Agreed, that should be aligned. I mean, it's both active, but the subject is different, once it's "we", once the "chapter". At other places we also use "you can do...". Not sure what I like best tbh. Maybe we should use the "you" approach consistently?

Regarding the matter at hand, I also don't like "the chapter discusses...". I guess here I'd really go for a passive form: "... but also an API for accessing constraint metadata, which will be introduced in the following".