I was reading about "eyeball planets", which are possibly suitable for life, and match this description (vaguely, IANAAstrophysicist). Basically, the idea is th

I was reading about "eyeball planets", which are possibly suitable for life, and match this description (vaguely, IANAAstrophysicist). Basically, the idea is that a planet of right size and roughly in the right distance to its star is tidally locked in a 1:1 resonance, so one side is always pointing at the star, and one always poiting away. Now, the perpetual noon point is very hot, and the perpetual midnight point is very cold, but you get a consistent temperature gradient inbetween. Somewhere there, it's about 20 deg C ~all the time. It's also somewhat tunable. If the planet is closer to the star, perhaps only the perpetual midnight is a happy spot, and the rest too hot. Or maybe the planet is further out, and only the perpetual noon is nice. And so on. Of course you also make the point about magnetic field requiring rotation, which is not addressed by this, but the temperature side at least maybe is OK.