I am writing my own harness, and I would love to hear more about what you have in mind.

Can you give an example of your use case?

i have a bunch of md templates at my disposal, which serve as the basis for my prompt toolbelt... these templates are populated and crystalized with concrete json instances... the json instances are tailored & scoped for various tasks... currently i have to synthesize a bunch of markdown artifacts that pollute my project directory and are at risk of becoming stale and out-of-sync... prompt-time middleware hooks that allow me to transform a json file into my final markdown prompt would alleviate these issues and improve developer ergonomics...