diff --git a/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs b/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs
index c24f24e..849022a 100644
--- a/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs
+++ b/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs
@@ -814,9 +814,7 @@ public static class MxGatewayClientCli
         TextWriter output,
         CancellationToken cancellationToken)
     {
-        DiscoverHierarchyReply reply = await client.GalaxyDiscoverHierarchyAsync(
-                new DiscoverHierarchyRequest(),
-                cancellationToken)
+        DiscoverHierarchyReply reply = await DiscoverAllGalaxyHierarchyAsync(client, cancellationToken)
             .ConfigureAwait(false);
 
         if (arguments.HasFlag("json"))
@@ -834,6 +832,39 @@ public static class MxGatewayClientCli
         return 0;
     }
 
+    private static async Task<DiscoverHierarchyReply> DiscoverAllGalaxyHierarchyAsync(
+        IMxGatewayCliClient client,
+        CancellationToken cancellationToken)
+    {
+        DiscoverHierarchyReply aggregate = new();
+        HashSet<string> seenPageTokens = new(StringComparer.Ordinal);
+        string pageToken = string.Empty;
+        do
+        {
+            DiscoverHierarchyReply page = await client.GalaxyDiscoverHierarchyAsync(
+                    new DiscoverHierarchyRequest
+                    {
+                        PageSize = 5000,
+                        PageToken = pageToken,
+                    },
+                    cancellationToken)
+                .ConfigureAwait(false);
+
+            aggregate.Objects.Add(page.Objects);
+            aggregate.TotalObjectCount = page.TotalObjectCount;
+            pageToken = page.NextPageToken;
+            if (!string.IsNullOrWhiteSpace(pageToken)
+                && !seenPageTokens.Add(pageToken))
+            {
+                throw new MxGatewayException(
+                    $"Galaxy DiscoverHierarchy returned a repeated page token '{pageToken}'.");
+            }
+        }
+        while (!string.IsNullOrWhiteSpace(pageToken));
+
+        return aggregate;
+    }
+
     private static async Task<int> GalaxyWatchAsync(
         CliArguments arguments,
         IMxGatewayCliClient client,
diff --git a/clients/dotnet/MxGateway.Client.Tests/GalaxyRepositoryClientTests.cs b/clients/dotnet/MxGateway.Client.Tests/GalaxyRepositoryClientTests.cs
index f55effe..c1cb75a 100644
--- a/clients/dotnet/MxGateway.Client.Tests/GalaxyRepositoryClientTests.cs
+++ b/clients/dotnet/MxGateway.Client.Tests/GalaxyRepositoryClientTests.cs
@@ -140,6 +140,26 @@ public sealed class GalaxyRepositoryClientTests
         Assert.False(call.CallOptions.CancellationToken.IsCancellationRequested);
     }
 
+    [Fact]
+    public async Task DiscoverHierarchyAsync_WithRepeatedPageToken_ThrowsProtocolError()
+    {
+        FakeGalaxyRepositoryTransport transport = CreateTransport();
+        transport.DiscoverHierarchyReplies.Enqueue(new DiscoverHierarchyReply
+        {
+            NextPageToken = "7:1",
+        });
+        transport.DiscoverHierarchyReplies.Enqueue(new DiscoverHierarchyReply
+        {
+            NextPageToken = "7:1",
+        });
+        await using GalaxyRepositoryClient client = CreateClient(transport);
+
+        MxGatewayException exception = await Assert.ThrowsAsync<MxGatewayException>(
+            async () => await client.DiscoverHierarchyAsync());
+
+        Assert.Contains("repeated page token", exception.Message, StringComparison.Ordinal);
+    }
+
     [Fact]
     public async Task TestConnectionAsync_RetriesOnTransientGrpcFailure()
     {
diff --git a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs
index 80552d9..612b0ee 100644
--- a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs
+++ b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs
@@ -207,8 +207,10 @@ public sealed class MxGatewayClientCliTests
         using var output = new StringWriter();
         using var error = new StringWriter();
         FakeCliClient fakeClient = new();
-        fakeClient.GalaxyDiscoverHierarchyReply = new DiscoverHierarchyReply
+        fakeClient.GalaxyDiscoverHierarchyReplies.Enqueue(new DiscoverHierarchyReply
         {
+            NextPageToken = "7:1",
+            TotalObjectCount = 2,
             Objects =
             {
                 new GalaxyObject
@@ -227,7 +229,21 @@ public sealed class MxGatewayClientCliTests
                     },
                 },
             },
-        };
+        });
+        fakeClient.GalaxyDiscoverHierarchyReplies.Enqueue(new DiscoverHierarchyReply
+        {
+            TotalObjectCount = 2,
+            Objects =
+            {
+                new GalaxyObject
+                {
+                    GobjectId = 8,
+                    TagName = "DelmiaReceiver_002",
+                    ContainedName = "DelmiaReceiver",
+                    ParentGobjectId = 1,
+                },
+            },
+        });
 
