diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3828494f..1065a575 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -80,7 +80,7 @@ jobs:
 
   interop-tests:
     name: Interop tests - Multi-node consensus
-    runs-on: ubuntu-latest
+    runs-on: macos-15
     timeout-minutes: 10
     steps:
       - name: Checkout leanSpec
diff --git a/packages/testing/src/consensus_testing/test_fixtures/fork_choice.py b/packages/testing/src/consensus_testing/test_fixtures/fork_choice.py
index 0a0138b6..f48b74c1 100644
--- a/packages/testing/src/consensus_testing/test_fixtures/fork_choice.py
+++ b/packages/testing/src/consensus_testing/test_fixtures/fork_choice.py
@@ -235,7 +235,9 @@ def make_fixture(self) -> Self:
                     # Time advancement may trigger slot boundaries.
                     # At slot boundaries, pending attestations may become active.
                     # Always act as aggregator to ensure gossip signatures are aggregated
-                    store = store.on_tick(Uint64(step.time), has_proposal=False, is_aggregator=True)
+                    store, _ = store.on_tick(
+                        Uint64(step.time), has_proposal=False, is_aggregator=True
+                    )
 
                 elif isinstance(step, BlockStep):
                     # Build a complete signed block from the lightweight spec.
@@ -264,7 +266,7 @@ def make_fixture(self) -> Self:
                     # Always act as aggregator to ensure gossip signatures are aggregated
                     slot_duration_seconds = block.slot * SECONDS_PER_SLOT
                     block_time = store.config.genesis_time + slot_duration_seconds
-                    store = store.on_tick(block_time, has_proposal=True, is_aggregator=True)
+                    store, _ = store.on_tick(block_time, has_proposal=True, is_aggregator=True)
 
                     # Process the block through Store.
                     # This validates, applies state transition, and updates head.
@@ -408,7 +410,7 @@ def _build_block_from_spec(
         # First, aggregate any gossip signatures into payloads
         # This ensures that signatures from previous blocks (like proposer attestations)
         # are available for extraction
-        aggregation_store = working_store.aggregate_committee_signatures()
+        aggregation_store, _ = working_store.aggregate_committee_signatures()
 
         # Now combine aggregated payloads from both sources
         aggregated_payloads = (
diff --git a/src/lean_spec/subspecs/chain/service.py b/src/lean_spec/subspecs/chain/service.py
index 17a86e20..16ab4d3f 100644
--- a/src/lean_spec/subspecs/chain/service.py
+++ b/src/lean_spec/subspecs/chain/service.py
@@ -125,9 +125,10 @@ async def run(self) -> None:
             #
             # This minimal service does not produce blocks.
             # Block production requires validator keys.
-            new_store = self.sync_service.store.on_tick(
+            new_store, new_aggregated_attestations = self.sync_service.store.on_tick(
                 time=current_time,
                 has_proposal=False,
+                is_aggregator=self.sync_service.is_aggregator,
             )
 
             # Update sync service's store reference.
@@ -137,6 +138,11 @@ async def run(self) -> None:
             # the updated time.
             self.sync_service.store = new_store
 
+            # Publish any new aggregated attestations produced this tick
+            if new_aggregated_attestations:
+                for agg in new_aggregated_attestations:
+                    await self.sync_service.publish_aggregated_attestation(agg)
+
             logger.info(
                 "Tick: slot=%d interval=%d time=%d head=%s finalized=slot%d",
                 self.clock.current_slot(),
@@ -162,11 +168,18 @@ async def _initial_tick(self) -> Interval | None:
 
         # Only tick if we're past genesis.
         if current_time >= self.clock.genesis_time:
-            new_store = self.sync_service.store.on_tick(
+            new_store, new_aggregated_attestations = self.sync_service.store.on_tick(
                 time=current_time,
                 has_proposal=False,
+                is_aggregator=self.sync_service.is_aggregator,
             )
             self.sync_service.store = new_store
+
+            # Publish any aggregated attestations produced during catch-up.
+            if new_aggregated_attestations:
+                for agg in new_aggregated_attestations:
+                    await self.sync_service.publish_aggregated_attestation(agg)
+
             return self.clock.total_intervals()
 
         return None
diff --git a/src/lean_spec/subspecs/forkchoice/store.py b/src/lean_spec/subspecs/forkchoice/store.py
index 7faefd9c..ba036278 100644
--- a/src/lean_spec/subspecs/forkchoice/store.py
+++ b/src/lean_spec/subspecs/forkchoice/store.py
@@ -494,7 +494,6 @@ def on_gossip_aggregated_attestation(
         new_attestation_data_by_root = dict(self.attestation_data_by_root)
         new_attestation_data_by_root[data_root] = data
 
-        store = self
         for vid in validator_ids:
             # Update Proof Map
             #
@@ -503,7 +502,7 @@ def on_gossip_aggregated_attestation(
             new_aggregated_payloads.setdefault(key, []).append(proof)
 
         # Return store with updated aggregated payloads and attestation data
-        return store.model_copy(
+        return self.model_copy(
             update={
                 "latest_new_aggregated_payloads": new_aggregated_payloads,
                 "attestation_data_by_root": new_attestation_data_by_root,
@@ -862,28 +861,7 @@ def update_head(self) -> "Store":
         )
 
     def accept_new_attestations(self) -> "Store":
-        """
-        Process pending aggregated payloads and update forkchoice head.
-
-        Moves aggregated payloads from latest_new_aggregated_payloads to
-        latest_known_aggregated_payloads, making them eligible to contribute to
-        fork choice weights. This migration happens at specific interval ticks.
-
-        The Interval Tick System
-        -------------------------
-        Aggregated payloads progress through intervals:
-        - Interval 0: Block proposal
-        - Interval 1: Validators cast attestations (enter "new")
-        - Interval 2: Aggregators create proofs & broadcast
-        - Interval 3: Safe target update
-        - Interval 4: Process accumulated attestations
-
-        This staged progression ensures proper timing and prevents premature
-        influence on fork choice decisions.
-
-        Returns:
-            New Store with migrated aggregated payloads and updated head.
-        """
+        """Process pending aggregated payloads and update forkchoice head."""
         # Merge new aggregated payloads into known aggregated payloads
         merged_aggregated_payloads = dict(self.latest_known_aggregated_payloads)
         for sig_key, proofs in self.latest_new_aggregated_payloads.items():
@@ -943,7 +921,7 @@ def update_safe_target(self) -> "Store":
 
         return self.model_copy(update={"safe_target": safe_target})
 
-    def aggregate_committee_signatures(self) -> "Store":
+    def aggregate_committee_signatures(self) -> tuple["Store", list[SignedAggregatedAttestation]]:
         """
         Aggregate committee signatures for attestations in committee_signatures.
 
@@ -951,7 +929,7 @@ def aggregate_committee_signatures(self) -> "Store":
         Attestations are reconstructed from gossip_signatures using attestation_data_by_root.
 
         Returns:
-            New Store with updated latest_new_aggregated_payloads.
+            Tuple of (new Store with updated payloads, list of new SignedAggregatedAttestation).
         """
         new_aggregated_payloads = dict(self.latest_new_aggregated_payloads)
 
@@ -976,13 +954,14 @@ def aggregate_committee_signatures(self) -> "Store":
             committee_signatures,
         )
 
-        # iterate to broadcast aggregated attestations
+        # Create list for broadcasting
+        new_aggregates: list[SignedAggregatedAttestation] = []
         for aggregated_attestation, aggregated_signature in aggregated_results:
-            _ = SignedAggregatedAttestation(
+            agg = SignedAggregatedAttestation(
                 data=aggregated_attestation.data,
                 proof=aggregated_signature,
             )
-            # Note: here we should broadcast the aggregated signature to committee_aggregators topic
+            new_aggregates.append(agg)
 
         # Compute new aggregated payloads
         new_gossip_sigs = dict(self.gossip_signatures)
@@ -1004,9 +983,11 @@ def aggregate_committee_signatures(self) -> "Store":
                 "latest_new_aggregated_payloads": new_aggregated_payloads,
                 "gossip_signatures": new_gossip_sigs,
             }
-        )
+        ), new_aggregates
 
-    def tick_interval(self, has_proposal: bool, is_aggregator: bool = False) -> "Store":
+    def tick_interval(
+        self, has_proposal: bool, is_aggregator: bool = False
+    ) -> tuple["Store", list[SignedAggregatedAttestation]]:
         """
         Advance store time by one interval and perform interval-specific actions.
 
