Make system prompt for chain configurable

[OskarStark]

Closes

• Configure a default system prompt for a chain llm-chain#171

Leverage

• feat: add system prompt processor llm-chain#186

If I am correct, it is not needed to register it also as an OutputProcessor, right?

[OskarStark]

The processor is used and the system_prompt is added to the request, so it works.

But lets say we have this flow:

1. Empty MessageBag
2. Add UserMessage to MessageBag
3. Call the chain with MessageBag with 1 User message
4. Internally the chain adds the system prompt message from the config
5. In our call() method we now have a MessageBag with System + User message
6. We get the response, but our Bag does not have access to the system message anymore

In my world, I would like to end up somehow with a MessageBag (System, User, Assistant) - 3 messages, but in this case I would need access to the system prompt 🤔

[OskarStark]

I mean technically if I add another user message and call the chain again the system prompt would be prepended again, yes.

I would like to a) persist the correct version, because the user could chat again in my thread in a few weeks, so the system prompt could change in the meantime and b) also have it somewhere for debugging.

[chr-hertel]

If I am correct, it is not needed to register it also as an OutputProcessor, right?

correct 👍

[chr-hertel]

but you are right. the MessageBag from lib user land is never changed, it is cloned while changed.

debugging with the bundle features would show the extended MessageBag with the system prompt tho.

currently it's default behavior that the lib's user has to manage all messages themselves - the processor just adds it on the fly and it is intransparent. same with all the tool call messages. they also don't appear in the user's MessageBag - which is by design

[chr-hertel]

PR looks good to me 👍 would test it later