I’m also wondering if anyone knows of a complete and free POSIX shell implementation?
There is a work-in-progress shell by emersion aiming to be strictly POSIX compliant and no more: https://git.sr.ht/~emersion/mrsh
There is a work-in-progress shell by emersion aiming to be strictly POSIX compliant and no more: https://git.sr.ht/~emersion/mrsh