I don't know; I just read what's written on their home page:

    Evervault Cages
    Process the data you encrypt with Relay or our SDK by deploying your code in Cages — isolated serverless functions hosted on Evervault.

    Cages automatically decrypt your data in an isolated environment, so you can still process data without handling it in plaintext.

perhaps I misunderstood what that feature is; if that's true I suspect it's not entirely my fault, but there is something misleading in the product description.

No, you're right, I missed that feature.