message: Only support snapshot for old clients.
diff: import * as api from "@prague/client-api";
  -import { IUser, MessageType } from "@prague/runtime-definitions";
  +import { ISequencedDocumentSystemMessage, IUser, MessageType } from "@prague/runtime-definitions";
  import * as winston from "winston";
  import * as core from "../core";
  import { IContext } from "../kafka-service/lambdas";
  @@ -41,9 +41,15 @@ export class TmzLambda extends SequencedLambda {
  let helpContent: string[];
  if (sequencedMessage.operation.metadata) {
  helpContent = sequencedMessage.operation.metadata.content.tasks;
  + helpContent = helpContent.indexOf("snapshot") === -1 ? [] : ["snapshot"];
  } else {
  + if (sequencedMessage.operation.contents) {
  helpContent = sequencedMessage.operation.contents.tasks;
  helpContent = helpContent.indexOf("snapshot") === -1 ? [] : ["snapshot"];
  + } else {
  + // tslint:disable max-line-length
  + helpContent = JSON.parse((sequencedMessage.operation as ISequencedDocumentSystemMessage).data).tasks;
  + }
  }
  await this.trackDocument(
  