fix: reserve IDs starting and ending with '__' for internal use

internal/config/validationutil/validationutil.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"regexp"
+	"strings"
 )
 
 var (
@@ -26,6 +27,9 @@ func SanitizeID(id string) string {
 // It returns an error if the ID contains invalid characters, is empty, or is too long.
 // The maxLen parameter is the maximum length of the ID. If maxLen is 0, the ID length is not checked.
 func ValidateID(id string, maxLen int) error {
+	if strings.HasPrefix(id, "__") && strings.HasSuffix(id, "__") {
+		return errors.New("IDs starting and ending with '__' are reserved by backrest")
+	}
 	if !idRegex.MatchString(id) {
 		return ErrInvalidChars
 	}