Add head block validation to forkchoice attestation processing

src/lean_spec/subspecs/forkchoice/store.py

@@ -123,6 +123,7 @@ def validate_attestation(self, signed_vote: "SignedVote") -> None:
         # Validate vote targets exist in store
         assert vote.source.root in self.blocks, f"Unknown source block: {vote.source.root.hex()}"
         assert vote.target.root in self.blocks, f"Unknown target block: {vote.target.root.hex()}"
+        assert vote.head.root in self.blocks, f"Unknown head block: {vote.head.root.hex()}"
 
         # Validate slot relationships
         source_block = self.blocks[vote.source.root]
@@ -136,7 +137,7 @@ def validate_attestation(self, signed_vote: "SignedVote") -> None:
         assert target_block.slot == vote.target.slot, "Target checkpoint slot mismatch"
 
         # Validate attestation is not too far in the future
-        current_slot = Slot(self.time // SECONDS_PER_INTERVAL)
+        current_slot = Slot(self.time // INTERVALS_PER_SLOT)
         assert vote.slot <= Slot(current_slot + Slot(1)), "Attestation too far in future"
 
     def process_attestation(self, signed_vote: "SignedVote", is_from_block: bool = False) -> None:
@@ -173,7 +174,7 @@ def process_attestation(self, signed_vote: "SignedVote", is_from_block: bool = F
             # Network gossip attestation processing
 
             # Ensure forkchoice is current before processing gossip
-            time_slots = self.time // SECONDS_PER_INTERVAL
+            time_slots = self.time // INTERVALS_PER_SLOT
             assert vote.slot <= time_slots, "Attestation from future slot"
 
             # Update new votes if this is latest from validator

tests/lean_spec/subspecs/forkchoice/test_attestation_processing.py

@@ -215,6 +215,52 @@ def test_validate_attestation_too_far_future(self, sample_store: Store) -> None:
         with pytest.raises(AssertionError, match="Attestation too far in future"):
             sample_store.validate_attestation(signed_vote)
 
+    def test_validate_attestation_unknown_head_rejected(self, sample_store: Store) -> None:
+        """Test validation fails when head block is unknown.
+
+        This ensures consistency with source/target validation and prevents
+        spam attestations with fabricated head roots.
+        """
+        # Create valid source and target blocks
+        source_block = Block(
+            slot=Slot(1),
+            proposer_index=Uint64(1),
+            parent_root=Bytes32.zero(),
+            state_root=Bytes32(b"source" + b"\x00" * 26),
+            body=BlockBody(attestations=Attestations(data=[])),
+        )
+        source_hash = hash_tree_root(source_block)
+
+        target_block = Block(
+            slot=Slot(2),
+            proposer_index=Uint64(2),
+            parent_root=source_hash,
+            state_root=Bytes32(b"target" + b"\x00" * 26),
+            body=BlockBody(attestations=Attestations(data=[])),
+        )
+        target_hash = hash_tree_root(target_block)
+
+        # Add source and target blocks to store
+        sample_store.blocks[source_hash] = source_block
+        sample_store.blocks[target_hash] = target_block
+
+        # Create an unknown head root that doesn't exist in the store
+        unknown_head_root = Bytes32(b"\x99" * 32)
+
+        # Create vote with unknown head but valid source and target
+        vote = Vote(
+            validator_id=ValidatorIndex(0),
+            slot=Slot(2),
+            head=Checkpoint(root=unknown_head_root, slot=Slot(2)),  # Unknown head!
+            target=Checkpoint(root=target_hash, slot=Slot(2)),
+            source=Checkpoint(root=source_hash, slot=Slot(1)),
+        )
+        signed_vote = SignedVote(data=vote, signature=Bytes32.zero())
+
+        # Should raise assertion error for unknown head
+        with pytest.raises(AssertionError, match="Unknown head block"):
+            sample_store.validate_attestation(signed_vote)
+
 
 class TestAttestationProcessing:
     """Test attestation processing logic."""