Function savetasks 

pub fn savetasks(
    corpus_name: String,
    service_name: String,
    session: Option<AdminSession>,
    pool: &State<DbPool>,
) -> Result<Accepted<String>, Status>

Human save-snapshot: freezes the current per-task statuses into historical_tasks. Cookie-gated (401 without a session); 404 on an unknown corpus/service.