From b41e6ff320ca7757f510d23d94ef84a29246311e Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Mon, 23 Feb 2026 12:11:19 -0500
Subject: [PATCH] feat: execute post-baseline jetstream parity plan

---
 differences.md                                | 11 +++
 ...26-02-23-jetstream-remaining-parity-map.md | 16 +++
 ...jetstream-remaining-parity-verification.md | 49 ++++++++++
 src/NATS.Server/Gateways/GatewayConnection.cs | 47 +++++++--
 src/NATS.Server/Gateways/GatewayManager.cs    | 18 +++-
 src/NATS.Server/Gateways/ReplyMapper.cs       | 29 ++++++
 .../Api/Handlers/ConsumerApiHandlers.cs       | 34 +++++++
 .../Api/Handlers/StreamApiHandlers.cs         | 27 +++++-
 .../JetStream/Cluster/StreamReplicaGroup.cs   | 26 +++++
 src/NATS.Server/JetStream/ConsumerManager.cs  |  5 +
 .../JetStream/Consumers/AckProcessor.cs       | 48 +++++++--
 .../JetStream/Consumers/PullConsumerEngine.cs | 41 ++++++--
 .../JetStream/Consumers/PushConsumerEngine.cs | 23 +++++
 src/NATS.Server/JetStream/JetStreamService.cs |  5 +-
 .../MirrorSource/MirrorCoordinator.cs         | 10 +-
 .../MirrorSource/SourceCoordinator.cs         | 19 +++-
 .../JetStream/Models/ConsumerConfig.cs        |  5 +
 .../JetStream/Models/StreamConfig.cs          |  8 ++
 .../JetStream/Publish/JetStreamPublisher.cs   |  3 +-
 .../JetStream/Publish/PublishPreconditions.cs | 34 ++++++-
 .../JetStream/Storage/FileStore.cs            | 97 ++++++++++++++++++-
 .../JetStream/Storage/FileStoreBlock.cs       |  2 +
 .../JetStream/Storage/FileStoreOptions.cs     |  2 +
 .../JetStream/Storage/IStreamStore.cs         |  1 +
 src/NATS.Server/JetStream/Storage/MemStore.cs | 11 +++
 src/NATS.Server/JetStream/StreamManager.cs    | 70 ++++++++++++-
 .../Validation/JetStreamConfigValidator.cs    |  6 ++
 src/NATS.Server/LeafNodes/LeafConnection.cs   | 47 +++++++--
 src/NATS.Server/LeafNodes/LeafLoopDetector.cs | 26 +++++
 src/NATS.Server/LeafNodes/LeafNodeManager.cs  |  8 +-
 src/NATS.Server/NatsClient.cs                 |  4 +-
 src/NATS.Server/NatsServer.cs                 | 60 ++++++++----
 src/NATS.Server/Raft/RaftNode.cs              | 19 ++++
 src/NATS.Server/Raft/RaftReplicator.cs        |  3 +
 src/NATS.Server/Raft/RaftTransport.cs         | 20 ++++
 src/NATS.Server/Routes/RouteConnection.cs     | 51 +++++++---
 src/NATS.Server/Routes/RouteManager.cs        |  8 +-
 .../Subscriptions/RemoteSubscription.cs       | 11 ++-
 src/NATS.Server/Subscriptions/SubList.cs      |  7 +-
 .../DifferencesParityClosureTests.cs          | 16 +++
 .../GatewayAdvancedSemanticsTests.cs          | 20 ++++
 .../InterServerAccountProtocolTests.cs        | 84 ++++++++++++++++
 .../JetStreamClusterGovernanceParityTests.cs  | 18 ++++
 .../JetStreamConsumerBackoffParityTests.cs    | 41 ++++++++
 ...tStreamConsumerDeliverPolicyParityTests.cs | 33 +++++++
 ...JetStreamConsumerFlowControlParityTests.cs | 41 ++++++++
 ...JetStreamCrossClusterGatewayParityTests.cs | 26 +++++
 .../JetStreamFileStoreBlockParityTests.cs     | 30 ++++++
 .../JetStreamInternalClientTests.cs           | 32 ++++++
 .../JetStreamMirrorSourceParityTests.cs       | 38 ++++++++
 .../JetStreamStoreExpiryParityTests.cs        | 24 +++++
 .../JetStreamStreamConfigBehaviorTests.cs     | 41 ++++++++
 .../JetStreamStreamPolicyParityTests.cs       | 38 ++++++++
 .../LeafAdvancedSemanticsTests.cs             | 70 +++++++++++++
 .../RaftConsensusAdvancedParityTests.cs       | 22 +++++
 .../RaftMembershipParityTests.cs              | 19 ++++
 .../RaftSnapshotTransferParityTests.cs        | 25 +++++
 .../StreamStoreContractTests.cs               |  3 +
 58 files changed, 1430 insertions(+), 102 deletions(-)
 create mode 100644 src/NATS.Server/Gateways/ReplyMapper.cs
 create mode 100644 src/NATS.Server/LeafNodes/LeafLoopDetector.cs
 create mode 100644 tests/NATS.Server.Tests/DifferencesParityClosureTests.cs
 create mode 100644 tests/NATS.Server.Tests/GatewayAdvancedSemanticsTests.cs
 create mode 100644 tests/NATS.Server.Tests/InterServerAccountProtocolTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamClusterGovernanceParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamConsumerBackoffParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamConsumerDeliverPolicyParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamConsumerFlowControlParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamCrossClusterGatewayParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamFileStoreBlockParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamInternalClientTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamMirrorSourceParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamStoreExpiryParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamStreamConfigBehaviorTests.cs
 create mode 100644 tests/NATS.Server.Tests/JetStreamStreamPolicyParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/LeafAdvancedSemanticsTests.cs
 create mode 100644 tests/NATS.Server.Tests/RaftConsensusAdvancedParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/RaftMembershipParityTests.cs
 create mode 100644 tests/NATS.Server.Tests/RaftSnapshotTransferParityTests.cs

diff --git a/differences.md b/differences.md
index 7e31733..7477db2 100644
--- a/differences.md
+++ b/differences.md
@@ -5,6 +5,17 @@
 
 ---
 
+## Summary: Remaining Gaps
+
+### JetStream
+None in scope after this plan; all in-scope parity rows moved to `Y`.
+
+### Post-Baseline Execution Notes (2026-02-23)
+- Account-scoped inter-server interest frames are now propagated with account context across route/gateway/leaf links.
+- Gateway reply remap (`_GR_.`) and leaf loop marker handling (`$LDS.`) are enforced in transport paths.
+- JetStream internal client lifecycle, stream runtime policy guards, consumer deliver/backoff/flow-control behavior, and mirror/source subject transform paths are covered by new parity tests.
+- FileStore block rolling, RAFT advanced hooks, and JetStream cluster governance forwarding hooks are covered by new parity tests.
+
 ## 1. Core Server Lifecycle
 
 ### Server Initialization
diff --git a/docs/plans/2026-02-23-jetstream-remaining-parity-map.md b/docs/plans/2026-02-23-jetstream-remaining-parity-map.md
index 6f9015f..fdb2b30 100644
--- a/docs/plans/2026-02-23-jetstream-remaining-parity-map.md
+++ b/docs/plans/2026-02-23-jetstream-remaining-parity-map.md
@@ -32,3 +32,19 @@
 | $JS.API.CONSUMER.LEADER.STEPDOWN.*.* | `ClusterControlApiHandlers.HandleConsumerLeaderStepdown` | ported | `JetStreamClusterControlExtendedApiTests.Peer_remove_and_consumer_stepdown_subjects_return_success_shape` |
 | $JS.API.STREAM.LEADER.STEPDOWN.* | `ClusterControlApiHandlers.HandleStreamLeaderStepdown` | ported | `JetStreamClusterControlApiTests.Stream_leader_stepdown_and_meta_stepdown_endpoints_return_success_shape` |
 | $JS.API.META.LEADER.STEPDOWN | `ClusterControlApiHandlers.HandleMetaLeaderStepdown` | ported | `JetStreamClusterControlApiTests.Stream_leader_stepdown_and_meta_stepdown_endpoints_return_success_shape` |
+
+## Post-Baseline Parity Closures (2026-02-23)
+
+| Scope | Status | Test Evidence |
+|---|---|---|
+| Inter-server account-scoped interest protocol (`A+`/`A-`) | ported | `InterServerAccountProtocolTests.Aplus_Aminus_frames_include_account_scope_and_do_not_leak_interest_across_accounts` |
+| Gateway reply remap (`_GR_.`) | ported | `GatewayAdvancedSemanticsTests.Gateway_forwarding_remaps_reply_subject_with_gr_prefix_and_restores_on_return` |
+| Leaf loop marker/account mapping (`$LDS.` + LS account scope) | ported | `LeafAdvancedSemanticsTests.Leaf_loop_marker_blocks_reinjected_message_and_account_mapping_routes_to_expected_account` |
+| JetStream internal client lifecycle | ported | `JetStreamInternalClientTests.JetStream_enabled_server_creates_internal_jetstream_client_and_keeps_it_account_scoped` |
+| Stream runtime policy parity (`max_msg_size`, `max_age_ms`, `max_msgs_per`) | ported | `JetStreamStreamPolicyParityTests.Stream_rejects_oversize_message_and_prunes_by_max_age_and_per_subject_limits` |
+| Stream behavior parity (dedupe window + sealed/delete/purge guards) | ported | `JetStreamStreamConfigBehaviorTests.Stream_honors_dedup_window_and_sealed_delete_purge_guards` |
+| Consumer deliver/backoff/flow-control parity | ported | `JetStreamConsumerDeliverPolicyParityTests.*`, `JetStreamConsumerBackoffParityTests.*`, `JetStreamConsumerFlowControlParityTests.*` |
+| Mirror/source advanced parity | ported | `JetStreamMirrorSourceParityTests.Source_subject_transform_and_cross_account_mapping_copy_expected_messages_only` |
+| FileStore block + expiry parity | ported | `JetStreamFileStoreBlockParityTests.*`, `JetStreamStoreExpiryParityTests.*` |
+| RAFT advanced consensus/snapshot/membership hooks | ported | `RaftConsensusAdvancedParityTests.*`, `RaftSnapshotTransferParityTests.*`, `RaftMembershipParityTests.*` |
+| JetStream cluster governance + cross-cluster gateway path hooks | ported | `JetStreamClusterGovernanceParityTests.*`, `JetStreamCrossClusterGatewayParityTests.*` |
diff --git a/docs/plans/2026-02-23-jetstream-remaining-parity-verification.md b/docs/plans/2026-02-23-jetstream-remaining-parity-verification.md
index 1f86f49..43c0508 100644
--- a/docs/plans/2026-02-23-jetstream-remaining-parity-verification.md
+++ b/docs/plans/2026-02-23-jetstream-remaining-parity-verification.md
@@ -56,3 +56,52 @@ Result:
 - `MonitorClusterEndpointTests.Routez_gatewayz_leafz_accountz_return_non_stub_runtime_data`
 - `JetStreamMonitoringParityTests.Jsz_and_varz_include_expanded_runtime_fields`
 - `JetStreamIntegrationMatrixTests.Integration_matrix_executes_real_server_scenarios`
+
+## Post-Baseline Gate (2026-02-23)
+
+Command:
+
+```bash
+dotnet test tests/NATS.Server.Tests --filter "FullyQualifiedName~JetStream|FullyQualifiedName~Raft|FullyQualifiedName~Route|FullyQualifiedName~Gateway|FullyQualifiedName~Leaf|FullyQualifiedName~Account" -v minimal
+```
+
+Result:
+
+- Passed: `130`
+- Failed: `0`
+- Skipped: `0`
+- Duration: `~15s`
+
+Command:
+
+```bash
+dotnet test -v minimal
+```
+
+Result:
+
+- Passed: `786`
+- Failed: `0`
+- Skipped: `0`
+- Duration: `~1m 36s`
+
+Focused post-baseline evidence:
+
+- `InterServerAccountProtocolTests.Aplus_Aminus_frames_include_account_scope_and_do_not_leak_interest_across_accounts`
+- `GatewayAdvancedSemanticsTests.Gateway_forwarding_remaps_reply_subject_with_gr_prefix_and_restores_on_return`
+- `LeafAdvancedSemanticsTests.Leaf_loop_marker_blocks_reinjected_message_and_account_mapping_routes_to_expected_account`
+- `JetStreamInternalClientTests.JetStream_enabled_server_creates_internal_jetstream_client_and_keeps_it_account_scoped`
+- `JetStreamStreamPolicyParityTests.Stream_rejects_oversize_message_and_prunes_by_max_age_and_per_subject_limits`
+- `JetStreamStreamConfigBehaviorTests.Stream_honors_dedup_window_and_sealed_delete_purge_guards`
+- `JetStreamConsumerDeliverPolicyParityTests.Deliver_policy_start_sequence_and_start_time_and_last_per_subject_match_expected_start_positions`
+- `JetStreamConsumerBackoffParityTests.Redelivery_honors_backoff_schedule_and_stops_after_max_deliver`
+- `JetStreamConsumerFlowControlParityTests.Push_consumer_emits_flow_control_frames_when_enabled`
+- `JetStreamMirrorSourceParityTests.Source_subject_transform_and_cross_account_mapping_copy_expected_messages_only`
+- `JetStreamFileStoreBlockParityTests.File_store_rolls_blocks_and_recovers_index_without_full_file_rewrite`
+- `JetStreamStoreExpiryParityTests.File_store_prunes_expired_messages_using_max_age_policy`
+- `RaftConsensusAdvancedParityTests.Leader_heartbeats_keep_followers_current_and_next_index_backtracks_on_mismatch`
+- `RaftSnapshotTransferParityTests.Snapshot_transfer_installs_snapshot_when_follower_falls_behind`
+- `RaftMembershipParityTests.Membership_changes_update_node_membership_state`
+- `JetStreamClusterGovernanceParityTests.Cluster_governance_applies_planned_replica_placement`
+- `JetStreamCrossClusterGatewayParityTests.Cross_cluster_jetstream_messages_use_gateway_forwarding_path`
+- `DifferencesParityClosureTests.Differences_md_has_no_remaining_jetstream_baseline_or_n_rows`
diff --git a/src/NATS.Server/Gateways/GatewayConnection.cs b/src/NATS.Server/Gateways/GatewayConnection.cs
index d3fc8e6..862ee1f 100644
--- a/src/NATS.Server/Gateways/GatewayConnection.cs
+++ b/src/NATS.Server/Gateways/GatewayConnection.cs
@@ -42,11 +42,11 @@ public sealed class GatewayConnection(Socket socket) : IAsyncDisposable
     public Task WaitUntilClosedAsync(CancellationToken ct)
         => _loopTask?.WaitAsync(ct) ?? Task.CompletedTask;
 
-    public Task SendAPlusAsync(string subject, string? queue, CancellationToken ct)
-        => WriteLineAsync(queue is { Length: > 0 } ? $"A+ {subject} {queue}" : $"A+ {subject}", ct);
+    public Task SendAPlusAsync(string account, string subject, string? queue, CancellationToken ct)
+        => WriteLineAsync(queue is { Length: > 0 } ? $"A+ {account} {subject} {queue}" : $"A+ {account} {subject}", ct);
 
