As agentic AI moves beyond support to execute tasks inside workflows, trust becomes unavoidable. The risk comes less from AI acting alone than from engineering workflows that fail to express system-level behaviour in an executable form. System-first engineering, implemented through model-based design, provides shared, executable system models across mechanical, electrical and software domains. Deterministic, repeatable verification and simulation reduce dependence on hardware testing and allow changes to be assessed early against system-level criteria.