Currently pressing delete deletes the selected entities. In most cases this is of course the intended behavior but when creating custom ruby tools this may not always be the case. For instance delete is used in my townhouse system plugin to delete nodes defining the building position.
For now a workaround is to simply empty the selection while your tool is activated but I think it should be possible to have something selected, e.g. component being edited by a plugin, while deleting an “abstract” object used in the custom tool, such as handle of some sort.
Maybe the tool interface could use an “expectBubblingDelete” method that returns a boolean similar to the expectsStartupModelNotifications method of the AppObserver class to allow plugin developers to control this behavior.