code: public CompletableFuture<TxnStatus> commitTxn(final String scope, final String stream, final UUID txId,
                                                    final OperationContext contextOpt) {
          final OperationContext context = getNonNullOperationContext(scope, stream, contextOpt);
          return withRetriesAsync(() -> sealTxnBody(hostId, scope, stream, true, txId, null, context),
                  RETRYABLE_PREDICATE, 3, executor);
      }
docs: Commit transaction.
  
  @param scope      stream scope.
  @param stream     stream name.
  @param txId       transaction id.
  @param contextOpt optional context
  @return true/false.