         int exitCode = await MxGatewayClientCli.RunAsync(
             [
@@ -242,10 +258,14 @@ public sealed class MxGatewayClientCliTests
             _ => fakeClient);
 
         Assert.Equal(0, exitCode);
-        Assert.Single(fakeClient.GalaxyDiscoverHierarchyRequests);
+        Assert.Equal(2, fakeClient.GalaxyDiscoverHierarchyRequests.Count);
+        Assert.Equal(5000, fakeClient.GalaxyDiscoverHierarchyRequests[0].PageSize);
+        Assert.Equal("", fakeClient.GalaxyDiscoverHierarchyRequests[0].PageToken);
+        Assert.Equal("7:1", fakeClient.GalaxyDiscoverHierarchyRequests[1].PageToken);
         string text = output.ToString();
-        Assert.Contains("objects=1", text);
+        Assert.Contains("objects=2", text);
         Assert.Contains("DelmiaReceiver_001", text);
+        Assert.Contains("DelmiaReceiver_002", text);
         Assert.Contains("attributes=1", text);
         Assert.Equal(string.Empty, error.ToString());
     }
@@ -411,6 +431,8 @@ public sealed class MxGatewayClientCliTests
 
         public DiscoverHierarchyReply GalaxyDiscoverHierarchyReply { get; set; } = new();
 
+        public Queue<DiscoverHierarchyReply> GalaxyDiscoverHierarchyReplies { get; } = new();
+
         public List<TestConnectionRequest> GalaxyTestConnectionRequests { get; } = [];
 
         public List<GetLastDeployTimeRequest> GalaxyGetLastDeployTimeRequests { get; } = [];
@@ -438,7 +460,10 @@ public sealed class MxGatewayClientCliTests
             CancellationToken cancellationToken)
         {
             GalaxyDiscoverHierarchyRequests.Add(request);
-            return Task.FromResult(GalaxyDiscoverHierarchyReply);
+            return Task.FromResult(
+                GalaxyDiscoverHierarchyReplies.TryDequeue(out DiscoverHierarchyReply? reply)
+                    ? reply
+                    : GalaxyDiscoverHierarchyReply);
         }
 
         public List<WatchDeployEventsRequest> GalaxyWatchDeployEventsRequests { get; } = [];
diff --git a/clients/dotnet/MxGateway.Client/GalaxyRepositoryClient.cs b/clients/dotnet/MxGateway.Client/GalaxyRepositoryClient.cs
index 4ec132c..09aa041 100644
--- a/clients/dotnet/MxGateway.Client/GalaxyRepositoryClient.cs
+++ b/clients/dotnet/MxGateway.Client/GalaxyRepositoryClient.cs
@@ -146,6 +146,7 @@ public sealed class GalaxyRepositoryClient : IAsyncDisposable
     public async Task<IReadOnlyList<GalaxyObject>> DiscoverHierarchyAsync(CancellationToken cancellationToken = default)
     {
         List<GalaxyObject> objects = [];
+        HashSet<string> seenPageTokens = new(StringComparer.Ordinal);
         string pageToken = string.Empty;
         do
         {
@@ -160,6 +161,12 @@ public sealed class GalaxyRepositoryClient : IAsyncDisposable
 
