Function plan_series_indexes 

pub(crate) fn plan_series_indexes(
    buckets: Vec<SeriesBucket>,
    index_buckets: BTreeMap<Timestamp, IndexBucket>,
    ttl: Option<TimeToLive>,
    now_ms: i64,
) -> SeriesIndexPlan

Plans whole-bucket replacements when source SST summaries change. The returned bucket map is publishable only after every planned build and the catalog writes succeed.