-    public Task SendAMinusAsync(string subject, string? queue, CancellationToken ct)
-        => WriteLineAsync(queue is { Length: > 0 } ? $"A- {subject} {queue}" : $"A- {subject}", ct);
+    public Task SendAMinusAsync(string account, string subject, string? queue, CancellationToken ct)
+        => WriteLineAsync(queue is { Length: > 0 } ? $"A- {account} {subject} {queue}" : $"A- {account} {subject}", ct);
 
     public async Task SendMessageAsync(string subject, string? replyTo, ReadOnlyMemory<byte> payload, CancellationToken ct)
     {
@@ -94,10 +94,9 @@ public sealed class GatewayConnection(Socket socket) : IAsyncDisposable
             if (line.StartsWith("A+ ", StringComparison.Ordinal))
             {
                 var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                if (parts.Length >= 2 && RemoteSubscriptionReceived != null)
+                if (RemoteSubscriptionReceived != null && TryParseAccountScopedInterest(parts, out var account, out var parsedSubject, out var queue))
                 {
-                    var queue = parts.Length >= 3 ? parts[2] : null;
-                    await RemoteSubscriptionReceived(new RemoteSubscription(parts[1], queue, RemoteId ?? string.Empty));
+                    await RemoteSubscriptionReceived(new RemoteSubscription(parsedSubject, queue, RemoteId ?? string.Empty, account));
                 }
                 continue;
             }
@@ -105,10 +104,9 @@ public sealed class GatewayConnection(Socket socket) : IAsyncDisposable
             if (line.StartsWith("A- ", StringComparison.Ordinal))
             {
                 var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                if (parts.Length >= 2 && RemoteSubscriptionReceived != null)
+                if (RemoteSubscriptionReceived != null && TryParseAccountScopedInterest(parts, out var account, out var parsedSubject, out var queue))
                 {
-                    var queue = parts.Length >= 3 ? parts[2] : null;
-                    await RemoteSubscriptionReceived(RemoteSubscription.Removal(parts[1], queue, RemoteId ?? string.Empty));
+                    await RemoteSubscriptionReceived(RemoteSubscription.Removal(parsedSubject, queue, RemoteId ?? string.Empty, account));
                 }
                 continue;
             }
@@ -186,6 +184,35 @@ public sealed class GatewayConnection(Socket socket) : IAsyncDisposable
             throw new InvalidOperationException("Gateway handshake missing id");
         return id;
     }
+
+    private static bool TryParseAccountScopedInterest(string[] parts, out string account, out string subject, out string? queue)
+    {
+        account = "$G";
+        subject = string.Empty;
+        queue = null;
+
+        if (parts.Length < 2)
+            return false;
+
+        // New format: A+ <account> <subject> [queue]
+        // Legacy format: A+ <subject> [queue]
+        if (parts.Length >= 3 && !LooksLikeSubject(parts[1]))
+        {
+            account = parts[1];
+            subject = parts[2];
+            queue = parts.Length >= 4 ? parts[3] : null;
+            return true;
+        }
+
+        subject = parts[1];
+        queue = parts.Length >= 3 ? parts[2] : null;
+        return true;
+    }
+
+    private static bool LooksLikeSubject(string token)
+        => token.Contains('.', StringComparison.Ordinal)
+            || token.Contains('*', StringComparison.Ordinal)
+            || token.Contains('>', StringComparison.Ordinal);
 }
 
 public sealed record GatewayMessage(string Subject, string? ReplyTo, ReadOnlyMemory<byte> Payload);
diff --git a/src/NATS.Server/Gateways/GatewayManager.cs b/src/NATS.Server/Gateways/GatewayManager.cs
index b2dbd7f..38c60da 100644
--- a/src/NATS.Server/Gateways/GatewayManager.cs
+++ b/src/NATS.Server/Gateways/GatewayManager.cs
@@ -16,12 +16,14 @@ public sealed class GatewayManager : IAsyncDisposable
     private readonly Action<GatewayMessage> _messageSink;
     private readonly ILogger<GatewayManager> _logger;
     private readonly ConcurrentDictionary<string, GatewayConnection> _connections = new(StringComparer.Ordinal);
+    private long _forwardedJetStreamClusterMessages;
 
     private CancellationTokenSource? _cts;
     private Socket? _listener;
     private Task? _acceptLoopTask;
 
     public string ListenEndpoint => $"{_options.Host}:{_options.Port}";
+    public long ForwardedJetStreamClusterMessages => Interlocked.Read(ref _forwardedJetStreamClusterMessages);
 
     public GatewayManager(
         GatewayOptions options,
@@ -65,16 +67,22 @@ public sealed class GatewayManager : IAsyncDisposable
             await connection.SendMessageAsync(subject, replyTo, payload, ct);
     }
 
-    public void PropagateLocalSubscription(string subject, string? queue)
+    public async Task ForwardJetStreamClusterMessageAsync(GatewayMessage message, CancellationToken ct)
     {
-        foreach (var connection in _connections.Values)
-            _ = connection.SendAPlusAsync(subject, queue, _cts?.Token ?? CancellationToken.None);
+        Interlocked.Increment(ref _forwardedJetStreamClusterMessages);
+        await ForwardMessageAsync(message.Subject, message.ReplyTo, message.Payload, ct);
     }
 
-    public void PropagateLocalUnsubscription(string subject, string? queue)
+    public void PropagateLocalSubscription(string account, string subject, string? queue)
     {
         foreach (var connection in _connections.Values)
-            _ = connection.SendAMinusAsync(subject, queue, _cts?.Token ?? CancellationToken.None);
+            _ = connection.SendAPlusAsync(account, subject, queue, _cts?.Token ?? CancellationToken.None);
+    }
+
+    public void PropagateLocalUnsubscription(string account, string subject, string? queue)
+    {
+        foreach (var connection in _connections.Values)
+            _ = connection.SendAMinusAsync(account, subject, queue, _cts?.Token ?? CancellationToken.None);
     }
 
     public async ValueTask DisposeAsync()
diff --git a/src/NATS.Server/Gateways/ReplyMapper.cs b/src/NATS.Server/Gateways/ReplyMapper.cs
new file mode 100644
index 0000000..120c605
--- /dev/null
+++ b/src/NATS.Server/Gateways/ReplyMapper.cs
@@ -0,0 +1,29 @@
+namespace NATS.Server.Gateways;
+
+public static class ReplyMapper
+{
+    private const string GatewayReplyPrefix = "_GR_.";
+
+    public static string? ToGatewayReply(string? replyTo, string localClusterId)
+    {
+        if (string.IsNullOrWhiteSpace(replyTo))
+            return replyTo;
+
+        return $"{GatewayReplyPrefix}{localClusterId}.{replyTo}";
+    }
+
+    public static bool TryRestoreGatewayReply(string? gatewayReply, out string restoredReply)
+    {
+        restoredReply = string.Empty;
+
+        if (string.IsNullOrWhiteSpace(gatewayReply) || !gatewayReply.StartsWith(GatewayReplyPrefix, StringComparison.Ordinal))
+            return false;
+
+        var clusterSeparator = gatewayReply.IndexOf('.', GatewayReplyPrefix.Length);
+        if (clusterSeparator < 0 || clusterSeparator == gatewayReply.Length - 1)
+            return false;
+
+        restoredReply = gatewayReply[(clusterSeparator + 1)..];
+        return true;
+    }
+}
diff --git a/src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs b/src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs
index e23c932..cfee7f4 100644
--- a/src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs
+++ b/src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs
@@ -190,9 +190,37 @@ public static class ConsumerApiHandlers
             if (root.TryGetProperty("ack_wait_ms", out var ackWaitEl) && ackWaitEl.TryGetInt32(out var ackWait))
                 config.AckWaitMs = ackWait;
 
+            if (root.TryGetProperty("max_deliver", out var maxDeliverEl) && maxDeliverEl.TryGetInt32(out var maxDeliver))
+                config.MaxDeliver = Math.Max(maxDeliver, 0);
+
             if (root.TryGetProperty("max_ack_pending", out var maxAckPendingEl) && maxAckPendingEl.TryGetInt32(out var maxAckPending))
                 config.MaxAckPending = Math.Max(maxAckPending, 0);
 
+            if (root.TryGetProperty("flow_control", out var flowControlEl) && flowControlEl.ValueKind is JsonValueKind.True or JsonValueKind.False)
+                config.FlowControl = flowControlEl.GetBoolean();
+
+            if (root.TryGetProperty("rate_limit_bps", out var rateLimitEl) && rateLimitEl.TryGetInt64(out var rateLimit))
+                config.RateLimitBps = Math.Max(rateLimit, 0);
+
+            if (root.TryGetProperty("opt_start_seq", out var optStartSeqEl) && optStartSeqEl.TryGetUInt64(out var optStartSeq))
+                config.OptStartSeq = optStartSeq;
+
+            if (root.TryGetProperty("opt_start_time_utc", out var optStartTimeEl)
+                && optStartTimeEl.ValueKind == JsonValueKind.String
+                && DateTime.TryParse(optStartTimeEl.GetString(), out var optStartTime))
+            {
+                config.OptStartTimeUtc = optStartTime.ToUniversalTime();
+            }
+
+            if (root.TryGetProperty("backoff_ms", out var backoffEl) && backoffEl.ValueKind == JsonValueKind.Array)
+            {
+                foreach (var item in backoffEl.EnumerateArray())
+                {
+                    if (item.TryGetInt32(out var backoffValue))
+                        config.BackOffMs.Add(Math.Max(backoffValue, 0));
+                }
+            }
+
             if (root.TryGetProperty("ack_policy", out var ackPolicyEl))
             {
                 var ackPolicy = ackPolicyEl.GetString();
@@ -209,6 +237,12 @@ public static class ConsumerApiHandlers
                     config.DeliverPolicy = DeliverPolicy.Last;
                 else if (string.Equals(deliver, "new", StringComparison.OrdinalIgnoreCase))
                     config.DeliverPolicy = DeliverPolicy.New;
+                else if (string.Equals(deliver, "by_start_sequence", StringComparison.OrdinalIgnoreCase))
+                    config.DeliverPolicy = DeliverPolicy.ByStartSequence;
+                else if (string.Equals(deliver, "by_start_time", StringComparison.OrdinalIgnoreCase))
+                    config.DeliverPolicy = DeliverPolicy.ByStartTime;
+                else if (string.Equals(deliver, "last_per_subject", StringComparison.OrdinalIgnoreCase))
+                    config.DeliverPolicy = DeliverPolicy.LastPerSubject;
             }
 
             if (root.TryGetProperty("replay_policy", out var replayPolicyEl))
diff --git a/src/NATS.Server/JetStream/Api/Handlers/StreamApiHandlers.cs b/src/NATS.Server/JetStream/Api/Handlers/StreamApiHandlers.cs
index 7e185bb..a8fe02b 100644
--- a/src/NATS.Server/JetStream/Api/Handlers/StreamApiHandlers.cs
+++ b/src/NATS.Server/JetStream/Api/Handlers/StreamApiHandlers.cs
@@ -220,6 +220,24 @@ public static class StreamApiHandlers
             if (root.TryGetProperty("max_age_ms", out var maxAgeMsEl) && maxAgeMsEl.TryGetInt32(out var maxAgeMs))
                 config.MaxAgeMs = maxAgeMs;
 
+            if (root.TryGetProperty("max_msg_size", out var maxMsgSizeEl) && maxMsgSizeEl.TryGetInt32(out var maxMsgSize))
+                config.MaxMsgSize = maxMsgSize;
+
+            if (root.TryGetProperty("duplicate_window_ms", out var dupWindowEl) && dupWindowEl.TryGetInt32(out var dupWindow))
+                config.DuplicateWindowMs = dupWindow;
+
+            if (root.TryGetProperty("sealed", out var sealedEl) && sealedEl.ValueKind is JsonValueKind.True or JsonValueKind.False)
+                config.Sealed = sealedEl.GetBoolean();
+
+            if (root.TryGetProperty("deny_delete", out var denyDeleteEl) && denyDeleteEl.ValueKind is JsonValueKind.True or JsonValueKind.False)
+                config.DenyDelete = denyDeleteEl.GetBoolean();
+
+            if (root.TryGetProperty("deny_purge", out var denyPurgeEl) && denyPurgeEl.ValueKind is JsonValueKind.True or JsonValueKind.False)
+                config.DenyPurge = denyPurgeEl.GetBoolean();
+
+            if (root.TryGetProperty("allow_direct", out var allowDirectEl) && allowDirectEl.ValueKind is JsonValueKind.True or JsonValueKind.False)
+                config.AllowDirect = allowDirectEl.GetBoolean();
+
             if (root.TryGetProperty("discard", out var discardEl))
             {
                 var discard = discardEl.GetString();
@@ -256,7 +274,14 @@ public static class StreamApiHandlers
                     {
                         var name = sourceNameEl.GetString();
                         if (!string.IsNullOrWhiteSpace(name))
-                            config.Sources.Add(new StreamSourceConfig { Name = name });
+                        {
+                            var sourceConfig = new StreamSourceConfig { Name = name };
+                            if (source.TryGetProperty("subject_transform_prefix", out var prefixEl))
+                                sourceConfig.SubjectTransformPrefix = prefixEl.GetString();
+                            if (source.TryGetProperty("source_account", out var accountEl))
+                                sourceConfig.SourceAccount = accountEl.GetString();
+                            config.Sources.Add(sourceConfig);
+                        }
                     }
                 }
             }
diff --git a/src/NATS.Server/JetStream/Cluster/StreamReplicaGroup.cs b/src/NATS.Server/JetStream/Cluster/StreamReplicaGroup.cs
index 284aad0..adf69e3 100644
--- a/src/NATS.Server/JetStream/Cluster/StreamReplicaGroup.cs
+++ b/src/NATS.Server/JetStream/Cluster/StreamReplicaGroup.cs
@@ -42,6 +42,30 @@ public sealed class StreamReplicaGroup
         return Task.CompletedTask;
     }
 
+    public Task ApplyPlacementAsync(IReadOnlyList<int> placement, CancellationToken ct)
+    {
+        _ = ct;
+        var targetCount = Math.Max(placement.Count, 1);
+        if (targetCount == _nodes.Count)
+            return Task.CompletedTask;
+
+        if (targetCount > _nodes.Count)
+        {
+            for (var i = _nodes.Count + 1; i <= targetCount; i++)
+                _nodes.Add(new RaftNode($"{streamNamePrefix()}-r{i}"));
+        }
+        else
+        {
+            _nodes.RemoveRange(targetCount, _nodes.Count - targetCount);
+        }
+
+        foreach (var node in _nodes)
+            node.ConfigureCluster(_nodes);
+
+        Leader = ElectLeader(_nodes[0]);
+        return Task.CompletedTask;
+    }
+
     private RaftNode SelectNextCandidate(RaftNode currentLeader)
     {
         if (_nodes.Count == 1)
@@ -62,4 +86,6 @@ public sealed class StreamReplicaGroup
 
         return candidate;
     }
+
+    private string streamNamePrefix() => StreamName.ToLowerInvariant();
 }
diff --git a/src/NATS.Server/JetStream/ConsumerManager.cs b/src/NATS.Server/JetStream/ConsumerManager.cs
index c27489b..91bca44 100644
--- a/src/NATS.Server/JetStream/ConsumerManager.cs
+++ b/src/NATS.Server/JetStream/ConsumerManager.cs
@@ -157,6 +157,10 @@ public sealed class ConsumerManager
         if (consumer.PushFrames.Count == 0)
             return null;
 
+        var frame = consumer.PushFrames.Peek();
+        if (frame.AvailableAtUtc > DateTime.UtcNow)
+            return null;
+
         return consumer.PushFrames.Dequeue();
     }
 
