I agree, every program should be built this way. It also speeds up development early on, and makes it easier to have multiple front ends.

Well now I’m writing my own thing :) but that will be a while. I haven’t found anything better so far.

Btw I also find the d2 lang nicer and more uniform, while mermaid is a bit more graphviz dot-like.

May be personal preference, but d2 blows mermaid out of the water. And it is a single executable, no npm needed.