But in that case nobody was accessing a service. If I use Tesla’s servers/service without permission in my app, then they could legally terminate my access (or, perhaps try to get it taken off the App Store). If I simply reimplement the Tesla service myself (even though that’d be useless with a production car unless you rewrote the telemetry stuff), they can’t sue me under the Oracle-Google decision, as I understand it.

I don't think this is the same issue. From what I understand, the Tesla api is accessed through Tesla's servers via a remote api service run by Tesla, and not by directly interacting with the car itself.

_Technically_ it is a crime to access a remote computer without permission -- Computer Fraud and Abuse Act [1].

[1]: https://en.wikipedia.org/wiki/Computer_Fraud_and_Abuse_Act

No. In this case it's about permission to use a network-accessible service, not about copying a header file / interface definition or other code.

In the wiki article, this deals with the "Remote APIs" definition, not the "Libraries and frameworks" definition. https://en.wikipedia.org/wiki/API#Usage