I check in the generated code so I only run pggen at dev time, not build time. I do intend to move to build time codegen with Bazel but I built out tooling to launch new instances of Bazel managed Postgres in 200 ms so not that painful.
More advanced database setups can point pggen at a running instance of Postgres meaning you can bring your own database which is important to support custom extensions and advanced database hackery.