Langchain query using Pinecone and ParentDocumentRetriever returns no results

I am really not understanding how to retrieve the parent documents using Langchain’s ParentDocumentRetriever when using Pinecone. The following code is working for creating the embeddings and inserting them into Pinecone:

const pinecone = new Pinecone();

const pineconeIndex = pinecone.Index(process.env.PINECONE_INDEX);
const docstore = new InMemoryStore();

const vectorstore = await PineconeStore.fromExistingIndex(
  new OpenAIEmbeddings(),
  { pineconeIndex }
);

const retriever = new ParentDocumentRetriever({
  vectorstore,
  docstore,
  childSplitter: new HTMLSplitter(),
  parentK: 5,
});

// We must add the parent documents via the retriever's addDocuments method
await retriever.addDocuments(docs);

const retrievedDocs = await retriever.getRelevantDocuments("What is emptiness?");

console.log(retrievedDocs);

The retrievedDocs contains a few parent documents, as expected.

Now that my index is created, I would like to subsequently perform the same operation, but without the await retriever.addDocuments(docs):

const pinecone = new Pinecone();

const pineconeIndex = pinecone.Index(process.env.PINECONE_INDEX);
const docstore = new InMemoryStore();

const vectorstore = await PineconeStore.fromExistingIndex(
  new OpenAIEmbeddings(),
  { pineconeIndex }
);

const retriever = new ParentDocumentRetriever({
  vectorstore,
  docstore,
  childSplitter: new HTMLSplitter(),
  parentK: 5,
});

const retrievedDocs = await retriever.getRelevantDocuments("What is emptiness?");

console.log(retrievedDocs);

This yields no results. The documentation is really rather unclear on this: am I expected to implement my own document store containing all of the parent documents with their accompanying IDs or something like that? Can I save the InMemoryStore to the filesystem, or use the LocalFileStore? Does this document store pertain just to the parent documents?

I am not sure how to use LocalFileStore since dropping it in as a replacement causes my IDE to become unhappy, because it extends BaseStore<string, Uint8Array>, whereas InMemoryStore extends BaseStore<string, T>.

In summary, how would I use Pinecone as a vector store in combination with ParentDocumentRetriever? What document store do I use?

It seems to me that this would be a pretty common use case; where might I find an example?