How does Cloud Build handle the Package Manager?

I have a project that I trimmed out some packages, uploaded the resultant Packages/manifest.json file, and now I'm getting an error in the output log of WebGL Cloud Build:

Code (CSharp):

1. 162: [Unity] Initializing Unity.PackageManager (PackageManager) v2018.2.7 for Unity v2018.2.7f1
2. 163: [Unity] System.SystemException: Error running gmcs: Cannot find the specified file

The error is not a showstopper, so the build does finish successfully, and the game does run. But it is a little larger than I'm hoping it will be once I trim out all of the packages I don't want.

If I don't make any changes to packages, and don't have the Packages/manifest.json file uploaded in the repo, I do not get this error.

I am wondering whether Package Manager works with Cloud Build, and if it does, what I need to do to get it to work properly. Any thoughts?

 

Anyone else experiencing this, or curious, this was validated by Unity Support:

"I am looking into this issue and I was able to get the same error message (but build built successfully) just by building an empty project in Unity 2018.2.5f1. This could be a new issue so I will need to investigate further. I will let you know in this ticket as soon as I have more information."