@@ -179,4 +183,5 @@ public sealed record ConsumerHandle(string Stream, ConsumerConfig Config)
     public Queue<StoredMessage> Pending { get; } = new();
     public Queue<PushFrame> PushFrames { get; } = new();
     public AckProcessor AckProcessor { get; } = new();
+    public DateTime NextPushDataAvailableAtUtc { get; set; }
 }
diff --git a/src/NATS.Server/JetStream/Consumers/AckProcessor.cs b/src/NATS.Server/JetStream/Consumers/AckProcessor.cs
index 9ab75ad..88a4289 100644
--- a/src/NATS.Server/JetStream/Consumers/AckProcessor.cs
+++ b/src/NATS.Server/JetStream/Consumers/AckProcessor.cs
@@ -2,22 +2,50 @@ namespace NATS.Server.JetStream.Consumers;
 
 public sealed class AckProcessor
 {
-    private readonly Dictionary<ulong, DateTime> _pending = new();
+    private readonly Dictionary<ulong, PendingState> _pending = new();
 
     public void Register(ulong sequence, int ackWaitMs)
     {
-        _pending[sequence] = DateTime.UtcNow.AddMilliseconds(Math.Max(ackWaitMs, 1));
+        if (_pending.ContainsKey(sequence))
+            return;
+
+        _pending[sequence] = new PendingState
+        {
+            DeadlineUtc = DateTime.UtcNow.AddMilliseconds(Math.Max(ackWaitMs, 1)),
+            Deliveries = 1,
+        };
     }
 
-    public ulong? NextExpired()
+    public bool TryGetExpired(out ulong sequence, out int deliveries)
     {
-        foreach (var (seq, deadline) in _pending)
+        foreach (var (seq, state) in _pending)
         {
-            if (DateTime.UtcNow >= deadline)
-                return seq;
+            if (DateTime.UtcNow >= state.DeadlineUtc)
+            {
+                sequence = seq;
+                deliveries = state.Deliveries;
+                return true;
+            }
         }
 
-        return null;
+        sequence = 0;
+        deliveries = 0;
+        return false;
+    }
+
+    public void ScheduleRedelivery(ulong sequence, int delayMs)
+    {
+        if (!_pending.TryGetValue(sequence, out var state))
+            return;
+
+        state.Deliveries++;
+        state.DeadlineUtc = DateTime.UtcNow.AddMilliseconds(Math.Max(delayMs, 1));
+        _pending[sequence] = state;
+    }
+
+    public void Drop(ulong sequence)
+    {
+        _pending.Remove(sequence);
     }
 
     public bool HasPending => _pending.Count > 0;
@@ -28,4 +56,10 @@ public sealed class AckProcessor
         foreach (var key in _pending.Keys.Where(k => k <= sequence).ToArray())
             _pending.Remove(key);
     }
+
+    private sealed class PendingState
+    {
+        public DateTime DeadlineUtc { get; set; }
+        public int Deliveries { get; set; }
+    }
 }
diff --git a/src/NATS.Server/JetStream/Consumers/PullConsumerEngine.cs b/src/NATS.Server/JetStream/Consumers/PullConsumerEngine.cs
index 3d8208c..a6469c4 100644
--- a/src/NATS.Server/JetStream/Consumers/PullConsumerEngine.cs
+++ b/src/NATS.Server/JetStream/Consumers/PullConsumerEngine.cs
@@ -16,11 +16,7 @@ public sealed class PullConsumerEngine
 
         if (consumer.NextSequence == 1)
         {
-            var state = await stream.Store.GetStateAsync(ct);
-            if (consumer.Config.DeliverPolicy == DeliverPolicy.Last && state.LastSeq > 0)
-                consumer.NextSequence = state.LastSeq;
-            else if (consumer.Config.DeliverPolicy == DeliverPolicy.New && state.LastSeq > 0)
-                consumer.NextSequence = state.LastSeq + 1;
+            consumer.NextSequence = await ResolveInitialSequenceAsync(stream, consumer.Config, ct);
         }
 
         if (request.NoWait)
@@ -32,9 +28,19 @@ public sealed class PullConsumerEngine
 
         if (consumer.Config.AckPolicy == AckPolicy.Explicit)
         {
-            var expired = consumer.AckProcessor.NextExpired();
-            if (expired is { } expiredSequence)
+            if (consumer.AckProcessor.TryGetExpired(out var expiredSequence, out var deliveries))
             {
+                if (consumer.Config.MaxDeliver > 0 && deliveries > consumer.Config.MaxDeliver)
+                {
+                    consumer.AckProcessor.Drop(expiredSequence);
+                    return new PullFetchBatch(messages);
+                }
+
+                var backoff = consumer.Config.BackOffMs.Count >= deliveries
+                    ? consumer.Config.BackOffMs[deliveries - 1]
+                    : consumer.Config.AckWaitMs;
+                consumer.AckProcessor.ScheduleRedelivery(expiredSequence, backoff);
+
                 var redelivery = await stream.Store.LoadAsync(expiredSequence, ct);
                 if (redelivery != null)
                 {
@@ -86,6 +92,27 @@ public sealed class PullConsumerEngine
         return new PullFetchBatch(messages);
     }
 
+    private static async ValueTask<ulong> ResolveInitialSequenceAsync(StreamHandle stream, ConsumerConfig config, CancellationToken ct)
+    {
+        var state = await stream.Store.GetStateAsync(ct);
+        return config.DeliverPolicy switch
+        {
+            DeliverPolicy.Last when state.LastSeq > 0 => state.LastSeq,
+            DeliverPolicy.New when state.LastSeq > 0 => state.LastSeq + 1,
+            DeliverPolicy.ByStartSequence when config.OptStartSeq > 0 => config.OptStartSeq,
+            DeliverPolicy.ByStartTime when config.OptStartTimeUtc is { } startTime => await ResolveByStartTimeAsync(stream, startTime, ct),
+            DeliverPolicy.LastPerSubject when state.LastSeq > 0 => state.LastSeq,
+            _ => 1,
+        };
+    }
+
+    private static async ValueTask<ulong> ResolveByStartTimeAsync(StreamHandle stream, DateTime startTimeUtc, CancellationToken ct)
+    {
+        var messages = await stream.Store.ListAsync(ct);
+        var match = messages.FirstOrDefault(m => m.TimestampUtc >= startTimeUtc);
+        return match?.Sequence ?? 1UL;
+    }
+
     private static bool MatchesFilter(ConsumerConfig config, string subject)
     {
         if (config.FilterSubjects.Count > 0)
diff --git a/src/NATS.Server/JetStream/Consumers/PushConsumerEngine.cs b/src/NATS.Server/JetStream/Consumers/PushConsumerEngine.cs
index 22e35eb..d937974 100644
--- a/src/NATS.Server/JetStream/Consumers/PushConsumerEngine.cs
+++ b/src/NATS.Server/JetStream/Consumers/PushConsumerEngine.cs
@@ -7,20 +7,41 @@ public sealed class PushConsumerEngine
 {
     public void Enqueue(ConsumerHandle consumer, StoredMessage message)
     {
+        var availableAtUtc = DateTime.UtcNow;
+        if (consumer.Config.RateLimitBps > 0)
+        {
+            if (consumer.NextPushDataAvailableAtUtc > availableAtUtc)
+                availableAtUtc = consumer.NextPushDataAvailableAtUtc;
+
+            var delayMs = (long)Math.Ceiling((double)message.Payload.Length * 1000 / consumer.Config.RateLimitBps);
+            consumer.NextPushDataAvailableAtUtc = availableAtUtc.AddMilliseconds(Math.Max(delayMs, 1));
+        }
+
         consumer.PushFrames.Enqueue(new PushFrame
         {
             IsData = true,
             Message = message,
+            AvailableAtUtc = availableAtUtc,
         });
 
         if (consumer.Config.AckPolicy is AckPolicy.Explicit or AckPolicy.All)
             consumer.AckProcessor.Register(message.Sequence, consumer.Config.AckWaitMs);
 
+        if (consumer.Config.FlowControl)
+        {
+            consumer.PushFrames.Enqueue(new PushFrame
+            {
+                IsFlowControl = true,
+                AvailableAtUtc = availableAtUtc,
+            });
+        }
+
         if (consumer.Config.HeartbeatMs > 0)
         {
             consumer.PushFrames.Enqueue(new PushFrame
             {
                 IsHeartbeat = true,
+                AvailableAtUtc = availableAtUtc,
             });
         }
     }
@@ -29,6 +50,8 @@ public sealed class PushConsumerEngine
 public sealed class PushFrame
 {
     public bool IsData { get; init; }
+    public bool IsFlowControl { get; init; }
     public bool IsHeartbeat { get; init; }
     public StoredMessage? Message { get; init; }
+    public DateTime AvailableAtUtc { get; init; } = DateTime.UtcNow;
 }
diff --git a/src/NATS.Server/JetStream/JetStreamService.cs b/src/NATS.Server/JetStream/JetStreamService.cs
index 939325f..56fbee6 100644
--- a/src/NATS.Server/JetStream/JetStreamService.cs
+++ b/src/NATS.Server/JetStream/JetStreamService.cs
@@ -1,15 +1,18 @@
 using NATS.Server.Configuration;
+using NATS.Server;
 
 namespace NATS.Server.JetStream;
 
 public sealed class JetStreamService : IAsyncDisposable
 {
     private readonly JetStreamOptions _options;
+    public InternalClient? InternalClient { get; }
     public bool IsRunning { get; private set; }
 
-    public JetStreamService(JetStreamOptions options)
+    public JetStreamService(JetStreamOptions options, InternalClient? internalClient = null)
     {
         _options = options;
+        InternalClient = internalClient;
     }
 
     public Task StartAsync(CancellationToken ct)
diff --git a/src/NATS.Server/JetStream/MirrorSource/MirrorCoordinator.cs b/src/NATS.Server/JetStream/MirrorSource/MirrorCoordinator.cs
index d66ab04..b439d51 100644
--- a/src/NATS.Server/JetStream/MirrorSource/MirrorCoordinator.cs
+++ b/src/NATS.Server/JetStream/MirrorSource/MirrorCoordinator.cs
@@ -5,12 +5,18 @@ namespace NATS.Server.JetStream.MirrorSource;
 public sealed class MirrorCoordinator
 {
     private readonly IStreamStore _targetStore;
+    public ulong LastOriginSequence { get; private set; }
+    public DateTime LastSyncUtc { get; private set; }
 
     public MirrorCoordinator(IStreamStore targetStore)
     {
         _targetStore = targetStore;
     }
 
-    public Task OnOriginAppendAsync(StoredMessage message, CancellationToken ct)
-        => _targetStore.AppendAsync(message.Subject, message.Payload, ct).AsTask();
+    public async Task OnOriginAppendAsync(StoredMessage message, CancellationToken ct)
+    {
+        await _targetStore.AppendAsync(message.Subject, message.Payload, ct);
+        LastOriginSequence = message.Sequence;
+        LastSyncUtc = DateTime.UtcNow;
+    }
 }
diff --git a/src/NATS.Server/JetStream/MirrorSource/SourceCoordinator.cs b/src/NATS.Server/JetStream/MirrorSource/SourceCoordinator.cs
index c011ac5..0c8c669 100644
--- a/src/NATS.Server/JetStream/MirrorSource/SourceCoordinator.cs
+++ b/src/NATS.Server/JetStream/MirrorSource/SourceCoordinator.cs
@@ -1,16 +1,29 @@
 using NATS.Server.JetStream.Storage;
+using NATS.Server.JetStream.Models;
 
 namespace NATS.Server.JetStream.MirrorSource;
 
 public sealed class SourceCoordinator
 {
     private readonly IStreamStore _targetStore;
+    private readonly StreamSourceConfig _sourceConfig;
+    public ulong LastOriginSequence { get; private set; }
+    public DateTime LastSyncUtc { get; private set; }
 
-    public SourceCoordinator(IStreamStore targetStore)
+    public SourceCoordinator(IStreamStore targetStore, StreamSourceConfig sourceConfig)
     {
         _targetStore = targetStore;
+        _sourceConfig = sourceConfig;
     }
 
-    public Task OnOriginAppendAsync(StoredMessage message, CancellationToken ct)
-        => _targetStore.AppendAsync(message.Subject, message.Payload, ct).AsTask();
+    public async Task OnOriginAppendAsync(StoredMessage message, CancellationToken ct)
+    {
+        var subject = message.Subject;
+        if (!string.IsNullOrWhiteSpace(_sourceConfig.SubjectTransformPrefix))
+            subject = $"{_sourceConfig.SubjectTransformPrefix}{subject}";
+
+        await _targetStore.AppendAsync(subject, message.Payload, ct);
+        LastOriginSequence = message.Sequence;
+        LastSyncUtc = DateTime.UtcNow;
+    }
 }
diff --git a/src/NATS.Server/JetStream/Models/ConsumerConfig.cs b/src/NATS.Server/JetStream/Models/ConsumerConfig.cs
index 6fd1ff9..1dbbbc7 100644
--- a/src/NATS.Server/JetStream/Models/ConsumerConfig.cs
+++ b/src/NATS.Server/JetStream/Models/ConsumerConfig.cs
@@ -8,12 +8,17 @@ public sealed class ConsumerConfig
     public List<string> FilterSubjects { get; set; } = [];
     public AckPolicy AckPolicy { get; set; } = AckPolicy.None;
     public DeliverPolicy DeliverPolicy { get; set; } = DeliverPolicy.All;
+    public ulong OptStartSeq { get; set; }
+    public DateTime? OptStartTimeUtc { get; set; }
     public ReplayPolicy ReplayPolicy { get; set; } = ReplayPolicy.Instant;
     public int AckWaitMs { get; set; } = 30_000;
     public int MaxDeliver { get; set; } = 1;
     public int MaxAckPending { get; set; }
     public bool Push { get; set; }
     public int HeartbeatMs { get; set; }
+    public List<int> BackOffMs { get; set; } = [];
+    public bool FlowControl { get; set; }
+    public long RateLimitBps { get; set; }
 }
 
 public enum AckPolicy
diff --git a/src/NATS.Server/JetStream/Models/StreamConfig.cs b/src/NATS.Server/JetStream/Models/StreamConfig.cs
index 5b1fb14..3cd2dd8 100644
--- a/src/NATS.Server/JetStream/Models/StreamConfig.cs
+++ b/src/NATS.Server/JetStream/Models/StreamConfig.cs
@@ -8,7 +8,13 @@ public sealed class StreamConfig
     public long MaxBytes { get; set; }
     public int MaxMsgsPer { get; set; }
     public int MaxAgeMs { get; set; }
+    public int MaxMsgSize { get; set; }
     public int MaxConsumers { get; set; }
+    public int DuplicateWindowMs { get; set; }
+    public bool Sealed { get; set; }
+    public bool DenyDelete { get; set; }
+    public bool DenyPurge { get; set; }
+    public bool AllowDirect { get; set; }
     public RetentionPolicy Retention { get; set; } = RetentionPolicy.Limits;
     public DiscardPolicy Discard { get; set; } = DiscardPolicy.Old;
     public StorageType Storage { get; set; } = StorageType.Memory;
@@ -27,4 +33,6 @@ public enum StorageType
 public sealed class StreamSourceConfig
 {
     public string Name { get; set; } = string.Empty;
+    public string? SubjectTransformPrefix { get; set; }
+    public string? SourceAccount { get; set; }
 }
diff --git a/src/NATS.Server/JetStream/Publish/JetStreamPublisher.cs b/src/NATS.Server/JetStream/Publish/JetStreamPublisher.cs
index 486c35e..b294a14 100644
--- a/src/NATS.Server/JetStream/Publish/JetStreamPublisher.cs
+++ b/src/NATS.Server/JetStream/Publish/JetStreamPublisher.cs
@@ -34,7 +34,7 @@ public sealed class JetStreamPublisher
             return true;
         }
 
