diff --git a/node/src/tests/checkpointing/joining.rs b/node/src/tests/checkpointing/joining.rs
index 7b62b421..9d81f3da 100644
--- a/node/src/tests/checkpointing/joining.rs
+++ b/node/src/tests/checkpointing/joining.rs
@@ -369,6 +369,214 @@ fn test_node_joins_later_with_checkpoint() {
     });
 }
 
+/// A node joining from a checkpoint that carries the `last_block` +
+/// `finalized_header` artifacts (a `SyncCheckpoint`) must seed the checkpoint
+/// epoch's finalized header into finalizer storage at startup, via the syncer's
+/// pre-consensus replay of the terminal block — NOT via live block delivery.
+///
+/// Boundary aux-data derives `prev_epoch_header_hash` from
+/// `get_most_recent_finalized_header()`, falling back to the genesis hash when
+/// the finalized-header DB is empty. If the checkpoint header is never seeded, a
+/// checkpoint-joined node's first boundary header would link to genesis instead
+/// of the checkpoint epoch's header. The pre-consensus replay is what prevents
+/// that, yet every other checkpoint test exercises only the state-only /
+/// live-sync path (`checkpoint_last_block: None`), so the replay-seeding path is
+/// otherwise uncovered.
+///
+/// To prove the header is seeded by the replay and not by network sync, the
+/// joiner is registered but deliberately left UNLINKED: it can receive no blocks
+/// from peers, so a populated `get_finalized_header(E)` can only be the result of
+/// the startup replay.
+#[test_traced("INFO")]
+fn test_checkpoint_join_replays_and_seeds_finalized_header() {
+    let n = 5;
+    let link = Link {
+        latency: Duration::from_millis(80),
+        jitter: Duration::from_millis(10),
+        success_rate: 1.0,
+    };
+    let cfg = deterministic::Config::default().with_seed(0);
+    let executor = Runner::from(cfg);
+    executor.start(|context| async move {
+        let (network, mut oracle) = Network::new(
+            context.with_label("network"),
+            simulated::Config {
+                max_size: 1024 * 1024,
+                disconnect_on_block: false,
+                tracked_peer_sets: NZUsize!(n as usize * 10),
+            },
+        );
+        network.start();
+
+        // Register participants.
+        let mut key_stores = Vec::new();
+        let mut validators = Vec::new();
+        for i in 0..n {
+            let mut rng = StdRng::seed_from_u64(i as u64);
+            let node_key = PrivateKey::random(&mut rng);
+            let node_public_key = node_key.public_key();
+            let consensus_key = bls12381::PrivateKey::random(&mut rng);
+            let consensus_public_key = consensus_key.public_key();
+            key_stores.push(KeyStore {
+                node_key,
+                consensus_key,
+            });
+            validators.push((node_public_key, consensus_public_key));
+        }
+        validators.sort_by(|lhs, rhs| lhs.0.cmp(&rhs.0));
+        key_stores.sort_by_key(|ks| ks.node_key.public_key());
+
+        let node_public_keys: Vec<_> = validators.iter().map(|(pk, _)| pk.clone()).collect();
+        let initial_node_public_keys = &node_public_keys[..node_public_keys.len() - 1];
+
+        let mut registrations =
+            common::register_validators(&oracle, initial_node_public_keys).await;
+        common::link_validators(&mut oracle, initial_node_public_keys, link.clone(), None).await;
+
+        let genesis_hash =
+            from_hex_formatted(common::GENESIS_HASH).expect("failed to decode genesis hash");
+        let genesis_hash: [u8; 32] = genesis_hash
+            .try_into()
+            .expect("failed to convert genesis hash");
+
+        let engine_client_network = MockEngineNetworkBuilder::new(genesis_hash).build();
+        let initial_state =
+            get_initial_state(genesis_hash, &validators, None, None, 32_000_000_000);
+
+        // Start the initial validators.
+        let key_store_joining_later = key_stores.pop().unwrap();
+        let mut consensus_state_queries = HashMap::new();
+        for (idx, key_store) in key_stores.into_iter().enumerate() {
+            let public_key = key_store.node_key.public_key();
+            let uid = format!("validator_{public_key}");
+            let namespace = String::from("_SUMMIT");
+            let engine_client = engine_client_network.create_client(uid.clone());
+            let config = get_default_engine_config(
+                engine_client,
+                SimulatedOracle::new(oracle.clone()),
+                uid.clone(),
+                genesis_hash,
+                namespace,
+                key_store,
+                validators.clone(),
+                initial_state.clone(),
+            );
+            let engine = Engine::new(context.with_label(&uid), config).await;
+            consensus_state_queries.insert(idx, engine.finalizer_mailbox.clone());
+            let (pending, recovered, resolver, orchestrator, broadcast) =
+                registrations.remove(&public_key).unwrap();
+            engine.start(pending, recovered, resolver, orchestrator, broadcast);
+        }
+
+        // Wait for a checkpoint, then capture the full checkpoint artifacts:
+        // the checkpoint bytes, the epoch-terminal `last_block`, and the
+        // certified finalized header for that epoch.
