fix: prevent GTK widget crash on Fedora startup dialog (#268)

The first-run dialog was crashing on Fedora/Wayland when clicking any
button with the error: gtk_widget_get_scale_factor: assertion
'GTK_IS_WIDGET (widget)' failed.

Root cause: Direct destroy() calls from button click handlers caused
race conditions where GTK tried to access widget properties after the
widget was marked for destruction but before event processing completed.

Fix: Use GTK's proper dialog response signal pattern instead of direct
destroy() calls. Buttons are now added with response IDs, and the
response signal handler sets the result. This lets GTK manage the
dialog lifecycle properly and prevents the race condition.

Fixes #267

src/vocalinux/ui/first_run_dialog.py

@@ -14,6 +14,11 @@ from gi.repository import Gtk
 
 logger = logging.getLogger(__name__)
 
+# Custom response IDs for dialog buttons
+RESPONSE_YES = 1
+RESPONSE_NO = 2
+RESPONSE_LATER = 3
+
 
 class FirstRunDialog(Gtk.Dialog):
     """Dialog shown on first run to configure autostart preference."""
@@ -26,6 +31,19 @@ class FirstRunDialog(Gtk.Dialog):
         )
         self.set_default_size(440, 280)
 
+        # Map response IDs to result strings
+        self._response_map = {
+            RESPONSE_YES: "yes",
+            RESPONSE_NO: "no",
+            RESPONSE_LATER: "later",
+            Gtk.ResponseType.DELETE_EVENT: None,
+        }
+        self.result = None
+
+        # Connect to response signal to handle button clicks properly
+        # This avoids race conditions when destroying the dialog from button handlers
+        self.connect("response", self._on_response)
+
         box = self.get_content_area()
         box.set_spacing(16)
         box.set_margin_start(24)
@@ -69,38 +87,39 @@ class FirstRunDialog(Gtk.Dialog):
         button_box.set_halign(Gtk.Align.CENTER)
         button_box.set_margin_top(16)
 
-        yes_button = Gtk.Button(label="Yes, start on login")
+        # Use add_button with response IDs instead of custom click handlers
+        # This ensures proper dialog lifecycle management and avoids GTK widget
+        # access issues on Wayland (gtk_widget_get_scale_factor assertion failures)
+        yes_button = self.add_button("Yes, start on login", RESPONSE_YES)
         yes_button.get_style_context().add_class("suggested-action")
-        yes_button.connect("clicked", self._on_yes_clicked)
+
+        no_button = self.add_button("No, I'll start manually", RESPONSE_NO)
+        later_button = self.add_button("Ask me later", RESPONSE_LATER)
+
+        # Reparent buttons to our custom button box for proper layout
+        # First remove them from the dialog's action area
+        self.get_action_area().remove(yes_button)
+        self.get_action_area().remove(no_button)
+        self.get_action_area().remove(later_button)
+
+        # Add them to our custom button box
         button_box.pack_start(yes_button, False, False, 0)
-
-        no_button = Gtk.Button(label="No, I'll start manually")
-        no_button.connect("clicked", self._on_no_clicked)
         button_box.pack_start(no_button, False, False, 0)
-
-        later_button = Gtk.Button(label="Ask me later")
-        later_button.connect("clicked", self._on_later_clicked)
         button_box.pack_start(later_button, False, False, 0)
 
         box.pack_start(button_box, False, False, 0)
 
-        self.result = None
         self.show_all()
 
-    def _on_yes_clicked(self, widget):
-        """Handle Yes button click."""
-        self.result = "yes"
-        self.destroy()
+    def _on_response(self, dialog, response_id):
+        """Handle dialog response signals properly.
 
-    def _on_no_clicked(self, widget):
-        """Handle No button click."""
-        self.result = "no"
-        self.destroy()
-
-    def _on_later_clicked(self, widget):
-        """Handle Later button click."""
-        self.result = "later"
-        self.destroy()
+        Using the response signal instead of direct destroy() calls from button
+        handlers prevents race conditions on Wayland where GTK may try to access
+        widget properties (like scale_factor) after the widget is marked for
+        destruction but before the event processing completes.
+        """
+        self.result = self._response_map.get(response_id, None)
 
 
 def show_first_run_dialog(parent: Optional[Gtk.Window] = None) -> Optional[str]: