Function confirm_write_durability 

pub async fn confirm_write_durability(
    runtime: &NodeRuntime,
    coordinator: Option<&CheckpointCoordinator>,
    index: LogIndex,
) -> Result<(), DurabilityError>

Confirms that a committed write has reached the configured durability boundary.

Synchronous archive I/O failures are retried with bounded backoff until the archive recovers or the runtime begins shutdown.