             objects.AddRange(reply.Objects);
             pageToken = reply.NextPageToken;
+            if (!string.IsNullOrWhiteSpace(pageToken)
+                && !seenPageTokens.Add(pageToken))
+            {
+                throw new MxGatewayException(
+                    $"Galaxy DiscoverHierarchy returned a repeated page token '{pageToken}'.");
+            }
         }
         while (!string.IsNullOrWhiteSpace(pageToken));
 
diff --git a/clients/go/mxgateway/galaxy.go b/clients/go/mxgateway/galaxy.go
index d75d46a..7d45641 100644
--- a/clients/go/mxgateway/galaxy.go
+++ b/clients/go/mxgateway/galaxy.go
@@ -3,6 +3,7 @@ package mxgateway
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"time"
 
@@ -148,6 +149,7 @@ func (c *GalaxyClient) DiscoverHierarchy(ctx context.Context) ([]*GalaxyObject,
 	defer cancel()
 
 	var objects []*GalaxyObject
+	seenPageTokens := make(map[string]struct{})
 	pageToken := ""
 	for {
 		reply, err := c.raw.DiscoverHierarchy(callCtx, &pb.DiscoverHierarchyRequest{
@@ -162,6 +164,10 @@ func (c *GalaxyClient) DiscoverHierarchy(ctx context.Context) ([]*GalaxyObject,
 		if pageToken == "" {
 			break
 		}
+		if _, seen := seenPageTokens[pageToken]; seen {
+			return nil, fmt.Errorf("mxgateway: galaxy discover hierarchy returned repeated page token %q", pageToken)
+		}
+		seenPageTokens[pageToken] = struct{}{}
 	}
 	return objects, nil
 }
diff --git a/clients/go/mxgateway/galaxy_test.go b/clients/go/mxgateway/galaxy_test.go
index be4124f..dfd29de 100644
--- a/clients/go/mxgateway/galaxy_test.go
+++ b/clients/go/mxgateway/galaxy_test.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"net"
+	"strings"
 	"testing"
 	"time"
 
@@ -159,6 +160,25 @@ func TestGalaxyDiscoverHierarchyReturnsObjects(t *testing.T) {
 	}
 }
 
+func TestGalaxyDiscoverHierarchyRejectsRepeatedPageToken(t *testing.T) {
+	fake := &fakeGalaxyServer{
+		discoverReplies: []*pb.DiscoverHierarchyReply{
+			{NextPageToken: "7:1"},
+			{NextPageToken: "7:1"},
+		},
+	}
+	client, cleanup := newGalaxyBufconnClient(t, fake)
+	defer cleanup()
+
+	_, err := client.DiscoverHierarchy(context.Background())
+	if err == nil {
+		t.Fatal("DiscoverHierarchy() error = nil, want repeated token error")
+	}
+	if !strings.Contains(err.Error(), "repeated page token") {
+		t.Fatalf("error = %v, want repeated page token", err)
+	}
+}
+
 func TestGalaxyDialReturnsGatewayErrorOnRpcFailure(t *testing.T) {
 	fake := &fakeGalaxyServer{failTest: true}
 	client, cleanup := newGalaxyBufconnClient(t, fake)
diff --git a/clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClient.java b/clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClient.java
index d1295bd..da6a74d 100644
--- a/clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClient.java
+++ b/clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClient.java
@@ -133,6 +133,7 @@ public final class GalaxyRepositoryClient implements AutoCloseable {
     public List<GalaxyObject> discoverHierarchy() {
         try {
             java.util.ArrayList<GalaxyObject> objects = new java.util.ArrayList<>();
+            java.util.HashSet<String> seenPageTokens = new java.util.HashSet<>();
             String pageToken = "";
             do {
                 DiscoverHierarchyReply reply = rawBlockingStub().discoverHierarchy(DiscoverHierarchyRequest.newBuilder()
@@ -141,6 +142,10 @@ public final class GalaxyRepositoryClient implements AutoCloseable {
                         .build());
                 objects.addAll(reply.getObjectsList());
                 pageToken = reply.getNextPageToken();
+                if (!pageToken.isBlank() && !seenPageTokens.add(pageToken)) {
+                    throw new MxGatewayException(
+                            "galaxy discover hierarchy returned repeated page token: " + pageToken);
+                }
             } while (!pageToken.isBlank());
             return objects;
         } catch (RuntimeException error) {
@@ -152,7 +157,7 @@ public final class GalaxyRepositoryClient implements AutoCloseable {
     }
 
