only after mutations

cmd/cart/main.go

@@ -117,14 +117,16 @@ func main() {
 	promotionService := promotions.NewPromotionService(nil)
 
 	reg := cart.NewCartMultationRegistry()
-	reg.RegisterProcessor(actor.NewMutationProcessor(func(g *cart.CartGrain) error {
+	reg.RegisterProcessor(
+		actor.NewMutationProcessor(func(g *cart.CartGrain) error {
 			ctx := promotions.NewContextFromCart(g)
 			_, actions := promotionService.EvaluateAll(promotionData.State.Promotions, ctx)
 			for _, action := range actions {
 				log.Printf("apply: %V", action)
 			}
 			return nil
-	}), actor.NewMutationProcessor(func(g *cart.CartGrain) error {
+		}),
+		actor.NewMutationProcessor(func(g *cart.CartGrain) error {
 			g.UpdateTotals()
 			return nil
 		}))

pkg/actor/mutation_registry.go

@@ -225,12 +225,14 @@ func (r *ProtoMutationRegistry) Apply(grain any, msg ...proto.Message) ([]ApplyR
 		results = append(results, ApplyResult{Error: err, Type: rt.Name(), Mutation: m})
 	}
 
+	if len(results) > 0 {
 		for _, processor := range r.processors {
 			err := processor.Process(grain)
 			if err != nil {
 				return results, err
 			}
 		}
+	}
 	return results, nil
 }