I think they were on high alert up until recently and are now in the process of trying to figure out how to get along with them. On the border areas, there were a handful of markets in the mountain villages where they allowed Afghans to cross the border to sell products. These markets were shut down once the Taliban took over but have recently been re-opened (within the last month or two).

As of last year but probably since the Taliban came to power, Tajikistan has has military checkpoints along the border. Also, I don't know about for all seasons but during the summer, the river seemed too fast to be crossable along most parts of the border.