Fit the split on a double-click only once the handle's drag ends

The split's own drag is still going during the second press of a
double-click, so the least movement before the release put the handle
back under the pointer right after it was fitted. The fit now waits for
that drag to end.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/gui/window.cpp

@@ -227,10 +227,30 @@ Gtk::Widget& EffectorWindow::buildChainTab() {
         auto click = Gtk::GestureClick::create();
         click->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
         // The split's drag ends every press on the handle, which starts the
-        // click's count over, so the second press is counted here.
+        // click's count over, so the second press is counted here. And that
+        // drag is still going on during the second press -- the least jitter
+        // puts the handle back under the pointer -- so the fit waits for it
+        // to end.
+        std::vector<Glib::RefPtr<Gtk::GestureDrag>> drags;
+        const auto controllers = split->observe_controllers();
+        for (guint i = 0; i < controllers->get_n_items(); ++i) {
+            auto other = std::dynamic_pointer_cast<Gtk::Gesture>(controllers->get_object(i));
+            if (other) click->group(other);
+            if (auto drag = std::dynamic_pointer_cast<Gtk::GestureDrag>(other)) drags.push_back(drag);
+        }
         auto lastPress = std::make_shared<guint32>(0);
+        auto refitPending = std::make_shared<bool>(false);
+        for (const auto& drag : drags) {
+            drag->signal_drag_end().connect([this, refitPending](double, double) {
+                if (!*refitPending) return;
+                *refitPending = false;
+                refitChainSplit();
+            });
+        }
         auto* gesture = click.get();  // not the RefPtr: the gesture owns this slot
-        click->signal_pressed().connect([this, split, handle, gesture, lastPress](int, double x, double y) {
+        const bool waitForDrag = !drags.empty();
+        click->signal_pressed().connect(
+            [this, split, handle, gesture, lastPress, refitPending, waitForDrag](int, double x, double y) {
             // The handle is thin, and the drag takes presses a little past it.
             const auto bounds = handle->compute_bounds(*split);
             constexpr double slack = 6.0;
@@ -244,16 +264,15 @@ Gtk::Widget& EffectorWindow::buildChainTab() {
             const int doubleClick = Gtk::Settings::get_default()->property_gtk_double_click_time();
             if (*lastPress != 0 && now - *lastPress <= static_cast<guint32>(doubleClick)) {
                 *lastPress = 0;
-                refitChainSplit();
+                if (waitForDrag) {
+                    *refitPending = true;
+                } else {
+                    refitChainSplit();
+                }
             } else {
                 *lastPress = now;
             }
         });
-        const auto controllers = split->observe_controllers();
-        for (guint i = 0; i < controllers->get_n_items(); ++i) {
-            auto drag = std::dynamic_pointer_cast<Gtk::Gesture>(controllers->get_object(i));
-            if (drag) click->group(drag);
-        }
         split->add_controller(click);
     }
     rebuildChainRows();