Function bootstrap_epoch_window 

pub async fn bootstrap_epoch_window(
    coordinator: &EpochMembershipCoordinator<SeqTypes>,
    epoch_height: u64,
    step_timeout: Duration,
) -> Result<EpochNumber>

Walk forward from the highest already-known epoch until peers can no longer serve the next epoch root leaf, populating the membership with stake tables for every epoch up through N+1 (where N is the current epoch). Returns N.

Preconditions: reload_stake should have run before this — it populates the membership from local persistence so the walk skips epochs we already know.