Function load_threads 

pub fn load_threads(
    paths: &[PathBuf],
    workers: usize,
    report: &mut ExportReport,
) -> Result<Vec<RolloutThread>>

Parses rollout files on workers threads, keeping one copy of each Codex thread.

Codex moves rollouts into archived_sessions while it runs, so one thread can be discovered twice; the copy with more recorded requests wins.