kernel: add UiSurface::bind_drag (RmlUi drag events with surface-local coords)

Forwards RmlUi Dragstart/Drag/Dragend for a named callback as DragPhase
{start,move,end} with surface-local x/y, so an extension can drive an
interactive drag from a captured ui-surface touch (the touch bus never
sees it). Mirrors bind_event's error-isolation + hot-reload handling.

1 files changed, 4 insertions, 0 deletions

diff --git a/packages/kernel/src/server.cpp b/packages/kernel/src/server.cpp
index cbd23c3..66f2cc3 100644
--- a/packages/kernel/src/server.cpp
+++ b/packages/kernel/src/server.cpp
@@ -105,6 +105,10 @@ auto Server::ui_click_element(const char* tag, int index) -> bool {
     return impl_->substrate != nullptr && impl_->substrate->click_element(tag, index);
 }
 
+auto Server::ui_drag_element(const char* tag, int index, double dx, double dy) -> bool {
+    return impl_->substrate != nullptr && impl_->substrate->drag_element(tag, index, dx, dy);
+}
+
 auto Server::ui_reload_surface() -> bool {
     return impl_->substrate != nullptr && impl_->substrate->reload_first_surface();
 }