Cross-Architecture Co-Design: Emotion-Free Critique and Friction-Expressive AI as a Practical Pathway to ``AI That Can Say No''

Collaborative design among humans often suffers from emotional friction, particularly when critique and revision are perceived as evaluations of personal competence or identity. While artificial intelligence has been introduced as a supportive tool, reliance on a single model tends to reproduce biases and premature convergence. This paper proposes \emph{Cross-Architecture Co-Design}, a methodology that coordinates multiple AI systems with distinct architectures and reasoning tendencies under differentiated roles. Central to this approach is the introduction of \emph{friction-expressive AI}, which provides rational resistance to revisions based on internal objective functions and structural consistency rather than emotion or agency. Through a practical case study, we argue that this framework offers a stable and implementable pathway toward an ``AI that can say no'' without presupposing personhood or ethical autonomy.