@@ -1048,11 +1029,12 @@ def tick_interval(self, has_proposal: bool, is_aggregator: bool = False) -> "Sto
             is_aggregator: Whether the node is an aggregator.
 
         Returns:
-            New Store with advanced time and interval-specific updates applied.
+            Tuple of (new store with advanced time, list of new signed aggregated attestation).
         """
         # Advance time by one interval
         store = self.model_copy(update={"time": self.time + Uint64(1)})
         current_interval = store.time % INTERVALS_PER_SLOT
+        new_aggregates: list[SignedAggregatedAttestation] = []
 
         if current_interval == Uint64(0):
             # Start of slot - process attestations if proposal exists
@@ -1061,7 +1043,7 @@ def tick_interval(self, has_proposal: bool, is_aggregator: bool = False) -> "Sto
         elif current_interval == Uint64(2):
             # Aggregation interval - aggregators create proofs
             if is_aggregator:
-                store = store.aggregate_committee_signatures()
+                store, new_aggregates = store.aggregate_committee_signatures()
         elif current_interval == Uint64(3):
             # Fast confirm - update safe target based on received proofs
             store = store.update_safe_target()
@@ -1069,9 +1051,11 @@ def tick_interval(self, has_proposal: bool, is_aggregator: bool = False) -> "Sto
             # End of slot - accept accumulated attestations
             store = store.accept_new_attestations()
 
-        return store
+        return store, new_aggregates
 
-    def on_tick(self, time: Uint64, has_proposal: bool, is_aggregator: bool = False) -> "Store":
+    def on_tick(
+        self, time: Uint64, has_proposal: bool, is_aggregator: bool = False
+    ) -> tuple["Store", list[SignedAggregatedAttestation]]:
         """
         Advance forkchoice store time to given timestamp.
 
@@ -1085,7 +1069,8 @@ def on_tick(self, time: Uint64, has_proposal: bool, is_aggregator: bool = False)
             is_aggregator: Whether the node is an aggregator.
 
         Returns:
-            New Store with time advanced and all interval actions performed.
+            Tuple of (new store with time advanced,
+            list of all produced signed aggregated attestation).
         """
         # Calculate target time in intervals
         time_delta_ms = (time - self.config.genesis_time) * Uint64(1000)
@@ -1093,14 +1078,16 @@ def on_tick(self, time: Uint64, has_proposal: bool, is_aggregator: bool = False)
 
         # Tick forward one interval at a time
         store = self
+        all_new_aggregates: list[SignedAggregatedAttestation] = []
         while store.time < tick_interval_time:
             # Check if proposal should be signaled for next interval
             should_signal_proposal = has_proposal and (store.time + Uint64(1)) == tick_interval_time
 
             # Advance by one interval with appropriate signaling
-            store = store.tick_interval(should_signal_proposal, is_aggregator)
+            store, new_aggregates = store.tick_interval(should_signal_proposal, is_aggregator)
+            all_new_aggregates.extend(new_aggregates)
 
-        return store
+        return store, all_new_aggregates
 
     def get_proposal_head(self, slot: Slot) -> tuple["Store", Bytes32]:
         """
@@ -1128,7 +1115,7 @@ def get_proposal_head(self, slot: Slot) -> tuple["Store", Bytes32]:
         slot_time = self.config.genesis_time + slot_duration_seconds
 
         # Advance time to current slot (ticking intervals)
-        store = self.on_tick(slot_time, True)
+        store, _ = self.on_tick(slot_time, True)
 
         # Process any pending attestations before proposal
         store = store.accept_new_attestations()
@@ -1174,8 +1161,11 @@ def get_attestation_target(self) -> Checkpoint:
         #
         # This ensures the target doesn't advance too far ahead of safe target,
         # providing a balance between liveness and safety.
+        #
+        # We allow the target to be up to 1 slot ahead of the safe target
+        # to ensure the chain can actually start advancing from genesis.
         for _ in range(JUSTIFICATION_LOOKBACK_SLOTS):
-            if self.blocks[target_block_root].slot > self.blocks[self.safe_target].slot:
+            if self.blocks[target_block_root].slot > self.blocks[self.safe_target].slot + Slot(1):
                 target_block_root = self.blocks[target_block_root].parent_root
             else:
                 break
@@ -1192,7 +1182,7 @@ def get_attestation_target(self) -> Checkpoint:
         # Create checkpoint from selected target block
         target_block = self.blocks[target_block_root]
 
-        return Checkpoint(root=hash_tree_root(target_block), slot=target_block.slot)
+        return Checkpoint(root=target_block_root, slot=target_block.slot)
 
     def produce_attestation_data(self, slot: Slot) -> AttestationData:
         """
@@ -1299,7 +1289,7 @@ def produce_block_with_signatures(
         #
         # The builder iteratively collects valid attestations.
         # It returns the final block, post-state, and signature proofs.
-        final_block, final_post_state, _, signatures = head_state.build_block(
+        final_block, final_post_state, collected_attestations, signatures = head_state.build_block(
             slot=slot,
             proposer_index=validator_index,
             parent_root=head_root,
diff --git a/src/lean_spec/subspecs/networking/client/event_source.py b/src/lean_spec/subspecs/networking/client/event_source.py
index 3a6e300f..593f11f2 100644
--- a/src/lean_spec/subspecs/networking/client/event_source.py
+++ b/src/lean_spec/subspecs/networking/client/event_source.py
@@ -106,7 +106,7 @@
 
 from lean_spec.snappy import SnappyDecompressionError, frame_decompress
 from lean_spec.subspecs.containers import SignedBlockWithAttestation
-from lean_spec.subspecs.containers.attestation import SignedAttestation
+from lean_spec.subspecs.containers.attestation import SignedAggregatedAttestation, SignedAttestation
 from lean_spec.subspecs.networking.config import (
     GOSSIPSUB_DEFAULT_PROTOCOL_ID,
     GOSSIPSUB_PROTOCOL_ID_V12,
@@ -130,6 +130,7 @@
 )
 from lean_spec.subspecs.networking.reqresp.message import Status
 from lean_spec.subspecs.networking.service.events import (
+    GossipAggregatedAttestationEvent,
     GossipAttestationEvent,
     GossipBlockEvent,
     NetworkEvent,
@@ -325,7 +326,7 @@ def decode_message(
         self,
         topic_str: str,
         compressed_data: bytes,
-    ) -> SignedBlockWithAttestation | SignedAttestation | None:
+    ) -> SignedBlockWithAttestation | SignedAttestation | SignedAggregatedAttestation | None:
         """
         Decode a gossip message from topic and compressed data.
 