+        let source_query = consensus_state_queries.get(&0).unwrap();
+        let (checkpoint, last_block) = loop {
+            if let Some(pair) = source_query.clone().get_latest_checkpoint().await.0 {
+                break pair;
+            }
+            context.sleep(Duration::from_secs(1)).await;
+        };
+
+        // Let the network advance well past the checkpoint epoch's terminal so
+        // the source node has durably stored that epoch's finalized header.
+        loop {
+            if source_query.get_latest_height().await >= 20 {
+                break;
+            }
+            context.sleep(Duration::from_secs(1)).await;
+        }
+
+        // The checkpoint state is captured at the penultimate block, so its epoch
+        // is the checkpoint epoch E; `last_block` is E's terminal.
+        let checkpoint_state = ConsensusState::try_from(&checkpoint).unwrap();
+        let checkpoint_epoch = checkpoint_state.get_epoch();
+        let source_header = source_query
+            .clone()
+            .get_finalized_header(checkpoint_epoch)
+            .await
+            .expect("source node must have stored the checkpoint epoch's finalized header");
+        // Sanity: the finalized header certifies exactly the terminal `last_block`.
+        assert_eq!(
+            source_header.finalization().proposal.payload,
+            last_block.digest(),
+            "finalized header must certify the checkpoint's last_block"
+        );
+
+        // Register the joining validator but do NOT link it: with no peers it
+        // cannot receive any block over the network, so anything the finalizer
+        // stores can only have come from the checkpoint replay.
+        let public_key = key_store_joining_later.node_key.public_key();
+        let mut late_registrations =
+            common::register_validators(&oracle, &[public_key.clone()]).await;
+
+        let uid = format!("validator_{public_key}");
+        let namespace = String::from("_SUMMIT");
+        let engine_client = engine_client_network.create_client(uid.clone());
+        // Prime the joiner's execution client at the checkpoint (penultimate)
+        // height so replaying the terminal block executes as the next block.
+        let eth_hash = checkpoint_state.get_forkchoice().head_block_hash.into();
+        engine_client.load_checkpoint(checkpoint_state.get_latest_height(), eth_hash);
+
+        let mut config = get_default_engine_config(
+            engine_client,
+            SimulatedOracle::new(oracle.clone()),
+            uid.clone(),
+            genesis_hash,
+            namespace,
+            key_store_joining_later,
+            validators.clone(),
+            checkpoint_state.clone(),
+        );
+        // The artifacts that make this a `SyncCheckpoint` join rather than a
+        // state-only join. This is exactly what the other checkpoint tests omit.
+        config.checkpoint_last_block = Some(last_block.clone());
+        config.checkpoint_finalized_header = Some(source_header.clone());
+
+        let engine = Engine::new(context.with_label(&uid), config).await;
+        let joiner_query = engine.finalizer_mailbox.clone();
+        let (pending, recovered, resolver, orchestrator, broadcast) =
+            late_registrations.remove(&public_key).unwrap();
+        engine.start(pending, recovered, resolver, orchestrator, broadcast);
+
+        // The replay runs in the syncer's `run()` before the consensus loop.
+        // Poll until the finalizer has processed it (bounded); an unlinked node
+        // has no other way to obtain the terminal block.
+        let mut seeded = None;
+        for _ in 0..30 {
+            if let Some(header) = joiner_query
+                .clone()
+                .get_finalized_header(checkpoint_epoch)
+                .await
+            {
+                seeded = Some(header);
+                break;
+            }
+            context.sleep(Duration::from_secs(1)).await;
+        }
+
+        let seeded = seeded.expect(
+            "checkpoint-joined finalizer must seed the checkpoint epoch's finalized header \
+             from the startup replay (get_most_recent_finalized_header would otherwise fall \
+             back to genesis at the next boundary)",
+        );
+        assert_eq!(
+            seeded.header().get_digest(),
+            source_header.header().get_digest(),
+            "seeded finalized header must match the checkpoint epoch's terminal header"
+        );
+        // The terminal was executed and the finalizer advanced past the
+        // penultimate checkpoint height, confirming the replay ran end to end.
+        assert!(
+            joiner_query.get_latest_height().await > checkpoint_state.get_latest_height(),
+            "finalizer must have advanced past the checkpoint (penultimate) height via replay"
+        );
+
+        context.auditor().state()
+    });
+}
+
 #[test_traced("INFO")]
 fn test_node_joins_later_with_checkpoint_not_in_genesis() {
     // Creates a network of 5 nodes, and starts only 4 of them.