Ok, I am trying to answer your questions more specifically. My previous answer was off the top of my head because I was on my phone. Now I've logged in and tried to understand exactly what you're asking.
>When the files for project A,B,C are you in Cloud Shell within the Console UI?
I am not sure what is meant by "Console UI". This is through the website at
https://console.cloud.google.com/ , is that what is meant by "Console UI?" At any rate, I'm seeing the files in the cloud shell terminal. They also appear in the Cloud Shell Editor.
> How are you switching between projects via CLI or through different web browser tabs each logged into their own project?
There is a dropdown on the top header which opens a modal titled "Select a project". So switching projects this way and then clicking the "Activate Cloud Shell" is the primary way I am switching between projects. I have found I can also switch from within the cloud share terminal by clicking the dropdown arrow near the new tab icon (the big plus). I also have tested this switching through the command gcloud config set project B
The result is the same for all.