Blast radius (agent systems)

Blast radius is the count or fraction of downstream agents and steps one fault reaches before it is contained, read across a specific topology rather than reported as a single global figure. The operational move that makes it concrete: fix the injection point, then count reached nodes as a share of everything reachable from it. In an orchestrator with N workers, a poisoned worker output the orchestrator trusts can reach every sibling that reads shared state; in a chain of depth D, an uncaught error at step k reaches the remaining steps. Same fault, different radius, because the graph differs.

Radius is measured per fault and per topology, so it is reported as a distribution over injection points, never one headline number. It sets the numerator that containment rate works against and the exposure that cascade resistance scores at the architecture level. See the multi-agent failure-mode taxonomy for where blast radius sits among propagation metrics.