Verdict
Blast Radius answers the question agents usually hand-wave: what else could this change break? It traces dependents and callers, then requires the one safety-critical assumption to be proven by running code rather than asserted in prose.
Best for
Small-looking changes to shared code, public interfaces, data shapes, or configuration where the real risk lives downstream.
Keep in mind
Tracing has diminishing returns in weakly typed or dynamically wired codebases, and the extra verification step is exactly the kind of thing a rushed agent will skip unless you ask for it explicitly.
Example task
Before we rename this field, map every reader and writer and prove with a test run that nothing outside the module depends on the old shape.