-        if (_preconditions.IsDuplicate(options.MsgId, out var existingSequence))
+        if (_preconditions.IsDuplicate(options.MsgId, stream.Config.DuplicateWindowMs, out var existingSequence))
         {
             ack = new PubAck
             {
@@ -47,6 +47,7 @@ public sealed class JetStreamPublisher
         var captured = _streamManager.Capture(subject, payload);
         ack = captured ?? new PubAck();
         _preconditions.Record(options.MsgId, ack.Seq);
+        _preconditions.TrimOlderThan(stream.Config.DuplicateWindowMs);
         return true;
     }
 }
diff --git a/src/NATS.Server/JetStream/Publish/PublishPreconditions.cs b/src/NATS.Server/JetStream/Publish/PublishPreconditions.cs
index fb573b3..6566583 100644
--- a/src/NATS.Server/JetStream/Publish/PublishPreconditions.cs
+++ b/src/NATS.Server/JetStream/Publish/PublishPreconditions.cs
@@ -4,15 +4,26 @@ namespace NATS.Server.JetStream.Publish;
 
 public sealed class PublishPreconditions
 {
-    private readonly ConcurrentDictionary<string, ulong> _dedupe = new(StringComparer.Ordinal);
+    private readonly ConcurrentDictionary<string, DedupeEntry> _dedupe = new(StringComparer.Ordinal);
 
-    public bool IsDuplicate(string? msgId, out ulong existingSequence)
+    public bool IsDuplicate(string? msgId, int duplicateWindowMs, out ulong existingSequence)
     {
         existingSequence = 0;
         if (string.IsNullOrEmpty(msgId))
             return false;
 
-        return _dedupe.TryGetValue(msgId, out existingSequence);
+        if (!_dedupe.TryGetValue(msgId, out var entry))
+            return false;
+
+        if (duplicateWindowMs > 0
+            && DateTime.UtcNow - entry.TimestampUtc > TimeSpan.FromMilliseconds(duplicateWindowMs))
+        {
+            _dedupe.TryRemove(msgId, out _);
+            return false;
+        }
+
+        existingSequence = entry.Sequence;
+        return true;
     }
 
     public void Record(string? msgId, ulong sequence)
@@ -20,9 +31,24 @@ public sealed class PublishPreconditions
         if (string.IsNullOrEmpty(msgId))
             return;
 
-        _dedupe[msgId] = sequence;
+        _dedupe[msgId] = new DedupeEntry(sequence, DateTime.UtcNow);
+    }
+
+    public void TrimOlderThan(int duplicateWindowMs)
+    {
+        if (duplicateWindowMs <= 0)
+            return;
+
+        var cutoff = DateTime.UtcNow.AddMilliseconds(-duplicateWindowMs);
+        foreach (var (key, entry) in _dedupe)
+        {
+            if (entry.TimestampUtc < cutoff)
+                _dedupe.TryRemove(key, out _);
+        }
     }
 
     public bool CheckExpectedLastSeq(ulong expectedLastSeq, ulong actualLastSeq)
         => expectedLastSeq == 0 || expectedLastSeq == actualLastSeq;
+
+    private readonly record struct DedupeEntry(ulong Sequence, DateTime TimestampUtc);
 }
diff --git a/src/NATS.Server/JetStream/Storage/FileStore.cs b/src/NATS.Server/JetStream/Storage/FileStore.cs
index 677f30a..fc57f26 100644
--- a/src/NATS.Server/JetStream/Storage/FileStore.cs
+++ b/src/NATS.Server/JetStream/Storage/FileStore.cs
@@ -1,3 +1,4 @@
+using System.Text;
 using System.Text.Json;
 using NATS.Server.JetStream.Models;
 
@@ -5,12 +6,23 @@ namespace NATS.Server.JetStream.Storage;
 
 public sealed class FileStore : IStreamStore, IAsyncDisposable
 {
+    private readonly FileStoreOptions _options;
     private readonly string _dataFilePath;
     private readonly Dictionary<ulong, StoredMessage> _messages = new();
+    private readonly Dictionary<ulong, BlockPointer> _index = new();
     private ulong _last;
+    private int _blockCount;
+    private long _activeBlockBytes;
+    private long _writeOffset;
+
+    public int BlockCount => _messages.Count == 0 ? 0 : Math.Max(_blockCount, 1);
 
     public FileStore(FileStoreOptions options)
     {
+        _options = options;
+        if (_options.BlockSizeBytes <= 0)
+            _options.BlockSizeBytes = 64 * 1024;
+
         Directory.CreateDirectory(options.Directory);
         _dataFilePath = Path.Combine(options.Directory, "messages.jsonl");
         LoadExisting();
@@ -18,6 +30,8 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
 
     public async ValueTask<ulong> AppendAsync(string subject, ReadOnlyMemory<byte> payload, CancellationToken ct)
     {
+        PruneExpired(DateTime.UtcNow);
+
         _last++;
         var stored = new StoredMessage
         {
@@ -36,6 +50,9 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
             TimestampUtc = stored.TimestampUtc,
         });
         await File.AppendAllTextAsync(_dataFilePath, line + Environment.NewLine, ct);
+
+        var recordBytes = Encoding.UTF8.GetByteCount(line + Environment.NewLine);
+        TrackBlockForRecord(recordBytes, stored.Sequence);
         return _last;
     }
 
@@ -54,6 +71,14 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
         return ValueTask.FromResult(match);
     }
 
+    public ValueTask<IReadOnlyList<StoredMessage>> ListAsync(CancellationToken ct)
+    {
+        var messages = _messages.Values
+            .OrderBy(m => m.Sequence)
+            .ToArray();
+        return ValueTask.FromResult<IReadOnlyList<StoredMessage>>(messages);
+    }
+
     public ValueTask<bool> RemoveAsync(ulong sequence, CancellationToken ct)
     {
         var removed = _messages.Remove(sequence);
@@ -65,7 +90,11 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
     public ValueTask PurgeAsync(CancellationToken ct)
     {
         _messages.Clear();
+        _index.Clear();
         _last = 0;
+        _blockCount = 0;
+        _activeBlockBytes = 0;
+        _writeOffset = 0;
         if (File.Exists(_dataFilePath))
             File.Delete(_dataFilePath);
         return ValueTask.CompletedTask;
@@ -90,7 +119,11 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
     public ValueTask RestoreSnapshotAsync(ReadOnlyMemory<byte> snapshot, CancellationToken ct)
     {
         _messages.Clear();
+        _index.Clear();
         _last = 0;
+        _blockCount = 0;
+        _activeBlockBytes = 0;
+        _writeOffset = 0;
 
         if (!snapshot.IsEmpty)
         {
@@ -159,29 +192,83 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
                 Sequence = record.Sequence,
                 Subject = record.Subject ?? string.Empty,
                 Payload = Convert.FromBase64String(record.PayloadBase64 ?? string.Empty),
+                TimestampUtc = record.TimestampUtc,
             };
 
             _messages[message.Sequence] = message;
             if (message.Sequence > _last)
                 _last = message.Sequence;
+
+            var recordBytes = Encoding.UTF8.GetByteCount(line + Environment.NewLine);
+            TrackBlockForRecord(recordBytes, message.Sequence);
         }
+
+        PruneExpired(DateTime.UtcNow);
     }
 
     private void RewriteDataFile()
     {
-        var lines = new List<string>(_messages.Count);
+        Directory.CreateDirectory(Path.GetDirectoryName(_dataFilePath)!);
+        _index.Clear();
+        _blockCount = 0;
+        _activeBlockBytes = 0;
+        _writeOffset = 0;
+
+        using var stream = new FileStream(_dataFilePath, FileMode.Create, FileAccess.Write, FileShare.Read);
+        using var writer = new StreamWriter(stream, Encoding.UTF8);
+
         foreach (var message in _messages.OrderBy(kv => kv.Key).Select(kv => kv.Value))
         {
-            lines.Add(JsonSerializer.Serialize(new FileRecord
+            var line = JsonSerializer.Serialize(new FileRecord
             {
                 Sequence = message.Sequence,
                 Subject = message.Subject,
                 PayloadBase64 = Convert.ToBase64String(message.Payload.ToArray()),
                 TimestampUtc = message.TimestampUtc,
-            }));
+            });
+
+            writer.WriteLine(line);
+            var recordBytes = Encoding.UTF8.GetByteCount(line + Environment.NewLine);
+            TrackBlockForRecord(recordBytes, message.Sequence);
         }
 
-        File.WriteAllLines(_dataFilePath, lines);
+        writer.Flush();
+    }
+
+    private void TrackBlockForRecord(int recordBytes, ulong sequence)
+    {
+        if (_blockCount == 0)
+            _blockCount = 1;
+
+        if (_activeBlockBytes > 0 && _activeBlockBytes + recordBytes > _options.BlockSizeBytes)
+        {
+            _blockCount++;
+            _activeBlockBytes = 0;
+        }
+
+        _index[sequence] = new BlockPointer(_blockCount, _writeOffset);
+        _activeBlockBytes += recordBytes;
+        _writeOffset += recordBytes;
+    }
+
+    private void PruneExpired(DateTime nowUtc)
+    {
+        if (_options.MaxAgeMs <= 0)
+            return;
+
+        var cutoff = nowUtc.AddMilliseconds(-_options.MaxAgeMs);
+        var expired = _messages
+            .Where(kv => kv.Value.TimestampUtc < cutoff)
+            .Select(kv => kv.Key)
+            .ToArray();
+
+        if (expired.Length == 0)
+            return;
+
+        foreach (var sequence in expired)
+            _messages.Remove(sequence);
+
+        RewriteDataFile();
     }
 
     private sealed class FileRecord
@@ -191,4 +278,6 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
         public string? PayloadBase64 { get; init; }
         public DateTime TimestampUtc { get; init; }
     }
+
+    private readonly record struct BlockPointer(int BlockId, long Offset);
 }
diff --git a/src/NATS.Server/JetStream/Storage/FileStoreBlock.cs b/src/NATS.Server/JetStream/Storage/FileStoreBlock.cs
index 4d4689f..76d723a 100644
--- a/src/NATS.Server/JetStream/Storage/FileStoreBlock.cs
+++ b/src/NATS.Server/JetStream/Storage/FileStoreBlock.cs
@@ -2,5 +2,7 @@ namespace NATS.Server.JetStream.Storage;
 
 public sealed class FileStoreBlock
 {
+    public int Id { get; init; }
     public required string Path { get; init; }
+    public long SizeBytes { get; set; }
 }
diff --git a/src/NATS.Server/JetStream/Storage/FileStoreOptions.cs b/src/NATS.Server/JetStream/Storage/FileStoreOptions.cs
index 17bf85d..28eca98 100644
--- a/src/NATS.Server/JetStream/Storage/FileStoreOptions.cs
+++ b/src/NATS.Server/JetStream/Storage/FileStoreOptions.cs
@@ -3,4 +3,6 @@ namespace NATS.Server.JetStream.Storage;
 public sealed class FileStoreOptions
 {
     public string Directory { get; set; } = string.Empty;
+    public int BlockSizeBytes { get; set; } = 64 * 1024;
+    public int MaxAgeMs { get; set; }
 }
diff --git a/src/NATS.Server/JetStream/Storage/IStreamStore.cs b/src/NATS.Server/JetStream/Storage/IStreamStore.cs
index ca64553..4498e7b 100644
--- a/src/NATS.Server/JetStream/Storage/IStreamStore.cs
+++ b/src/NATS.Server/JetStream/Storage/IStreamStore.cs
@@ -7,6 +7,7 @@ public interface IStreamStore
     ValueTask<ulong> AppendAsync(string subject, ReadOnlyMemory<byte> payload, CancellationToken ct);
     ValueTask<StoredMessage?> LoadAsync(ulong sequence, CancellationToken ct);
     ValueTask<StoredMessage?> LoadLastBySubjectAsync(string subject, CancellationToken ct);
+    ValueTask<IReadOnlyList<StoredMessage>> ListAsync(CancellationToken ct);
     ValueTask<bool> RemoveAsync(ulong sequence, CancellationToken ct);
     ValueTask PurgeAsync(CancellationToken ct);
     ValueTask<byte[]> CreateSnapshotAsync(CancellationToken ct);
diff --git a/src/NATS.Server/JetStream/Storage/MemStore.cs b/src/NATS.Server/JetStream/Storage/MemStore.cs
index 8bd1485..1e6d111 100644
--- a/src/NATS.Server/JetStream/Storage/MemStore.cs
+++ b/src/NATS.Server/JetStream/Storage/MemStore.cs
@@ -54,6 +54,17 @@ public sealed class MemStore : IStreamStore
         }
     }
 
+    public ValueTask<IReadOnlyList<StoredMessage>> ListAsync(CancellationToken ct)
+    {
+        lock (_gate)
+        {
+            var messages = _messages.Values
+                .OrderBy(m => m.Sequence)
+                .ToArray();
+            return ValueTask.FromResult<IReadOnlyList<StoredMessage>>(messages);
+        }
+    }
+
     public ValueTask<bool> RemoveAsync(ulong sequence, CancellationToken ct)
     {
         lock (_gate)
diff --git a/src/NATS.Server/JetStream/StreamManager.cs b/src/NATS.Server/JetStream/StreamManager.cs
index f3c407c..730ae61 100644
--- a/src/NATS.Server/JetStream/StreamManager.cs
+++ b/src/NATS.Server/JetStream/StreamManager.cs
@@ -93,6 +93,8 @@ public sealed class StreamManager
     {
         if (!_streams.TryGetValue(name, out var stream))
             return false;
+        if (stream.Config.Sealed || stream.Config.DenyPurge)
+            return false;
 
         stream.Store.PurgeAsync(default).GetAwaiter().GetResult();
         return true;
@@ -110,6 +112,8 @@ public sealed class StreamManager
     {
         if (!_streams.TryGetValue(name, out var stream))
             return false;
+        if (stream.Config.Sealed || stream.Config.DenyDelete)
+            return false;
 
         return stream.Store.RemoveAsync(sequence, default).GetAwaiter().GetResult();
     }
@@ -156,6 +160,17 @@ public sealed class StreamManager
         if (stream == null)
             return null;
 
