http-cache-semantics | Parses HTTP headers | HTTP library

I see this on two different machines. When I navigate to the folder that contains my package.json file and execute the command yarn list, it lists a bunch of packages that I haven't installed. If I execute the command yarn check then it complains that most of the packages aren't installed.

So, what changed since the last time this worked correctly? Where is yarn finding all of the extraneous packages, and how do I convince it that they really aren't there?

Here are all of the relevant files in my project directory:

package.json