Function write_final 

pub async fn write_final(
    conn: &Connection,
    snapshots_dir: &Path,
    ts: &str,
    archive_path: Option<&Path>,
) -> Result<PathBuf>

Write the final snapshot on clean shutdown (§5.1.7).

Called after the Write Actor has stopped, so the state it folds is quiescent — nothing can commit between the fold and the write. Returns the snapshot’s path so a caller can log or verify it.

This was a Ok(()) stub that close() never called, which meant every restart replayed the log from whatever snapshot happened to be lying around rather than from the shutdown anchor.