If you ran a webserver hosting Great Cat Pictures on some Macs, for instance, your customers might pay a subscription fee to access your site, meaning they are paying for you to do processing and storage on their behalf. So that's an example that's clearly not leasing or subletting the devices.

Likewise, you might read it that Circle is simply providing a service to users, and the users are paying a fee for the service.

But a CI service will set up your dev account, your container image, to run your jobs. It'll even let you shell in, and it tears it all down when you're done.

And it really starts to look like leasing when they also charge for time used on various hosts. (IIRC, Circle charges for this a bit obliquely as max parallelism.)

If it went to court, Circle might argue the hosts can only be used within their larger CI system, that they don't guarantee a particular task will complete on a given host, and that they're not providing other requirements for virtual hosts, e.g. dedicated routing or names. And then Apple's lawyers might counter all that.

So this is where I think lawyers would start digging through case law to figure out where providing a service ends and leasing begins.