feat: port session 19 — JetStream Core

- JetStreamTypes: JetStreamConfig, JetStreamStats, JetStreamAccountLimits,
  JetStreamTier, JetStreamAccountStats, JetStream engine, JsAccount, JsaUsage
- JetStreamApiTypes: 50+ JSApi request/response types, API subject constants
- JetStreamErrors: JsApiError + JsApiErrors with all 203 error codes
- JetStreamVersioning: version constants and API level helpers
- JetStreamBatching: Batching, BatchGroup, BatchStagedDiff, BatchApply
- Removed JetStreamConfig/JetStreamState stubs from NatsServerTypes.cs
- 374 features complete (IDs 1368-1519, 1751-1972)

dotnet/src/ZB.MOM.NatsNet.Server/JetStream/JetStreamVersioning.cs

@@ -0,0 +1,106 @@
+// Copyright 2024-2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Adapted from server/jetstream_versioning.go in the NATS server Go source.
+
+namespace ZB.MOM.NatsNet.Server;
+
+/// <summary>
+/// JetStream API level versioning constants and helpers.
+/// Mirrors server/jetstream_versioning.go.
+/// </summary>
+public static class JetStreamVersioning
+{
+    /// <summary>Maximum supported JetStream API level for this server.</summary>
+    public const int JsApiLevel = 3;
+
+    /// <summary>Metadata key that carries the required API level for a stream or consumer asset.</summary>
+    public const string JsRequiredLevelMetadataKey = "_nats.req.level";
+
+    /// <summary>Metadata key that carries the server version that created/updated the asset.</summary>
+    public const string JsServerVersionMetadataKey = "_nats.ver";
+
+    /// <summary>Metadata key that carries the server API level that created/updated the asset.</summary>
+    public const string JsServerLevelMetadataKey = "_nats.level";
+
+    // ---- API level feature gates ----
+    // These document which API level each feature requires.
+    // They correspond to the requires() calls in setStaticStreamMetadata / setStaticConsumerMetadata.
+
+    /// <summary>API level required for per-message TTL and SubjectDeleteMarkerTTL (v2.11).</summary>
+    public const int ApiLevelForTTL = 1;
+
+    /// <summary>API level required for consumer PauseUntil (v2.11).</summary>
+    public const int ApiLevelForConsumerPause = 1;
+
+    /// <summary>API level required for priority groups (v2.11).</summary>
+    public const int ApiLevelForPriorityGroups = 1;
+
+    /// <summary>API level required for counter CRDTs (v2.12).</summary>
+    public const int ApiLevelForCounters = 2;
+
+    /// <summary>API level required for atomic batch publishing (v2.12).</summary>
+    public const int ApiLevelForAtomicPublish = 2;
+
+    /// <summary>API level required for message scheduling (v2.12).</summary>
+    public const int ApiLevelForMsgSchedules = 2;
+
+    /// <summary>API level required for async persist mode (v2.12).</summary>
+    public const int ApiLevelForAsyncPersist = 2;
+
+    // ---- Helper methods ----
+
+    /// <summary>
+    /// Returns the required API level string from stream or consumer metadata,
+    /// or an empty string if not set.
+    /// Mirrors <c>getRequiredApiLevel</c>.
+    /// </summary>
+    public static string GetRequiredApiLevel(IDictionary<string, string>? metadata)
+    {
+        if (metadata is not null && metadata.TryGetValue(JsRequiredLevelMetadataKey, out var l) && l.Length > 0)
+            return l;
+        return string.Empty;
+    }
+
+    /// <summary>
+    /// Returns whether this server supports the required API level encoded in the asset's metadata.
+    /// Mirrors <c>supportsRequiredApiLevel</c>.
+    /// </summary>
+    public static bool SupportsRequiredApiLevel(IDictionary<string, string>? metadata)
+    {
+        var l = GetRequiredApiLevel(metadata);
+        if (l.Length == 0) return true;
+        return int.TryParse(l, out var level) && level <= JsApiLevel;
+    }
+
+    /// <summary>
+    /// Removes dynamic (per-response) versioning fields from metadata.
+    /// These should never be stored; only added in API responses.
+    /// Mirrors <c>deleteDynamicMetadata</c>.
+    /// </summary>
+    public static void DeleteDynamicMetadata(IDictionary<string, string> metadata)
+    {
+        metadata.Remove(JsServerVersionMetadataKey);
+        metadata.Remove(JsServerLevelMetadataKey);
+    }
+
+    /// <summary>
+    /// Returns whether a request should be rejected based on the Nats-Required-Api-Level header value.
+    /// Mirrors <c>errorOnRequiredApiLevel</c>.
+    /// </summary>
+    public static bool ErrorOnRequiredApiLevel(string? reqApiLevelHeader)
+    {
+        if (string.IsNullOrEmpty(reqApiLevelHeader)) return false;
+        return !int.TryParse(reqApiLevelHeader, out var minLevel) || JsApiLevel < minLevel;
+    }
+}