There's no justification for dependency from TransientModel in kernel. Generation session tracks hint objects coming through log and registers appropriate transient models as 'to keep', there seems to be no reason to do it here explicitly once again.
Refactor the way transient models are created and tracked: towards better support for incremental+inplace+transients case (need 'real' model reference to be available during generation, otherwise incremental cache is broken. and the way message hints are augmented is awful, too.)