The scenario you describe seems worrisome, but I would consider that not getting feedback on your product is a huge danger of its own. Unless you have a big private network that you can share discreetly with, but that has its own problems in that you're getting feedback only from people that know you.

Also, I think that the probability of this happening is possibly lower than you think, as it assumes that your posting is wildly popular AND popular enough that someone at a big tech co. thinks it's worth building AND that person is convincing enough to convince his team to build your product AND they're able to move as fast as you're saying AND they execute well enough AND there is not room enough for more than one co. in the market you're after.

Even if you do manage to keep things a secret and choose a different path, who is to say that the alternative path doesn't somehow end up exposing you even more due to the large number of unknowns that you'll encounter as a founder?

You may even be able to move faster than Zoom as a solo dev depending on the circumstances. In the long run, I really don't think that a posting to HN will destroy a co. Most of the time it will be something else like lack of motivation, time, resources, etc.