Both "better coffee" and "faster code" are measurable targets. Somewhat vaguely defined, but nobody is stopping the Barista or Claude from asking clarifying questions.

If I gave a human this task I would expect them to transform the vague goal into measurable metrics, confirm that the metrics match customer (==my) expectations then measure their improvements on these metrics.

This kind of stuff is a major topic for MBAs, but it's really not beyond what you could expect from a programmer or a barista. If I ask you for a better coffee, what you deliver should be better on some metric you can name, otherwise it's simply not better. Bonus points if it's better in a way I care about