yarl requires APIs from Cython >= 3.0 without actually specifying that it needs Cython > 3.0 in its pyproject.toml. This causes a fresh Gaudi bootstrap pipeline to fail when no previous project has build Cython 3.0.

In my test case, bootstrap had Cython-0.29.37-2-cp311-cp311-linux_x86_64.whl. Because the old version satisfies requirement Cython, Fromager installed the old version into the build env.

Solution: require Cython >= 3.0 in an override.