Thanks for writing the post, I found it quite useful.
Small nit regarding
As a result - and this is the interesting bit - you're constantly being negatively reinforced for even thinking about the topic.
I think what you're referring to is known as positive punishment. Negative reinforcement refers to the removal of an aversive outcome to increase certain behavior.
Thanks a lot for writing this. Got a lot of useful pointers.
One important failure mode which I went through is to totally ignore my impostory thoughts by just inverting the feeling (just try to enforce the belief that I am not an impostor) . That might help with some symptoms but doesn't solve the entire problem. I would also caution against your advice of taking ambitious projects on the grounds of - a) Reversing every advice you get b) Without the right social framework to deal with your impostor syndrome, it has a non trivial chance of actually exacerbating the problem.
What personally worked for me is to take the signal seriously (to the effect that it's something to be worked on and not ignored) but not take my internal criticisms seriously. And take small steps in establishing trust with a few people initially and then scaling it up. Increasingly I find the framing of my work as being part of a team, useful in dealing with it. It makes me prioritize things better than just aiming for personal perfection.