     public CompletableFuture<List<GalaxyObject>> discoverHierarchyAsync() {
-        return discoverHierarchyPageAsync("", new java.util.ArrayList<>());
+        return discoverHierarchyPageAsync("", new java.util.ArrayList<>(), new java.util.HashSet<>());
     }
 
     /**
@@ -268,7 +273,7 @@ public final class GalaxyRepositoryClient implements AutoCloseable {
     }
 
     private CompletableFuture<List<GalaxyObject>> discoverHierarchyPageAsync(
-            String pageToken, java.util.ArrayList<GalaxyObject> objects) {
+            String pageToken, java.util.ArrayList<GalaxyObject> objects, java.util.HashSet<String> seenPageTokens) {
         DiscoverHierarchyRequest request = DiscoverHierarchyRequest.newBuilder()
                 .setPageSize(DISCOVER_HIERARCHY_PAGE_SIZE)
                 .setPageToken(pageToken)
@@ -278,7 +283,13 @@ public final class GalaxyRepositoryClient implements AutoCloseable {
             if (reply.getNextPageToken().isBlank()) {
                 return CompletableFuture.completedFuture(objects);
             }
-            return discoverHierarchyPageAsync(reply.getNextPageToken(), objects);
+            if (!seenPageTokens.add(reply.getNextPageToken())) {
+                CompletableFuture<List<GalaxyObject>> failed = new CompletableFuture<>();
+                failed.completeExceptionally(new MxGatewayException(
+                        "galaxy discover hierarchy returned repeated page token: " + reply.getNextPageToken()));
+                return failed;
+            }
+            return discoverHierarchyPageAsync(reply.getNextPageToken(), objects, seenPageTokens);
         });
     }
 
diff --git a/clients/java/mxgateway-client/src/test/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClientTests.java b/clients/java/mxgateway-client/src/test/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClientTests.java
index fdd0461..034e43d 100644
--- a/clients/java/mxgateway-client/src/test/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClientTests.java
+++ b/clients/java/mxgateway-client/src/test/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClientTests.java
@@ -3,6 +3,7 @@ package com.dohertylan.mxgateway.client;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.protobuf.Timestamp;
@@ -174,6 +175,27 @@ final class GalaxyRepositoryClientTests {
         assertFalse(stream.hasNext());
     }
 
