Strengthen validation retries and checkpoint safety

internal/modules/dnd/validate/enemyevents/engagements/validator.go

@@ -54,6 +54,7 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 				Message: diagnostics.Aggregate("duplicate enemy engagement", []string{
 					fmt.Sprintf("subject %s has more than one engagement in one combat scene", diagnostics.Quote(event.Name)),
 				}),
+				CorrectionGuidance: "Return at most one engagement event for each contextual enemy name within the same combat scene.",
 			}, nil
 		}
 		seen[identity] = struct{}{}