Provide different state root to db migrator

beacon_node/beacon_chain/src/canonical_head.rs

@@ -396,7 +396,23 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
         // If the finalized checkpoint changed, perform some updates.
         if new_view.finalized_checkpoint != old_view.finalized_checkpoint {
-            if let Err(e) = self.after_finalization(new_head, new_view, finalized_proto_block) {
+            // The store migration task requires the *state at the slot of the finalized epoch*,
+            // rather than the state of the latest finalized block. These two values will only
+            // differ when the first slot of the finalized epoch is a skip slot.
+            let new_finalized_slot = new_view
+                .finalized_checkpoint
+                .epoch
+                .start_slot(T::EthSpec::slots_per_epoch());
+            let new_finalized_state_root = self
+                .state_root_at_slot(new_finalized_slot)?
+                .ok_or(Error::MissingFinalizedStateRoot(new_finalized_slot))?;
+
+            if let Err(e) = self.after_finalization(
+                new_head,
+                new_view,
+                finalized_proto_block,
+                new_finalized_state_root,
+            ) {
                 crit!(
                     self.log,
                     "Error updating finalization";
@@ -585,6 +601,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         new_head: &BeaconSnapshot<T::EthSpec>,
         new_view: ForkChoiceView,
         finalized_proto_block: ProtoBlock,
+        new_finalized_state_root: Hash256,
     ) -> Result<(), Error> {
         self.op_pool
             .prune_all(&new_head.beacon_state, self.epoch()?);
@@ -620,7 +637,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 });
 
             chain.store_migrator.process_finalization(
-                finalized_proto_block.state_root.into(),
+                new_finalized_state_root.into(),
                 new_view.finalized_checkpoint,
                 chain.head_tracker.clone(),
             )?;
@@ -635,6 +652,9 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                         SseFinalizedCheckpoint {
                             epoch: new_view.finalized_checkpoint.epoch,
                             block: new_view.finalized_checkpoint.root,
+                            // Provide the state root of the latest finalized block, rather than the
+                            // specific state root at the first slot of the finalized epoch (which
+                            // might be a skip slot).
                             state: finalized_proto_block.state_root,
                         },
                     ));