Function assemble 

pub fn assemble(
    reg: &LoadedRegistry,
    label: &str,
    window_cadence: Cadence,
    start: NaiveDate,
    end: NaiveDate,
    today: NaiveDate,
) -> Result<ReportData>

Assemble the report payload for [start, end], labelled label.

window_cadence is the cadence of the reporting window itself (weekly report → Weekly) and anchors the upcoming horizon to the next calendar period. today separates open from gap periods and anchors SLA/overdue math — pin it (--today) for deterministic output.