Debian manages to build Chromium, Firefox, and LLVM on servers of multiple architectures, including quite slow riscv64 machines, without any network access to the builds for any architecture.

https://buildd.debian.org/status/package.php?p=firefox-esr

See Bootstrappable Builds for starting from almost nothing, so far only GNU Guix and StageX have worked out how to start from the BB work to get a full distro. Should be fairly trivial for other distros too if they cared.

https://bootstrappable.org/ https://guix.gnu.org/blog/2023/the-full-source-bootstrap-bui... https://stagex.tools/