I think that's all the edge cases handled. You can more loot around fairly arbitrarily.

gui/dnd_loot.cpp

@@ -61,8 +61,8 @@ namespace gui {
         END(Event::CLOSE);
         break;
       case LOOT_SELECT:
-        $grab_source = start_grab($loot_ui.$gui, data);
-        if($grab_source) state(DNDState::LOOTING);
+        commit_move($loot_ui.$gui, $grab_source, data);
+        state(DNDState::LOOTING);
         break;
       case INV_SELECT:
         if(commit_drop($loot_ui.$gui,
@@ -91,7 +91,8 @@ namespace gui {
         }
         break;
       case INV_SELECT:
-        $grab_source = start_grab($status_ui.$gui, data);
+        // BUG: should I do a bool here and not transition?
+        commit_move($status_ui.$gui, $grab_source, data);
         state(DNDState::LOOTING);
         break;
       default:
@@ -195,15 +196,19 @@ namespace gui {
     }
   }
 
-  void DNDLoot::open() {
+  // BUG: should I do this in the commit_ functions or in the FSM?
+  void DNDLoot::clear_grab() {
     $grab_source = std::nullopt;
     $grab_sprite = nullptr;
+  }
+
+  void DNDLoot::open() {
+    clear_grab();
     $loot_ui.active = true;
   }
 
   void DNDLoot::close() {
-    $grab_source = std::nullopt;
-    $grab_sprite = nullptr;
+    clear_grab();
     $loot_ui.active = false;
   }
 
@@ -242,6 +247,7 @@ namespace gui {
 
     if(drop.commit(grab.world_entity)) {
       grab.commit();
+      clear_grab();
       return true;
     } else {
       return false;
@@ -256,6 +262,7 @@ namespace gui {
     auto& drop = gui.get<guecs::DropTarget>(drop_id);
     drop.commit(grab.world_entity);
 
+    clear_grab();
     // BUG: if the drop fails then need to put the grab back?
     // How to confirm the drop will work before doing it?
     // Or, maybe save the commit?
@@ -269,6 +276,8 @@ namespace gui {
     dbc::check($grab_source != std::nullopt, "attempt to commit_drop but no grab_source set");
     auto& grab = $status_ui.$gui.get<guecs::GrabSource>(*$grab_source);
     grab.commit();
-    return $status_ui.drop_item(grab.world_entity);
+    bool result = $status_ui.drop_item(grab.world_entity);
+    clear_grab();
+    return result;
   }
 }

gui/dnd_loot.hpp

@@ -54,6 +54,8 @@ namespace gui {
 
       bool throw_on_floor();
 
+      void clear_grab();
+
       sf::Vector2f mouse_position();
   };
 }