Don't use stale targets lingering since last churning

In Genesis sync mode, when we aren't actively churning,
the targets basis in the TVar can become stale when
ledger state judgement flips. We don't want to use these
targets when that happens and so we add a check for this condition,
and instead set the targets in the private OG state based on
the targets appropriate for the current ledger state judgement.
When churn wakes up for the next round, it will use the appropriate
targets basis and then we can use the targets that churn modifies
and provides us with.

ouroboros-network/src/Ouroboros/Network/PeerSelection/Governor/Monitor.hs

@@ -71,17 +71,39 @@ targetPeers :: (MonadSTM m, Ord peeraddr)
             => PeerSelectionActions peeraddr peerconn m
             -> PeerSelectionState peeraddr peerconn
             -> Guarded (STM m) (TimedDecision m peeraddr peerconn)
-targetPeers PeerSelectionActions{ readPeerSelectionTargets }
+targetPeers PeerSelectionActions{ readPeerSelectionTargets,
+                                  peerTargets = ConsensusModePeerTargets {
+                                    deadlineTargets,
+                                    syncTargets } }
             st@PeerSelectionState{
               publicRootPeers,
               localRootPeers,
               targets,
               bootstrapPeersFlag,
               hasOnlyBootstrapPeers,
-              ledgerStateJudgement
+              ledgerStateJudgement,
+              consensusMode
             } =
     Guarded Nothing $ do
-      targets'  <- readPeerSelectionTargets
+      churnTargets <- readPeerSelectionTargets
+      -- Genesis consensus mode:
+      -- we check if targets proposed by churn are stale
+      -- in the sense that they are the targets for
+      -- opposite value of the current ledger state judgement.
+      -- This indicates that we aren't churning currently, and
+      -- furthermore it means that the ledger state has flipped since
+      -- we last churned. Therefore we can't set the targets from
+      -- the TVar, and instead we set the appropriate targets
+      -- for the mode we are in.
+      let targets' =
+            case (ledgerStateJudgement, consensusMode) of
+              (YoungEnough, GenesisMode)
+                | churnTargets == syncTargets ->
+                  deadlineTargets
+              (TooOld, GenesisMode)
+                | churnTargets == deadlineTargets ->
+                  syncTargets
+              _otherwise -> churnTargets
 
       -- nb. first check is redundant in Genesis mode
       check (   isNodeAbleToMakeProgress bootstrapPeersFlag
@@ -578,10 +600,7 @@ monitorLedgerStateJudgement :: ( MonadSTM m
                             => PeerSelectionActions peeraddr peerconn m
                             -> PeerSelectionState peeraddr peerconn
                             -> Guarded (STM m) (TimedDecision m peeraddr peerconn)
-monitorLedgerStateJudgement PeerSelectionActions{ readLedgerStateJudgement,
-                                                  peerTargets = ConsensusModePeerTargets{
-                                                    praosTargets,
-                                                    genesisSyncTargets } }
+monitorLedgerStateJudgement PeerSelectionActions{ readLedgerStateJudgement }
                             st@PeerSelectionState{ bootstrapPeersFlag,
                                                    publicRootPeers,
                                                    knownPeers,
@@ -594,17 +613,13 @@ monitorLedgerStateJudgement PeerSelectionActions{ readLedgerStateJudgement,
     Guarded Nothing $ do
       lsj <- readLedgerStateJudgement
       check (lsj /= ledgerStateJudgement)
-      let targets = case lsj of
-            YoungEnough -> praosTargets
-            TooOld      -> genesisSyncTargets
 
       return $ \_now ->
         Decision {
           decisionTrace = [TraceLedgerStateJudgementChanged lsj],
           decisionJobs  = [],
           decisionState = st {
-              ledgerStateJudgement = lsj,
-              targets } }
+              ledgerStateJudgement = lsj } }
 
   | PraosMode <- consensusMode
   , isBootstrapPeersEnabled bootstrapPeersFlag =