avoid sending redundant LC finality updates (#4546)

When the epoch boundary block is missed, we incorrectly assume that the
next couple blocks improve finality, leading to repeated pushes of the
same light client finality update and incorrectly ignoring some gossip.

beacon_chain/consensus_object_pools/blockchain_dag_light_client.nim

@@ -559,20 +559,29 @@ proc createLightClientUpdates(
   if is_later and latest.assign_attested_header_with_migration(attested_bid):
     template forkyLatest: untyped = latest.forky(data_fork)
     load_attested_data(attested_bid)
-    let finalized_slot = attested_data.finalized_slot
+    var finalized_slot = attested_data.finalized_slot
     if finalized_slot == forkyLatest.finalized_header.beacon.slot:
       forkyLatest.finality_branch = attested_data.finality_branch
-    elif finalized_slot == GENESIS_SLOT:
-      forkyLatest.finalized_header.reset()
-      forkyLatest.finality_branch = attested_data.finality_branch
-    elif finalized_slot >= dag.tail.slot and
-        load_finalized_bid(finalized_slot) and
-        forkyLatest.assign_finalized_header(finalized_bid):
-      forkyLatest.finality_branch = attested_data.finality_branch
-      newFinality = true
-    else:
+    elif finalized_slot < dag.tail.slot or
+        not load_finalized_bid(finalized_slot):
       forkyLatest.finalized_header.reset()
       forkyLatest.finality_branch.reset()
+    else:
+      if finalized_bid.slot != finalized_slot:
+        finalized_slot = finalized_bid.slot
+        attested_data.finalized_slot = finalized_slot
+        dag.lcDataStore.cache.data[attested_bid] = attested_data
+      if finalized_slot == forkyLatest.finalized_header.beacon.slot:
+        forkyLatest.finality_branch = attested_data.finality_branch
+      elif finalized_slot == GENESIS_SLOT:
+        forkyLatest.finalized_header.reset()
+        forkyLatest.finality_branch = attested_data.finality_branch
+      elif forkyLatest.assign_finalized_header(finalized_bid):
+        forkyLatest.finality_branch = attested_data.finality_branch
+        newFinality = true
+      else:
+        forkyLatest.finalized_header.reset()
+        forkyLatest.finality_branch.reset()
     forkyLatest.sync_aggregate = sync_aggregate
     forkyLatest.signature_slot = signature_slot
     newOptimistic = true
@@ -648,7 +657,7 @@ proc createLightClientUpdates(
   withLcDataFork(dag.cfg.lcDataForkAtEpoch(parent_bid.slot.epoch)):
     when lcDataFork > LightClientDataFork.None:
       dag.createLightClientUpdates(state, blck, parent_bid, lcDataFork)
-  
+
 proc initLightClientDataCache*(dag: ChainDAGRef) =
   ## Initialize cached light client data
   if not dag.shouldImportLcData:

beacon_chain/gossip_processing/light_client_processor.nim

@@ -295,8 +295,7 @@ template withReportedProgress(
     obj: SomeForkedLightClientObject | Nothing, body: untyped): bool =
   block:
     let
-      oldIsInitialized =
-        self.store[].kind != LightClientDataFork.None
+      oldIsInitialized = self.store[].kind > LightClientDataFork.None
       oldNextCommitteeKnown = withForkyStore(self.store[]):
         when lcDataFork > LightClientDataFork.None:
           forkyStore.is_next_sync_committee_known
@@ -324,7 +323,7 @@ template withReportedProgress(
       didProgress = false
       didSignificantProgress = false
 
-    let newIsInitialized = self.store[].kind != LightClientDataFork.None
+    let newIsInitialized = self.store[].kind > LightClientDataFork.None
     if newIsInitialized > oldIsInitialized:
       didProgress = true
       didSignificantProgress = true