Currently, it is not possible to perform any checks on a page after the request has been detached. In onEndRequest, the PageMap lock has already been cleared, making it unsafe to access the pages involved in the request. Would it be possible to add an extra callback method (ie. onAfterTargetDetach()) to RequestCycle directly after detaching the request targets? We need such a callback to check (in development mode) if all models are detached correctly.