Function
The course, its lessons and their videos
The video to open and why (start, continue or rewatch), or null for a course with no videos
Reads this learner's completion marks, playback positions and the course's
own continue-watching record from the learner store, and hands them to
courseOverviewProgress — the rule the board uses — so any surface built on
this hook opens the same video as the board.
Before the learner store is seeded every slice reads empty, so the target is
the course's first video with kind start. Gate on
useIsLearnerStoreSeeded where that would mislead.
Client hook: the video the learner continues a course with, decided exactly as the course overview's continue tile decides it (capability
continue-target).