diff --git a/crates/blockchain/src/store.rs b/crates/blockchain/src/store.rs
index 4bb01bc..ac37527 100644
--- a/crates/blockchain/src/store.rs
+++ b/crates/blockchain/src/store.rs
@@ -626,26 +626,15 @@ pub fn get_attestation_target_with_checkpoints(
 
 /// Produce attestation data for the given slot.
 ///
-/// The attestation source comes from the head state's justified checkpoint,
-/// not the store-wide global max. This ensures voting aligns with the block
-/// builder's attestation filter (which also uses head state).
+/// The source comes from the store's global `latest_justified` checkpoint.
+/// When the store's justified has advanced past the head state (a minority
+/// fork justified a slot the head chain hasn't seen yet), the next block
+/// produced on the head chain is expected to close the gap via the
+/// fixed-point attestation loop in `build_block`.
 ///
-/// See: <https://github.com/leanEthereum/leanSpec/pull/506>
+/// See: <https://github.com/leanEthereum/leanSpec/pull/595>
 pub fn produce_attestation_data(store: &Store, slot: u64) -> AttestationData {
     let head_root = store.head();
-    let head_state = store.get_state(&head_root).expect("head state exists");
-
-    // Derive source from head state's justified checkpoint.
-    // At genesis the checkpoint root is H256::ZERO; substitute the real
-    // genesis block root so attestation validation can look it up.
-    let source = if head_state.latest_block_header.slot == 0 {
-        Checkpoint {
-            root: head_root,
-            slot: head_state.latest_justified.slot,
-        }
-    } else {
-        head_state.latest_justified
-    };
 
     let head_checkpoint = Checkpoint {
         root: head_root,
@@ -655,15 +644,13 @@ pub fn produce_attestation_data(store: &Store, slot: u64) -> AttestationData {
             .slot,
     };
 
-    // Calculate the target checkpoint for this attestation
     let target_checkpoint = get_attestation_target(store);
 
-    // Construct attestation data
     AttestationData {
         slot,
         head: head_checkpoint,
         target: target_checkpoint,
-        source,
+        source: store.latest_justified(),
     }
 }
 
@@ -729,6 +716,19 @@ pub fn produce_block_with_signatures(
         )?
     };
 
+    // Invariant (leanSpec #595): the produced block must not lag the store's
+    // justified checkpoint. Otherwise peers processing this block would never
+    // see justification advance, degrading liveness: the fixed-point loop in
+    // `build_block` is expected to incorporate pool attestations that close
+    // any divergence inherited from a minority fork.
+    let store_justified_slot = store.latest_justified().slot;
+    if post_checkpoints.justified.slot < store_justified_slot {
+        return Err(StoreError::JustifiedDivergenceNotClosed {
+            block_justified_slot: post_checkpoints.justified.slot,
+            store_justified_slot,
+        });
+    }
+
     metrics::observe_block_aggregated_payloads(signatures.len());
 
     Ok((block, signatures, post_checkpoints))
@@ -832,6 +832,16 @@ pub enum StoreError {
 
     #[error("Block contains {count} distinct AttestationData entries; maximum is {max}")]
     TooManyAttestationData { count: usize, max: usize },
+
+    #[error(
+        "Produced block justified slot {block_justified_slot} \
+         is behind store justified slot {store_justified_slot}; \
+         fixed-point attestation loop did not converge"
+    )]
+    JustifiedDivergenceNotClosed {
+        block_justified_slot: u64,
+        store_justified_slot: u64,
+    },
 }
 
 /// Compute the bitwise union (OR) of two AggregationBits bitfields.
@@ -1485,73 +1495,6 @@ mod tests {
         );
     }
 
-    /// Attestation source must come from the head state's justified checkpoint,
-    /// not the store-wide global max.
-    ///
-    /// When a non-head fork block advances store.latest_justified past
-    /// head_state.latest_justified, using the store value causes every
-    /// attestation to be rejected by the block builder (which filters
-    /// by head state), producing blocks with 0 attestations.
-    ///
-    /// See: <https://github.com/leanEthereum/leanSpec/pull/506>
-    #[test]
-    fn produce_attestation_data_uses_head_state_justified() {
-        use ethlambda_storage::backend::InMemoryBackend;
-        use std::sync::Arc;
-
-        // Create a store at genesis with 3 validators.
-        let genesis_state = State::from_genesis(1000, vec![]);
-        let genesis_block = Block {
-            slot: 0,
-            proposer_index: 0,
-            parent_root: H256::ZERO,
-            state_root: H256::ZERO,
-            body: BlockBody {
-                attestations: AggregatedAttestations::default(),
-            },
-        };
-        let backend = Arc::new(InMemoryBackend::new());
-        let mut store = Store::get_forkchoice_store(backend, genesis_state, genesis_block);
-
-        let head_root = store.head();
-
-        // The head state's justified checkpoint is what the block builder
-        // filters attestations against. At genesis the root is H256::ZERO,
-        // so we apply the same correction used in produce_attestation_data.
-        let head_state = store.get_state(&head_root).expect("head state exists");
-        let head_justified = Checkpoint {
-            root: head_root,
-            slot: head_state.latest_justified.slot,
-        };
-
-        // Simulate a non-head fork advancing the store's global justified
-        // past what the head chain has seen.
-        let higher_justified = Checkpoint {
-            root: H256([0x99; 32]),
-            slot: 42,
-        };
-        store.update_checkpoints(ForkCheckpoints::new(
-            head_root,
-            Some(higher_justified),
-            None,
-        ));
-
-        // Precondition: the global max is strictly ahead of the head state.
-        assert!(
-            store.latest_justified().slot > head_justified.slot,
-            "store justified should be ahead of head state justified"
-        );
-
-        // Produce attestation data. The source must come from the head state
-        // (slot 0), not from the global max (slot 42).
-        let attestation = produce_attestation_data(&store, 1);
-
-        assert_eq!(
-            attestation.source, head_justified,
-            "source must match head state's justified checkpoint, not store-wide max"
-        );
-    }
-
     fn make_att_data(slot: u64) -> AttestationData {
         AttestationData {
             slot,