[client] Serialize window operations while a slot is being created

Callers arriving after the window is published but before the creator
has drained the queue took the existing-window fast path and could run
ahead of older queued operations, so a newer SetURL could be overwritten
by an older one. withWindow now queues every caller while the creating
flag is set and clears the flag only once the queue is seen empty under
the lock.

A factory panic or a nil window left the creating flag set and the slot
dead; creation and drain now reset that state on early exit.

hideOtherWindows records the windows it hid only when no restore ran
in between, tracked by a generation counter, and re-shows them otherwise,
so a restore racing the hide cannot strand hidden windows.

client/ui/services/windowmanager.go

@@ -131,6 +131,7 @@ type WindowManager struct {
 	newMain        func(startURL string) *application.WebviewWindow
 	creating       map[string]bool
 	pendingOps     map[string][]windowOp
+	restoreGen     uint64
 	ready          map[uint]bool
 	showPending    map[uint]bool
 	pendingTab     map[uint]string
@@ -567,6 +568,11 @@ func (s *WindowManager) ensureMain(startURL string, op windowOp) {
 
 func (s *WindowManager) withWindow(name string, slot **application.WebviewWindow, factory func() *application.WebviewWindow, op windowOp) {
 	s.mu.Lock()
+	if s.creating[name] {
+		s.pendingOps[name] = append(s.pendingOps[name], op)
+		s.mu.Unlock()
+		return
+	}
 	if w := *slot; w != nil {
 		s.mu.Unlock()
 		op(w, false)
@@ -576,29 +582,66 @@ func (s *WindowManager) withWindow(name string, slot **application.WebviewWindow
 		s.mu.Unlock()
 		return
 	}
-	if s.creating[name] {
-		s.pendingOps[name] = append(s.pendingOps[name], op)
-		s.mu.Unlock()
-		return
-	}
 	s.creating[name] = true
 	s.mu.Unlock()
 
-	w := factory()
-
-	s.mu.Lock()
-	*slot = w
-	delete(s.creating, name)
-	queued := s.pendingOps[name]
-	delete(s.pendingOps, name)
-	s.mu.Unlock()
-
+	w := s.createWindow(name, slot, factory)
 	if w == nil {
 		return
 	}
+	s.finishCreation(name, w, op)
+}
+
+func (s *WindowManager) createWindow(name string, slot **application.WebviewWindow, factory func() *application.WebviewWindow) *application.WebviewWindow {
+	created := false
+	defer func() {
+		if created {
+			return
+		}
+		s.mu.Lock()
+		delete(s.creating, name)
+		delete(s.pendingOps, name)
+		s.mu.Unlock()
+	}()
+
+	w := factory()
+	if w == nil {
+		return nil
+	}
+	s.mu.Lock()
+	*slot = w
+	s.mu.Unlock()
+	created = true
+	return w
+}
+
+func (s *WindowManager) finishCreation(name string, w *application.WebviewWindow, op windowOp) {
+	finished := false
+	defer func() {
+		if finished {
+			return
+		}
+		s.mu.Lock()
+		delete(s.creating, name)
+		delete(s.pendingOps, name)
+		s.mu.Unlock()
+	}()
+
 	op(w, true)
-	for _, queuedOp := range queued {
-		queuedOp(w, false)
+	for {
+		s.mu.Lock()
+		queued := s.pendingOps[name]
+		delete(s.pendingOps, name)
+		if len(queued) == 0 {
+			delete(s.creating, name)
+			finished = true
+			s.mu.Unlock()
+			return
+		}
+		s.mu.Unlock()
+		for _, queuedOp := range queued {
+			queuedOp(w, false)
+		}
 	}
 }
 
@@ -927,6 +970,10 @@ func (s *WindowManager) retitleAll() {
 }
 
 func (s *WindowManager) hideOtherWindows(keepName string) {
+	s.mu.Lock()
+	gen := s.restoreGen
+	s.mu.Unlock()
+
 	var hidden []application.Window
 	for _, w := range s.app.Window.GetAll() {
 		if w == nil || w.Name() == keepName || !w.IsVisible() {
@@ -938,9 +985,19 @@ func (s *WindowManager) hideOtherWindows(keepName string) {
 	if len(hidden) == 0 {
 		return
 	}
+
 	s.mu.Lock()
-	s.hiddenForLogin = append(s.hiddenForLogin, hidden...)
+	restored := s.restoreGen != gen
+	if !restored {
+		s.hiddenForLogin = append(s.hiddenForLogin, hidden...)
+	}
 	s.mu.Unlock()
+	if !restored {
+		return
+	}
+	for _, w := range hidden {
+		w.Show()
+	}
 }
 
 // restoreHiddenWindows re-shows windows hidden by hideOtherWindows. If the main
@@ -951,6 +1008,7 @@ func (s *WindowManager) restoreHiddenWindows() {
 	s.mu.Lock()
 	hidden := s.hiddenForLogin
 	s.hiddenForLogin = nil
+	s.restoreGen++
 	mainWindow := s.mainWindow
 	s.mu.Unlock()