All of this is fascinating, and I really appreciate the info. I am going to go back and do some research with esy and then compare it to the dune build process.
Not clear where the symlink or the cygwin VSCODE terminal is better, I suspect the first supports npm run commands.
But in the final analysis if esy can build both reasonml and ocaml and I can get it to work: (see https://github.com/esy-ocaml/hello-reason/issues/62 ) then I inclined to esy.