Can now go down a level.

src/gui/fsm.cpp

@@ -431,7 +431,8 @@ namespace gui {
           event(Event::ATTACK, data);
           break;
         case eGUI::STAIRS_DOWN:
-          dbc::sentinel("make me!");
+          next_level();
+          state(State::IDLE);
           break;
         case eGUI::DEATH: {
             $status_ui.update();

src/gui/status_ui.cpp

@@ -66,16 +66,22 @@ namespace gui {
     $body_ui.update();
 
     for(const auto& [slot, cell] : $gui.cells()) {
-
       if(inventory.has(slot)) {
         auto gui_id = $gui.entity(slot);
         auto world_entity = inventory.get(slot);
 
+        dbc::check(world->has<components::Sprite>(world_entity),
+            fmt::format("inventory {} has missing sprite", slot));
+
         auto& sprite = world->get<components::Sprite>(world_entity);
+
         $gui.set_init<guecs::Icon>(gui_id, {sprite.name});
+
         guecs::GrabSource grabber{ world_entity,
           [&, gui_id]() { return remove_slot(gui_id); }};
+
         grabber.setSprite($gui, gui_id);
+
         $gui.set<guecs::GrabSource>(gui_id, grabber);
       } else {
         auto gui_id = $gui.entity(slot);