@@ -393,6 +394,8 @@ def decode_message(
                     return SignedBlockWithAttestation.decode_bytes(ssz_bytes)
                 case TopicKind.ATTESTATION_SUBNET:
                     return SignedAttestation.decode_bytes(ssz_bytes)
+                case TopicKind.AGGREGATED_ATTESTATION:
+                    return SignedAggregatedAttestation.decode_bytes(ssz_bytes)
         except SSZSerializationError as e:
             raise GossipMessageError(f"SSZ decode failed: {e}") from e
 
@@ -816,6 +819,9 @@ async def _handle_gossipsub_message(self, event: GossipsubMessageEvent) -> None:
                 case TopicKind.ATTESTATION_SUBNET:
                     if isinstance(message, SignedAttestation):
                         await self._emit_gossip_attestation(message, event.peer_id)
+                case TopicKind.AGGREGATED_ATTESTATION:
+                    if isinstance(message, SignedAggregatedAttestation):
+                        await self._emit_gossip_aggregated_attestation(message, event.peer_id)
 
             logger.debug("Processed gossipsub message %s from %s", topic.kind.value, event.peer_id)
 
@@ -1168,6 +1174,25 @@ async def _emit_gossip_attestation(
             GossipAttestationEvent(attestation=attestation, peer_id=peer_id, topic=topic)
         )
 
+    async def _emit_gossip_aggregated_attestation(
+        self,
+        signed_attestation: SignedAggregatedAttestation,
+        peer_id: PeerId,
+    ) -> None:
+        """
+        Emit a gossip aggregated attestation event.
+
+        Args:
+            signed_attestation: Aggregated attestation received from gossip.
+            peer_id: Peer that sent it.
+        """
+        topic = GossipTopic(kind=TopicKind.AGGREGATED_ATTESTATION, fork_digest=self._fork_digest)
+        await self._events.put(
+            GossipAggregatedAttestationEvent(
+                signed_attestation=signed_attestation, peer_id=peer_id, topic=topic
+            )
+        )
+
     async def _accept_streams(self, peer_id: PeerId, conn: QuicConnection) -> None:
         """
         Accept incoming streams from a connection.
@@ -1464,6 +1489,15 @@ async def _handle_gossip_stream(self, peer_id: PeerId, stream: Stream) -> None:
                         # Type mismatch indicates a bug in decode_message.
                         logger.warning("Attestation topic but got %s", type(message).__name__)
 
+                case TopicKind.AGGREGATED_ATTESTATION:
+                    if isinstance(message, SignedAggregatedAttestation):
+                        await self._emit_gossip_aggregated_attestation(message, peer_id)
+                    else:
+                        logger.warning(
+                            "Aggregated attestation topic but got %s",
+                            type(message).__name__,
+                        )
+
             logger.debug("Received gossip %s from %s", topic.kind.value, peer_id)
 
         except GossipMessageError as e:
diff --git a/src/lean_spec/subspecs/networking/service/events.py b/src/lean_spec/subspecs/networking/service/events.py
index 4a18eeb6..9095cfca 100644
--- a/src/lean_spec/subspecs/networking/service/events.py
+++ b/src/lean_spec/subspecs/networking/service/events.py
@@ -24,7 +24,7 @@
 from dataclasses import dataclass
 
 from lean_spec.subspecs.containers import SignedBlockWithAttestation
-from lean_spec.subspecs.containers.attestation import SignedAttestation
+from lean_spec.subspecs.containers.attestation import SignedAggregatedAttestation, SignedAttestation
 from lean_spec.subspecs.networking.gossipsub.topic import GossipTopic
 from lean_spec.subspecs.networking.reqresp.message import Status
 from lean_spec.subspecs.networking.transport import PeerId
@@ -67,6 +67,25 @@ class GossipAttestationEvent:
     """Topic the attestation was received on (includes fork digest)."""
 
 
+@dataclass(frozen=True, slots=True)
+class GossipAggregatedAttestationEvent:
+    """
+    Aggregated attestation received via gossip subscription.
+
+    Fired when a signed aggregated attestation arrives from the gossipsub network.
+    Aggregates contain multiple validator votes combined into a single proof.
+    """
+
+    signed_attestation: SignedAggregatedAttestation
+    """The signed aggregated attestation."""
+
+    peer_id: PeerId
+    """Peer that propagated this aggregated attestation to us."""
+
+    topic: GossipTopic
+    """Topic the aggregated attestation was received on."""
+
+
 @dataclass(frozen=True, slots=True)
 class PeerStatusEvent:
     """
@@ -113,6 +132,7 @@ class PeerDisconnectedEvent:
 NetworkEvent = (
     GossipBlockEvent
     | GossipAttestationEvent
+    | GossipAggregatedAttestationEvent
     | PeerStatusEvent
     | PeerConnectedEvent
     | PeerDisconnectedEvent
diff --git a/src/lean_spec/subspecs/networking/service/service.py b/src/lean_spec/subspecs/networking/service/service.py
index 57f8fb1a..80eb8f7a 100644
--- a/src/lean_spec/subspecs/networking/service/service.py
+++ b/src/lean_spec/subspecs/networking/service/service.py
@@ -28,13 +28,14 @@
 
 from lean_spec.snappy import frame_compress
 from lean_spec.subspecs.containers import SignedBlockWithAttestation
-from lean_spec.subspecs.containers.attestation import SignedAttestation
+from lean_spec.subspecs.containers.attestation import SignedAggregatedAttestation, SignedAttestation
 from lean_spec.subspecs.networking.client.event_source import LiveNetworkEventSource
 from lean_spec.subspecs.networking.gossipsub.topic import GossipTopic
 from lean_spec.subspecs.networking.peer.info import PeerInfo
 from lean_spec.subspecs.networking.types import ConnectionState
 
 from .events import (
+    GossipAggregatedAttestationEvent,
     GossipAttestationEvent,
     GossipBlockEvent,
     NetworkEvent,
@@ -146,14 +147,22 @@ async def _handle_event(self, event: NetworkEvent) -> None:
                 )
                 await self.sync_service.on_gossip_block(block, peer_id)
 
-            case GossipAttestationEvent(attestation=attestation, peer_id=peer_id):
+            case GossipAttestationEvent(attestation=attestation, peer_id=peer_id, topic=topic):
                 #
                 # SyncService will validate signature and update forkchoice.
                 await self.sync_service.on_gossip_attestation(
                     attestation=attestation,
+                    subnet_id=topic.subnet_id or 0,
                     peer_id=peer_id,
                 )
 
+            case GossipAggregatedAttestationEvent(signed_attestation=att, peer_id=peer_id):
+                # Route aggregated attestations to sync service.
+                #
+                # Aggregates contain multiple validator votes and are used
+                # to advance justification and finalization.
+                await self.sync_service.on_gossip_aggregated_attestation(att, peer_id)
+
             case PeerStatusEvent(peer_id=peer_id, status=status):
                 # Route peer status updates to sync service.
                 #
@@ -234,3 +243,19 @@ async def publish_attestation(self, attestation: SignedAttestation, subnet_id: i
 
         await self.event_source.publish(str(topic), compressed)
         logger.debug("Published attestation for slot %s", attestation.message.slot)
+
+    async def publish_aggregated_attestation(
+        self, signed_attestation: SignedAggregatedAttestation
+    ) -> None:
+        """
+        Publish an aggregated attestation to the aggregation gossip topic.
+
+        Args:
+            signed_attestation: Aggregated attestation to publish.
+        """
+        topic = GossipTopic.committee_aggregation(self.fork_digest)
+        ssz_bytes = signed_attestation.encode_bytes()
+        compressed = frame_compress(ssz_bytes)
+
+        await self.event_source.publish(str(topic), compressed)
+        logger.debug("Published aggregated attestation for slot %s", signed_attestation.data.slot)
diff --git a/src/lean_spec/subspecs/node/node.py b/src/lean_spec/subspecs/node/node.py
index 55bc09c7..ceb979ab 100644
--- a/src/lean_spec/subspecs/node/node.py
+++ b/src/lean_spec/subspecs/node/node.py
@@ -21,7 +21,7 @@
 from lean_spec.subspecs.chain import SlotClock
 from lean_spec.subspecs.chain.config import ATTESTATION_COMMITTEE_COUNT, INTERVALS_PER_SLOT
 from lean_spec.subspecs.chain.service import ChainService
-from lean_spec.subspecs.containers import Block, BlockBody, State
+from lean_spec.subspecs.containers import Block, BlockBody, SignedBlockWithAttestation, State
 from lean_spec.subspecs.containers.attestation import SignedAttestation
 from lean_spec.subspecs.containers.block.types import AggregatedAttestations
 from lean_spec.subspecs.containers.slot import Slot
@@ -238,6 +238,12 @@ def from_genesis(cls, config: NodeConfig) -> Node:
             is_aggregator=config.is_aggregator,
         )
 
