What a program listens to in state, by key, as run reconciles it: empty for a program without
subscriptions. A parent lists each child's under [<child>, key], or [<child>, id, key] for children by id, so
that a test can check who listens, e.g. HashMap.has(subscriptionsOf(app)(state), ['Clock', 'ticks']).
What a program listens to in
state, by key, asrunreconciles it: empty for a program withoutsubscriptions. A parent lists each child's under[<child>, key], or[<child>, id, key]for children by id, so that a test can check who listens, e.g.HashMap.has(subscriptionsOf(app)(state), ['Clock', 'ticks']).