Function
false until the learner store is seeded, true afterwards
Enrollments, completion marks and the rest of the learner's state reach the
browser after the page renders, so anything that reads them would first show
an empty learner — Enroll to someone already enrolled, for one. Gate that
markup on this hook and render a neutral shape until it turns true.
Always false on the server.
Client hook: reports whether the learner store has been seeded with this learner's state.