langchain/memory/vectorstore.py/VectorStoreRetrieverMemory/save_context
class VectorStoreRetrieverMemory:    def save_context(self, inputs: Dict[str, Any], outputs: Dict[str, str]) -> None:
        """Save context from this conversation to buffer."""
        documents = self._form_documents(inputs, outputs)
        self.retriever.add_documents(documents)