I would add that a founder should not only have "worked on the biz" but also objectively de-risked the company (i.e. can show revenue/customers/working prototyp

I would add that a founder should not only have "worked on the biz" but also objectively de-risked the company (i.e. can show revenue/customers/working prototype/major funding/etc). For example, being employed full-time while merely thinking about the company for six months isn't enough to de-risk it. (I say this because many founders vastly overestimate their earlier contributions.) Coming in, the founding engineer should see an objectively de-risked environment. If the company cannot afford a near-market salary (e.g. only received a $50K investment), then they'd have to compensate mostly as equity, aka as a co-founder.