fix: subscribe to subnet when aggregating only

bin/ethlambda/src/main.rs

@@ -134,6 +134,7 @@ async fn main() -> eyre::Result<()> {
         store.clone(),
         first_validator_id,
         options.attestation_committee_count,
+        options.is_aggregator,
     ));
 
     ethlambda_rpc::start_rpc_server(metrics_socket, store)
@@ -143,8 +144,8 @@ async fn main() -> eyre::Result<()> {
     info!("Node initialized");
 
     tokio::select! {
-        _ = p2p_handle => {
-            panic!("P2P node task has exited unexpectedly");
+        result = p2p_handle => {
+            panic!("P2P node task has exited unexpectedly: {result:?}");
         }
         _ = tokio::signal::ctrl_c() => {
             // Ctrl-C received, shutting down

crates/net/p2p/src/lib.rs

@@ -66,7 +66,8 @@ pub async fn start_p2p(
     store: Store,
     validator_id: Option<u64>,
     attestation_committee_count: u64,
-) {
+    is_aggregator: bool,
+) -> Result<(), libp2p::gossipsub::SubscriptionError> {
     let config = libp2p::gossipsub::ConfigBuilder::default()
         // d
         .mesh_n(8)
@@ -176,22 +177,27 @@ pub async fn start_p2p(
         .subscribe(&aggregation_topic)
         .unwrap();
 
-    // Subscribe to attestation subnet topic (validators subscribe to their committee's subnet)
+    // Build attestation subnet topic (needed for publishing even without subscribing)
     // attestation_committee_count is validated to be >= 1 by clap at CLI parse time.
     let subnet_id = validator_id.map(|vid| vid % attestation_committee_count);
     let attestation_topic_kind = match subnet_id {
         Some(id) => format!("{ATTESTATION_SUBNET_TOPIC_PREFIX}_{id}"),
-        // Non-validators subscribe to subnet 0 to receive attestations
+        // Non-validators use subnet 0 for publishing
         None => format!("{ATTESTATION_SUBNET_TOPIC_PREFIX}_0"),
     };
     let attestation_topic_str =
         format!("/leanconsensus/{network}/{attestation_topic_kind}/ssz_snappy");
     let attestation_topic = libp2p::gossipsub::IdentTopic::new(attestation_topic_str);
-    swarm
-        .behaviour_mut()
-        .gossipsub
-        .subscribe(&attestation_topic)
-        .unwrap();
+
+    // Only aggregators subscribe to attestation subnets; non-aggregators
+    // publish via gossipsub's fanout mechanism without subscribing.
+    if is_aggregator {
+        swarm
+            .behaviour_mut()
+            .gossipsub
+            .subscribe(&attestation_topic)?;
+        info!(%attestation_topic_kind, "Subscribed to attestation subnet");
+    }
 
     info!(socket=%listening_socket, "P2P node started");
 
@@ -214,6 +220,7 @@ pub async fn start_p2p(
     };
 
     event_loop(server).await;
+    Ok(())
 }
 
 /// [libp2p Behaviour](libp2p::swarm::NetworkBehaviour) combining Gossipsub and Request-Response Behaviours