Periodic 60s sweep re-warms ScoreCache from /data/scores whenever
{band, valid_time} pairs are on disk but absent in local ETS.
Covers the three silent-fail modes of the NOTIFY/LISTEN path:
dropped notifies on reconnect, missing listener, and stale NFS
reads. Each pod reconciles its own cache — no PubSub fan-out,
no coordination required. Rescue on File.Error handles the
rare window where an atomic-rename write races the reader.
docs/runbook_propagation_pipeline.md names every failure mode
in the Rust↔Elixir seam and what recovers it.
