message: Add validation that base summary does not change underneath us.
  This is enforced today by pausing op processing and thus not being able to process summary acks.
  That said, if it were to change, we would be in big trouble, so worth adding defense in depth.
diff: @@ -2622,15 +2622,7 @@ export class ContainerRuntime extends TypedEventEmitter<IContainerRuntimeEvents>
  const summaryRefSeqNum = this.deltaManager.lastSequenceNumber;
  const minimumSequenceNumber = this.deltaManager.minimumSequenceNumber;
  const message = `Summary @${summaryRefSeqNum}:${this.deltaManager.minimumSequenceNumber}`;
  -
  - // We should be here is we haven't processed be here. If we are of if the last message's sequence number
  - // doesn't match the last processed sequence number, log an error.
  - if (summaryRefSeqNum !== this.deltaManager.lastMessage?.sequenceNumber) {
  - summaryNumberLogger.sendErrorEvent({
  - eventName: "LastSequenceMismatch",
  - error: message,
  - });
  - }
  + const lastAck = this.summaryCollection.latestAck;
  this.summarizerNode.startSummary(summaryRefSeqNum, summaryNumberLogger);
  @@ -2660,6 +2652,16 @@ export class ContainerRuntime extends TypedEventEmitter<IContainerRuntimeEvents>
  error: `lastSequenceNumber changed before uploading to storage. ${this.deltaManager.lastSequenceNumber} !== ${summaryRefSeqNum}`,
  };
  }
  + assert(summaryRefSeqNum === this.deltaManager.lastMessage?.sequenceNumber,
  + "it's one and the same thing");
  +
  + if (lastAck !== this.summaryCollection.latestAck) {
  + return {
  + continue: false,
  + // eslint-disable-next-line max-len
  + error: `Last summary changed while summarizing. ${this.summaryCollection.latestAck} !== ${lastAck}`,
  + };
  + }
  return { continue: true };
  };
  @@ -2733,7 +2735,6 @@ export class ContainerRuntime extends TypedEventEmitter<IContainerRuntimeEvents>
  return { stage: "generate", ...generateSummaryData, error: continueResult.error };
  }
  - const lastAck = this.summaryCollection.latestAck;
  const summaryContext: ISummaryContext =
  lastAck === undefined
  ? {
  