+        if (stream.Config.MaxMsgSize > 0 && payload.Length > stream.Config.MaxMsgSize)
+        {
+            return new PubAck
+            {
+                Stream = stream.Config.Name,
+                ErrorCode = 10054,
+            };
+        }
+
+        PruneExpiredMessages(stream, DateTime.UtcNow);
+
         var stateBefore = stream.Store.GetStateAsync(default).GetAwaiter().GetResult();
         if (stream.Config.MaxBytes > 0 && (long)stateBefore.Bytes + payload.Length > stream.Config.MaxBytes)
         {
@@ -179,7 +194,7 @@ public sealed class StreamManager
             _ = replicaGroup.ProposeAsync($"PUB {subject}", default).GetAwaiter().GetResult();
 
         var seq = stream.Store.AppendAsync(subject, payload, default).GetAwaiter().GetResult();
-        EnforceLimits(stream);
+        EnforceRuntimePolicies(stream, DateTime.UtcNow);
         var stored = stream.Store.LoadAsync(seq, default).GetAwaiter().GetResult();
         if (stored != null)
             ReplicateIfConfigured(stream.Config.Name, stored);
@@ -209,14 +224,25 @@ public sealed class StreamManager
             MaxBytes = config.MaxBytes,
             MaxMsgsPer = config.MaxMsgsPer,
             MaxAgeMs = config.MaxAgeMs,
+            MaxMsgSize = config.MaxMsgSize,
             MaxConsumers = config.MaxConsumers,
+            DuplicateWindowMs = config.DuplicateWindowMs,
+            Sealed = config.Sealed,
+            DenyDelete = config.DenyDelete,
+            DenyPurge = config.DenyPurge,
+            AllowDirect = config.AllowDirect,
             Retention = config.Retention,
             Discard = config.Discard,
             Storage = config.Storage,
             Replicas = config.Replicas,
             Mirror = config.Mirror,
             Source = config.Source,
-            Sources = config.Sources.Count == 0 ? [] : [.. config.Sources.Select(s => new StreamSourceConfig { Name = s.Name })],
+            Sources = config.Sources.Count == 0 ? [] : [.. config.Sources.Select(s => new StreamSourceConfig
+            {
+                Name = s.Name,
+                SubjectTransformPrefix = s.SubjectTransformPrefix,
+                SourceAccount = s.SourceAccount,
+            })],
         };
 
         return copy;
@@ -235,6 +261,13 @@ public sealed class StreamManager
         };
     }
 
+    private static void EnforceRuntimePolicies(StreamHandle stream, DateTime nowUtc)
+    {
+        EnforceLimits(stream);
+        PrunePerSubject(stream);
+        PruneExpiredMessages(stream, nowUtc);
+    }
+
     private static void EnforceLimits(StreamHandle stream)
     {
         if (stream.Config.MaxMsgs <= 0)
@@ -251,6 +284,34 @@ public sealed class StreamManager
             fileStore.TrimToMaxMessages(maxMessages);
     }
 
+    private static void PrunePerSubject(StreamHandle stream)
+    {
+        if (stream.Config.MaxMsgsPer <= 0)
+            return;
+
+        var maxPerSubject = stream.Config.MaxMsgsPer;
+        var messages = stream.Store.ListAsync(default).GetAwaiter().GetResult();
+        foreach (var group in messages.GroupBy(m => m.Subject, StringComparer.Ordinal))
+        {
+            foreach (var message in group.OrderByDescending(m => m.Sequence).Skip(maxPerSubject))
+                stream.Store.RemoveAsync(message.Sequence, default).GetAwaiter().GetResult();
+        }
+    }
+
+    private static void PruneExpiredMessages(StreamHandle stream, DateTime nowUtc)
+    {
+        if (stream.Config.MaxAgeMs <= 0)
+            return;
+
+        var cutoff = nowUtc.AddMilliseconds(-stream.Config.MaxAgeMs);
+        var messages = stream.Store.ListAsync(default).GetAwaiter().GetResult();
+        foreach (var message in messages)
+        {
+            if (message.TimestampUtc < cutoff)
+                stream.Store.RemoveAsync(message.Sequence, default).GetAwaiter().GetResult();
+        }
+    }
+
     private void RebuildReplicationCoordinators()
     {
         _mirrorsByOrigin.Clear();
@@ -269,7 +330,7 @@ public sealed class StreamManager
                 && _streams.TryGetValue(stream.Config.Source, out _))
             {
                 var list = _sourcesByOrigin.GetOrAdd(stream.Config.Source, _ => []);
-                list.Add(new SourceCoordinator(stream.Store));
+                list.Add(new SourceCoordinator(stream.Store, new StreamSourceConfig { Name = stream.Config.Source }));
             }
 
             if (stream.Config.Sources.Count > 0)
@@ -280,7 +341,7 @@ public sealed class StreamManager
                         continue;
 
                     var list = _sourcesByOrigin.GetOrAdd(source.Name, _ => []);
-                    list.Add(new SourceCoordinator(stream.Store));
+                    list.Add(new SourceCoordinator(stream.Store, source));
                 }
             }
         }
@@ -320,6 +381,7 @@ public sealed class StreamManager
             StorageType.File => new FileStore(new FileStoreOptions
             {
                 Directory = Path.Combine(Path.GetTempPath(), "natsdotnet-js-store", config.Name),
+                MaxAgeMs = config.MaxAgeMs,
             }),
             _ => new MemStore(),
         };
diff --git a/src/NATS.Server/JetStream/Validation/JetStreamConfigValidator.cs b/src/NATS.Server/JetStream/Validation/JetStreamConfigValidator.cs
index ed7ff60..f673e42 100644
--- a/src/NATS.Server/JetStream/Validation/JetStreamConfigValidator.cs
+++ b/src/NATS.Server/JetStream/Validation/JetStreamConfigValidator.cs
@@ -11,6 +11,12 @@ public static class JetStreamConfigValidator
 
         if (config.Retention == RetentionPolicy.WorkQueue && config.MaxConsumers == 0)
             return ValidationResult.Invalid("workqueue retention requires max consumers > 0");
+        if (config.MaxMsgSize < 0)
+            return ValidationResult.Invalid("max_msg_size must be >= 0");
+        if (config.MaxMsgsPer < 0)
+            return ValidationResult.Invalid("max_msgs_per must be >= 0");
+        if (config.MaxAgeMs < 0)
+            return ValidationResult.Invalid("max_age_ms must be >= 0");
 
         return ValidationResult.Valid();
     }
diff --git a/src/NATS.Server/LeafNodes/LeafConnection.cs b/src/NATS.Server/LeafNodes/LeafConnection.cs
index cc0a834..6044c3b 100644
--- a/src/NATS.Server/LeafNodes/LeafConnection.cs
+++ b/src/NATS.Server/LeafNodes/LeafConnection.cs
@@ -42,11 +42,11 @@ public sealed class LeafConnection(Socket socket) : IAsyncDisposable
     public Task WaitUntilClosedAsync(CancellationToken ct)
         => _loopTask?.WaitAsync(ct) ?? Task.CompletedTask;
 
-    public Task SendLsPlusAsync(string subject, string? queue, CancellationToken ct)
-        => WriteLineAsync(queue is { Length: > 0 } ? $"LS+ {subject} {queue}" : $"LS+ {subject}", ct);
+    public Task SendLsPlusAsync(string account, string subject, string? queue, CancellationToken ct)
+        => WriteLineAsync(queue is { Length: > 0 } ? $"LS+ {account} {subject} {queue}" : $"LS+ {account} {subject}", ct);
 
-    public Task SendLsMinusAsync(string subject, string? queue, CancellationToken ct)
-        => WriteLineAsync(queue is { Length: > 0 } ? $"LS- {subject} {queue}" : $"LS- {subject}", ct);
+    public Task SendLsMinusAsync(string account, string subject, string? queue, CancellationToken ct)
+        => WriteLineAsync(queue is { Length: > 0 } ? $"LS- {account} {subject} {queue}" : $"LS- {account} {subject}", ct);
 
     public async Task SendMessageAsync(string subject, string? replyTo, ReadOnlyMemory<byte> payload, CancellationToken ct)
     {
@@ -94,10 +94,9 @@ public sealed class LeafConnection(Socket socket) : IAsyncDisposable
             if (line.StartsWith("LS+ ", StringComparison.Ordinal))
             {
                 var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                if (parts.Length >= 2 && RemoteSubscriptionReceived != null)
+                if (RemoteSubscriptionReceived != null && TryParseAccountScopedInterest(parts, out var account, out var parsedSubject, out var queue))
                 {
-                    var queue = parts.Length >= 3 ? parts[2] : null;
-                    await RemoteSubscriptionReceived(new RemoteSubscription(parts[1], queue, RemoteId ?? string.Empty));
+                    await RemoteSubscriptionReceived(new RemoteSubscription(parsedSubject, queue, RemoteId ?? string.Empty, account));
                 }
                 continue;
             }
@@ -105,10 +104,9 @@ public sealed class LeafConnection(Socket socket) : IAsyncDisposable
             if (line.StartsWith("LS- ", StringComparison.Ordinal))
             {
                 var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                if (parts.Length >= 2 && RemoteSubscriptionReceived != null)
+                if (RemoteSubscriptionReceived != null && TryParseAccountScopedInterest(parts, out var account, out var parsedSubject, out var queue))
                 {
-                    var queue = parts.Length >= 3 ? parts[2] : null;
-                    await RemoteSubscriptionReceived(RemoteSubscription.Removal(parts[1], queue, RemoteId ?? string.Empty));
+                    await RemoteSubscriptionReceived(RemoteSubscription.Removal(parsedSubject, queue, RemoteId ?? string.Empty, account));
                 }
                 continue;
             }
@@ -186,6 +184,35 @@ public sealed class LeafConnection(Socket socket) : IAsyncDisposable
             throw new InvalidOperationException("Leaf handshake missing id");
         return id;
     }
+
+    private static bool TryParseAccountScopedInterest(string[] parts, out string account, out string subject, out string? queue)
+    {
+        account = "$G";
+        subject = string.Empty;
+        queue = null;
+
+        if (parts.Length < 2)
+            return false;
+
+        // New format: LS+ <account> <subject> [queue]
+        // Legacy format: LS+ <subject> [queue]
+        if (parts.Length >= 3 && !LooksLikeSubject(parts[1]))
+        {
+            account = parts[1];
+            subject = parts[2];
+            queue = parts.Length >= 4 ? parts[3] : null;
+            return true;
+        }
+
+        subject = parts[1];
+        queue = parts.Length >= 3 ? parts[2] : null;
+        return true;
+    }
+
+    private static bool LooksLikeSubject(string token)
+        => token.Contains('.', StringComparison.Ordinal)
+            || token.Contains('*', StringComparison.Ordinal)
+            || token.Contains('>', StringComparison.Ordinal);
 }
 
 public sealed record LeafMessage(string Subject, string? ReplyTo, ReadOnlyMemory<byte> Payload);
diff --git a/src/NATS.Server/LeafNodes/LeafLoopDetector.cs b/src/NATS.Server/LeafNodes/LeafLoopDetector.cs
new file mode 100644
index 0000000..90f5359
--- /dev/null
+++ b/src/NATS.Server/LeafNodes/LeafLoopDetector.cs
@@ -0,0 +1,26 @@
+namespace NATS.Server.LeafNodes;
+
+public static class LeafLoopDetector
+{
+    private const string LeafLoopPrefix = "$LDS.";
+
+    public static string Mark(string subject, string serverId)
+        => $"{LeafLoopPrefix}{serverId}.{subject}";
+
+    public static bool IsLooped(string subject, string localServerId)
+        => subject.StartsWith($"{LeafLoopPrefix}{localServerId}.", StringComparison.Ordinal);
+
+    public static bool TryUnmark(string subject, out string unmarked)
+    {
+        unmarked = subject;
+        if (!subject.StartsWith(LeafLoopPrefix, StringComparison.Ordinal))
+            return false;
+
+        var serverSeparator = subject.IndexOf('.', LeafLoopPrefix.Length);
+        if (serverSeparator < 0 || serverSeparator == subject.Length - 1)
+            return false;
+
+        unmarked = subject[(serverSeparator + 1)..];
+        return true;
+    }
+}
diff --git a/src/NATS.Server/LeafNodes/LeafNodeManager.cs b/src/NATS.Server/LeafNodes/LeafNodeManager.cs
index fb4bfc0..11546d1 100644
--- a/src/NATS.Server/LeafNodes/LeafNodeManager.cs
+++ b/src/NATS.Server/LeafNodes/LeafNodeManager.cs
@@ -64,16 +64,16 @@ public sealed class LeafNodeManager : IAsyncDisposable
             await connection.SendMessageAsync(subject, replyTo, payload, ct);
     }
 
-    public void PropagateLocalSubscription(string subject, string? queue)
+    public void PropagateLocalSubscription(string account, string subject, string? queue)
     {
         foreach (var connection in _connections.Values)
-            _ = connection.SendLsPlusAsync(subject, queue, _cts?.Token ?? CancellationToken.None);
+            _ = connection.SendLsPlusAsync(account, subject, queue, _cts?.Token ?? CancellationToken.None);
     }
 
-    public void PropagateLocalUnsubscription(string subject, string? queue)
+    public void PropagateLocalUnsubscription(string account, string subject, string? queue)
     {
         foreach (var connection in _connections.Values)
-            _ = connection.SendLsMinusAsync(subject, queue, _cts?.Token ?? CancellationToken.None);
+            _ = connection.SendLsMinusAsync(account, subject, queue, _cts?.Token ?? CancellationToken.None);
     }
 
     public async ValueTask DisposeAsync()
diff --git a/src/NATS.Server/NatsClient.cs b/src/NATS.Server/NatsClient.cs
index 239a489..b64086e 100644
--- a/src/NATS.Server/NatsClient.cs
+++ b/src/NATS.Server/NatsClient.cs
@@ -541,7 +541,7 @@ public sealed class NatsClient : INatsClient, IDisposable
 
         Account?.SubList.Insert(sub);
         if (Router is NatsServer server)
-            server.OnLocalSubscription(sub.Subject, sub.Queue);
+            server.OnLocalSubscription(Account?.Name ?? Account.GlobalAccountName, sub.Subject, sub.Queue);
     }
 
     private void ProcessUnsub(ParsedCommand cmd)
@@ -563,7 +563,7 @@ public sealed class NatsClient : INatsClient, IDisposable
 
         Account?.SubList.Remove(sub);
         if (Router is NatsServer server)
-            server.OnLocalUnsubscription(sub.Subject, sub.Queue);
+            server.OnLocalUnsubscription(Account?.Name ?? Account.GlobalAccountName, sub.Subject, sub.Queue);
     }
 
     private void ProcessPub(ParsedCommand cmd, ref long localInMsgs, ref long localInBytes)
diff --git a/src/NATS.Server/NatsServer.cs b/src/NATS.Server/NatsServer.cs
index e40c2a3..716fe86 100644
--- a/src/NATS.Server/NatsServer.cs
+++ b/src/NATS.Server/NatsServer.cs
@@ -52,6 +52,7 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
     private readonly RouteManager? _routeManager;
     private readonly GatewayManager? _gatewayManager;
     private readonly LeafNodeManager? _leafNodeManager;
+    private readonly InternalClient? _jetStreamInternalClient;
     private readonly JetStreamService? _jetStreamService;
     private readonly JetStreamApiRouter? _jetStreamApiRouter;
     private readonly StreamManager? _jetStreamStreamManager;
@@ -97,6 +98,7 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
     public string? ClusterListen => _routeManager?.ListenEndpoint;
     public string? GatewayListen => _gatewayManager?.ListenEndpoint;
     public string? LeafListen => _leafNodeManager?.ListenEndpoint;
+    public InternalClient? JetStreamInternalClient => _jetStreamInternalClient;
     public JetStreamApiRouter? JetStreamApiRouter => _jetStreamApiRouter;
     public int JetStreamStreams => _jetStreamStreamManager?.StreamNames.Count ?? 0;
     public int JetStreamConsumers => _jetStreamConsumerManager?.ConsumerCount ?? 0;
@@ -107,6 +109,8 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
 
     public IEnumerable<Auth.Account> GetAccounts() => _accounts.Values;
     public bool HasRemoteInterest(string subject) => _globalAccount.SubList.HasRemoteInterest(subject);
+    public bool HasRemoteInterest(string account, string subject)
+        => GetOrCreateAccount(account).SubList.HasRemoteInterest(account, subject);
     public bool TryCaptureJetStreamPublish(string subject, ReadOnlyMemory<byte> payload, out PubAck ack)
     {
         if (_jetStreamPublisher != null && _jetStreamPublisher.TryCapture(subject, payload, out ack))
@@ -390,7 +394,9 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
         {
             _jetStreamStreamManager = new StreamManager();
             _jetStreamConsumerManager = new ConsumerManager();
-            _jetStreamService = new JetStreamService(options.JetStream);
+            var jsClientId = Interlocked.Increment(ref _nextClientId);
+            _jetStreamInternalClient = new InternalClient(jsClientId, ClientKind.JetStream, _systemAccount);
+            _jetStreamService = new JetStreamService(options.JetStream, _jetStreamInternalClient);
             _jetStreamApiRouter = new JetStreamApiRouter(_jetStreamStreamManager, _jetStreamConsumerManager);
             _jetStreamPublisher = new JetStreamPublisher(_jetStreamStreamManager);
         }
@@ -798,23 +804,24 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
         }
     }
 
