How to store additional metadata in the thread?

[ouvreboite]

TLDR: what's is the best practice to store conversational metadata?

The AgentThread seems to have the good role to store metadata related to a conversation, but it's sealed.
The two extensions points that I'm seeing are:

• The ChatMessageStore, that can put info into the ChatClientAgentThread.ThreadState.StoreState (fed from ChatMessageStore.Serialize())
• The AIContextProvider, that can put info into the ChatClientAgentThread.ThreadState.AIContextProviderState (fed from AIContextProvider.Serialize())

Both ChatMessageStore and AIContextProvider have a very limited surface area (they can mostly interact with incoming/outgoing messages).

But what if we want to store custom metadata that are not from the messages?

For example some user-specific data extracted during the tools invokations but that are not meant to be in the tool output, so would not end up in the messages, or some user specific data fetched only at the start of the conversation?