+ /// The last block height at which no [`UpdateOrigin::ChainSync`] monitor updates were present
+ /// in `pending_monitor_updates`.
+ /// If it's been more than [`LATENCY_GRACE_PERIOD_BLOCKS`] since we started waiting on a chain
+ /// sync event, we let monitor events return to `ChannelManager` because we cannot hold them up
+ /// forever or we'll end up with HTLC preimages waiting to feed back into an upstream channel
+ /// forever, risking funds loss.
+ last_chain_persist_height: AtomicUsize,