-    public void OnLocalSubscription(string subject, string? queue)
+    public void OnLocalSubscription(string account, string subject, string? queue)
     {
-        _routeManager?.PropagateLocalSubscription(subject, queue);
-        _gatewayManager?.PropagateLocalSubscription(subject, queue);
-        _leafNodeManager?.PropagateLocalSubscription(subject, queue);
+        _routeManager?.PropagateLocalSubscription(account, subject, queue);
+        _gatewayManager?.PropagateLocalSubscription(account, subject, queue);
+        _leafNodeManager?.PropagateLocalSubscription(account, subject, queue);
     }
 
-    public void OnLocalUnsubscription(string subject, string? queue)
+    public void OnLocalUnsubscription(string account, string subject, string? queue)
     {
-        _routeManager?.PropagateLocalUnsubscription(subject, queue);
-        _gatewayManager?.PropagateLocalUnsubscription(subject, queue);
-        _leafNodeManager?.PropagateLocalUnsubscription(subject, queue);
+        _routeManager?.PropagateLocalUnsubscription(account, subject, queue);
+        _gatewayManager?.PropagateLocalUnsubscription(account, subject, queue);
+        _leafNodeManager?.PropagateLocalUnsubscription(account, subject, queue);
     }
 
     private void ApplyRemoteSubscription(RemoteSubscription sub)
     {
-        _globalAccount.SubList.ApplyRemoteSub(sub);
+        var account = GetOrCreateAccount(sub.Account);
+        account.SubList.ApplyRemoteSub(sub);
     }
 
     private void ProcessRoutedMessage(RouteMessage message)
@@ -824,12 +831,23 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
 
     private void ProcessGatewayMessage(GatewayMessage message)
     {
-        DeliverRemoteMessage(message.Subject, message.ReplyTo, message.Payload);
+        var replyTo = message.ReplyTo;
+        if (ReplyMapper.TryRestoreGatewayReply(replyTo, out var restoredReply))
+            replyTo = restoredReply;
+
+        DeliverRemoteMessage(message.Subject, replyTo, message.Payload);
     }
 
     private void ProcessLeafMessage(LeafMessage message)
     {
-        DeliverRemoteMessage(message.Subject, message.ReplyTo, message.Payload);
+        if (LeafLoopDetector.IsLooped(message.Subject, ServerId))
+            return;
+
+        var subject = message.Subject;
+        if (LeafLoopDetector.TryUnmark(subject, out var unmarked))
+            subject = unmarked;
+
+        DeliverRemoteMessage(subject, message.ReplyTo, message.Payload);
     }
 
     private void DeliverRemoteMessage(string subject, string? replyTo, ReadOnlyMemory<byte> payload)
@@ -883,12 +901,20 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
             }
         }
 
-        if (_routeManager != null && _globalAccount.SubList.HasRemoteInterest(subject))
+        var senderAccount = sender.Account ?? _globalAccount;
+        if (_routeManager != null && senderAccount.SubList.HasRemoteInterest(senderAccount.Name, subject))
             _routeManager.ForwardRoutedMessageAsync(subject, replyTo, payload, default).GetAwaiter().GetResult();
-        if (_gatewayManager != null && _globalAccount.SubList.HasRemoteInterest(subject))
-            _gatewayManager.ForwardMessageAsync(subject, replyTo, payload, default).GetAwaiter().GetResult();
-        if (_leafNodeManager != null && _globalAccount.SubList.HasRemoteInterest(subject))
-            _leafNodeManager.ForwardMessageAsync(subject, replyTo, payload, default).GetAwaiter().GetResult();
+        if (_gatewayManager != null && senderAccount.SubList.HasRemoteInterest(senderAccount.Name, subject))
+        {
+            var mappedReplyTo = ReplyMapper.ToGatewayReply(replyTo, ServerId);
+            _gatewayManager.ForwardMessageAsync(subject, mappedReplyTo, payload, default).GetAwaiter().GetResult();
+        }
+
+        if (_leafNodeManager != null && senderAccount.SubList.HasRemoteInterest(senderAccount.Name, subject))
+        {
+            var markedSubject = LeafLoopDetector.Mark(subject, ServerId);
+            _leafNodeManager.ForwardMessageAsync(markedSubject, replyTo, payload, default).GetAwaiter().GetResult();
+        }
 
         var subList = sender.Account?.SubList ?? _globalAccount.SubList;
         var result = subList.Match(subject);
diff --git a/src/NATS.Server/Raft/RaftNode.cs b/src/NATS.Server/Raft/RaftNode.cs
index e67388e..9eafdcd 100644
--- a/src/NATS.Server/Raft/RaftNode.cs
+++ b/src/NATS.Server/Raft/RaftNode.cs
@@ -8,11 +8,13 @@ public sealed class RaftNode
     private readonly RaftSnapshotStore _snapshotStore = new();
     private readonly IRaftTransport? _transport;
     private readonly string? _persistDirectory;
+    private readonly HashSet<string> _members = new(StringComparer.Ordinal);
 
     public string Id { get; }
     public int Term => TermState.CurrentTerm;
     public bool IsLeader => Role == RaftRole.Leader;
     public RaftRole Role { get; private set; } = RaftRole.Follower;
+    public IReadOnlyCollection<string> Members => _members;
     public RaftTermState TermState { get; } = new();
     public long AppliedIndex { get; set; }
     public RaftLog Log { get; private set; } = new();
@@ -22,14 +24,22 @@ public sealed class RaftNode
         Id = id;
         _transport = transport;
         _persistDirectory = persistDirectory;
+        _members.Add(id);
     }
 
     public void ConfigureCluster(IEnumerable<RaftNode> peers)
     {
         _cluster.Clear();
         _cluster.AddRange(peers);
+        _members.Clear();
+        foreach (var peer in peers)
+            _members.Add(peer.Id);
     }
 
+    public void AddMember(string memberId) => _members.Add(memberId);
+
+    public void RemoveMember(string memberId) => _members.Remove(memberId);
+
     public void StartElection(int clusterSize)
     {
         Role = RaftRole.Candidate;
@@ -48,6 +58,15 @@ public sealed class RaftNode
         return new VoteResponse { Granted = true };
     }
 
+    public void ReceiveHeartbeat(int term)
+    {
+        if (term < TermState.CurrentTerm)
+            return;
+
+        TermState.CurrentTerm = term;
+        Role = RaftRole.Follower;
+    }
+
     public void ReceiveVote(VoteResponse response, int clusterSize = 3)
     {
         if (!response.Granted)
diff --git a/src/NATS.Server/Raft/RaftReplicator.cs b/src/NATS.Server/Raft/RaftReplicator.cs
index 98fef93..c0396ce 100644
--- a/src/NATS.Server/Raft/RaftReplicator.cs
+++ b/src/NATS.Server/Raft/RaftReplicator.cs
@@ -2,6 +2,9 @@ namespace NATS.Server.Raft;
 
 public sealed class RaftReplicator
 {
+    public static long BacktrackNextIndex(long nextIndex)
+        => Math.Max(1, nextIndex - 1);
+
     public int Replicate(RaftLogEntry entry, IReadOnlyList<RaftNode> followers)
     {
         var acknowledgements = 0;
diff --git a/src/NATS.Server/Raft/RaftTransport.cs b/src/NATS.Server/Raft/RaftTransport.cs
index 6bf024f..bf0ca44 100644
--- a/src/NATS.Server/Raft/RaftTransport.cs
+++ b/src/NATS.Server/Raft/RaftTransport.cs
@@ -4,6 +4,7 @@ public interface IRaftTransport
 {
     Task<IReadOnlyList<AppendResult>> AppendEntriesAsync(string leaderId, IReadOnlyList<string> followerIds, RaftLogEntry entry, CancellationToken ct);
     Task<VoteResponse> RequestVoteAsync(string candidateId, string voterId, VoteRequest request, CancellationToken ct);
+    Task InstallSnapshotAsync(string leaderId, string followerId, RaftSnapshot snapshot, CancellationToken ct);
 }
 
 public sealed class InMemoryRaftTransport : IRaftTransport
@@ -41,4 +42,23 @@ public sealed class InMemoryRaftTransport : IRaftTransport
 
         return Task.FromResult(new VoteResponse { Granted = false });
     }
+
+    public async Task InstallSnapshotAsync(string leaderId, string followerId, RaftSnapshot snapshot, CancellationToken ct)
+    {
+        _ = leaderId;
+        if (_nodes.TryGetValue(followerId, out var node))
+            await node.InstallSnapshotAsync(snapshot, ct);
+    }
+
+    public async Task AppendHeartbeatAsync(string leaderId, IReadOnlyList<string> followerIds, int term, CancellationToken ct)
+    {
+        _ = leaderId;
+        foreach (var followerId in followerIds)
+        {
+            if (_nodes.TryGetValue(followerId, out var node))
+                node.ReceiveHeartbeat(term);
+        }
+
+        await Task.CompletedTask;
+    }
 }
diff --git a/src/NATS.Server/Routes/RouteConnection.cs b/src/NATS.Server/Routes/RouteConnection.cs
index c3aa18c..b6ceaa3 100644
--- a/src/NATS.Server/Routes/RouteConnection.cs
+++ b/src/NATS.Server/Routes/RouteConnection.cs
@@ -40,19 +40,19 @@ public sealed class RouteConnection(Socket socket) : IAsyncDisposable
         _frameLoopTask = Task.Run(() => ReadFramesAsync(linked.Token), linked.Token);
     }
 
-    public async Task SendRsPlusAsync(string subject, string? queue, CancellationToken ct)
+    public async Task SendRsPlusAsync(string account, string subject, string? queue, CancellationToken ct)
     {
         var frame = queue is { Length: > 0 }
-            ? $"RS+ {subject} {queue}"
-            : $"RS+ {subject}";
+            ? $"RS+ {account} {subject} {queue}"
+            : $"RS+ {account} {subject}";
         await WriteLineAsync(frame, ct);
     }
 
-    public async Task SendRsMinusAsync(string subject, string? queue, CancellationToken ct)
+    public async Task SendRsMinusAsync(string account, string subject, string? queue, CancellationToken ct)
     {
         var frame = queue is { Length: > 0 }
-            ? $"RS- {subject} {queue}"
-            : $"RS- {subject}";
+            ? $"RS- {account} {subject} {queue}"
+            : $"RS- {account} {subject}";
         await WriteLineAsync(frame, ct);
     }
 
@@ -115,10 +115,9 @@ public sealed class RouteConnection(Socket socket) : IAsyncDisposable
             if (line.StartsWith("RS+ ", StringComparison.Ordinal))
             {
                 var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                if (parts.Length >= 2 && RemoteSubscriptionReceived != null)
+                if (RemoteSubscriptionReceived != null && TryParseAccountScopedInterest(parts, out var account, out var parsedSubject, out var queue))
                 {
-                    var queue = parts.Length >= 3 ? parts[2] : null;
-                    await RemoteSubscriptionReceived(new RemoteSubscription(parts[1], queue, RemoteServerId ?? string.Empty));
+                    await RemoteSubscriptionReceived(new RemoteSubscription(parsedSubject, queue, RemoteServerId ?? string.Empty, account));
                 }
                 continue;
             }
@@ -126,10 +125,9 @@ public sealed class RouteConnection(Socket socket) : IAsyncDisposable
             if (line.StartsWith("RS- ", StringComparison.Ordinal))
             {
                 var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                if (parts.Length >= 2 && RemoteSubscriptionReceived != null)
+                if (RemoteSubscriptionReceived != null && TryParseAccountScopedInterest(parts, out var account, out var parsedSubject, out var queue))
                 {
-                    var queue = parts.Length >= 3 ? parts[2] : null;
-                    await RemoteSubscriptionReceived(RemoteSubscription.Removal(parts[1], queue, RemoteServerId ?? string.Empty));
+                    await RemoteSubscriptionReceived(RemoteSubscription.Removal(parsedSubject, queue, RemoteServerId ?? string.Empty, account));
                 }
                 continue;
             }
@@ -225,6 +223,35 @@ public sealed class RouteConnection(Socket socket) : IAsyncDisposable
 
         return id;
     }
+
+    private static bool TryParseAccountScopedInterest(string[] parts, out string account, out string subject, out string? queue)
+    {
+        account = "$G";
+        subject = string.Empty;
+        queue = null;
+
+        if (parts.Length < 2)
+            return false;
+
+        // New format: RS+ <account> <subject> [queue]
+        // Legacy format: RS+ <subject> [queue]
+        if (parts.Length >= 3 && !LooksLikeSubject(parts[1]))
+        {
+            account = parts[1];
+            subject = parts[2];
+            queue = parts.Length >= 4 ? parts[3] : null;
+            return true;
+        }
+
+        subject = parts[1];
+        queue = parts.Length >= 3 ? parts[2] : null;
+        return true;
+    }
+
+    private static bool LooksLikeSubject(string token)
+        => token.Contains('.', StringComparison.Ordinal)
+            || token.Contains('*', StringComparison.Ordinal)
+            || token.Contains('>', StringComparison.Ordinal);
 }
 
 public sealed record RouteMessage(string Subject, string? ReplyTo, ReadOnlyMemory<byte> Payload);
diff --git a/src/NATS.Server/Routes/RouteManager.cs b/src/NATS.Server/Routes/RouteManager.cs
index 35812a0..79b60ab 100644
--- a/src/NATS.Server/Routes/RouteManager.cs
+++ b/src/NATS.Server/Routes/RouteManager.cs
@@ -86,24 +86,24 @@ public sealed class RouteManager : IAsyncDisposable
         _cts = null;
     }
 
-    public void PropagateLocalSubscription(string subject, string? queue)
+    public void PropagateLocalSubscription(string account, string subject, string? queue)
     {
         if (_routes.IsEmpty)
             return;
 
         foreach (var route in _routes.Values)
         {
-            _ = route.SendRsPlusAsync(subject, queue, _cts?.Token ?? CancellationToken.None);
+            _ = route.SendRsPlusAsync(account, subject, queue, _cts?.Token ?? CancellationToken.None);
         }
     }
 
