That's quite a good amount of boilerplate to create a custom, project-specific handling of errors, which itself can have bugs. During reading I thought "anyhow, at this point you are half way to reinvent the wheel and write your own "anyhow'".

I agree with avoiding an explosion of dependencies; but not at any cost. In any case if custom error handling works, then why not. It's just that it feels like a deviation to do extra work on designing and implementing an ideal error handling system with all the cool features, instead of spending that same time working on the actual target of the project itself.