+        # Wire up aggregated attestation publishing.
+        #
+        # SyncService delegates aggregate publishing to NetworkService
+        # via a callback, avoiding a circular dependency.
+        sync_service._publish_agg_fn = network_service.publish_aggregated_attestation
+
         # Create API server if configured
         api_server: ApiServer | None = None
         if config.api_config is not None:
@@ -260,12 +266,19 @@ def from_genesis(cls, config: NodeConfig) -> Node:
             async def publish_attestation_wrapper(attestation: SignedAttestation) -> None:
                 subnet_id = attestation.validator_id.compute_subnet_id(ATTESTATION_COMMITTEE_COUNT)
                 await network_service.publish_attestation(attestation, subnet_id)
+                # Also route locally so we can aggregate our own attestation
+                await sync_service.on_gossip_attestation(attestation, subnet_id, peer_id=None)
+
+            async def publish_block_wrapper(block: SignedBlockWithAttestation) -> None:
+                await network_service.publish_block(block)
+                # Also route locally so we update our own store
+                await sync_service.on_gossip_block(block, peer_id=None)
 
             validator_service = ValidatorService(
                 sync_service=sync_service,
                 clock=clock,
                 registry=config.validator_registry,
-                on_block=network_service.publish_block,
+                on_block=publish_block_wrapper,
                 on_attestation=publish_attestation_wrapper,
             )
 
diff --git a/src/lean_spec/subspecs/sync/block_cache.py b/src/lean_spec/subspecs/sync/block_cache.py
index 2b8de0b0..fc803df7 100644
--- a/src/lean_spec/subspecs/sync/block_cache.py
+++ b/src/lean_spec/subspecs/sync/block_cache.py
@@ -103,7 +103,7 @@ class PendingBlock:
     slot order to ensure parents are processed before children.
     """
 
-    received_from: PeerId
+    received_from: PeerId | None
     """
     Peer that sent this block.
 
@@ -112,6 +112,7 @@ class PendingBlock:
         - If invalid, they get penalized.
 
     This creates incentives for good behavior.
+    None for self-produced blocks.
     """
 
     received_at: float = field(default_factory=time)
@@ -165,7 +166,7 @@ def __contains__(self, root: Bytes32) -> bool:
     def add(
         self,
         block: SignedBlockWithAttestation,
-        peer: PeerId,
+        peer: PeerId | None,
         backfill_depth: int = 0,
     ) -> PendingBlock:
         """
diff --git a/src/lean_spec/subspecs/sync/head_sync.py b/src/lean_spec/subspecs/sync/head_sync.py
index b14d0592..96610c9e 100644
--- a/src/lean_spec/subspecs/sync/head_sync.py
+++ b/src/lean_spec/subspecs/sync/head_sync.py
@@ -143,7 +143,7 @@ class HeadSync:
     async def on_gossip_block(
         self,
         block: SignedBlockWithAttestation,
-        peer_id: PeerId,
+        peer_id: PeerId | None,
         store: Store,
     ) -> tuple[HeadSyncResult, Store]:
         """
@@ -217,7 +217,7 @@ async def on_gossip_block(
     async def _process_block_with_descendants(
         self,
         block: SignedBlockWithAttestation,
-        peer_id: PeerId,
+        peer_id: PeerId | None,
         store: Store,
     ) -> tuple[HeadSyncResult, Store]:
         """
@@ -283,7 +283,7 @@ async def _process_cached_descendants(
         self,
         parent_root: Bytes32,
         store: Store,
-        peer_id: PeerId,
+        peer_id: PeerId | None,
     ) -> int:
         """
         Process any cached blocks that descend from the given parent.
@@ -351,7 +351,7 @@ async def _process_cached_descendants(
     async def _cache_and_backfill(
         self,
         block: SignedBlockWithAttestation,
-        peer_id: PeerId,
+        peer_id: PeerId | None,
         store: Store,
     ) -> tuple[HeadSyncResult, Store]:
         """
diff --git a/src/lean_spec/subspecs/sync/service.py b/src/lean_spec/subspecs/sync/service.py
index 299791f6..3b74d42f 100644
--- a/src/lean_spec/subspecs/sync/service.py
+++ b/src/lean_spec/subspecs/sync/service.py
@@ -38,14 +38,15 @@
 
 import asyncio
 import logging
-from collections.abc import Callable
+from collections.abc import Callable, Coroutine
 from dataclasses import dataclass, field
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 from lean_spec.subspecs import metrics
 from lean_spec.subspecs.chain.clock import SlotClock
 from lean_spec.subspecs.containers import (
     Block,
+    SignedAggregatedAttestation,
     SignedAttestation,
     SignedBlockWithAttestation,
 )
@@ -67,6 +68,8 @@
 
 BlockProcessor = Callable[[Store, SignedBlockWithAttestation], Store]
 
+PublishAggFn = Callable[[SignedAggregatedAttestation], Coroutine[Any, Any, None]]
+
 
 def default_block_processor(
     store: Store,
@@ -76,6 +79,10 @@ def default_block_processor(
     return store.on_block(block)
 
 
+async def _noop_publish_agg(signed_attestation: SignedAggregatedAttestation) -> None:
+    """No-op default for aggregated attestation publishing."""
+
+
 @dataclass(slots=True)
 class SyncProgress:
     """
@@ -156,6 +163,9 @@ class SyncService:
     process_block: BlockProcessor = field(default=default_block_processor)
     """Block processor function. Defaults to Store.on_block()."""
 
+    _publish_agg_fn: PublishAggFn = field(default=_noop_publish_agg)
+    """Callback for publishing aggregated attestations to the network."""
+
     _state: SyncState = field(default=SyncState.IDLE)
     """Current sync state."""
 
@@ -346,7 +356,7 @@ async def on_peer_status(self, peer_id: PeerId, status: Status) -> None:
     async def on_gossip_block(
         self,
         block: SignedBlockWithAttestation,
-        peer_id: PeerId,
+        peer_id: PeerId | None,
     ) -> None:
         """
         Handle block received via gossip.
@@ -402,7 +412,8 @@ async def on_gossip_block(
     async def on_gossip_attestation(
         self,
         attestation: SignedAttestation,
-        peer_id: PeerId,  # noqa: ARG002
+        subnet_id: int,
+        peer_id: PeerId | None = None,
     ) -> None:
         """
         Handle attestation received via gossip.
@@ -416,7 +427,8 @@ async def on_gossip_attestation(
 
         Args:
             attestation: The signed attestation received.
-            peer_id: The peer that propagated the attestation (unused for now).
+            subnet_id: Subnet ID the attestation was received on.
+            peer_id: The peer that propagated the attestation (optional).
         """
         # Guard: Only process gossip in states that accept it.
         #
@@ -452,6 +464,45 @@ async def on_gossip_attestation(
             # These are expected during normal operation and don't indicate bugs.
             pass
 
