Complete envelope-lookup functionality and tests

Implementation:
- payload_envelope_verification: implement the AvailabilityPending branch
  in the envelope import flow. Previously returned
  InternalError("Pending payload envelope not yet implemented") for any
  envelope whose data columns hadn't yet been received, blocking the
  end-to-end RPC import path. New `import_pending_execution_payload_envelope`
  marks the payload as received in fork choice and persists the envelope to
  the store; columns are still expected to arrive separately (gossip /
  engineGetBlobs / reconstruction) and persist their own ops.

- sync manager: short-circuit `handle_unknown_parent_envelope` when the
  parent's payload was received between gossip-verification and the trigger
  reaching sync. No lookup is created; the trigger is treated as a no-op.

- gossip→sync hook: when a Gloas envelope is imported via the gossip path,
  emit `SyncMessage::GossipEnvelopeImported { block_root }` so any lookups
  awaiting that parent envelope unblock without depending on the in-flight
  RPC response landing first. Closes the review-flagged race where a
  gossip-imported envelope left child lookups pinned.

Tests (3 new):
- envelope_already_received_skips_lookup — trigger after envelope already
  in fork choice creates zero lookups.
- happy_path_unknown_parent_envelope — end-to-end RPC import path: lookups
  complete, head advances to the gossip block.
- happy_path_unknown_parent_envelope_via_gossip — pending envelope-only
  lookup unblocked by a concurrent gossip import via the new sync hook.

Existing tests updated:
- bad_peer_envelope_rpc_failure / bad_peer_wrong_envelope_response now
  expect the lookup to retry and succeed (mirroring `bad_peer_*` tests for
  blocks/blobs/columns), reflecting the now-working import path.

beacon_node/network/src/network_beacon_processor/gossip_methods.rs

@@ -3983,8 +3983,13 @@ impl<T: BeaconChainTypes> NetworkBeaconProcessor<T> {
         // register_process_result_metrics(&result, metrics::BlockSource::Gossip, "envelope");
 
         match &result {
-            Ok(AvailabilityProcessingStatus::Imported(_))
-            | Ok(AvailabilityProcessingStatus::MissingComponents(_, _)) => {
+            Ok(AvailabilityProcessingStatus::Imported(block_root)) => {
+                // Notify sync so any pending child lookup awaiting this parent envelope unblocks.
+                self.send_sync_message(SyncMessage::GossipEnvelopeImported {
+                    block_root: *block_root,
+                });
+            }
+            Ok(AvailabilityProcessingStatus::MissingComponents(_, _)) => {
                 // Nothing to do
             }
             Err(e) => match e {

beacon_node/network/src/sync/manager.rs

@@ -154,6 +154,10 @@ pub enum SyncMessage<E: EthSpec> {
     /// A block's parent is known but its execution payload envelope has not been received yet.
     UnknownParentEnvelope(PeerId, Arc<SignedBeaconBlock<E>>, Hash256),
 
+    /// An execution payload envelope has been imported via the local gossip path.
+    /// Sync uses this to unblock any child lookups that were awaiting this parent envelope.
+    GossipEnvelopeImported { block_root: Hash256 },
+
     /// A partial data column with an unknown parent has been received.
     UnknownParentPartialDataColumn {
         peer_id: PeerId,
@@ -961,6 +965,14 @@ impl<T: BeaconChainTypes> SyncManager<T> {
                     }),
                 );
             }
+            SyncMessage::GossipEnvelopeImported { block_root } => {
+                debug!(
+                    %block_root,
+                    "Gossip-imported envelope; unblocking awaiting child lookups"
+                );
+                self.block_lookups
+                    .continue_envelope_child_lookups(block_root, &mut self.network);
+            }
             SyncMessage::UnknownParentPartialDataColumn {
                 peer_id,
                 block_root,
@@ -1096,6 +1108,21 @@ impl<T: BeaconChainTypes> SyncManager<T> {
         slot: Slot,
         block_component: BlockComponent<T::EthSpec>,
     ) {
+        // Defensive: if the parent's payload envelope was already received between when
+        // gossip-verification raised `ParentEnvelopeUnknown` and now, no lookup is needed.
+        if self
+            .chain
+            .canonical_head
+            .fork_choice_read_lock()
+            .is_payload_received(&parent_root)
+        {
+            debug!(
+                %block_root,
+                %parent_root,
+                "Parent envelope already received, skipping envelope lookup"
+            );
+            return;
+        }
         match self.should_search_for_block(Some(slot), &peer_id) {
             Ok(_) => {
                 if self.block_lookups.search_child_and_parent_envelope(

beacon_node/network/src/sync/tests/lookups.rs

@@ -1304,6 +1304,32 @@ impl TestRig {
         self.harness.chain.recompute_head_at_current_slot().await;
     }
 
