decoherence in discrete steps — the fourth axiom of Structural Cognition Structure becomes observable in quantized steps of decoherence, not a smooth curve. The first three axioms (structure precedes semantics / coupling is cognition / observer self-reference) answer "what structural cognition is"; the fourth answers "how structure collapses from one steady state to the next, and how it re-founds itself." Any framework without it can describe structure but cannot describe structural transition. This is the last wall of the four axioms. Lin Xiaohei (林小黑) | gitee.com/samforce/structural-cognition | WeChat 今晚狗蛋看局