Crossing the Gap is the 42nd cutscene in Run 3, including all hidden and optional cutscenes.
This is a very important cutscene, as this marks the end of the Bridge Building minigame and unlocks the N-Tunnel afterward. This is also a major cutscene.
After you use the Student to collect a number of boxes for the Bridge Building minigame, when you push the last (3rd) box to the rendezvous point in Level B-13, you will meet the Runner with a pile of ringed boxes.
The Student remarks that the Runner has been busy, after she looks at the pile of boxes. Then she asks the Runner if that's enough, and the Runner still thinks it is not enough since they can meet another large gap like this, but the Student says she has planned ahead too much and says she doesn't want to collect a hundred more boxes. The Runner agrees and they jump across the boxes to reach the N-Tunnel.