+    async def on_gossip_aggregated_attestation(
+        self,
+        signed_attestation: SignedAggregatedAttestation,
+        peer_id: PeerId,  # noqa: ARG002
+    ) -> None:
+        """
+        Handle aggregated attestation received via gossip.
+
+        Aggregated attestations are collections of individual votes for the same
+        target, signed by an aggregator. They provide efficient propagation of
+        consensus weight.
+
+        Args:
+            signed_attestation: The signed aggregated attestation received.
+            peer_id: The peer that propagated the aggregate (unused for now).
+        """
+        if not self._state.accepts_gossip:
+            return
+
+        try:
+            self.store = self.store.on_gossip_aggregated_attestation(signed_attestation)
+        except (AssertionError, KeyError):
+            # Aggregation validation failed.
+            pass
+
+    async def publish_aggregated_attestation(
+        self,
+        signed_attestation: SignedAggregatedAttestation,
+    ) -> None:
+        """
+        Publish an aggregated attestation to the network.
+
+        Called by the chain service when this node acts as an aggregator.
+
+        Args:
+            signed_attestation: The aggregate to publish.
+        """
+        await self._publish_agg_fn(signed_attestation)
+
     async def start_sync(self) -> None:
         """
         Start or resume synchronization.
diff --git a/src/lean_spec/subspecs/validator/service.py b/src/lean_spec/subspecs/validator/service.py
index 217ed724..e01f3c01 100644
--- a/src/lean_spec/subspecs/validator/service.py
+++ b/src/lean_spec/subspecs/validator/service.py
@@ -323,7 +323,10 @@ async def _produce_attestations(self, slot: Slot) -> None:
         Args:
             slot: Current slot number.
         """
+        # Ensure we are attesting to the latest known head
+        self.sync_service.store = self.sync_service.store.update_head()
         store = self.sync_service.store
+
         head_state = store.states.get(store.head)
         if head_state is None:
             return
diff --git a/tests/consensus/devnet/fc/test_attestation_target_selection.py b/tests/consensus/devnet/fc/test_attestation_target_selection.py
index 8044a7fa..c4f6c994 100644
--- a/tests/consensus/devnet/fc/test_attestation_target_selection.py
+++ b/tests/consensus/devnet/fc/test_attestation_target_selection.py
@@ -17,24 +17,21 @@ def test_attestation_target_at_genesis_initially(
     fork_choice_test: ForkChoiceTestFiller,
 ) -> None:
     """
-    Attestation target starts at genesis before safe target updates.
+    Attestation target starts near genesis before safe target updates.
 
     Scenario
     --------
     Process two blocks at slots 1 and 2.
 
     Expected:
-        - After slot 1: target = slot 0 (genesis/finalized)
-        - After slot 2: target = slot 0 (genesis/finalized)
-        - Target root automatically validated against block at slot 0
+        - After slot 1: target = slot 1 (1 slot ahead of safe target allowed)
+        - After slot 2: target = slot 1 (walkback stops at safe_target + 1)
 
     Why This Matters
     ----------------
-    Initially, the safe target is at genesis (slot 0), so the attestation
-    target walks back from head to genesis.
-
-    This conservative behavior ensures validators don't attest too far ahead
-    before there's sufficient attestation weight to advance the safe target.
+    Initially, the safe target is at genesis (slot 0). The attestation target
+    is allowed up to 1 slot ahead of safe target to ensure the chain can
+    start advancing from genesis.
     """
     fork_choice_test(
         steps=[
@@ -42,14 +39,14 @@ def test_attestation_target_at_genesis_initially(
                 block=BlockSpec(slot=Slot(1)),
                 checks=StoreChecks(
                     head_slot=Slot(1),
-                    attestation_target_slot=Slot(0),
+                    attestation_target_slot=Slot(1),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(2)),
                 checks=StoreChecks(
                     head_slot=Slot(2),
-                    attestation_target_slot=Slot(0),  # Still genesis
+                    attestation_target_slot=Slot(1),
                 ),
             ),
         ],
@@ -87,35 +84,35 @@ def test_attestation_target_advances_with_attestations(
                 block=BlockSpec(slot=Slot(1)),
                 checks=StoreChecks(
                     head_slot=Slot(1),
-                    attestation_target_slot=Slot(0),  # Still at genesis
+                    attestation_target_slot=Slot(1),  # 1 slot ahead of safe target allowed
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(2)),
                 checks=StoreChecks(
                     head_slot=Slot(2),
-                    attestation_target_slot=Slot(0),  # Still at genesis
+                    attestation_target_slot=Slot(1),  # Walks back to safe_target + 1
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(3)),
                 checks=StoreChecks(
                     head_slot=Slot(3),
-                    attestation_target_slot=Slot(0),  # Still at genesis
+                    attestation_target_slot=Slot(1),  # Walks back to safe_target + 1
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(4)),
                 checks=StoreChecks(
                     head_slot=Slot(4),
-                    attestation_target_slot=Slot(1),  # Advances to slot 1
+                    attestation_target_slot=Slot(1),  # 3-step walkback from 4 → 1
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(5)),
                 checks=StoreChecks(
                     head_slot=Slot(5),
-                    attestation_target_slot=Slot(2),  # Continues advancing
+                    attestation_target_slot=Slot(2),  # 3-step walkback from 5 → 2
                 ),
             ),
         ],
@@ -150,21 +147,21 @@ def test_attestation_target_with_slot_gaps(
                 block=BlockSpec(slot=Slot(1)),
                 checks=StoreChecks(
                     head_slot=Slot(1),
-                    attestation_target_slot=Slot(0),
+                    attestation_target_slot=Slot(1),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(3)),
                 checks=StoreChecks(
                     head_slot=Slot(3),
-                    attestation_target_slot=Slot(0),
+                    attestation_target_slot=Slot(1),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(5)),
                 checks=StoreChecks(
                     head_slot=Slot(5),
-                    attestation_target_slot=Slot(0),
+                    attestation_target_slot=Slot(1),  # Walks back 5→3→1, stops at safe_target+1
                 ),
             ),
         ],
@@ -201,56 +198,56 @@ def test_attestation_target_with_extended_chain(
                 block=BlockSpec(slot=Slot(1)),
                 checks=StoreChecks(
                     head_slot=Slot(1),
-                    attestation_target_slot=Slot(0),  # Genesis
+                    attestation_target_slot=Slot(1),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(2)),
                 checks=StoreChecks(
                     head_slot=Slot(2),
-                    attestation_target_slot=Slot(0),  # Still genesis
+                    attestation_target_slot=Slot(1),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(3)),
                 checks=StoreChecks(
                     head_slot=Slot(3),
-                    attestation_target_slot=Slot(0),  # Still genesis
+                    attestation_target_slot=Slot(1),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(4)),
                 checks=StoreChecks(
                     head_slot=Slot(4),
-                    attestation_target_slot=Slot(1),  # Advances to slot 1
+                    attestation_target_slot=Slot(1),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(5)),
                 checks=StoreChecks(
                     head_slot=Slot(5),
-                    attestation_target_slot=Slot(2),  # Stable at 2
+                    attestation_target_slot=Slot(2),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(6)),
                 checks=StoreChecks(
                     head_slot=Slot(6),
-                    attestation_target_slot=Slot(3),  # Continues to advance
+                    attestation_target_slot=Slot(3),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(7)),
                 checks=StoreChecks(
                     head_slot=Slot(7),
-                    attestation_target_slot=Slot(4),  # Continues advancing
+                    attestation_target_slot=Slot(4),
                 ),
             ),
             BlockStep(
                 block=BlockSpec(slot=Slot(8)),
                 checks=StoreChecks(
                     head_slot=Slot(8),
-                    attestation_target_slot=Slot(5),  # Continues advancing
+                    attestation_target_slot=Slot(5),
                 ),
             ),
         ],
@@ -296,39 +293,39 @@ def test_attestation_target_justifiable_constraint(
                     head_slot=Slot(i),
                     attestation_target_slot=Slot(
                         # Mapping of current slot -> expected target slot
-                        # delta = current_slot - JUSTIFICATION_LOOKBACK_SLOTS - finalized_slot
-                        # delta = current_slot - 3 - 0
+                        # With +1 allowance: walkback stops at safe_target + 1
+                        # delta = target_slot - finalized_slot
                         {
-                            1: 0,  # 3-slot walkback reaches safe target at slot 0
-                            2: 0,  # 3-slot walkback reaches safe target at slot 0
-                            3: 0,  # 3-slot walkback reaches safe target at slot 0
-                            4: 1,  # delta = 4 - 3 - 0 = 1, Rule 1: delta 1 ≤ 5
-                            5: 2,  # delta = 5 - 3 - 0 = 2, Rule 1: delta 2 ≤ 5
-                            6: 3,  # delta = 6 - 3 - 0 = 3, Rule 1: delta 3 ≤ 5
-                            7: 4,  # delta = 7 - 3 - 0 = 4, Rule 1: delta 4 ≤ 5
-                            8: 5,  # delta = 8 - 3 - 0 = 5, Rule 1: delta 5 ≤ 5
-                            9: 6,  # delta = 6 - 0 = 6, Rule 3: pronic number (2*3)
-                            10: 6,  # delta = 10 - 3 - 0 = 7
-                            11: 6,  # delta = 11 - 3 - 0 = 8
-                            12: 9,  # delta = 9 - 0 = 9, Rule 2: perfect square (3^2)
-                            13: 9,  # delta = 13 - 3 - 0 = 10
-                            14: 9,  # delta = 14 - 3 - 0 = 11
-                            15: 12,  # delta = 15 - 3 - 0 = 12, Rule 3: pronic number (3*4)
-                            16: 12,  # delta = 16 - 3 - 0 = 13
-                            17: 12,  # delta = 17 - 3 - 0 = 14
-                            18: 12,  # delta = 18 - 3 - 0 = 15
-                            19: 16,  # delta = 19 - 3 - 0 = 16, Rule 2: perfect square (4^2)
-                            20: 16,  # delta = 20 - 3 - 0 = 17
-                            21: 16,  # delta = 21 - 3 - 0 = 18
-                            22: 16,  # delta = 22 - 3 - 0 = 19
-                            23: 20,  # delta = 23 - 3 - 0 = 20, Rule 3: pronic number (4*5)
-                            24: 20,  # delta = 24 - 3 - 0 = 21
-                            25: 20,  # delta = 25 - 3 - 0 = 22
-                            26: 20,  # delta = 26 - 3 - 0 = 23
-                            27: 20,  # delta = 27 - 3 - 0 = 24
-                            28: 25,  # delta = 28 - 3 - 0 = 25, Rule 2: perfect square (5^2)
-                            29: 25,  # delta = 29 - 3 - 0 = 26
-                            30: 25,  # delta = 30 - 3 - 0 = 27
+                            1: 1,  # At safe_target + 1, no walkback needed
+                            2: 1,  # Walks back to safe_target + 1
+                            3: 1,  # Walks back to safe_target + 1
+                            4: 1,  # 3-step walkback from 4 → 1
+                            5: 2,  # 3-step walkback from 5 → 2, delta 2 ≤ 5
+                            6: 3,  # 3-step walkback from 6 → 3, delta 3 ≤ 5
+                            7: 4,  # 3-step walkback from 7 → 4, delta 4 ≤ 5
+                            8: 5,  # 3-step walkback from 8 → 5, delta 5 ≤ 5
+                            9: 6,  # delta = 6, pronic number (2*3)
+                            10: 6,  # delta = 7, not justifiable → walks to 6
+                            11: 6,  # delta = 8, not justifiable → walks to 6
+                            12: 9,  # delta = 9, perfect square (3^2)
+                            13: 9,  # delta = 10, not justifiable → walks to 9
+                            14: 9,  # delta = 11, not justifiable → walks to 9
+                            15: 12,  # delta = 12, pronic number (3*4)
+                            16: 12,  # delta = 13, not justifiable → walks to 12
+                            17: 12,  # delta = 14, not justifiable → walks to 12
+                            18: 12,  # delta = 15, not justifiable → walks to 12
+                            19: 16,  # delta = 16, perfect square (4^2)
+                            20: 16,  # delta = 17, not justifiable → walks to 16
+                            21: 16,  # delta = 18, not justifiable → walks to 16
+                            22: 16,  # delta = 19, not justifiable → walks to 16
+                            23: 20,  # delta = 20, pronic number (4*5)
+                            24: 20,  # delta = 21, not justifiable → walks to 20
+                            25: 20,  # delta = 22, not justifiable → walks to 20
+                            26: 20,  # delta = 23, not justifiable → walks to 20
+                            27: 20,  # delta = 24, not justifiable → walks to 20
+                            28: 25,  # delta = 25, perfect square (5^2)
+                            29: 25,  # delta = 26, not justifiable → walks to 25
+                            30: 25,  # delta = 27, not justifiable → walks to 25
                         }[i]
                     ),
                 ),
diff --git a/tests/interop/helpers/node_runner.py b/tests/interop/helpers/node_runner.py
index 71bc288a..3b92ff68 100644
--- a/tests/interop/helpers/node_runner.py
+++ b/tests/interop/helpers/node_runner.py
@@ -12,6 +12,7 @@
 from dataclasses import dataclass, field
 from typing import cast
 
