silkworm stealing is in the svn.
spy or great spy must be on a foreign tile with silk and a plantation and have the crop rotation tech. the silkworms appear as a promotion. when the spy is back in your territory, on a plains or grasslands tile with no feature or bonus, you can cultivate the silkworms there, creating a silk resource.
the Byzantine gold goal is replaced by silkworm cultivation.
Having problems with the silkworm mechanics. When playing a Byz I sent a spy to steal a silkworm from the silk near Shu. The spy was then detected the turn after I got the Silkworm promotion. I sent another one, but now I don't have the option to steal silkworms from that or any other plantation. Is there any way to achieve this now?