feat: log when publishing to 0 data column peers

packages/beacon-node/src/api/impl/beacon/blocks/index.ts

@@ -281,6 +281,7 @@ export function getBeaconBlockApi({
     const sentPeersArr = await promiseAllMaybeAsync<number | void>(publishPromises);
 
     if (isForkPostFulu(fork)) {
+      let columnsPublishedWithZeroPeers = 0;
       // sent peers per topic are logged in network.publishGossip(), here we only track metrics for it
       // starting from fulu, we have to push to 128 subnets so need to make sure we have enough sent peers per topic
       // + 1 because we publish to beacon_block first
@@ -289,6 +290,16 @@ export function getBeaconBlockApi({
         const sentPeers = sentPeersArr[i + 1] as number;
         // sent peers could be 0 as we set `allowPublishToZeroTopicPeers=true` in network.publishDataColumnSidecar() api
         metrics?.dataColumns.sentPeersPerSubnet.observe(sentPeers);
+        if (sentPeers === 0) {
+          columnsPublishedWithZeroPeers++;
+        }
+      }
+      if (columnsPublishedWithZeroPeers > 0) {
+        chain.logger.warn("Published data columns to 0 peers, increased risk of reorg", {
+          slot,
+          blockRoot,
+          columns: columnsPublishedWithZeroPeers,
+        });
       }
     }