message: Unify error message
diff: @@ -70,7 +70,7 @@ fn parse_query(v: Variant) -> (String, Expr) {
  /// Extract the nested query -> response mapping out of an enum variant.
  fn parse_subquery(v: Variant) -> Expr {
  let submsg = match v.fields {
  - syn::Fields::Named(_) => panic!("nested query response can only contain tuple structs"),
  + syn::Fields::Named(_) => panic!("a struct variant is not a valid subquery"),
  syn::Fields::Unnamed(fields) => {
  if fields.unnamed.len() != 1 {
  panic!("invalid number of subquery parameters");
  @@ -392,7 +392,7 @@ mod tests {
  }
  #[test]
  - #[should_panic(expected = "nested query response can only contain tuple structs")]
  + #[should_panic(expected = "a struct variant is not a valid subquery")]
  fn nested_mixed() {
  let input: ItemEnum = parse_quote! {
  #[derive(Serialize, Deserialize, Clone, Debug, PartialEq, JsonSchema, QueryResponses)]
  