That seems completely sane and fair

I agree it’s fair, but I don’t think it’s “open-source”. Open source means “free”; requiring me to give you something in return is transactional.

copy-left is referred to as open source and some even claim it's _more_ open source, but thanks for the information, I wasn't aware of the that detail.

edit: oh it's not copyleft, but specifically quid pro quo so tesla gives you their patents if you give them yours

Yes, it seems we need some kind of designation like copyleft for the context of patents or maybe already exists one.

Quid pro quo is well adjusted for the context.

A copy left style arrangement would require you to not enforce your patents against anyone who signs and upholds the agreement, not just with Tesla. If that was the case, I probably wouldn't have quibbled with the term "open source" being applied.