+    @Test
+    void discoverHierarchyRejectsRepeatedPageToken() throws Exception {
+        TestService service = new TestService() {
+            @Override
+            public void discoverHierarchy(
+                    DiscoverHierarchyRequest request, StreamObserver<DiscoverHierarchyReply> responseObserver) {
+                responseObserver.onNext(DiscoverHierarchyReply.newBuilder()
+                        .setNextPageToken("7:1")
+                        .build());
+                responseObserver.onCompleted();
+            }
+        };
+
+        try (InProcessGalaxy g = InProcessGalaxy.start(service, new AtomicReference<>());
+                GalaxyRepositoryClient client = g.client("")) {
+            MxGatewayException error = assertThrows(MxGatewayException.class, client::discoverHierarchy);
+
+            assertTrue(error.getMessage().contains("repeated page token"));
+        }
+    }
+
     @Test
     void watchDeployEventsReceivesEventsInOrder() throws Exception {
         DeployEvent first = DeployEvent.newBuilder()
diff --git a/clients/python/src/mxgateway/galaxy.py b/clients/python/src/mxgateway/galaxy.py
index bcf632d..1ba022e 100644
--- a/clients/python/src/mxgateway/galaxy.py
+++ b/clients/python/src/mxgateway/galaxy.py
@@ -18,7 +18,7 @@ import grpc
 from google.protobuf.timestamp_pb2 import Timestamp
 
 from .auth import merge_metadata
-from .errors import map_rpc_error
+from .errors import MxGatewayError, map_rpc_error
 from .generated import galaxy_repository_pb2 as galaxy_pb
 from .generated import galaxy_repository_pb2_grpc as galaxy_pb_grpc
 from .options import ClientOptions, create_channel
@@ -115,6 +115,7 @@ class GalaxyRepositoryClient:
         """Return the deployed Galaxy object hierarchy as raw proto messages."""
 
         objects: list[galaxy_pb.GalaxyObject] = []
+        seen_page_tokens: set[str] = set()
         page_token = ""
         while True:
             reply = await self._unary(
@@ -129,6 +130,11 @@ class GalaxyRepositoryClient:
             page_token = reply.next_page_token
             if not page_token:
                 return objects
+            if page_token in seen_page_tokens:
+                raise MxGatewayError(
+                    f"galaxy discover hierarchy returned repeated page token {page_token!r}"
+                )
+            seen_page_tokens.add(page_token)
 
     def watch_deploy_events(
         self,
diff --git a/clients/python/tests/test_galaxy.py b/clients/python/tests/test_galaxy.py
index 977e2ad..ee58f55 100644
--- a/clients/python/tests/test_galaxy.py
+++ b/clients/python/tests/test_galaxy.py
@@ -148,6 +148,22 @@ async def test_discover_hierarchy_returns_proto_objects() -> None:
     assert objects[1].attributes[0].full_tag_reference == "DelmiaReceiver_001.DownloadPath"
 
 
+@pytest.mark.asyncio
+async def test_discover_hierarchy_rejects_repeated_page_token() -> None:
+    stub = FakeGalaxyStub()
+    stub.discover_hierarchy.replies = [
+        galaxy_pb.DiscoverHierarchyReply(next_page_token="7:1"),
+        galaxy_pb.DiscoverHierarchyReply(next_page_token="7:1"),
+    ]
+    client = await GalaxyRepositoryClient.connect(
+        ClientOptions(endpoint="fake", plaintext=True),
+        stub=stub,
+    )
+
+    with pytest.raises(Exception, match="repeated page token"):
+        await client.discover_hierarchy()
+
+
 @pytest.mark.asyncio
 async def test_watch_deploy_events_yields_events_in_order() -> None:
     ts1 = Timestamp()
diff --git a/clients/rust/src/galaxy.rs b/clients/rust/src/galaxy.rs
index 72ae5ae..4a82af5 100644
--- a/clients/rust/src/galaxy.rs
+++ b/clients/rust/src/galaxy.rs
@@ -144,6 +144,7 @@ impl GalaxyClient {
     /// the object's identifying names plus its dynamic attributes.
     pub async fn discover_hierarchy(&mut self) -> Result<Vec<GalaxyObject>, Error> {
         let mut objects = Vec::new();
+        let mut seen_page_tokens = std::collections::HashSet::new();
         let mut page_token = String::new();
         loop {
             let response = self
@@ -159,6 +160,14 @@ impl GalaxyClient {
             if page_token.is_empty() {
                 return Ok(objects);
             }
+            if !seen_page_tokens.insert(page_token.clone()) {
+                return Err(Error::InvalidArgument {
+                    name: "page_token".to_owned(),
+                    detail: format!(
+                        "galaxy discover hierarchy returned repeated page token `{page_token}`"
+                    ),
+                });
+            }
         }
     }
 
