We ended up doing the same, own harness with a world view (schema.org) and map reduce rather than a RAG. Happy with the results and context hydration speed
I created a nice harness and visual workflow builder for my Gemini agent chains, works very well. I did this so it would create code the way I do, that is very editable.
In contrast, the vs code plugin was pretty bad, and did crazy things like mix languages
Was a pain to set up, but you can score the context completion and then if the score is under 98% or something, “ask” clarifying questions of the requesting agent or person or system