I'm not aware of a name, but I'm also curious if there is one because I had a hard time searching for it.

I came across it on ThePrimeagen's YouTube channel: https://youtu.be/u1WmiqlrqL0

I asked an LLM and it described the problem as "covariant typing of mutable collections" or "unsound covariance". I'm not mathematically educated in this area but that sounds right?

	▲	saghm 3 days ago \| parent [-]
		Yes, that's correct. If you're curious for a slightly more concrete source, Wikipedia covers this reasonably well (although citing one often decried source to validate another might not be particularly convincing to some people): https://en.wikipedia.org/wiki/Type_variance#Arrays