Added a hopeful quit blocking dialog.

src/SettingsDialog.zig

@@ -105,6 +105,10 @@ theme_buttons: [std.enums.values(Settings.Theme).len]*gtk.ToggleButton,
 /// changes which palette it is editing, so it has to be told.
 colors: *PaletteEditor,
 
+/// The confirm-before-quitting toggle. Held only so the switch can be built in
+/// one place and read in another; nothing re-checks it.
+confirm_quit: *gtk.Switch,
+
 /// Container the startup rows live in, so rows can be added and removed after
 /// the page is already on screen.
 startup_box: *gtk.Box,
@@ -140,6 +144,7 @@ pub fn present(alloc: std.mem.Allocator, parent: *gtk.Window, opts: Options) !vo
         .ctx = opts.ctx,
         .theme_buttons = undefined,
         .colors = undefined,
+        .confirm_quit = gtk.Switch.new(),
         .startup_box = gtk.Box.new(.vertical, 6),
         .error_label = gtk.Label.new(null),
     };
@@ -160,6 +165,7 @@ pub fn present(alloc: std.mem.Allocator, parent: *gtk.Window, opts: Options) !vo
     content.as(gtk.Widget).addCssClass("playpen-dialog-content");
 
     content.append(self.buildAppearance());
+    content.append(self.buildQuitting());
     content.append(self.buildStartup());
 
     self.error_label.setXalign(0);
@@ -324,6 +330,78 @@ fn onThemeToggled(button: *gtk.ToggleButton, self: *SettingsDialog) callconv(.c)
     self.colors.refresh();
 }
 
+// -------------------------------------------------------------------------
+// Quitting
+
+/// The Quitting section: whether closing the window asks first.
+///
+/// Above the startup list rather than below it. That list grows with the number
+/// of tabs someone opens at launch, and a single-row group underneath it would
+/// be reachable only by scrolling past every one of them.
+fn buildQuitting(self: *SettingsDialog) *gtk.Widget {
+    const group = gtk.Box.new(.vertical, 10);
+    group.as(gtk.Widget).addCssClass("playpen-settings-group");
+
+    const title = gtk.Label.new("Quitting");
+    title.setXalign(0);
+    title.as(gtk.Widget).addCssClass("playpen-settings-title");
+    group.append(title.as(gtk.Widget));
+
+    const row = gtk.Box.new(.horizontal, 12);
+
+    const labels = gtk.Box.new(.vertical, 2);
+    labels.as(gtk.Widget).setHexpand(1);
+    labels.as(gtk.Widget).setValign(.center);
+
+    const name = gtk.Label.new("Confirm before closing the window");
+    name.setXalign(0);
+    name.as(gtk.Widget).addCssClass("playpen-dialog-label");
+    labels.append(name.as(gtk.Widget));
+
+    const hint_label = gtk.Label.new(
+        "Closing the window exits every shell in every tab. Off, the window " ++
+            "goes the moment the window manager says so.",
+    );
+    hint_label.setXalign(0);
+    hint_label.setWrap(1);
+    hint_label.as(gtk.Widget).addCssClass("playpen-dialog-sublabel");
+    labels.append(hint_label.as(gtk.Widget));
+
+    row.append(labels.as(gtk.Widget));
+
+    self.confirm_quit.setActive(@intFromBool(Settings.get().confirm_quit));
+    self.confirm_quit.as(gtk.Widget).setValign(.center);
+    _ = gobject.Object.signals.notify.connect(
+        self.confirm_quit,
+        *SettingsDialog,
+        &onConfirmQuitChanged,
+        self,
+        .{ .detail = "active" },
+    );
+    row.append(self.confirm_quit.as(gtk.Widget));
+
+    group.append(row.as(gtk.Widget));
+
+    return group.as(gtk.Widget);
+}
+
+/// Straight to the file, as the theme picker does, rather than through
+/// `persist`: this is one flag, and `commit` would re-read every startup row to
+/// save it.
+fn onConfirmQuitChanged(
+    toggle: *gtk.Switch,
+    _: *gobject.ParamSpec,
+    self: *SettingsDialog,
+) callconv(.c) void {
+    Settings.get().confirm_quit = toggle.getActive() != 0;
+
+    Settings.get().save() catch {
+        self.showError("Could not write the settings file.");
+        return;
+    };
+    self.showError(null);
+}
+
 // -------------------------------------------------------------------------
 // Startup
 //