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

src/NATS.Server/JetStream/StreamManager.cs

@@ -1,4 +1,5 @@
 using System.Collections.Concurrent;
+using System.Text;
 using NATS.Server.Auth;
 using NATS.Server.JetStream.Api;
 using NATS.Server.JetStream.Cluster;
@@ -7,11 +8,12 @@ using NATS.Server.JetStream.Models;
 using NATS.Server.JetStream.Publish;
 using NATS.Server.JetStream.Snapshots;
 using NATS.Server.JetStream.Storage;
+using NATS.Server.JetStream.Validation;
 using NATS.Server.Subscriptions;
 
 namespace NATS.Server.JetStream;
 
-public sealed class StreamManager
+public sealed class StreamManager : IDisposable
 {
     private readonly Account? _account;
     private readonly ConsumerManager? _consumerManager;
@@ -25,12 +27,52 @@ public sealed class StreamManager
     private readonly ConcurrentDictionary<string, List<SourceCoordinator>> _sourcesByOrigin =
         new(StringComparer.Ordinal);
     private readonly StreamSnapshotService _snapshotService = new();
+    private readonly CancellationTokenSource _expiryTimerCts = new();
+    private Task? _expiryTimerTask;
 
     public StreamManager(JetStreamMetaGroup? metaGroup = null, Account? account = null, ConsumerManager? consumerManager = null)
     {
         _metaGroup = metaGroup;
         _account = account;
         _consumerManager = consumerManager;
+        _expiryTimerTask = RunExpiryTimerAsync(_expiryTimerCts.Token);
+    }
+
+    public void Dispose()
+    {
+        _expiryTimerCts.Cancel();
+        _expiryTimerCts.Dispose();
+    }
+
+    /// <summary>
+    /// Periodically prunes expired messages from streams with MaxAge configured.
+    /// Go reference: stream.go — expireMsgs runs on a timer (checkMaxAge interval).
+    /// </summary>
+    private async Task RunExpiryTimerAsync(CancellationToken ct)
+    {
+        using var timer = new PeriodicTimer(TimeSpan.FromSeconds(1));
+        while (!ct.IsCancellationRequested)
+        {
+            var ticked = false;
+            try
+            {
+                ticked = await timer.WaitForNextTickAsync(ct);
+            }
+            catch (OperationCanceledException)
+            {
+                return; // Shutdown requested via Dispose — exit the timer loop
+            }
+
+            if (!ticked)
+                return;
+
+            var nowUtc = DateTime.UtcNow;
+            foreach (var stream in _streams.Values)
+            {
+                if (stream.Config.MaxAgeMs > 0)
+                    PruneExpiredMessages(stream, nowUtc);
+            }
+        }
     }
 
     public IReadOnlyCollection<string> StreamNames => _streams.Keys.ToArray();
@@ -39,10 +81,31 @@ public sealed class StreamManager
     public IReadOnlyList<string> ListNames()
         => [.. _streams.Keys.OrderBy(x => x, StringComparer.Ordinal)];
 
+    public IReadOnlyList<JetStreamStreamInfo> ListStreamInfos()
+    {
+        return _streams.OrderBy(kv => kv.Key, StringComparer.Ordinal)
+            .Select(kv =>
+            {
+                var state = kv.Value.Store.GetStateAsync(default).GetAwaiter().GetResult();
+                return new JetStreamStreamInfo
+                {
+                    Config = kv.Value.Config,
+                    State = state,
+                };
+            })
+            .ToList();
+    }
+
     public JetStreamApiResponse CreateOrUpdate(StreamConfig config)
     {
-        if (string.IsNullOrWhiteSpace(config.Name))
-            return JetStreamApiResponse.ErrorResponse(400, "stream name required");
+        if (!JetStreamConfigValidator.IsValidName(config.Name))
+            return JetStreamApiResponse.ErrorResponse(400, "invalid stream name");
+
+        if (Encoding.UTF8.GetByteCount(config.Description) > JetStreamApiLimits.JSMaxDescriptionLen)
+            return JetStreamApiResponse.ErrorResponse(400, "stream description is too long");
+
+        if (!JetStreamConfigValidator.IsMetadataWithinLimit(config.Metadata))
+            return JetStreamApiResponse.ErrorResponse(400, "stream metadata exceeds maximum size");
 
         var normalized = NormalizeConfig(config);
 
@@ -302,6 +365,8 @@ public sealed class StreamManager
         if (stream == null)
             return null;
 
+
+
         if (stream.Config.MaxMsgSize > 0 && payload.Length > stream.Config.MaxMsgSize)
         {
             return new PubAck