> Might annoy or alienate a CEO (maybe that’s a warning sign?)

Yes, this is a warning sign. A CEO of a startup should know that employees take on risk by joining and that prudent candidates will want to take the financial health of the company into consideration when comparing offers.

Its really dependent on the candidate and the position. A quality senior engineer may be gauging the feasibility of ideas that may take _years_ to come to fruition. That requires a lot of non-technical information and both trust and a good working relationship with sr. management. If they are not willing to freely share information, they probably won't utilize the caliber employee who would typically request it. Its no guarantee but personally when I've interviewed people who have asked these types of in depth and / or difficult to answer questions they've turned out to be orders of magnitude higher quality. They know what successful companies look like, and aren't interested in taking chances on companies that won't or can't utilize them to their potential. Doing so requires sharing enough information and trust that the employee can help steer the ship.

Def might, if your tone is off/the CEO is neurotic. If some rando came in trying to gauge how long he could hang on to a job rather than how he can contribute to the idea I'd be a bit put off.

The best candidates dig into product and market and get all the info they need from that.