ScoreboardCadence.Due(phase, lastAnalytics, lastSubscribers, now) is the creator's rule as a pure
function: watch hours ONLY during a live stream, every 30 minutes (Analytics answers in days and
test/record sessions have no public audience, so querying then is pure waste); subscribers whenever
the app is working, every 60 s; and nothing at all when idle.
Deliberately returns 'no poll' rather than 'analytics only' — a poll kind the poller cannot perform
is a bug waiting for a caller.
Remaining for the scoreboard: the HTTP providers behind this policy (watch hours via Analytics
reports.query, subscribers via channels.list) and the timer that calls Due(). Recorded in HANDOFF.
