Well, Monday morning and BART is making up for being incident-free last week by announcing:

There is another train that needs to be ??? and we’re single tracking. What I’m going to do now is I’m going to have to change ends and go back at the other end, pull the … pull it the other way and then eventually we are change ends again then go to SFO so there will be a minor delay for that.

And sure enough, just after making that announcement, he ran through the train to get to the back and drove us back into Colma station (that we had just left). Then, to minimise the delay, another driver got in the front and drove us out again. The original driver walked back through the train, and was back at the controls before we arrived at San Bruno.