@@ -517,6 +526,37 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn discover_hierarchy_rejects_repeated_page_token() {
+        let state = Arc::new(FakeState::default());
+        state
+            .discover_replies
+            .lock()
+            .unwrap()
+            .push_back(DiscoverHierarchyReply {
+                objects: Vec::new(),
+                next_page_token: "7:1".to_owned(),
+                total_object_count: 1,
+            });
+        state
+            .discover_replies
+            .lock()
+            .unwrap()
+            .push_back(DiscoverHierarchyReply {
+                objects: Vec::new(),
+                next_page_token: "7:1".to_owned(),
+                total_object_count: 1,
+            });
+        let endpoint = spawn_fake(state).await;
+        let mut client = GalaxyClient::connect(ClientOptions::new(endpoint))
+            .await
+            .unwrap();
+
+        let error = client.discover_hierarchy().await.unwrap_err();
+
+        assert!(error.to_string().contains("repeated page token"));
+    }
+
     #[tokio::test]
     async fn watch_deploy_events_yields_events_in_order() {
         let state = Arc::new(FakeState::default());
diff --git a/src/MxGateway.Server/Galaxy/GalaxyHierarchyCache.cs b/src/MxGateway.Server/Galaxy/GalaxyHierarchyCache.cs
index 1c1e544..8cc4655 100644
--- a/src/MxGateway.Server/Galaxy/GalaxyHierarchyCache.cs
+++ b/src/MxGateway.Server/Galaxy/GalaxyHierarchyCache.cs
@@ -99,6 +99,14 @@ public sealed class GalaxyHierarchyCache : IGalaxyHierarchyCache
                     LastQueriedAt = queriedAt,
                     LastSuccessAt = queriedAt,
                     LastError = null,
+                    DashboardSummary = previous.DashboardSummary with
+                    {
+                        Status = DashboardGalaxyStatus.Healthy,
+                        LastQueriedAt = queriedAt,
+                        LastSuccessAt = queriedAt,
+                        LastDeployTime = deployTime,
+                        LastError = null,
+                    },
                 };
                 Volatile.Write(ref _current, refreshed);
                 _firstLoad.TrySetResult();
diff --git a/src/MxGateway.Server/Grpc/GalaxyRepositoryGrpcService.cs b/src/MxGateway.Server/Grpc/GalaxyRepositoryGrpcService.cs
index 7fd404d..60ca68f 100644
--- a/src/MxGateway.Server/Grpc/GalaxyRepositoryGrpcService.cs
+++ b/src/MxGateway.Server/Grpc/GalaxyRepositoryGrpcService.cs
@@ -68,7 +68,8 @@ public sealed class GalaxyRepositoryGrpcService(
                 ResolveUnavailableMessage(entry)));
         }
 
-        int offset = ParsePageToken(request.PageToken);
+        PageToken pageToken = ParsePageToken(request.PageToken, entry.Sequence);
+        int offset = pageToken.Offset;
         if (offset > entry.Objects.Count)
         {
             throw new RpcException(new Status(
@@ -90,7 +91,7 @@ public sealed class GalaxyRepositoryGrpcService(
         int nextOffset = offset + take;
         if (nextOffset < entry.Objects.Count)
         {
-            reply.NextPageToken = nextOffset.ToString(System.Globalization.CultureInfo.InvariantCulture);
+            reply.NextPageToken = FormatPageToken(entry.Sequence, nextOffset);
         }
 
         return reply;
@@ -182,15 +183,30 @@ public sealed class GalaxyRepositoryGrpcService(
         return Math.Min(pageSize, MaxDiscoverPageSize);
     }
 
