feat: complete jetstream mirror source strict runtime parity

src/NATS.Server/JetStream/MirrorSource/SourceCoordinator.cs

@@ -18,6 +18,13 @@ public sealed class SourceCoordinator
 
     public async Task OnOriginAppendAsync(StoredMessage message, CancellationToken ct)
     {
+        if (!string.IsNullOrWhiteSpace(_sourceConfig.SourceAccount)
+            && !string.IsNullOrWhiteSpace(message.Account)
+            && !string.Equals(_sourceConfig.SourceAccount, message.Account, StringComparison.Ordinal))
+        {
+            return;
+        }
+
         var subject = message.Subject;
         if (!string.IsNullOrWhiteSpace(_sourceConfig.SubjectTransformPrefix))
             subject = $"{_sourceConfig.SubjectTransformPrefix}{subject}";

src/NATS.Server/JetStream/Storage/StoredMessage.cs

@@ -6,5 +6,6 @@ public sealed class StoredMessage
     public string Subject { get; init; } = string.Empty;
     public ReadOnlyMemory<byte> Payload { get; init; }
     public DateTime TimestampUtc { get; init; } = DateTime.UtcNow;
+    public string? Account { get; init; }
     public bool Redelivered { get; init; }
 }