Fix E2E test gaps and add comprehensive E2E + parity test suites

- Fix pull consumer fetch: send original stream subject in HMSG (not inbox)
  so NATS client distinguishes data messages from control messages
- Fix MaxAge expiry: add background timer in StreamManager for periodic pruning
- Fix JetStream wire format: Go-compatible anonymous objects with string enums,
  proper offset-based pagination for stream/consumer list APIs
- Add 42 E2E black-box tests (core messaging, auth, TLS, accounts, JetStream)
- Add ~1000 parity tests across all subsystems (gaps closure)
- Update gap inventory docs to reflect implementation status

tests/NATS.Server.Tests/Gateways/GatewayConnectionDirectionParityBatch2Tests.cs

@@ -0,0 +1,95 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using NATS.Server.Configuration;
+
+namespace NATS.Server.Tests.Gateways;
+
+public class GatewayConnectionDirectionParityBatch2Tests
+{
+    [Fact]
+    public async Task Gateway_manager_tracks_inbound_and_outbound_connection_sets()
+    {
+        var a = await StartServerAsync(MakeGatewayOptions("GW-A"));
+        var b = await StartServerAsync(MakeGatewayOptions("GW-B", a.Server.GatewayListen));
+
+        try
+        {
+            await WaitForCondition(() =>
+                a.Server.NumInboundGateways() == 1 &&
+                b.Server.NumOutboundGateways() == 1,
+                10000);
+
+            a.Server.NumInboundGateways().ShouldBe(1);
+            a.Server.NumOutboundGateways().ShouldBe(0);
+            b.Server.NumOutboundGateways().ShouldBe(1);
+            b.Server.NumInboundGateways().ShouldBe(0);
+
+            var aManager = a.Server.GatewayManager;
+            var bManager = b.Server.GatewayManager;
+            aManager.ShouldNotBeNull();
+            bManager.ShouldNotBeNull();
+
+            aManager!.HasInbound(b.Server.ServerId).ShouldBeTrue();
+            bManager!.HasInbound(a.Server.ServerId).ShouldBeFalse();
+
+            bManager.GetOutboundGatewayConnection(a.Server.ServerId).ShouldNotBeNull();
+            bManager.GetOutboundGatewayConnection("does-not-exist").ShouldBeNull();
+
+            aManager.GetInboundGatewayConnections().Count.ShouldBe(1);
+            aManager.GetOutboundGatewayConnections().Count.ShouldBe(0);
+            bManager.GetOutboundGatewayConnections().Count.ShouldBe(1);
+            bManager.GetInboundGatewayConnections().Count.ShouldBe(0);
+        }
+        finally
+        {
+            await DisposeServers(a, b);
+        }
+    }
+
+    private static NatsOptions MakeGatewayOptions(string gatewayName, string? remote = null)
+    {
+        return new NatsOptions
+        {
+            Host = "127.0.0.1",
+            Port = 0,
+            Gateway = new GatewayOptions
+            {
+                Name = gatewayName,
+                Host = "127.0.0.1",
+                Port = 0,
+                Remotes = remote is null ? [] : [remote],
+            },
+        };
+    }
+
+    private static async Task<(NatsServer Server, CancellationTokenSource Cts)> StartServerAsync(NatsOptions opts)
+    {
+        var server = new NatsServer(opts, NullLoggerFactory.Instance);
+        var cts = new CancellationTokenSource();
+        _ = server.StartAsync(cts.Token);
+        await server.WaitForReadyAsync();
+        return (server, cts);
+    }
+
+    private static async Task DisposeServers(params (NatsServer Server, CancellationTokenSource Cts)[] servers)
+    {
+        foreach (var (server, cts) in servers)
+        {
+            await cts.CancelAsync();
+            server.Dispose();
+            cts.Dispose();
+        }
+    }
+
+    private static async Task WaitForCondition(Func<bool> predicate, int timeoutMs)
+    {
+        using var cts = new CancellationTokenSource(timeoutMs);
+        while (!cts.IsCancellationRequested)
+        {
+            if (predicate())
+                return;
+            await Task.Yield();
+        }
+
+        throw new TimeoutException("Condition not met.");
+    }
+}