Function build 

pub fn build(
    rows: &[Row],
    catalog: &Catalog,
    now_ms: i64,
    since_override: Option<i64>,
) -> Report

Build the report: window totals plus a per-model breakdown for the period.

since_override pins the period start (from --period-start); otherwise the anniversary heuristic in month_start applies. Rows before the period are anniversary evidence only — never listed — so the table and the totals agree.