I think this is very interesting, but what are you specifying when you build a website?
I feel like this is the new "test driven development", which is totally a good idea, but also not totally useful for the actual process of building web apps, where most of your failure modes are weird CSS, JS, or server issues.
I would be happy to be proven wrong though
I don't know yet, but with Lasm I'll be spending a lot of effort finding out. And hopefully I'll get some help.
For me Lean is the key that has unlocked the idea of formal verification for general-purpose software engineering...before it was just an amazing technology that I couldn't practically touch in my profession and personal projects. That's changed now.