Just read the "Rx in Action" by Luis Atencio and tried to apply it to build an Agent Harness. I was pretty astonished of how easy it makes to manage things and how much complexity modern AI frameworks bringing comparing to it.
I was pretty impressed by capabilities of latest Gemma and Qwen models and tried different harnesses before I decide to start building my own and learn how it works in public.
I think that Agent Harness is just a stream of events that currently being overcomplicated and micromanaged. Fortunately the JavaScript ecosystem was evolving around the very same thing – event flow control.
So I picked Rx.js and start building, the results are surprisingly pleasant so far:
<200 lines of code for main conversation control.
~500 lines with tools.
Even this toy agent can hold pretty long conversation until it starts hallucinate.
I'm just concatenating the whole history, there's literally no context management yet!
The video attached is combined conversation + tools flow. I'm going to publish the Article on the tools next week.
If you're interested please read first one
https://vasilymitronov.substack.com/p/build-a-reactive-ai-agent-harness