Critical Decision Capacity: Bottleneck vs. Substitutable Degradation under Action Availability

Action availability is a structural resource: systems whose useful behaviour depends on conjunctive bottlenecks can collapse abruptly under random loss of that resource, while substitutable structure degrades smoothly. Critical Decision Capacity (CDC) is not merely a name for a failure threshold $f_c$: it is the CAC-linked critical capacity used as an intervention objective, with estimators ${\mathrm{CDC}}_{\mathrm{struct}}=1-f_c$, ${\mathrm{CDC}}_{\mathrm{value}}$, and optional ${\mathrm{CDC}}_{\mathrm{norm}}$ (coinciding only under stated assumptions). We prove a sufficient-condition dichotomy for path MDPs: sparse digraph bottlenecks admit a directed-bond percolation threshold (sharp-class mechanism), while submodular structure with bounded marginals is equi-Lipschitz (no discontinuous jump). Path-MDP hardening and Leduc blind transfer (frozen $G_{\star }$ rankings under degree-biased / vs-random failure) show the design chain; poker targeted > random fragility remains Tier B, not a competitive-IIG theorem.