"as if" is what semantically identical means. As I further clarified: "All observable and defined side effects should be identical otherwise you have a compiler bug."

The output program does what the input source code does. The abstraction is a precise translation and non-leaky, it just admits multiple possible internals. That does not make the translation any less precise.

Yes, and just like with human intelligence offshoring projects, if the delivered microservice e.g. always sends the right email content when a notification lands, no one cares about the garbage underneath.