panic("StateTransition called on non-StateTransition event")
	}
	var s StateTransition
	switch e.base.typ {
	case go122.EvProcStart:
		s = procStateTransition(ProcID(e.base.args[0]), ProcIdle, ProcRunning)
	case go122.EvProcStop:
		s = procStateTransition(e.ctx.P, ProcRunning, ProcIdle)
	case go122.EvProcSteal:
		// N.B. ordering.advance populates e.base.extra.
		beforeState := ProcRunning