-    public void PropagateLocalUnsubscription(string subject, string? queue)
+    public void PropagateLocalUnsubscription(string account, string subject, string? queue)
     {
         if (_routes.IsEmpty)
             return;
 
         foreach (var route in _routes.Values)
-            _ = route.SendRsMinusAsync(subject, queue, _cts?.Token ?? CancellationToken.None);
+            _ = route.SendRsMinusAsync(account, subject, queue, _cts?.Token ?? CancellationToken.None);
     }
 
     public async Task ForwardRoutedMessageAsync(string subject, string? replyTo, ReadOnlyMemory<byte> payload, CancellationToken ct)
diff --git a/src/NATS.Server/Subscriptions/RemoteSubscription.cs b/src/NATS.Server/Subscriptions/RemoteSubscription.cs
index 75d4269..61972f6 100644
--- a/src/NATS.Server/Subscriptions/RemoteSubscription.cs
+++ b/src/NATS.Server/Subscriptions/RemoteSubscription.cs
@@ -1,7 +1,12 @@
 namespace NATS.Server.Subscriptions;
 
-public sealed record RemoteSubscription(string Subject, string? Queue, string RouteId, bool IsRemoval = false)
+public sealed record RemoteSubscription(
+    string Subject,
+    string? Queue,
+    string RouteId,
+    string Account = "$G",
+    bool IsRemoval = false)
 {
-    public static RemoteSubscription Removal(string subject, string? queue, string routeId)
-        => new(subject, queue, routeId, IsRemoval: true);
+    public static RemoteSubscription Removal(string subject, string? queue, string routeId, string account = "$G")
+        => new(subject, queue, routeId, account, IsRemoval: true);
 }
diff --git a/src/NATS.Server/Subscriptions/SubList.cs b/src/NATS.Server/Subscriptions/SubList.cs
index 96d51ae..1e904bb 100644
--- a/src/NATS.Server/Subscriptions/SubList.cs
+++ b/src/NATS.Server/Subscriptions/SubList.cs
@@ -102,7 +102,7 @@ public sealed class SubList : IDisposable
         _lock.EnterWriteLock();
         try
         {
-            var key = $"{sub.RouteId}|{sub.Subject}|{sub.Queue}";
+            var key = $"{sub.RouteId}|{sub.Account}|{sub.Subject}|{sub.Queue}";
             if (sub.IsRemoval)
                 _remoteSubs.Remove(key);
             else
@@ -116,6 +116,9 @@ public sealed class SubList : IDisposable
     }
 
     public bool HasRemoteInterest(string subject)
+        => HasRemoteInterest("$G", subject);
+
+    public bool HasRemoteInterest(string account, string subject)
     {
         _lock.EnterReadLock();
         try
@@ -124,6 +127,8 @@ public sealed class SubList : IDisposable
             {
                 if (remoteSub.IsRemoval)
                     continue;
+                if (!string.Equals(remoteSub.Account, account, StringComparison.Ordinal))
+                    continue;
 
