Function query_breakdown 

pub fn query_breakdown(
    conn: &Connection,
    filter: &AnalyticsFilter,
    dim: Dim,
    metric: Metric,
    limit: usize,
) -> AnalyticsResult<BreakdownResult>

Run a breakdown query: aggregate one metric by a chosen dimension.

Returns rows ordered by the metric value descending, capped at limit. This answers questions like “which agent uses the most tokens?” or “which workspace has the most tool calls?”.