True once every member has reached a terminal state (completed/failed/skipped).
Current per-member status (a copy — safe for the caller to keep/render).
Aggregate counts + members, for dashboards and queue/sweep status.
Advance the fan-out one step at time nowMs: reconcile launched members
against the client's current instance list, recompute dependency gating,
then launch as many eligible members as the concurrency cap and the launch/
retry delays permit. Reentrancy-guarded (launching refreshes the client,
which re-fires the event that drives this). Returns true when nothing is
left to start.
True while some member has yet to start (pending or blocked).