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/WebSocket/WebSocketOptionsValidatorParityBatch2Tests.cs

@@ -0,0 +1,172 @@
+using NATS.Server.Auth;
+using NATS.Server.WebSocket;
+
+namespace NATS.Server.Tests.WebSocket;
+
+public class WebSocketOptionsValidatorParityBatch2Tests
+{
+    [Fact]
+    public void Validate_rejects_tls_listener_without_cert_key_when_not_no_tls()
+    {
+        var opts = new NatsOptions
+        {
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = false,
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeFalse();
+        result.Errors.ShouldContain(e => e.Contains("TLS", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Validate_rejects_invalid_allowed_origins()
+    {
+        var opts = new NatsOptions
+        {
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = true,
+                AllowedOrigins = ["not-a-uri"],
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeFalse();
+        result.Errors.ShouldContain(e => e.Contains("allowed origin", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Validate_rejects_no_auth_user_not_present_in_configured_users()
+    {
+        var opts = new NatsOptions
+        {
+            Users = [new User { Username = "alice", Password = "x" }],
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = true,
+                NoAuthUser = "bob",
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeFalse();
+        result.Errors.ShouldContain(e => e.Contains("NoAuthUser", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Validate_rejects_username_or_token_when_users_or_nkeys_are_set()
+    {
+        var opts = new NatsOptions
+        {
+            Users = [new User { Username = "alice", Password = "x" }],
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = true,
+                Username = "ws-user",
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeFalse();
+        result.Errors.ShouldContain(e => e.Contains("users", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Validate_rejects_jwt_cookie_without_trusted_operators()
+    {
+        var opts = new NatsOptions
+        {
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = true,
+                JwtCookie = "jwt",
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeFalse();
+        result.Errors.ShouldContain(e => e.Contains("JwtCookie", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Validate_rejects_reserved_response_headers_override()
+    {
+        var opts = new NatsOptions
+        {
+            TrustedKeys = ["OP1"],
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = true,
+                Headers = new Dictionary<string, string>
+                {
+                    ["Sec-WebSocket-Accept"] = "bad",
+                },
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeFalse();
+        result.Errors.ShouldContain(e => e.Contains("reserved", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Validate_rejects_tls_pinned_certs_when_websocket_tls_is_disabled()
+    {
+        var opts = new NatsOptions
+        {
+            TlsPinnedCerts = ["ABCDEF0123"],
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = true,
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeFalse();
+        result.Errors.ShouldContain(e => e.Contains("TLSPinnedCerts", StringComparison.OrdinalIgnoreCase));
+    }
+
+    [Fact]
+    public void Validate_accepts_valid_minimal_configuration()
+    {
+        var opts = new NatsOptions
+        {
+            TrustedKeys = ["OP1"],
+            Users = [new User { Username = "alice", Password = "x" }],
+            WebSocket = new WebSocketOptions
+            {
+                Port = 8080,
+                NoTls = true,
+                NoAuthUser = "alice",
+                AllowedOrigins = ["https://app.example.com"],
+                JwtCookie = "jwt",
+                Headers = new Dictionary<string, string>
+                {
+                    ["X-App-Version"] = "1",
+                },
+            },
+        };
+
+        var result = WebSocketOptionsValidator.Validate(opts);
+
+        result.IsValid.ShouldBeTrue();
+        result.Errors.ShouldBeEmpty();
+    }
+}