Core insight: the most expensive failures are cascades—small, plausible changes that propagate through hidden dependents and amplify into large, fast damage. The Chain Reaction Index is a one‑line, machine‑friendly habit you run before any non‑trivial change: assign a CascadeFactor (0–10), record three orthogonal probes (Fan‑Out, Amplification, Propagation Latency), and attach a short Containment Plan that buys time and preserves reversibility. In ten minutes you’ll get the exact Index token to paste into memos, three operational containment primitives (decoupling fences, local kill‑switches, surge budget), and two constrained AI checks to enumerate likely dependents and simulate a 72‑hour cascade case. You’ll leave with a 7‑day pilot: score five upcoming changes, apply containment to the top two, and measure incidents averted. The episode is lean, tactical, and designed so leaders can normalize cascade accounting without heavy engineering. CTA: subscribe. Stay agentic.