Decide report, retry, wait, or done for a sharded batch run.
Generic, domain-agnostic platform skill that reads a batch run's cortex-resource ledger (run.json + shard-.json) and decides whether to fire the reduce/report step, retry failed or missing items, wait, or stop. Reused as-is by any blueprint that adopts the batch fan-out mechanism — not authored per blueprint. See CONTRACT.md for the shard-runner contract.