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/ConsumerManager.cs

@@ -4,6 +4,7 @@ using NATS.Server.JetStream.Cluster;
 using NATS.Server.JetStream.Consumers;
 using NATS.Server.JetStream.Models;
 using NATS.Server.JetStream.Storage;
+using NATS.Server.JetStream.Validation;
 using NATS.Server.Subscriptions;
 
 namespace NATS.Server.JetStream;
@@ -40,6 +41,12 @@ public sealed class ConsumerManager : IDisposable
                 return JetStreamApiResponse.ErrorResponse(400, "durable name required");
         }
 
+        if (!JetStreamConfigValidator.IsValidName(config.DurableName))
+            return JetStreamApiResponse.ErrorResponse(400, "invalid durable name");
+
+        if (!JetStreamConfigValidator.IsMetadataWithinLimit(config.Metadata))
+            return JetStreamApiResponse.ErrorResponse(400, "consumer metadata exceeds maximum size");
+
         if (config.FilterSubjects.Count == 0 && !string.IsNullOrWhiteSpace(config.FilterSubject))
             config.FilterSubjects.Add(config.FilterSubject);
 
@@ -58,6 +65,8 @@ public sealed class ConsumerManager : IDisposable
         {
             ConsumerInfo = new JetStreamConsumerInfo
             {
+                Name = handle.Config.DurableName,
+                StreamName = stream,
                 Config = handle.Config,
             },
         };
@@ -71,6 +80,8 @@ public sealed class ConsumerManager : IDisposable
             {
                 ConsumerInfo = new JetStreamConsumerInfo
                 {
+                    Name = handle.Config.DurableName,
+                    StreamName = stream,
                     Config = handle.Config,
                 },
             };
@@ -95,6 +106,13 @@ public sealed class ConsumerManager : IDisposable
             .OrderBy(x => x, StringComparer.Ordinal)
             .ToArray();
 
+    public IReadOnlyList<JetStreamConsumerInfo> ListConsumerInfos(string stream)
+        => _consumers
+            .Where(kv => string.Equals(kv.Key.Stream, stream, StringComparison.Ordinal))
+            .OrderBy(kv => kv.Key.Name, StringComparer.Ordinal)
+            .Select(kv => new JetStreamConsumerInfo { Name = kv.Value.Config.DurableName, StreamName = stream, Config = kv.Value.Config })
+            .ToList();
+
     public bool Pause(string stream, string durableName, bool paused)
     {
         if (!_consumers.TryGetValue((stream, durableName), out var handle))