+from lean_spec.subspecs.chain.config import ATTESTATION_COMMITTEE_COUNT
 from lean_spec.subspecs.containers import Checkpoint, Validator
 from lean_spec.subspecs.containers.state import Validators
 from lean_spec.subspecs.containers.validator import ValidatorIndex
@@ -234,6 +235,7 @@ async def start_node(
         self,
         node_index: int,
         validator_indices: list[int] | None = None,
+        is_aggregator: bool = False,
         bootnodes: list[str] | None = None,
         *,
         start_services: bool = True,
@@ -244,6 +246,7 @@ async def start_node(
         Args:
             node_index: Index for this node (for logging/identification).
             validator_indices: Which validators this node controls.
+            is_aggregator: Whether this node is aggregator
             bootnodes: Addresses to connect to on startup.
             start_services: If True, start the node's services immediately.
                 If False, call test_node.start() manually after mesh is stable.
@@ -282,6 +285,7 @@ async def start_node(
             api_config=None,  # Disable API server for interop tests (not needed for P2P testing)
             validator_registry=validator_registry,
             fork_digest=self.fork_digest,
+            is_aggregator=is_aggregator,
         )
 
         node = Node.from_genesis(config)
@@ -350,9 +354,21 @@ async def start_node(
         await event_source.start_gossipsub()
 
         block_topic = f"/leanconsensus/{self.fork_digest}/block/ssz_snappy"
-        attestation_topic = f"/leanconsensus/{self.fork_digest}/attestation/ssz_snappy"
+        aggregation_topic = f"/leanconsensus/{self.fork_digest}/aggregation/ssz_snappy"
         event_source.subscribe_gossip_topic(block_topic)
-        event_source.subscribe_gossip_topic(attestation_topic)
+        event_source.subscribe_gossip_topic(aggregation_topic)
+
+        # Determine subnets for our validators and subscribe.
+        #
+        # Validators only subscribe to the subnets they are assigned to.
+        # This matches the Ethereum gossip specification.
+        if validator_indices:
+            from lean_spec.subspecs.chain.config import ATTESTATION_COMMITTEE_COUNT
+
+            for idx in validator_indices:
+                subnet_id = idx % int(ATTESTATION_COMMITTEE_COUNT)
+                topic = f"/leanconsensus/{self.fork_digest}/attestation_{subnet_id}/ssz_snappy"
+                event_source.subscribe_gossip_topic(topic)
 
         # Optionally start the node's services.
         #
@@ -408,9 +424,20 @@ async def start_all(
         # This allows the gossipsub mesh to form before validators start
         # producing blocks and attestations. Otherwise, early blocks/attestations
         # would be "Published message to 0 peers" because the mesh is empty.
+        aggregator_indices = set(range(int(ATTESTATION_COMMITTEE_COUNT)))
         for i in range(num_nodes):
             validator_indices = validators_per_node[i] if i < len(validators_per_node) else []
-            await self.start_node(i, validator_indices, start_services=False)
+
+            # A node is an aggregator if it controls any of the first
+            # ATTESTATION_COMMITTEE_COUNT validators.
+            is_node_aggregator = any(vid in aggregator_indices for vid in validator_indices)
+
+            await self.start_node(
+                i,
+                validator_indices,
+                is_aggregator=is_node_aggregator,
+                start_services=False,
+            )
 
             # Stagger node startup like Ream does.
             #
diff --git a/tests/interop/test_late_joiner.py b/tests/interop/test_late_joiner.py
index 343a1f63..53c7c919 100644
--- a/tests/interop/test_late_joiner.py
+++ b/tests/interop/test_late_joiner.py
@@ -24,7 +24,6 @@
 pytestmark = pytest.mark.interop
 
