What's a fair amount of equity for a technical co-founder?

Equal to all other founders, vesting across 4 years, one year cliff.

Truth be said?

Probably more than the rest unless you're a baller with great friends and family connections ($$$) to raise capital.

Just an idea and a prototype isn't worth anything. A great technical co-founder can make big bucks already working for big tech with less effort and no risk.

You might end up with an bad technical co-founder if you want to keep more control of the company, and the product being technical means your company will never be successful, as if it's a great idea, you'll have competitors and fail either now(more likely) or later down the road, as you'll have a tech. cofounder on board that isn't very good.

As you've mentioned, it's pre-seed so everything is worthless. Instead of thinking "how much do I give to my tech co-founder", I'd think: how do I get a great technical co-founder at all that will help us build this business? What can incentivise somebody that can work 10 years for a big tech company and retire... to come here and work his ass off to take this company off the ground?

In a place where technical cofounders are very common (e.g. Silicon Valley), probably equal across all founders. Where tech cofounders are rarer (e.g. SE Asia), we usually take a larger portion, but not too much that the other founders are demotivated. It's quite common for the CTO to have a higher share than the CEO here.