No, a bad lane change is not probable cause for a search. How you know that is, upon being pulled over for improper lane change, the police cannot demand a search of your car. I think we're talking past each other.

If you'd like to move the goal posts and talk about roadside detention, fine. But that's (a) not a search and (b) not relevant to the question of whether the border search exception means that tens of millions of Americans are continually exposed to warrantless searches of their devices by dint of living close to a border.

(I didn't say you hadn't read Martinez-Fuerte; I said you hadn't read it carefully. A decent-sized stretch in the middle of the opinion is about exactly this distinction, and reaffirms the fact that LEOs can't search you within a 100 mile range of the country's border).