 
-@pytest.mark.skip(reason="Interop test not passing - needs update (#359)")
 @pytest.mark.timeout(240)
 @pytest.mark.num_validators(3)
 async def test_late_joiner_sync(node_cluster: NodeCluster) -> None:
@@ -36,7 +35,7 @@ async def test_late_joiner_sync(node_cluster: NodeCluster) -> None:
     """
     validators_per_node = [[0], [1], [2]]
 
-    await node_cluster.start_node(0, validators_per_node[0])
+    await node_cluster.start_node(0, validators_per_node[0], is_aggregator=True)
     await node_cluster.start_node(1, validators_per_node[1])
 
     node0 = node_cluster.nodes[0]
diff --git a/tests/interop/test_multi_node.py b/tests/interop/test_multi_node.py
index d2edcfe5..19362504 100644
--- a/tests/interop/test_multi_node.py
+++ b/tests/interop/test_multi_node.py
@@ -44,7 +44,6 @@
 pytestmark = pytest.mark.interop
 
 
-@pytest.mark.skip(reason="Interop test not passing - needs update (#359)")
 @pytest.mark.timeout(120)
 @pytest.mark.num_validators(3)
 async def test_mesh_finalization(node_cluster: NodeCluster) -> None:
@@ -146,8 +145,10 @@ async def test_mesh_finalization(node_cluster: NodeCluster) -> None:
         #
         # - High new_atts, low known_atts = processing bottleneck
         # - Low counts everywhere = gossip not propagating
-        new_atts = [len(node._store.latest_new_attestations) for node in node_cluster.nodes]
-        known_atts = [len(node._store.latest_known_attestations) for node in node_cluster.nodes]
+        new_atts = [len(node._store.latest_new_aggregated_payloads) for node in node_cluster.nodes]
+        known_atts = [
+            len(node._store.latest_known_aggregated_payloads) for node in node_cluster.nodes
+        ]
 
         logger.info(
             "Progress: head=%s justified=%s finalized=%s new_atts=%s known_atts=%s",
@@ -200,7 +201,6 @@ async def test_mesh_finalization(node_cluster: NodeCluster) -> None:
     )
 
 
-@pytest.mark.skip(reason="Interop test not passing - needs update (#359)")
 @pytest.mark.timeout(120)
 @pytest.mark.num_validators(3)
 async def test_mesh_2_2_2_finalization(node_cluster: NodeCluster) -> None:
diff --git a/tests/lean_spec/helpers/builders.py b/tests/lean_spec/helpers/builders.py
index ae557bfc..594aae54 100644
--- a/tests/lean_spec/helpers/builders.py
+++ b/tests/lean_spec/helpers/builders.py
@@ -520,7 +520,7 @@ def make_signed_block_from_store(
 
     slot_duration = block.slot * SECONDS_PER_SLOT
     block_time = store.config.genesis_time + slot_duration
-    advanced_store = store.on_tick(block_time, has_proposal=True)
+    advanced_store, _ = store.on_tick(block_time, has_proposal=True)
 
     return advanced_store, signed_block
 
diff --git a/tests/lean_spec/subspecs/chain/test_service.py b/tests/lean_spec/subspecs/chain/test_service.py
index 8e2e9ac4..1406bf26 100644
--- a/tests/lean_spec/subspecs/chain/test_service.py
+++ b/tests/lean_spec/subspecs/chain/test_service.py
@@ -28,7 +28,9 @@ class MockStore:
     head: Bytes32 = field(default_factory=lambda: ZERO_HASH)
     latest_finalized: MockCheckpoint = field(default_factory=MockCheckpoint)
 
-    def on_tick(self, time: Uint64, has_proposal: bool) -> MockStore:
+    def on_tick(
+        self, time: Uint64, has_proposal: bool, is_aggregator: bool = False
+    ) -> tuple[MockStore, list]:
         """Record the tick call and return a new store."""
         new_store = MockStore(
             time=time,
@@ -37,7 +39,7 @@ def on_tick(self, time: Uint64, has_proposal: bool) -> MockStore:
             latest_finalized=self.latest_finalized,
         )
         new_store.tick_calls.append((time, has_proposal))
-        return new_store
+        return new_store, []
 
 
 @dataclass
@@ -45,6 +47,7 @@ class MockSyncService:
     """Mock sync service for testing ChainService."""
 
     store: MockStore = field(default_factory=MockStore)
+    is_aggregator: bool = False
 
 
 class TestChainServiceLifecycle:
diff --git a/tests/lean_spec/subspecs/forkchoice/test_attestation_target.py b/tests/lean_spec/subspecs/forkchoice/test_attestation_target.py
index 2cbc306f..c85721c8 100644
--- a/tests/lean_spec/subspecs/forkchoice/test_attestation_target.py
+++ b/tests/lean_spec/subspecs/forkchoice/test_attestation_target.py
@@ -163,7 +163,7 @@ def test_safe_target_requires_supermajority(
             store = store.on_gossip_attestation(signed_attestation, is_aggregator=True)
 
         # Aggregate the signatures
-        store = store.aggregate_committee_signatures()
+        store, _ = store.aggregate_committee_signatures()
 
         # Update safe target (uses latest_new_aggregated_payloads)
         store = store.update_safe_target()
@@ -207,7 +207,7 @@ def test_safe_target_advances_with_supermajority(
             store = store.on_gossip_attestation(signed_attestation, is_aggregator=True)
 
         # Aggregate the signatures
-        store = store.aggregate_committee_signatures()
+        store, _ = store.aggregate_committee_signatures()
 
         # Update safe target
         store = store.update_safe_target()
@@ -247,7 +247,7 @@ def test_update_safe_target_uses_new_attestations(
             store = store.on_gossip_attestation(signed_attestation, is_aggregator=True)
 
         # Aggregate into new payloads
-        store = store.aggregate_committee_signatures()
+        store, _ = store.aggregate_committee_signatures()
 
         # Update safe target should use new aggregated payloads
         store = store.update_safe_target()
@@ -301,7 +301,7 @@ def test_justification_with_supermajority_attestations(
             store = store.on_gossip_attestation(signed_attestation, is_aggregator=True)
 
         # Aggregate signatures before producing the next block
-        store = store.aggregate_committee_signatures()
+        store, _ = store.aggregate_committee_signatures()
 
         # Produce block 2 which includes these attestations
         store, block_2, signatures = store.produce_block_with_signatures(slot_2, proposer_2)
@@ -382,7 +382,7 @@ def test_justification_tracking_with_multiple_targets(
             )
             store = store.on_gossip_attestation(signed_attestation, is_aggregator=True)
 
-        store = store.aggregate_committee_signatures()
+        store, _ = store.aggregate_committee_signatures()
         store = store.update_safe_target()
 
         # Neither target should be justified with only half validators
@@ -527,7 +527,7 @@ def test_full_attestation_cycle(
             store = store.on_gossip_attestation(signed_attestation, is_aggregator=True)
 
         # Phase 3: Aggregate signatures into payloads
-        store = store.aggregate_committee_signatures()
+        store, _ = store.aggregate_committee_signatures()
 
         # Phase 4: Update safe target
         store = store.update_safe_target()
@@ -589,7 +589,7 @@ def test_attestation_target_after_on_block(
         # Process block via on_block on a fresh consumer store
         consumer_store = observer_store
         block_time = consumer_store.config.genesis_time + block.slot * Uint64(SECONDS_PER_SLOT)
-        consumer_store = consumer_store.on_tick(block_time, has_proposal=True)
+        consumer_store, _ = consumer_store.on_tick(block_time, has_proposal=True)
         consumer_store = consumer_store.on_block(signed_block)
 
         # Get attestation target after on_block
diff --git a/tests/lean_spec/subspecs/forkchoice/test_store_attestations.py b/tests/lean_spec/subspecs/forkchoice/test_store_attestations.py
index f02f73d4..982aa905 100644
--- a/tests/lean_spec/subspecs/forkchoice/test_store_attestations.py
+++ b/tests/lean_spec/subspecs/forkchoice/test_store_attestations.py
@@ -509,7 +509,7 @@ def test_aggregates_gossip_signatures_into_proof(self, key_manager: XmssKeyManag
         )
 
