The term is "swedged". It means being struck with a punch-like tool, upsetting the metal and permanently attaching the socket to the extension.
I can't find "swedged" in the online dictionary - which proves nothing, since trade terms are often missing - but I do find "swaged," with a definition that would work in this context; although I agree that "staked" is a better word, since "swaged" work seems to involve a tool specific to the purpose.
The trade definition of "staked" that I have understood doesn't appear in the online dictionary, either...d*** online dictionaries.