-    private static int ParsePageToken(string pageToken)
+    private static string FormatPageToken(long sequence, int offset)
+    {
+        return string.Concat(
+            sequence.ToString(System.Globalization.CultureInfo.InvariantCulture),
+            ":",
+            offset.ToString(System.Globalization.CultureInfo.InvariantCulture));
+    }
+
+    private static PageToken ParsePageToken(string pageToken, long currentSequence)
     {
         if (string.IsNullOrWhiteSpace(pageToken))
         {
-            return 0;
+            return new PageToken(currentSequence, Offset: 0);
         }
 
-        if (!int.TryParse(
-                pageToken,
+        string[] parts = pageToken.Split(':', count: 2);
+        if (parts.Length != 2
+            || !long.TryParse(
+                parts[0],
+                System.Globalization.NumberStyles.None,
+                System.Globalization.CultureInfo.InvariantCulture,
+                out long sequence)
+            || !int.TryParse(
+                parts[1],
                 System.Globalization.NumberStyles.None,
                 System.Globalization.CultureInfo.InvariantCulture,
                 out int offset)
@@ -201,9 +217,18 @@ public sealed class GalaxyRepositoryGrpcService(
                 "DiscoverHierarchy page_token is invalid."));
         }
 
-        return offset;
+        if (sequence != currentSequence)
+        {
+            throw new RpcException(new Status(
+                StatusCode.InvalidArgument,
+                "DiscoverHierarchy page_token is stale."));
+        }
+
+        return new PageToken(sequence, offset);
     }
 
+    private sealed record PageToken(long Sequence, int Offset);
+
     [System.Diagnostics.CodeAnalysis.SuppressMessage(
         "Style",
         "IDE0051:Remove unused private members",
diff --git a/src/MxGateway.Tests/Gateway/Grpc/GalaxyRepositoryGrpcServiceTests.cs b/src/MxGateway.Tests/Gateway/Grpc/GalaxyRepositoryGrpcServiceTests.cs
index a793681..7aecc65 100644
--- a/src/MxGateway.Tests/Gateway/Grpc/GalaxyRepositoryGrpcServiceTests.cs
+++ b/src/MxGateway.Tests/Gateway/Grpc/GalaxyRepositoryGrpcServiceTests.cs
@@ -24,7 +24,7 @@ public sealed class GalaxyRepositoryGrpcServiceTests
         Assert.Equal(2, reply.Objects.Count);
         Assert.Equal("Object_001", reply.Objects[0].TagName);
         Assert.Equal("Object_002", reply.Objects[1].TagName);
-        Assert.Equal("2", reply.NextPageToken);
+        Assert.Equal("7:2", reply.NextPageToken);
         Assert.Equal(3, reply.TotalObjectCount);
     }
 
@@ -37,7 +37,7 @@ public sealed class GalaxyRepositoryGrpcServiceTests
             new DiscoverHierarchyRequest
             {
                 PageSize = 2,
-                PageToken = "2",
+                PageToken = "7:2",
             },
             new TestServerCallContext());
 
@@ -50,7 +50,8 @@ public sealed class GalaxyRepositoryGrpcServiceTests
     [Theory]
     [InlineData("-1", 1)]
     [InlineData("not-an-offset", 1)]
-    [InlineData("4", 1)]
+    [InlineData("7:4", 1)]
+    [InlineData("6:2", 1)]
     [InlineData("", -1)]
     public async Task DiscoverHierarchy_WithInvalidPagingArguments_ReturnsInvalidArgument(
         string pageToken,
@@ -88,6 +89,7 @@ public sealed class GalaxyRepositoryGrpcServiceTests
         return GalaxyHierarchyCacheEntry.Empty with
         {
             Status = GalaxyCacheStatus.Healthy,
+            Sequence = 7,
             LastSuccessAt = DateTimeOffset.UtcNow,
             Objects = objects,
             DashboardSummary = DashboardGalaxySummary.Unknown with