fix(directory): preserve newer recovery registrations

src/Orleans.Runtime/GrainDirectory/GrainDirectoryPartition.cs

@@ -788,7 +788,7 @@ private async Task RecoverPartitionRange(DirectoryMembershipSnapshot current, Ri
             {
                 DebugAssertOwnership(current, entry.GrainId);
                 LogTraceRecoveredEntry(_logger, entry, current.Version);
-                _directory[entry.GrainId] = entry;
+                RecoverEntry(_directory, entry);
             }
         }
 
@@ -797,6 +797,16 @@ private async Task RecoverPartitionRange(DirectoryMembershipSnapshot current, Ri
         LogDebugCompletedRecoveringActivations(_logger, addedRange, current.Version, stopwatch.Elapsed);
     }
 
+    internal static void RecoverEntry(Dictionary<GrainId, GrainAddress> directory, GrainAddress recovered)
+    {
+        // Concurrent recovery responses can include an activation which was superseded in a newer membership view.
+        if (!directory.TryGetValue(recovered.GrainId, out var existing)
+            || recovered.MembershipVersion >= existing.MembershipVersion)
+        {
+            directory[recovered.GrainId] = recovered;
+        }
+    }
+
     private async IAsyncEnumerable<List<GrainAddress>> GetRegisteredActivations(DirectoryMembershipSnapshot current, RingRange range, bool isValidation)
     {
         // Membership is guaranteed to be at least as recent as the current view.

test/Orleans.GrainDirectory.Tests/GrainDirectory/GrainDirectoryPartitionTests.cs

@@ -173,6 +173,37 @@ public void GetSnapshotTransferRanges_ReturnsOnlyPreviousOwnerIntersections()
             addedRange: RingRange.Create(30, 40));
     }
 
+    [Fact]
+    public void RecoverEntry_PreservesNewestRegistrationRegardlessOfResponseOrder()
+    {
+        var grainId = GrainId.Create("recovery-test", "grain");
+        var oldRegistration = new GrainAddress
+        {
+            GrainId = grainId,
+            ActivationId = ActivationId.NewId(),
+            SiloAddress = TestSiloAddress,
+            MembershipVersion = new MembershipVersion(1),
+        };
+        var newRegistration = new GrainAddress
+        {
+            GrainId = grainId,
+            ActivationId = ActivationId.NewId(),
+            SiloAddress = ReplacementSiloAddress,
+            MembershipVersion = new MembershipVersion(2),
+        };
+
+        Dictionary<GrainId, GrainAddress> oldThenNew = [];
+        GrainDirectoryPartition.RecoverEntry(oldThenNew, oldRegistration);
+        GrainDirectoryPartition.RecoverEntry(oldThenNew, newRegistration);
+
+        Dictionary<GrainId, GrainAddress> newThenOld = [];
+        GrainDirectoryPartition.RecoverEntry(newThenOld, newRegistration);
+        GrainDirectoryPartition.RecoverEntry(newThenOld, oldRegistration);
+
+        Assert.Equal(newRegistration, oldThenNew[grainId]);
+        Assert.Equal(newRegistration, newThenOld[grainId]);
+    }
+
     private static void AssertRanges(RingRange previousOwnerRange, RingRange addedRange, params RingRange[] expected)
     {
         var actual = GrainDirectoryPartition.GetSnapshotTransferRanges(previousOwnerRange, addedRange).ToArray();