Generative design environments need support for human intervention as well as sound computational formalisms. A systematic approach to integrating the two, formal generation and the exploratory, is lacking. In this paper, we posit the possibility of a design support system that combines formal search with user driven exploration. Our approach is to cast the interaction between the user and the generative formalism as agent collaboration in a mixed-initiative environment. We describe the role of interaction and agency in an experimental mixed-initiative design support system, FOLDS and demonstrate its application.