Migrating JS from Yarn to NPM

In Ruby on Rails, the software ecosystem I predominantly work in these days, yarn has been the default package manager for the javascript side of things for a long time. (See my big write-up of the timeline & current state of frontend asset management in Rails). When many of the apps I regularly work on were written, that was a pretty reasonable choice! Yarn had some solid advantages over npm generally, way back when (that's less obviously true now; npm works just fine these days, and has some advantages over yarn). Yarn was also very clearly "the Rails way", one relative constant in a JS-with-Rails landscape that often pretty inscrutable to Rails devs who weren't as immersed in the frontend tooling ecosystem that was evolving in javascript-land. For many serious Rails devs, doing something "the Rails way" means it is obviously the right way to do it unless you have a darn good reason. (In the Rails doctrine, "the menu is omakase" and one should prioritize convention over…