Align 4 engineers' agents on one Java service

Your team of 4 is building a new Java microservice, and each engineer uses an AI agent for their own slice. After a week, the service is a patchwork.

One slice uses constructor injection and another uses field injection. Some code throws checked exceptions, some unchecked. Error responses come in 3 JSON shapes. It all works, but reviews are slow and the API is inconsistent.

How do you get the 4 of them producing consistent code, and what do you do about the week of code that already exists?