Function aggregate_flags 

pub fn aggregate_flags(
    sites: Vec<RetirementSiteInput>,
    root: &Path,
    workspaces: &[WorkspaceInfo],
    in_scope: &dyn Fn(&Path) -> bool,
) -> Vec<RetirementFlag>

Group flag sites into one row per flag and run the reason detectors.

root makes paths relative. workspaces adds the workspace root to the flag identity, so two packages that use the same flag name get two rows. Pass every site of the project: in_scope selects the sites the rows show, but the read reasons count the reads outside the scope too, so a --changed-since run does not call a widely read flag single-read. Rows come back sorted by name; finish_report applies the final order.