Function replay 

pub(crate) async fn replay(
    dir: &Path,
    node: u32,
    logs: Ingest<ExportLogsServiceRequest>,
    traces: Ingest<ExportTraceServiceRequest>,
    metrics: Ingest<ExportMetricsServiceRequest>,
) -> Result<(), Box<dyn Error>>

Push everything the log holds that no block claims back through the flushers, before the listeners open.

Ordering is the reason this is not a background task. A replayed frame keeps the sequence it already has, and Ingest::replay puts that sequence back among the log’s unpublished before it queues the frame, which is what stops a shard sealing beside it from computing a watermark over it — but that only covers frames already read off disk. A frame still sitting in a segment is in nobody’s pending set, so a live export sealing first would claim a watermark past it and the next boot would not replay it. Draining the whole log before the first new export is framed is the blunt guarantee that this never happens. It is also the reason nobody is waiting: the client that sent this either got its answer before the crash or gave up long before this process started.

One spawn_blocking for the whole log, not one per frame. The channel is bounded at ingest.queue and the sends are blocking, so the flushers set the pace and a multi-gigabyte log is decoded at the rate it can be sealed rather than into memory all at once.