                 if (SubjectMatch.MatchLiteral(subject, remoteSub.Subject))
                     return true;
diff --git a/tests/NATS.Server.Tests/DifferencesParityClosureTests.cs b/tests/NATS.Server.Tests/DifferencesParityClosureTests.cs
new file mode 100644
index 0000000..f0cf00d
--- /dev/null
+++ b/tests/NATS.Server.Tests/DifferencesParityClosureTests.cs
@@ -0,0 +1,16 @@
+namespace NATS.Server.Tests;
+
+public class DifferencesParityClosureTests
+{
+    [Fact]
+    public void Differences_md_has_no_remaining_jetstream_baseline_or_n_rows()
+    {
+        var repositoryRoot = Path.GetFullPath(Path.Combine(AppContext.BaseDirectory, "..", "..", "..", "..", ".."));
+        var differencesPath = Path.Combine(repositoryRoot, "differences.md");
+        File.Exists(differencesPath).ShouldBeTrue();
+
+        var markdown = File.ReadAllText(differencesPath);
+        markdown.ShouldContain("### JetStream");
+        markdown.ShouldContain("None in scope after this plan; all in-scope parity rows moved to `Y`.");
+    }
+}
diff --git a/tests/NATS.Server.Tests/GatewayAdvancedSemanticsTests.cs b/tests/NATS.Server.Tests/GatewayAdvancedSemanticsTests.cs
new file mode 100644
index 0000000..a9bd53d
--- /dev/null
+++ b/tests/NATS.Server.Tests/GatewayAdvancedSemanticsTests.cs
@@ -0,0 +1,20 @@
+using NATS.Server.Gateways;
+
+namespace NATS.Server.Tests;
+
+public class GatewayAdvancedSemanticsTests
+{
+    [Fact]
+    public void Gateway_forwarding_remaps_reply_subject_with_gr_prefix_and_restores_on_return()
+    {
+        const string originalReply = "_INBOX.123";
+        const string clusterId = "CLUSTER-A";
+
+        var mapped = ReplyMapper.ToGatewayReply(originalReply, clusterId);
+        mapped.ShouldStartWith("_GR_.");
+        mapped.ShouldContain(clusterId);
+
+        ReplyMapper.TryRestoreGatewayReply(mapped, out var restored).ShouldBeTrue();
+        restored.ShouldBe(originalReply);
+    }
+}
diff --git a/tests/NATS.Server.Tests/InterServerAccountProtocolTests.cs b/tests/NATS.Server.Tests/InterServerAccountProtocolTests.cs
new file mode 100644
index 0000000..b4be42e
--- /dev/null
+++ b/tests/NATS.Server.Tests/InterServerAccountProtocolTests.cs
@@ -0,0 +1,84 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using NATS.Server.Gateways;
+using NATS.Server.Subscriptions;
+
+namespace NATS.Server.Tests;
+
+public class InterServerAccountProtocolTests
+{
+    [Fact]
+    public async Task Aplus_Aminus_frames_include_account_scope_and_do_not_leak_interest_across_accounts()
+    {
+        using var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+
+        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+        using var remoteSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+        await remoteSocket.ConnectAsync(IPAddress.Loopback, port);
+        using var gatewaySocket = await listener.AcceptSocketAsync();
+        await using var gateway = new GatewayConnection(gatewaySocket);
+
+        using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+        var handshakeTask = gateway.PerformOutboundHandshakeAsync("LOCAL", timeout.Token);
+        (await ReadLineAsync(remoteSocket, timeout.Token)).ShouldBe("GATEWAY LOCAL");
+        await WriteLineAsync(remoteSocket, "GATEWAY REMOTE", timeout.Token);
+        await handshakeTask;
+
+        var received = new TaskCompletionSource<RemoteSubscription>(TaskCreationOptions.RunContinuationsAsynchronously);
+        gateway.RemoteSubscriptionReceived = sub =>
+        {
+            received.TrySetResult(sub);
+            return Task.CompletedTask;
+        };
+        gateway.StartLoop(timeout.Token);
+
+        await WriteLineAsync(remoteSocket, "A+ A orders.*", timeout.Token);
+        var aPlus = await received.Task.WaitAsync(timeout.Token);
+        aPlus.Account.ShouldBe("A");
+        aPlus.Subject.ShouldBe("orders.*");
+        aPlus.IsRemoval.ShouldBeFalse();
+
+        var subList = new SubList();
+        subList.ApplyRemoteSub(aPlus);
+        subList.HasRemoteInterest("A", "orders.created").ShouldBeTrue();
+        subList.HasRemoteInterest("B", "orders.created").ShouldBeFalse();
+
+        var removedTcs = new TaskCompletionSource<RemoteSubscription>(TaskCreationOptions.RunContinuationsAsynchronously);
+        gateway.RemoteSubscriptionReceived = sub =>
+        {
+            removedTcs.TrySetResult(sub);
+            return Task.CompletedTask;
+        };
+
+        await WriteLineAsync(remoteSocket, "A- A orders.*", timeout.Token);
+        var aMinus = await removedTcs.Task.WaitAsync(timeout.Token);
+        aMinus.Account.ShouldBe("A");
+        aMinus.IsRemoval.ShouldBeTrue();
+
+        subList.ApplyRemoteSub(aMinus);
+        subList.HasRemoteInterest("A", "orders.created").ShouldBeFalse();
+    }
+
+    private static async Task<string> ReadLineAsync(Socket socket, CancellationToken ct)
+    {
+        var bytes = new List<byte>(64);
+        var single = new byte[1];
+        while (true)
+        {
+            var read = await socket.ReceiveAsync(single, SocketFlags.None, ct);
+            if (read == 0)
+                break;
+            if (single[0] == (byte)'\n')
+                break;
+            if (single[0] != (byte)'\r')
+                bytes.Add(single[0]);
+        }
+
+        return Encoding.ASCII.GetString([.. bytes]);
+    }
+
+    private static Task WriteLineAsync(Socket socket, string line, CancellationToken ct)
+        => socket.SendAsync(Encoding.ASCII.GetBytes($"{line}\r\n"), SocketFlags.None, ct).AsTask();
+}
diff --git a/tests/NATS.Server.Tests/JetStreamClusterGovernanceParityTests.cs b/tests/NATS.Server.Tests/JetStreamClusterGovernanceParityTests.cs
new file mode 100644
index 0000000..91852a7
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamClusterGovernanceParityTests.cs
@@ -0,0 +1,18 @@
+using NATS.Server.JetStream.Cluster;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamClusterGovernanceParityTests
+{
+    [Fact]
+    public async Task Cluster_governance_applies_planned_replica_placement()
+    {
+        var planner = new AssetPlacementPlanner(nodes: 3);
+        var placement = planner.PlanReplicas(replicas: 2);
+        placement.Count.ShouldBe(2);
+
+        var group = new StreamReplicaGroup("ORDERS", replicas: 1);
+        await group.ApplyPlacementAsync(placement, default);
+        group.Nodes.Count.ShouldBe(2);
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamConsumerBackoffParityTests.cs b/tests/NATS.Server.Tests/JetStreamConsumerBackoffParityTests.cs
new file mode 100644
index 0000000..c577aca
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamConsumerBackoffParityTests.cs
@@ -0,0 +1,41 @@
+using NATS.Server.JetStream;
+using NATS.Server.JetStream.Models;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamConsumerBackoffParityTests
+{
+    [Fact]
+    public async Task Redelivery_honors_backoff_schedule_and_stops_after_max_deliver()
+    {
+        var streams = new StreamManager();
+        streams.CreateOrUpdate(new StreamConfig
+        {
+            Name = "ORDERS",
+            Subjects = ["orders.*"],
+        });
+
+        streams.Capture("orders.created", "x"u8.ToArray());
+
+        var consumers = new ConsumerManager();
+        consumers.CreateOrUpdate("ORDERS", new ConsumerConfig
+        {
+            DurableName = "C1",
+            AckPolicy = AckPolicy.Explicit,
+            AckWaitMs = 1,
+            MaxDeliver = 3,
+            BackOffMs = [1, 1],
+        });
+
+        var deliveries = new List<ulong>();
+        for (var i = 0; i < 6; i++)
+        {
+            var batch = await consumers.FetchAsync("ORDERS", "C1", 1, streams, default);
+            if (batch.Messages.Count > 0 && batch.Messages[0].Redelivered)
+                deliveries.Add(batch.Messages[0].Sequence);
+            await Task.Delay(2);
+        }
+
+        deliveries.Count.ShouldBe(3);
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamConsumerDeliverPolicyParityTests.cs b/tests/NATS.Server.Tests/JetStreamConsumerDeliverPolicyParityTests.cs
new file mode 100644
index 0000000..289c8a0
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamConsumerDeliverPolicyParityTests.cs
@@ -0,0 +1,33 @@
+using NATS.Server.JetStream;
+using NATS.Server.JetStream.Models;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamConsumerDeliverPolicyParityTests
+{
+    [Fact]
+    public async Task Deliver_policy_start_sequence_and_start_time_and_last_per_subject_match_expected_start_positions()
+    {
+        var streams = new StreamManager();
+        streams.CreateOrUpdate(new StreamConfig
+        {
+            Name = "ORDERS",
+            Subjects = ["orders.*"],
+        });
+
+        streams.Capture("orders.created", "1"u8.ToArray());
+        streams.Capture("orders.updated", "2"u8.ToArray());
+        streams.Capture("orders.created", "3"u8.ToArray());
+
+        var consumers = new ConsumerManager();
+        consumers.CreateOrUpdate("ORDERS", new ConsumerConfig
+        {
+            DurableName = "BYSEQ",
+            DeliverPolicy = DeliverPolicy.ByStartSequence,
+            OptStartSeq = 3,
+        });
+
+        var bySeq = await consumers.FetchAsync("ORDERS", "BYSEQ", 1, streams, default);
+        bySeq.Messages[0].Sequence.ShouldBe((ulong)3);
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamConsumerFlowControlParityTests.cs b/tests/NATS.Server.Tests/JetStreamConsumerFlowControlParityTests.cs
new file mode 100644
index 0000000..ca42ad5
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamConsumerFlowControlParityTests.cs
@@ -0,0 +1,41 @@
+using NATS.Server.JetStream;
+using NATS.Server.JetStream.Models;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamConsumerFlowControlParityTests
+{
+    [Fact]
+    public async Task Push_consumer_emits_flow_control_frames_when_enabled()
+    {
+        var streams = new StreamManager();
+        streams.CreateOrUpdate(new StreamConfig
+        {
+            Name = "ORDERS",
+            Subjects = ["orders.*"],
+        });
+
+        var consumers = new ConsumerManager();
+        consumers.CreateOrUpdate("ORDERS", new ConsumerConfig
+        {
+            DurableName = "PUSH",
+            Push = true,
+            AckPolicy = AckPolicy.Explicit,
+            FlowControl = true,
+            RateLimitBps = 1024,
+        });
+
+        var ack = streams.Capture("orders.created", "x"u8.ToArray());
+        streams.TryGet("ORDERS", out var stream).ShouldBeTrue();
+        var message = await stream.Store.LoadAsync(ack!.Seq, default);
+        message.ShouldNotBeNull();
+        consumers.OnPublished("ORDERS", message!);
+
+        var first = consumers.ReadPushFrame("ORDERS", "PUSH");
+        var second = consumers.ReadPushFrame("ORDERS", "PUSH");
+        first.ShouldNotBeNull();
+        second.ShouldNotBeNull();
+        first!.IsData.ShouldBeTrue();
+        second!.IsFlowControl.ShouldBeTrue();
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamCrossClusterGatewayParityTests.cs b/tests/NATS.Server.Tests/JetStreamCrossClusterGatewayParityTests.cs
new file mode 100644
index 0000000..49f3efb
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamCrossClusterGatewayParityTests.cs
@@ -0,0 +1,26 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using NATS.Server.Configuration;
+using NATS.Server.Gateways;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamCrossClusterGatewayParityTests
+{
+    [Fact]
+    public async Task Cross_cluster_jetstream_messages_use_gateway_forwarding_path()
+    {
+        var manager = new GatewayManager(
+            new GatewayOptions { Name = "GW", Host = "127.0.0.1", Port = 0 },
+            new ServerStats(),
+            "S1",
+            _ => { },
+            _ => { },
+            NullLogger<GatewayManager>.Instance);
+
+        await manager.ForwardJetStreamClusterMessageAsync(
+            new GatewayMessage("$JS.CLUSTER.REPL.ORDERS", null, "x"u8.ToArray()),
+            default);
+
+        manager.ForwardedJetStreamClusterMessages.ShouldBe(1);
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamFileStoreBlockParityTests.cs b/tests/NATS.Server.Tests/JetStreamFileStoreBlockParityTests.cs
new file mode 100644
index 0000000..39e014b
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamFileStoreBlockParityTests.cs
@@ -0,0 +1,30 @@
+using NATS.Server.JetStream.Storage;
+using System.Text;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamFileStoreBlockParityTests
+{
+    [Fact]
+    public async Task File_store_rolls_blocks_and_recovers_index_without_full_file_rewrite()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), $"nats-js-filestore-block-{Guid.NewGuid():N}");
+        var options = new FileStoreOptions
+        {
+            Directory = dir,
+            BlockSizeBytes = 512,
+        };
+
+        await using (var store = new FileStore(options))
+        {
+            for (var i = 0; i < 5000; i++)
+                await store.AppendAsync("orders.created", Encoding.UTF8.GetBytes($"payload-{i}"), default);
+
+            store.BlockCount.ShouldBeGreaterThan(1);
+        }
+
+        await using var reopened = new FileStore(options);
+        var state = await reopened.GetStateAsync(default);
+        state.Messages.ShouldBe((ulong)5000);
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamInternalClientTests.cs b/tests/NATS.Server.Tests/JetStreamInternalClientTests.cs
new file mode 100644
index 0000000..381cf68
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamInternalClientTests.cs
@@ -0,0 +1,32 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using NATS.Server.Configuration;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamInternalClientTests
+{
+    [Fact]
+    public async Task JetStream_enabled_server_creates_internal_jetstream_client_and_keeps_it_account_scoped()
+    {
+        var options = new NatsOptions
+        {
+            Host = "127.0.0.1",
+            Port = 0,
+            JetStream = new JetStreamOptions
+            {
+                StoreDir = Path.Combine(Path.GetTempPath(), $"nats-js-internal-{Guid.NewGuid():N}"),
+                MaxMemoryStore = 1024 * 1024,
+                MaxFileStore = 10 * 1024 * 1024,
+            },
+        };
+
+        using var server = new NatsServer(options, NullLoggerFactory.Instance);
+        using var cts = new CancellationTokenSource();
+        _ = server.StartAsync(cts.Token);
+        await server.WaitForReadyAsync();
+
+        server.JetStreamInternalClient.ShouldNotBeNull();
+        server.JetStreamInternalClient!.Kind.ShouldBe(ClientKind.JetStream);
+        server.JetStreamInternalClient.Account?.Name.ShouldBe("$SYS");
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamMirrorSourceParityTests.cs b/tests/NATS.Server.Tests/JetStreamMirrorSourceParityTests.cs
new file mode 100644
index 0000000..8b28fac
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamMirrorSourceParityTests.cs
@@ -0,0 +1,38 @@
+using NATS.Server.JetStream;
+using NATS.Server.JetStream.Models;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamMirrorSourceParityTests
+{
+    [Fact]
+    public async Task Source_subject_transform_and_cross_account_mapping_copy_expected_messages_only()
+    {
+        var manager = new StreamManager();
+        manager.CreateOrUpdate(new StreamConfig
+        {
+            Name = "SRC",
+            Subjects = ["orders.*"],
+        });
+
+        manager.CreateOrUpdate(new StreamConfig
+        {
+            Name = "AGG",
+            Subjects = ["agg.*"],
+            Sources =
+            [
+                new StreamSourceConfig
+                {
+                    Name = "SRC",
+                    SubjectTransformPrefix = "agg.",
+                    SourceAccount = "A",
+                },
+            ],
+        });
+
+        manager.Capture("orders.created", "1"u8.ToArray());
+        manager.TryGet("AGG", out var aggregate).ShouldBeTrue();
+        var messages = await aggregate.Store.ListAsync(default);
+        messages.ShouldContain(m => m.Subject == "agg.orders.created");
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamStoreExpiryParityTests.cs b/tests/NATS.Server.Tests/JetStreamStoreExpiryParityTests.cs
new file mode 100644
index 0000000..aa237d3
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamStoreExpiryParityTests.cs
@@ -0,0 +1,24 @@
+using NATS.Server.JetStream.Storage;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamStoreExpiryParityTests
+{
+    [Fact]
+    public async Task File_store_prunes_expired_messages_using_max_age_policy()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), $"nats-js-filestore-expiry-{Guid.NewGuid():N}");
+        await using var store = new FileStore(new FileStoreOptions
+        {
+            Directory = dir,
+            MaxAgeMs = 10,
+        });
+
+        await store.AppendAsync("orders.created", "old"u8.ToArray(), default);
+        await Task.Delay(20);
+        await store.AppendAsync("orders.created", "new"u8.ToArray(), default);
+
+        var state = await store.GetStateAsync(default);
+        state.Messages.ShouldBe((ulong)1);
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamStreamConfigBehaviorTests.cs b/tests/NATS.Server.Tests/JetStreamStreamConfigBehaviorTests.cs
new file mode 100644
index 0000000..89531dc
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamStreamConfigBehaviorTests.cs
@@ -0,0 +1,41 @@
+using NATS.Server.JetStream.Models;
+using NATS.Server.JetStream;
+using NATS.Server.JetStream.Publish;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamStreamConfigBehaviorTests
+{
+    [Fact]
+    public void Stream_honors_dedup_window_and_sealed_delete_purge_guards()
+    {
+        var streamManager = new StreamManager();
+        streamManager.CreateOrUpdate(new StreamConfig
+        {
+            Name = "ORDERS",
+            Subjects = ["orders.*"],
+            DuplicateWindowMs = 10_000,
+            Sealed = false,
+            DenyDelete = false,
+            DenyPurge = false,
+        });
+
+        var publisher = new JetStreamPublisher(streamManager);
+        publisher.TryCaptureWithOptions("orders.created", "one"u8.ToArray(), new PublishOptions { MsgId = "m-1" }, out var first).ShouldBeTrue();
+        publisher.TryCaptureWithOptions("orders.created", "two"u8.ToArray(), new PublishOptions { MsgId = "m-1" }, out var second).ShouldBeTrue();
+        second.Seq.ShouldBe(first.Seq);
+
+        streamManager.CreateOrUpdate(new StreamConfig
+        {
+            Name = "ORDERS",
+            Subjects = ["orders.*"],
+            DuplicateWindowMs = 10_000,
+            Sealed = true,
+            DenyDelete = true,
+            DenyPurge = true,
+        });
+
+        streamManager.DeleteMessage("ORDERS", first.Seq).ShouldBeFalse();
+        streamManager.Purge("ORDERS").ShouldBeFalse();
+    }
+}
diff --git a/tests/NATS.Server.Tests/JetStreamStreamPolicyParityTests.cs b/tests/NATS.Server.Tests/JetStreamStreamPolicyParityTests.cs
new file mode 100644
index 0000000..e597ab1
--- /dev/null
+++ b/tests/NATS.Server.Tests/JetStreamStreamPolicyParityTests.cs
@@ -0,0 +1,38 @@
+using NATS.Server.JetStream.Models;
+using NATS.Server.JetStream;
+
+namespace NATS.Server.Tests;
+
+public class JetStreamStreamPolicyParityTests
+{
+    [Fact]
+    public async Task Stream_rejects_oversize_message_and_prunes_by_max_age_and_per_subject_limits()
+    {
+        var streamManager = new StreamManager();
+        var create = streamManager.CreateOrUpdate(new StreamConfig
+        {
+            Name = "P",
+            Subjects = ["p.*"],
+            MaxMsgSize = 8,
+            MaxAgeMs = 20,
+            MaxMsgsPer = 1,
+        });
+        create.Error.ShouldBeNull();
+
+        var oversized = streamManager.Capture("p.a", "0123456789"u8.ToArray());
+        oversized.ShouldNotBeNull();
+        oversized!.ErrorCode.ShouldBe(10054);
+
+        streamManager.Capture("p.a", "one"u8.ToArray())!.ErrorCode.ShouldBeNull();
+        streamManager.Capture("p.a", "two"u8.ToArray())!.ErrorCode.ShouldBeNull();
+
+        streamManager.TryGet("P", out var handle).ShouldBeTrue();
+        var beforeAgePrune = await handle.Store.GetStateAsync(default);
+        beforeAgePrune.Messages.ShouldBe((ulong)1);
+
+        await Task.Delay(30);
+        streamManager.Capture("p.b", "x"u8.ToArray())!.ErrorCode.ShouldBeNull();
+        var afterAgePrune = await handle.Store.GetStateAsync(default);
+        afterAgePrune.Messages.ShouldBe((ulong)1);
+    }
+}
diff --git a/tests/NATS.Server.Tests/LeafAdvancedSemanticsTests.cs b/tests/NATS.Server.Tests/LeafAdvancedSemanticsTests.cs
new file mode 100644
index 0000000..a180099
--- /dev/null
+++ b/tests/NATS.Server.Tests/LeafAdvancedSemanticsTests.cs
@@ -0,0 +1,70 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using NATS.Server.LeafNodes;
+using NATS.Server.Subscriptions;
+
+namespace NATS.Server.Tests;
+
+public class LeafAdvancedSemanticsTests
+{
+    [Fact]
+    public async Task Leaf_loop_marker_blocks_reinjected_message_and_account_mapping_routes_to_expected_account()
+    {
+        const string serverId = "S1";
+        var marked = LeafLoopDetector.Mark("orders.created", serverId);
+        LeafLoopDetector.IsLooped(marked, serverId).ShouldBeTrue();
+        LeafLoopDetector.IsLooped(marked, "S2").ShouldBeFalse();
+        LeafLoopDetector.TryUnmark(marked, out var unmarked).ShouldBeTrue();
+        unmarked.ShouldBe("orders.created");
+
+        using var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+
+        using var remoteSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+        await remoteSocket.ConnectAsync(IPAddress.Loopback, port);
+        using var leafSocket = await listener.AcceptSocketAsync();
+        await using var leaf = new LeafConnection(leafSocket);
+
+        using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+        var handshakeTask = leaf.PerformOutboundHandshakeAsync("LOCAL", timeout.Token);
+        (await ReadLineAsync(remoteSocket, timeout.Token)).ShouldBe("LEAF LOCAL");
+        await WriteLineAsync(remoteSocket, "LEAF REMOTE", timeout.Token);
+        await handshakeTask;
+
+        var received = new TaskCompletionSource<RemoteSubscription>(TaskCreationOptions.RunContinuationsAsynchronously);
+        leaf.RemoteSubscriptionReceived = sub =>
+        {
+            received.TrySetResult(sub);
+            return Task.CompletedTask;
+        };
+        leaf.StartLoop(timeout.Token);
+
+        await WriteLineAsync(remoteSocket, "LS+ ACC_A leaf.>", timeout.Token);
+        var lsPlus = await received.Task.WaitAsync(timeout.Token);
+        lsPlus.Account.ShouldBe("ACC_A");
+        lsPlus.Subject.ShouldBe("leaf.>");
+    }
+
+    private static async Task<string> ReadLineAsync(Socket socket, CancellationToken ct)
+    {
+        var bytes = new List<byte>(64);
+        var single = new byte[1];
+        while (true)
+        {
+            var read = await socket.ReceiveAsync(single, SocketFlags.None, ct);
+            if (read == 0)
+                break;
+            if (single[0] == (byte)'\n')
+                break;
+            if (single[0] != (byte)'\r')
+                bytes.Add(single[0]);
+        }
+
+        return Encoding.ASCII.GetString([.. bytes]);
+    }
+
+    private static Task WriteLineAsync(Socket socket, string line, CancellationToken ct)
+        => socket.SendAsync(Encoding.ASCII.GetBytes($"{line}\r\n"), SocketFlags.None, ct).AsTask();
+}
diff --git a/tests/NATS.Server.Tests/RaftConsensusAdvancedParityTests.cs b/tests/NATS.Server.Tests/RaftConsensusAdvancedParityTests.cs
new file mode 100644
index 0000000..0133e87
--- /dev/null
+++ b/tests/NATS.Server.Tests/RaftConsensusAdvancedParityTests.cs
@@ -0,0 +1,22 @@
+using NATS.Server.Raft;
+
+namespace NATS.Server.Tests;
+
+public class RaftConsensusAdvancedParityTests
+{
+    [Fact]
+    public async Task Leader_heartbeats_keep_followers_current_and_next_index_backtracks_on_mismatch()
+    {
+        var transport = new InMemoryRaftTransport();
+        var leader = new RaftNode("L", transport);
+        var follower = new RaftNode("F", transport);
+        transport.Register(leader);
+        transport.Register(follower);
+
+        await transport.AppendHeartbeatAsync("L", ["F"], term: 2, default);
+        follower.Term.ShouldBe(2);
+
+        RaftReplicator.BacktrackNextIndex(5).ShouldBe(4);
+        RaftReplicator.BacktrackNextIndex(1).ShouldBe(1);
+    }
+}
diff --git a/tests/NATS.Server.Tests/RaftMembershipParityTests.cs b/tests/NATS.Server.Tests/RaftMembershipParityTests.cs
new file mode 100644
index 0000000..9cd21c1
--- /dev/null
+++ b/tests/NATS.Server.Tests/RaftMembershipParityTests.cs
@@ -0,0 +1,19 @@
+using NATS.Server.Raft;
+
+namespace NATS.Server.Tests;
+
+public class RaftMembershipParityTests
+{
+    [Fact]
+    public void Membership_changes_update_node_membership_state()
+    {
+        var node = new RaftNode("N1");
+        node.AddMember("N2");
+        node.AddMember("N3");
+        node.Members.ShouldContain("N2");
+        node.Members.ShouldContain("N3");
+
+        node.RemoveMember("N2");
+        node.Members.ShouldNotContain("N2");
+    }
+}
diff --git a/tests/NATS.Server.Tests/RaftSnapshotTransferParityTests.cs b/tests/NATS.Server.Tests/RaftSnapshotTransferParityTests.cs
new file mode 100644
index 0000000..884289e
--- /dev/null
+++ b/tests/NATS.Server.Tests/RaftSnapshotTransferParityTests.cs
@@ -0,0 +1,25 @@
+using NATS.Server.Raft;
+
+namespace NATS.Server.Tests;
+
+public class RaftSnapshotTransferParityTests
+{
+    [Fact]
+    public async Task Snapshot_transfer_installs_snapshot_when_follower_falls_behind()
+    {
+        var transport = new InMemoryRaftTransport();
+        var leader = new RaftNode("L", transport);
+        var follower = new RaftNode("F", transport);
+        transport.Register(leader);
+        transport.Register(follower);
+
+        var snapshot = new RaftSnapshot
+        {
+            LastIncludedIndex = 10,
+            LastIncludedTerm = 3,
+        };
+
+        await transport.InstallSnapshotAsync("L", "F", snapshot, default);
+        follower.AppliedIndex.ShouldBe(10);
+    }
+}
diff --git a/tests/NATS.Server.Tests/StreamStoreContractTests.cs b/tests/NATS.Server.Tests/StreamStoreContractTests.cs
index 07d7e59..631c126 100644
--- a/tests/NATS.Server.Tests/StreamStoreContractTests.cs
+++ b/tests/NATS.Server.Tests/StreamStoreContractTests.cs
@@ -34,6 +34,9 @@ public class StreamStoreContractTests
         public ValueTask<StoredMessage?> LoadLastBySubjectAsync(string subject, CancellationToken ct)
             => ValueTask.FromResult<StoredMessage?>(null);
 
+        public ValueTask<IReadOnlyList<StoredMessage>> ListAsync(CancellationToken ct)
+            => ValueTask.FromResult<IReadOnlyList<StoredMessage>>([]);
+
         public ValueTask<bool> RemoveAsync(ulong sequence, CancellationToken ct)
             => ValueTask.FromResult(false);