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).
I don't think talking about roadside detention is moving the goal posts at all -- it's an abrogation of the fourth amendment allowed within 100 miles of the border, and has knock-on effects that make searching easier.
I agree that the way the ACLU characterizes the rulings are wrong, and said as much in a parenthetical. But that's not the same as "thus we shouldn't be worried about the fourth amendment being ignored within 100 miles of the border".
Perhaps not in so many words...
tptacek states that a bad lane change can be given as an excuse for a stop, but not a search, because it is not probable cause. In the following comment, you reject that claim:
> Bad lane change is explicitly probable cause -- it's direct witnessing of a traffic code violation.
A reasonable interpretation of your comment would be an argument that a bad lane change is probable cause for a search. It makes no sense to differentiate "probable cause for a stop", because there is either no such test, or it should otherwise be the same standard as for a search.
On the other hand, I don't think tptacek has tried to give any advice as to whether a person should be worried about this or not.
Bad lane change is explicitly probable cause -- it's direct witnessing of a traffic code violation. It's usually pretextual: they have some other reason they don't want to articulate that might not pass constitutional muster, but pretextual stops and even searches are unfortunately allowed. And no, they're not supposed to pull you over to check your insurance absent some reason to think that there's a problem with it.
Stops without probable cause are bad not just because they are interruptions and wastes of time, but because they allow more opportunities for other abuses such as pretextual searches.
Administrative checks for commercial trucking (i.e. weigh stations) would be a better instance for stops that no one generally complains about.