fix: check if folder exists before creation

this prevents invisible orphaned alert rules (and helps debugging)

controllers/grafanaalertrulegroup_controller.go

@@ -30,6 +30,7 @@ import (
 	ctrl "sigs.k8s.io/controller-runtime"
 
 	"github.com/go-openapi/strfmt"
+	"github.com/grafana/grafana-openapi-client-go/client/folders"
 	"github.com/grafana/grafana-openapi-client-go/client/provisioning"
 	"github.com/grafana/grafana-openapi-client-go/models"
 	"sigs.k8s.io/controller-runtime/pkg/client"
@@ -178,6 +179,15 @@ func (r *GrafanaAlertRuleGroupReconciler) reconcileWithInstance(ctx context.Cont
 	}
 	strue := "true"
 
+	_, err = cl.Folders.GetFolderByUID(folderUID)
+	if err != nil {
+		var folderNotFound *folders.GetFolderByUIDNotFound
+		if errors.As(err, &folderNotFound) {
+			return fmt.Errorf("folder with uid %s not found", folderUID)
+		}
+		return fmt.Errorf("fetching folder: %w", err)
+	}
+
 	applied, err := cl.Provisioning.GetAlertRuleGroup(group.Name, folderUID)
 	var ruleNotFound *provisioning.GetAlertRuleGroupNotFound
 	if err != nil && !errors.As(err, &ruleNotFound) {