.ID()] = target
+	}
+	s.mu.Unlock()
+
+	if !fresh {
+		s.app.Event.Emit(EventSettingsOpen, target)
+	}
+	s.showWhenReady(w)
 }
 
 // OpenBrowserLogin shows the SSO popup, creating it on first use.
@@ -440,13 +471,167 @@ func (s *WindowManager) OpenMain() {
 // ShowMain brings the main window forward (re-centering on minimal WMs). The single entry
 // point every surface (tray, SIGUSR1, welcome) should use so centering applies uniformly.
 func (s *WindowManager) ShowMain() {
-	if s.mainWindow == nil {
+	s.showWhenReady(s.MainWindow())
+}
+
+func (s *WindowManager) MainWindow() *application.WebviewWindow {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.mainWindow == nil && s.newMain != nil {
+		s.mainWindow = s.newMain()
+		s.armReady(s.mainWindow)
+	}
+	return s.mainWindow
+}
+
+func (s *WindowManager) armReady(w *application.WebviewWindow) {
+	if w == nil {
 		return
 	}
-	s.mainWindow.Show()
-	s.mainWindow.Focus()
-	// Re-center (minimal-WM only; see centerWhenReady).
-	s.centerWhenReady(s.mainWindow)
+	created := time.Now()
+	w.RegisterHook(events.Common.WindowRuntimeReady, func(_ *application.WindowEvent) {
+		log.Infof("window %q runtime ready after %s", w.Name(), time.Since(created).Round(time.Millisecond))
+		timer := time.AfterFunc(paintedFallback, func() {
+			s.markReady(w, "fallback")
+		})
+		s.mu.Lock()
+		s.fallbackTimers[w.ID()] = timer
+		s.mu.Unlock()
+	})
+}
+
+func (s *WindowManager) watchPainted() {
+	s.app.Event.On(EventWindowPainted, func(e *application.CustomEvent) {
+		w := s.windowByName(e.Sender)
+		if w == nil {
+			log.Infof("painted event from unknown sender %q", e.Sender)
+			return
+		}
+		s.markReady(w, "painted")
+	})
+}
+
+func (s *WindowManager) forgetWindowLocked(w *application.WebviewWindow) {
+	if w == nil {
+		return
+	}
+
+	id := w.ID()
+	if timer := s.fallbackTimers[id]; timer != nil {
+		timer.Stop()
+	}
+	delete(s.fallbackTimers, id)
+	delete(s.ready, id)
+	delete(s.showPending, id)
+	delete(s.showAsked, id)
+	delete(s.pendingTab, id)
+
+	kept := s.hiddenForLogin[:0]
+	for _, hidden := range s.hiddenForLogin {
+		if hidden != application.Window(w) {
+			kept = append(kept, hidden)
+		}
+	}
+	s.hiddenForLogin = kept
+}
+
+func (s *WindowManager) windowByName(name string) *application.WebviewWindow {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	switch name {
+	case "main":
+		return s.mainWindow
+	case "settings":
+		return s.settings
+	default:
+		return nil
+	}
+}
+
+func (s *WindowManager) markReady(w *application.WebviewWindow, source string) {
+	id := w.ID()
+	s.mu.Lock()
+	already := s.ready[id]
+	s.ready[id] = true
+	wanted := s.showPending[id]
+	asked := s.showAsked[id]
+	tab, hasTab := s.pendingTab[id]
+	if timer := s.fallbackTimers[id]; timer != nil {
+		timer.Stop()
+		delete(s.fallbackTimers, id)
+	}
+	delete(s.showPending, id)
+	delete(s.showAsked, id)
+	delete(s.pendingTab, id)
+	s.mu.Unlock()
+
+	if already {
+		return
+	}
+
+	if hasTab {
+		s.app.Event.Emit(EventSettingsOpen, tab)
+	}
+
+	waited := "no show waiting"
+	if wanted && !asked.IsZero() {
+		waited = time.Since(asked).Round(time.Millisecond).String()
+	}
+	log.Infof("window %q ready via %s, show waited %s", w.Name(), source, waited)
+
+	if wanted {
+		s.showNow(w)
+	}
+}
+
+func (s *WindowManager) showWhenReady(w *application.WebviewWindow) {
+	if w == nil {
+		return
+	}
+
+	id := w.ID()
+	s.mu.Lock()
+	ready := s.ready[id]
+	if !ready {
+		s.showPending[id] = true
+		s.showAsked[id] = time.Now()
+	}
+	s.mu.Unlock()
+
+	if ready {
+		log.Infof("window %q already ready, showing now", w.Name())
+		s.showNow(w)
+		return
+	}
+	log.Infof("window %q not ready yet, deferring show", w.Name())
+}
+
+func (s *WindowManager) showNow(w *application.WebviewWindow) {
+	w.Show()
+	w.Focus()
+	s.centerWhenReady(w)
+}
+
+func (s *WindowManager) ShowMainAt(url string) {
+	w := s.MainWindow()
+	if w == nil {
+		return
+	}
+	w.SetURL(url)
+	s.showWhenReady(w)
+}
+
+func (s *WindowManager) SetMainFactory(f func() *application.WebviewWindow) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.newMain = f
+}
+
+func (s *WindowManager) ForgetMain() {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.forgetWindowLocked(s.mainWindow)
+	s.mainWindow = nil
 }
 
 // SetRecenterOnShow installs the recenterOnShow predicate (see the field).