cancelScenario

Cancel a single scenario by name without stopping the rest of the sweep. Looks up the scenario's coroutine job and issues a cooperative cancellation against it. Returns true when a running scenario was found; false when the name is unknown, has already finished, or hasn't started yet.

Cancelled scenarios produce a null snapshot in the commit phase, so RunEvent.ScenarioCompleted is emitted for them with snapshot == null. Sibling scenarios continue to run because simulate wraps each scenario's async in a supervisorScope, preventing one child's cancellation from propagating to the others.