Conditional assignment of marker interface during object creation

I am migrating an AT package to Dexterity where we need to assign a marker interface to new folders.
All folders created with id img should provide IImageLibrary. The former AT implementation used a content rule for event="Products.Archetypes.interfaces.IObjectInitializedEvent".

I tried to use event=zope.lifecycleevent.IObjectCreatedEvent but this preaks the Plone content rules control panel because this event is not registered with the related vocabulary in Plone:

  Module snoop.tracer, line 169, in simple_wrapper
  Module, line 81, in registeredRules
KeyError: <InterfaceClass zope.lifecycleevent.interfaces.IObjectCreatedEvent>

A registration with event=zope.lifecycleevent.IObjectModifiedEvent works for edit operations but not during the inital edit operation.

So what's the best way to hook into the object creation process - with or without content rules?

Wouldn't a regular event subscriber for zope.lifecycleevent.IObjectCreatedEvent work?
Without using p.a.contentrules that is.

There might an ObjectAdded rule, which should give you the added folder and it's container.

.....yes, of course...the heat...