Client Handling

[lukehinds]

Placeholder issue while I sketch this out.

We have many clients (assistants) and while some our conforming on the OpenAI standard, there is always some deviation that requires us to enter a special way of serializing input. In the same way as we have a modular providers system, we need to find a way of doing the same for clients (continue, cline, aider...). The logical parsing point would be a user-agent, but I have seen a few of the VS code extensions sending over the Generic Node UA.