> My partner doesn't have extremely disproportionate leverage over me

This is the most... hinged... thing you said. I totally agree that bargaining power is usually far more skewed in the employment case. I think unequal bargaining power is the root of much unfairness in the world, and that the only way to really counteract this is through organising, i.e., unionisation. It's far from a panacea, mind you.

With all that said: Fundamentally, I don't think that an employer should be obligated to employ someone indefinitely. If you do: Think about whether regulations enforcing this would make an employer more likely, or less likely, to hire someone they are on the fence about.