For example, user says "build a report with revenue and orders by month and show 100 most recent orders". The agent would write a spec that would get rendered by our frontend.
This runs fast, but we were drowning in feature requests for what the framework could render (e.g. "I don't want labels here", "I DO want labels there", "can this chart be a heatmap", etc.)
A few months ago, we let the agent just write HTML instead. It takes longer to generate, but you get unlimited customization.
There are a host of issues with the new approach (non-technical users debugging a monstrous app they created), but net-net our customers like it much better.