Question about the implementation of the MemorySaver

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Example Code

https://github.com/langchain-ai/langgraphjs/blob/27c9e8182753453c8461f56b023ef602f05397c9/libs/checkpoint/src/memory.ts#L316C6-L316C52

Description

I am deepping learning and understanding the Persistence in LangGraph.js.

And there is one small question to me about the implementation of the MemorySaver

The type definenation of the storage property in MemorySaver class is :

  // thread ID ->  checkpoint namespace -> checkpoint ID -> checkpoint mapping
  storage: Record<
    string,
    Record<string, Record<string, [Uint8Array, Uint8Array, string | undefined]>>
  > = {};

In the put() method, we can see how we store the data:

https://github.com/langchain-ai/langgraphjs/blob/27c9e8182753453c8461f56b023ef602f05397c9/libs/checkpoint/src/memory.ts#L316C6-L316C52

So my question is what's the difference between the id property of the checkpoint argument with the config.configurable.checkpoint_id?

And I also found there is a method getCheckpointId() will be used in getTurple() method, what's difference between these three checkIds？

export function getCheckpointId(config: RunnableConfig): string {
  return (
    config.configurable?.checkpoint_id || config.configurable?.thread_ts || ""
  );
}

Is there any more docs that I can learn more about the checkpoint and the mechanism of the checkpoint id?

System Info

The latest version of the langgraph.js