feat: complete final jetstream parity transport and runtime baselines

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

@@ -24,6 +24,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
             Sequence = _last,
             Subject = subject,
             Payload = payload.ToArray(),
+            TimestampUtc = DateTime.UtcNow,
         };
         _messages[_last] = stored;
 
@@ -32,6 +33,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
             Sequence = stored.Sequence,
             Subject = stored.Subject,
             PayloadBase64 = Convert.ToBase64String(stored.Payload.ToArray()),
+            TimestampUtc = stored.TimestampUtc,
         });
         await File.AppendAllTextAsync(_dataFilePath, line + Environment.NewLine, ct);
         return _last;
@@ -79,6 +81,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
                 Sequence = x.Sequence,
                 Subject = x.Subject,
                 PayloadBase64 = Convert.ToBase64String(x.Payload.ToArray()),
+                TimestampUtc = x.TimestampUtc,
             })
             .ToArray();
         return ValueTask.FromResult(JsonSerializer.SerializeToUtf8Bytes(snapshot));
@@ -101,6 +104,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
                         Sequence = record.Sequence,
                         Subject = record.Subject ?? string.Empty,
                         Payload = Convert.FromBase64String(record.PayloadBase64 ?? string.Empty),
+                        TimestampUtc = record.TimestampUtc,
                     };
                     _messages[record.Sequence] = message;
                     _last = Math.Max(_last, record.Sequence);
@@ -119,6 +123,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
             Messages = (ulong)_messages.Count,
             FirstSeq = _messages.Count == 0 ? 0UL : _messages.Keys.Min(),
             LastSeq = _last,
+            Bytes = (ulong)_messages.Values.Sum(m => m.Payload.Length),
         });
     }
 
@@ -172,6 +177,7 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
                 Sequence = message.Sequence,
                 Subject = message.Subject,
                 PayloadBase64 = Convert.ToBase64String(message.Payload.ToArray()),
+                TimestampUtc = message.TimestampUtc,
             }));
         }
 
@@ -183,5 +189,6 @@ public sealed class FileStore : IStreamStore, IAsyncDisposable
         public ulong Sequence { get; init; }
         public string? Subject { get; init; }
         public string? PayloadBase64 { get; init; }
+        public DateTime TimestampUtc { get; init; }
     }
 }