docs: @Trivial // traced by caller
      static <U> CompletableFuture<U> completedFuture(U value, Executor executor) {
          if (JAVA8) {
              return new ManagedCompletableFuture<U>(CompletableFuture.completedFuture(value), executor, null);
          } else {
              ManagedCompletableFuture<U> future = new ManagedCompletableFuture<U>(executor, null);
              future.super_complete(value);
              return future;
          }
      }