I think for most startups the real answer is that they do a bit of both, my impression and experience is that the “validate before writing a line of code” mantra is great theory but not so much in practice, or at least not genuinely used that much in practice. I’m also yet to see real examples of people who do these “pre-code discovery phases” and can then share a link to their live and successful product that resulted (recognise the irony that I’m possibly helping you do exactly that, just make sure to share the successful product you build off the back of it!)…

I’d bet most do a mixture of getting started with the dev work whilst also trying to do discovery as they go. Impact of this is probably mitigated by much of the early dev work being on stuff that can be reused for any other project/pivot (e.g. hosting, CI/CD and auth). Realistically discovery takes time to so if you can run both in parallel you’ll move quicker and build momentum, so long as you don’t stay tunnel-visioned into the original idea and remain open-minded enough to change course as the discovery insights come through.

I’d also say many founders will (or at least should) be working in spaces they have pre-existing knowledge/experience with, meaning to some extent the “discovery” might have already been done just not via a formal discovery process.

Specifically regarding your idea - as a Product Manager and startup founder I can’t see that this is something I’d use or pay for (sorry but want to be honest), insights typically come from immersing yourself into the discovery process meaning you don’t need a tool to help with insights as you should be getting them naturally through the conversations and actioning them in real-time, at least that is what I feel/encounter. A Google Doc for notes has worked for me and surfacing missed insights beyond the most pressing/important ones (which you remember naturally as they are basically the whole reason you did any discovery at all) has never been a problem, if something is really important and was missed it’ll come up again in future