Answer ReplicatedWithLeaderTerm to an empty AppendEntries after an entry of the sender's term

src/DotNext.Tests/Net/Cluster/Consensus/Raft/NetworkTransport/ConnectionOriented/Tcp/TcpTransportTests.cs

@@ -307,6 +307,28 @@ static RaftCluster CreateCluster(int port, bool coldStart,  IPersistentState wal
         }
     }
 
+    [Theory]
+    [InlineData(2L, HeartbeatResult.ReplicatedWithLeaderTerm)]
+    [InlineData(3L, HeartbeatResult.Replicated)]
+    public Task EmptyAppendEntriesAfterEntry(long senderTerm, HeartbeatResult expected)
+    {
+        return EmptyAppendEntriesAfterEntryCore(CreateCluster, senderTerm, expected);
+
+        static RaftCluster CreateCluster(int port, bool coldStart, IPersistentState wal)
+        {
+            var config = new RaftCluster.TcpConfiguration(new IPEndPoint(IPAddress.Loopback, port))
+            {
+                ColdStart = coldStart,
+                ConfigurationStorage = null,
+            };
+
+            return new(config)
+            {
+                AuditTrail = wal,
+            };
+        }
+    }
+
     [Fact]
     public Task ClusterRecovery()
     {

src/DotNext.Tests/Net/Cluster/Consensus/Raft/NetworkTransport/TransportTestSuite.cs

@@ -481,6 +481,23 @@ private protected async Task ClusterRecoveryCore(Func<int, bool, IPersistentStat
         await host3.StopAsync();
     }
 
+    private protected async Task EmptyAppendEntriesAfterEntryCore(Func<int, bool, IPersistentState, RaftCluster> clusterFactory, long senderTerm, HeartbeatResult expected)
+    {
+        // the follower's last entry is of term 2
+        await using var wal = CreateWal();
+        Equal(1L, await wal.AppendAsync(new BufferedEntry(2L, false, RandomBytes(16)), TestToken));
+        await using var follower = clusterFactory(3398, false, wal);
+        await follower.StartAsync(TestToken);
+
+        // a heartbeat with no entries after it: the follower's log holds an entry of the sender's term only if that one is
+        var result = await follower.As<ILocalMember>().AppendEntriesAsync(Random.Shared.Next<ClusterMemberId>(), senderTerm,
+            new LogEntryProducer<BufferedEntry>(), prevLogIndex: 1L, prevLogTerm: 2L, commitIndex: 1L, stateVersion: 0, TestToken);
+        Equal(expected, result.Value.Result);
+        Equal(1L, result.Value.LastIndex);
+
+        await follower.StopAsync(TestToken);
+    }
+
     private protected async Task LeadershipCore(Func<int, bool, IPersistentState, RaftCluster> clusterFactory)
     {
         // first node - cold start

src/cluster/DotNext.Net.Cluster/Net/Cluster/Consensus/Raft/RaftCluster.cs

@@ -714,7 +714,10 @@ protected async ValueTask<Result<ReplicationStatus>> AppendEntriesAsync<TEntry>(
                         {
                             Value = new()
                             {
-                                Result = IsReplicatedWithExpectedTerm(entries) ? HeartbeatResult.ReplicatedWithLeaderTerm : HeartbeatResult.Replicated,
+                                // an empty request whose preceding entry is of the sender's term proves the log holds the leader's entries of its term too
+                                Result = IsReplicatedWithExpectedTerm(entries) || (!notEmpty && prevLogTerm == senderTerm)
+                                    ? HeartbeatResult.ReplicatedWithLeaderTerm
+                                    : HeartbeatResult.Replicated,
                                 LastIndex = lastIndex,
                             }
                         };