Protocol State Drift: Why Declarative Procedures Fail at the Transition

Declarative procedures fail not because steps are absent or unknown, but because execution state is not structurally coupled to protocol state. This paper names and defines Protocol State Drift as a distinct failure class — separate from hallucination, from checklist omission, and from intent loss. The mechanism operates across domains: healthcare staffing, military accountability structures, autonomous agent pipelines, and operational protocol systems. A diagnostic distinction is developed between transition gates (which protect linear execution) and state gates (which protect non-linear invocation). The paper argues that checklist architecture — the dominant model for procedural reliability — cannot prevent this class of failure by design.