         # Perform aggregation
-        updated_store = store.aggregate_committee_signatures()
+        updated_store, _ = store.aggregate_committee_signatures()
 
         # Verify proofs were created and stored
         data_root = attestation_data.data_root_bytes()
@@ -537,7 +537,7 @@ def test_aggregated_proof_is_valid(self, key_manager: XmssKeyManager) -> None:
             attesting_validators=attesting_validators,
         )
 
-        updated_store = store.aggregate_committee_signatures()
+        updated_store, _ = store.aggregate_committee_signatures()
 
         data_root = attestation_data.data_root_bytes()
         sig_key = SignatureKey(ValidatorIndex(1), data_root)
@@ -567,7 +567,7 @@ def test_empty_gossip_signatures_produces_no_proofs(self, key_manager: XmssKeyMa
             attesting_validators=[],  # No attesters
         )
 
-        updated_store = store.aggregate_committee_signatures()
+        updated_store, _ = store.aggregate_committee_signatures()
 
         # Verify no proofs were created
         assert len(updated_store.latest_new_aggregated_payloads) == 0
@@ -619,7 +619,7 @@ def test_multiple_attestation_data_grouped_separately(
             }
         )
 
-        updated_store = store.aggregate_committee_signatures()
+        updated_store, _ = store.aggregate_committee_signatures()
 
         # Verify both validators have separate proofs
         sig_key_1 = SignatureKey(ValidatorIndex(1), data_root_1)
@@ -661,7 +661,7 @@ def test_interval_2_triggers_aggregation_for_aggregator(
         store = store.model_copy(update={"time": Uint64(1)})
 
         # Tick to interval 2 as aggregator
-        updated_store = store.tick_interval(has_proposal=False, is_aggregator=True)
+        updated_store, _ = store.tick_interval(has_proposal=False, is_aggregator=True)
 
         # Verify aggregation was performed
         data_root = attestation_data.data_root_bytes()
@@ -692,7 +692,7 @@ def test_interval_2_skips_aggregation_for_non_aggregator(
         store = store.model_copy(update={"time": Uint64(1)})
 
         # Tick to interval 2 as NON-aggregator
-        updated_store = store.tick_interval(has_proposal=False, is_aggregator=False)
+        updated_store, _ = store.tick_interval(has_proposal=False, is_aggregator=False)
 
         # Verify aggregation was NOT performed
         data_root = attestation_data.data_root_bytes()
@@ -731,7 +731,7 @@ def test_other_intervals_do_not_trigger_aggregation(self, key_manager: XmssKeyMa
             pre_tick_time = (target_interval - 1) % int(INTERVALS_PER_SLOT)
             test_store = store.model_copy(update={"time": Uint64(pre_tick_time)})
 
-            updated_store = test_store.tick_interval(has_proposal=False, is_aggregator=True)
+            updated_store, _ = test_store.tick_interval(has_proposal=False, is_aggregator=True)
 
             assert sig_key not in updated_store.latest_new_aggregated_payloads, (
                 f"Aggregation should NOT occur at interval {target_interval}"
@@ -754,7 +754,7 @@ def test_interval_0_accepts_attestations_with_proposal(
         store = store.model_copy(update={"time": Uint64(4)})
 
         # Tick to interval 0 with proposal
-        updated_store = store.tick_interval(has_proposal=True, is_aggregator=True)
+        updated_store, _ = store.tick_interval(has_proposal=True, is_aggregator=True)
 
         # Verify time advanced
         assert updated_store.time == Uint64(5)
@@ -812,7 +812,7 @@ def test_gossip_to_aggregation_to_storage(self, key_manager: XmssKeyManager) ->
 
         # Step 2: Advance to interval 2 (aggregation interval)
         store = store.model_copy(update={"time": Uint64(1)})
-        store = store.tick_interval(has_proposal=False, is_aggregator=True)
+        store, _ = store.tick_interval(has_proposal=False, is_aggregator=True)
 
         # Step 3: Verify aggregated proofs were created
         for vid in attesting_validators:
diff --git a/tests/lean_spec/subspecs/forkchoice/test_time_management.py b/tests/lean_spec/subspecs/forkchoice/test_time_management.py
index 36df3b51..c80eafb3 100644
--- a/tests/lean_spec/subspecs/forkchoice/test_time_management.py
+++ b/tests/lean_spec/subspecs/forkchoice/test_time_management.py
@@ -59,7 +59,7 @@ def test_on_tick_basic(self, sample_store: Store) -> None:
         initial_time = sample_store.time
         target_time = sample_store.config.genesis_time + Uint64(200)  # Much later time
 
-        sample_store = sample_store.on_tick(target_time, has_proposal=True)
+        sample_store, _ = sample_store.on_tick(target_time, has_proposal=True)
 
         # Time should advance
         assert sample_store.time > initial_time
@@ -69,7 +69,7 @@ def test_on_tick_no_proposal(self, sample_store: Store) -> None:
         initial_time = sample_store.time
         target_time = sample_store.config.genesis_time + Uint64(100)
 
-        sample_store = sample_store.on_tick(target_time, has_proposal=False)
+        sample_store, _ = sample_store.on_tick(target_time, has_proposal=False)
 
         # Time should still advance
         assert sample_store.time >= initial_time
@@ -80,7 +80,7 @@ def test_on_tick_already_current(self, sample_store: Store) -> None:
         current_target = sample_store.config.genesis_time + initial_time
 
         # Try to advance to current time (should be no-op)
-        sample_store = sample_store.on_tick(current_target, has_proposal=True)
+        sample_store, _ = sample_store.on_tick(current_target, has_proposal=True)
 
         # Should not change significantly (time can only increase)
         # Tolerance increased for 5-interval per slot system
@@ -91,7 +91,7 @@ def test_on_tick_small_increment(self, sample_store: Store) -> None:
         initial_time = sample_store.time
         target_time = sample_store.config.genesis_time + initial_time + Uint64(1)
 
-        sample_store = sample_store.on_tick(target_time, has_proposal=False)
+        sample_store, _ = sample_store.on_tick(target_time, has_proposal=False)
 
         # Should advance by small amount
         assert sample_store.time >= initial_time
@@ -105,7 +105,7 @@ def test_tick_interval_basic(self, sample_store: Store) -> None:
         initial_time = sample_store.time
 
         # Tick one interval forward
-        sample_store = sample_store.tick_interval(has_proposal=False)
+        sample_store, _ = sample_store.tick_interval(has_proposal=False)
 
         # Time should advance by one interval
         assert sample_store.time == initial_time + Uint64(1)
@@ -114,7 +114,7 @@ def test_tick_interval_with_proposal(self, sample_store: Store) -> None:
         """Test interval ticking with proposal."""
         initial_time = sample_store.time
 
-        sample_store = sample_store.tick_interval(has_proposal=True)
+        sample_store, _ = sample_store.tick_interval(has_proposal=True)
 
         # Time should advance
         assert sample_store.time == initial_time + Uint64(1)
@@ -125,7 +125,7 @@ def test_tick_interval_sequence(self, sample_store: Store) -> None:
 
         # Tick multiple intervals
         for i in range(5):
-            sample_store = sample_store.tick_interval(has_proposal=(i % 2 == 0))
+            sample_store, _ = sample_store.tick_interval(has_proposal=(i % 2 == 0))
 
         # Should have advanced by 5 intervals
         assert sample_store.time == initial_time + Uint64(5)
@@ -139,7 +139,7 @@ def test_tick_interval_actions_by_phase(self, sample_store: Store) -> None:
         # Tick through a complete slot cycle
         for interval in range(INTERVALS_PER_SLOT):
             has_proposal = interval == 0  # Proposal only in first interval
-            sample_store = sample_store.tick_interval(has_proposal=has_proposal)
+            sample_store, _ = sample_store.tick_interval(has_proposal=has_proposal)
 
             current_interval = sample_store.time % INTERVALS_PER_SLOT
             expected_interval = Uint64((interval + 1)) % INTERVALS_PER_SLOT