> The openui-lang parser converts a custom DSL emitted by an LLM into a React component tree.

> converts internal AST into the public OutputNode format consumed by the React renderer

Why not just have the LLM emit the JSON for OutputNode ? Why is a custom "language" and parser needed at all? And yes, there is a cost for marshaling data, so you should avoid doing it where possible, and do it in large chunks when its not possible to avoid. This is not an unknown phenomenon.