Bug Files in CacheServer don't use Unity.Build.Content but require its Classes CS0246

Using Unity version 2021.1.14f1, when I add the com.unityscriptablebuildpipeline@1.15.2 package, it always gives me 10 compile errors, for each use of FileID and FileType in the CacheServer folder:
"The type or namespace name 'FileType' could not be found"
Looking at the files, it looks like they aren't using Unity.Build.Content, and therefore can't access the classes. I can't update the package files myself; how do I fix this?