Is Haybarn a fork?
No — it's a derived distribution, the same relationship Ubuntu has to Debian. The engine source tracks upstream DuckDB and Haybarn ships on DuckDB's release cadence. What Haybarn adds around the engine (coordination with the extension catalog at release time, signing pipeline, package formats, extension distribution channels) is independent and tuned for the audience running it in production. Another precedent for the same shape: OpenSSH-portable to OpenBSD's OpenSSH.