> packages that use uv-build for their backend should use a semver range
This wouldn't necessarily solve Gentoo's problem. The only way to be sure to solve Gentoo's problem would be for every Python project that uses uv-build to specify one particular version. Then Gentoo could be sure that once that release of that project was built once, it would never change.
In other words, for a distro like Gentoo, the build backend is a dependency, and if it changes, that triggers a change in the build, even if the build backend change would not actually change the final wheel that got built.
This wouldn't necessarily solve Gentoo's problem. The only way to be sure to solve Gentoo's problem would be for every Python project that uses uv-build to specify one particular version. Then Gentoo could be sure that once that release of that project was built once, it would never change.
In other words, for a distro like Gentoo, the build backend is a dependency, and if it changes, that triggers a change in the build, even if the build backend change would not actually change the final wheel that got built.