For anyone who hasn't done interviews and are curious, the interview chain is not vetted in any way or form at most places. Typically in bigger companies there is a one or two hour session where you are told what you can and can't ask from a legal perspective. Sometimes there will also be a tech question bank you might be expected to ask questions from.

Having worked at four companies I have yet to see there being any serious discussions on merits of which questions to ask, the style of interview to be conducted, how to grade candidates reliably, or the amount of help and guidance to give candidates. In short as far as I can tell the whole tech interview process is generally a mess.

I have tried to push for discussions on all of the topics above and most engineers simply do not find the topic interesting enough to engage at length. There's a lot to discuss and everyone complains about the current state of the interview process across the whole field yet few do more than complain. Alas that is life.

As for vetting for "positive-only", I am not sure that's something that can even be done. Usually conducting interviews is part of your performance and you are expected to do them or it will reflect poorly on you as an employee. So every senior engineer or above typically will aim to do some amount of interviews and, let's say you are one of them and you are not very happy, when you get asked by your manager whether you are a positive employee, you are very unlikely to say no.

Also unhappiness is a pervasive quality regardless of title and you can very easily find high level managers and one year out of college engineers that are equally unhappy if you were to ask them candidly. This is a separate topic, but we as an industry have potential to make our workplaces incredibly engaging and rewarding but that potential somehow seems so very hard to achieve.