> BSD jails are architected wholly differently from what something like Docker provides. > Jails are first-class citizens that are baked deep into the system.

Both very true statements and worth remembering when considering:

> Additionally, iirc, the logic for FreeBSD jails never made it into the Darwin kernel.

You are quite correct, as Darwin is is based on XNU[0], which itself has roots in the Mach[1] microkernel. Since XNU[0] is an entirely different OS architecture than that of FreeBSD[3], jails[4] do not exist within it.

The XNU source can be found here[2].

0 - https://en.wikipedia.org/wiki/XNU

1 - https://en.wikipedia.org/wiki/Mach_(kernel)

2 - https://github.com/apple-oss-distributions/xnu

3 - https://cgit.freebsd.org/src/

4 - https://man.freebsd.org/cgi/man.cgi?query=jail&apropos=0&sek...