This long comment doesn't contradict my point because "The trunk ... changes very frequently". Requirements change, and thus, code changes. There is nothing you can do about it. It's cool when everything is modularized enough that you never need to change some parts of the code. But it doesn't mean those parts of the code are better than code that changes often.

Now, if you think a little more about this, there is a huge risk that some of your leaf code should be in a library. For example, SQL builders, ORMs, UI kits, markdown formatters, etc. When it's a publicly available package used by many devs around the world, the code in it often changes. The reason why your leaf code doesn't change is that you don't have a proper investment return for small changes because you are a single user. Code in libraries handles more useful use cases, it handles more edge cases, it provides better API, and it contains fewer bugs than code in leaf nodes. And all that's while code in libraries is constantly changed. And code in leaf nodes... I would say that the proper description for it is "used, but dead".