feat: return full messages from Agent API

[joshua-mo-143]

• I have looked for existing issues (including closed) about this

Feature Request

See relevant xitter interaction: https://x.com/maxxedgoof/status/2011082095825994101

[linear]

RIG-1136

[nickcorin]

Hey @joshua-mo-143, thanks for raising this. I'm just revealing myself here.

Happy to provide context, or extra hands where needed. 👍

[joshua-mo-143]

So, some thoughts I had about this:

We could have a trait for the output (ie AgentOutput) that then can be implemented for a given type to turn the completion response into whatever the output type is.

This would probably be blocked by the application of rig::telemetry::ProviderResponseExt over every single provider, but I think this would probably be worth it given that users may want to transform the output in other ways than just either returning a simple response or a full response.