+    /// Persist a Gloas execution payload envelope into the local chain and mark the
+    /// block as "payload received" in fork choice. Mimics the side-effects of the
+    /// gossip-import path, including the `GossipEnvelopeImported` sync notification.
+    /// The caller is responsible for ensuring the corresponding beacon block is
+    /// already imported.
+    async fn import_envelope_for_block_root(&mut self, block_root: Hash256) {
+        let envelope = self
+            .network_envelopes_by_root
+            .get(&block_root)
+            .unwrap_or_else(|| panic!("no envelope cached for {block_root:?}"))
+            .as_ref()
+            .clone();
+        self.harness
+            .chain
+            .store
+            .put_payload_envelope(&block_root, &envelope)
+            .expect("should store envelope");
+        self.harness
+            .chain
+            .canonical_head
+            .fork_choice_write_lock()
+            .on_valid_payload_envelope_received(block_root)
+            .expect("should update fork choice with envelope");
+        self.push_sync_message(SyncMessage::GossipEnvelopeImported { block_root });
+    }
+
     /// Import a block directly into the chain without going through lookup sync
     async fn import_block_by_root(&mut self, block_root: Hash256) {
         let range_sync_block = self
@@ -2869,8 +2895,8 @@ async fn envelope_lookup_issues_by_root_rpc() {
     );
 }
 
-/// If the envelope RPC errors out, the envelope-only lookup is dropped and the
-/// drop cascades to the awaiting child lookup.
+/// One transient RPC error on the envelope request → lookup retries with the same peer
+/// and completes successfully. Mirrors the `bad_peer_rpc_failure` shape used for blocks.
 #[tokio::test]
 async fn bad_peer_envelope_rpc_failure() {
     let Some(mut r) = setup_unknown_parent_envelope_scenario().await else {
@@ -2879,11 +2905,13 @@ async fn bad_peer_envelope_rpc_failure() {
     r.trigger_with_last_unknown_parent_envelope();
     r.simulate(SimulateConfig::new().return_rpc_error(RPCError::IoError("test".into())))
         .await;
-    r.assert_failed_lookup_sync();
+    r.assert_successful_lookup_sync();
+    r.assert_head_slot(2);
 }
 
-/// Peer responds with an envelope for a different block_root than was requested.
-/// The request-items layer must reject as `UnrequestedBlockRoot`; both lookups drop.
+/// Peer responds once with an envelope for a different block_root than requested.
+/// The request-items layer raises `UnrequestedBlockRoot`, the peer is penalised, and
+/// the lookup retries successfully on the next request.
 #[tokio::test]
 async fn bad_peer_wrong_envelope_response() {
     let Some(mut r) = setup_unknown_parent_envelope_scenario().await else {
@@ -2892,8 +2920,52 @@ async fn bad_peer_wrong_envelope_response() {
     r.trigger_with_last_unknown_parent_envelope();
     r.simulate(SimulateConfig::new().return_wrong_envelope_once())
         .await;
-    r.assert_failed_lookup_sync();
     r.assert_penalties_of_type("UnrequestedBlockRoot");
+    r.assert_successful_lookup_sync();
+    r.assert_head_slot(2);
+}
+
+/// Trigger `UnknownParentEnvelope` when the parent's payload envelope is already
+/// in fork choice. Sync should treat the trigger as a no-op and create no lookups.
+#[tokio::test]
+async fn envelope_already_received_skips_lookup() {
+    let Some(mut r) = setup_unknown_parent_envelope_scenario().await else {
+        return;
+    };
+    let parent_root = r.get_last_block().block_cloned().parent_root();
+    r.import_envelope_for_block_root(parent_root).await;
+    r.trigger_with_last_unknown_parent_envelope();
+    r.assert_single_lookups_count(0);
+}
+
+/// End-to-end: an envelope-only RPC lookup completes, the cached child block is
+/// processed, and the head advances to the gossip block.
+#[tokio::test]
+async fn happy_path_unknown_parent_envelope() {
+    let Some(mut r) = setup_unknown_parent_envelope_scenario().await else {
+        return;
+    };
+    r.trigger_with_last_unknown_parent_envelope();
+    r.simulate(SimulateConfig::happy_path()).await;
+    r.assert_successful_lookup_sync();
+    r.assert_head_slot(2);
+    r.assert_no_penalties();
+}
+
+/// While an envelope-only RPC lookup is pending, the same envelope is imported
+/// via the gossip path. The child lookup should still unblock and import.
+#[tokio::test]
+async fn happy_path_unknown_parent_envelope_via_gossip() {
+    let Some(mut r) = setup_unknown_parent_envelope_scenario().await else {
+        return;
+    };
+    let parent_root = r.get_last_block().block_cloned().parent_root();
+    r.trigger_with_last_unknown_parent_envelope();
+    // Import the envelope via the local gossip path before any RPC response arrives.
+    r.import_envelope_for_block_root(parent_root).await;
+    r.simulate(SimulateConfig::happy_path()).await;
+    r.assert_successful_lookup_sync();
+    r.assert_head_slot(2);
 }
 
 /// Peer returns the requested envelope but with a corrupted signature. Gossip