> Copyleft and the whole software licensing ecosystem are only applicable when producing software that actually required human effort.

Fixed that for you. Code generated by an LLM is not copyrightable (because copyright only protects human effort), so the codebase is automatically public domain and cannot be licensed at all.

They could theoretically copyright the prompts that they used, but as that's not part of the output, and the output doesn't deterministically arise from those prompts, they'd struggle to use that to back a copyright claim.