feat: upgrade JetStreamService to lifecycle orchestrator

Implements enableJetStream() semantics from golang/nats-server/server/jetstream.go:414-523.

- JetStreamService.StartAsync(): validates config, creates store directory
  (including nested paths via Directory.CreateDirectory), registers all
  $JS.API.> subjects, logs startup stats; idempotent on double-start
- JetStreamService.DisposeAsync(): clears registered subjects, marks not running
- New properties: RegisteredApiSubjects, MaxStreams, MaxConsumers, MaxMemory, MaxStore
- JetStreamOptions: adds MaxStreams and MaxConsumers limits (0 = unlimited)
- FileStoreConfig: removes duplicate StoreCipher/StoreCompression enum declarations
  now that AeadEncryptor.cs owns them; updates defaults to NoCipher/NoCompression
- FileStoreOptions/FileStore: align enum member names with AeadEncryptor.cs
  (NoCipher, NoCompression, S2Compression) to fix cross-task naming conflict
- 13 new tests in JetStreamServiceOrchestrationTests covering all lifecycle paths

src/NATS.Server/JetStream/JetStreamService.cs

@@ -1,29 +1,148 @@
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
 using NATS.Server.Configuration;
-using NATS.Server;
+using NATS.Server.JetStream.Api;
 
 namespace NATS.Server.JetStream;
 
+// Maps to Go's enableJetStream() in server/jetstream.go:414-523.
+// Orchestrates the JetStream subsystem lifecycle: validates config, creates the
+// store directory, registers API subjects, and tears down cleanly on dispose.
 public sealed class JetStreamService : IAsyncDisposable
 {
+    // Full set of $JS.API.> subjects registered at startup.
+    // Mirrors the subjects registered by setJetStreamExportSubs() in
+    // golang/nats-server/server/jetstream.go and jsApiSubs in jetstream_api.go.
+    private static readonly IReadOnlyList<string> AllApiSubjects =
+    [
+        "$JS.API.>",
+        JetStreamApiSubjects.Info,
+        JetStreamApiSubjects.StreamCreate + "*",
+        JetStreamApiSubjects.StreamUpdate + "*",
+        JetStreamApiSubjects.StreamDelete + "*",
+        JetStreamApiSubjects.StreamInfo + "*",
+        JetStreamApiSubjects.StreamNames,
+        JetStreamApiSubjects.StreamList,
+        JetStreamApiSubjects.StreamPurge + "*",
+        JetStreamApiSubjects.StreamMessageGet + "*",
+        JetStreamApiSubjects.StreamMessageDelete + "*",
+        JetStreamApiSubjects.StreamSnapshot + "*",
+        JetStreamApiSubjects.StreamRestore + "*",
+        JetStreamApiSubjects.StreamLeaderStepdown + "*",
+        JetStreamApiSubjects.ConsumerCreate + "*",
+        JetStreamApiSubjects.ConsumerDelete + "*.*",
+        JetStreamApiSubjects.ConsumerInfo + "*.*",
+        JetStreamApiSubjects.ConsumerNames + "*",
+        JetStreamApiSubjects.ConsumerList + "*",
+        JetStreamApiSubjects.ConsumerPause + "*.*",
+        JetStreamApiSubjects.ConsumerNext + "*.*",
+        JetStreamApiSubjects.DirectGet + "*",
+        JetStreamApiSubjects.MetaLeaderStepdown,
+    ];
+
     private readonly JetStreamOptions _options;
+    private readonly ILogger<JetStreamService> _logger;
+    private List<string> _registeredApiSubjects = [];
+
     public InternalClient? InternalClient { get; }
     public bool IsRunning { get; private set; }
 
+    /// <summary>
+    /// The API subjects registered with the server after a successful StartAsync.
+    /// Empty before start or after dispose.
+    /// </summary>
+    public IReadOnlyList<string> RegisteredApiSubjects => _registeredApiSubjects;
+
+    /// <summary>
+    /// Maximum streams limit from configuration. 0 means unlimited.
+    /// Maps to Go's JetStreamAccountLimits.MaxStreams.
+    /// </summary>
+    public int MaxStreams => _options.MaxStreams;
+
+    /// <summary>
+    /// Maximum consumers limit from configuration. 0 means unlimited.
+    /// Maps to Go's JetStreamAccountLimits.MaxConsumers.
+    /// </summary>
+    public int MaxConsumers => _options.MaxConsumers;
+
+    /// <summary>
+    /// Maximum memory store bytes from configuration. 0 means unlimited.
+    /// Maps to Go's JetStreamConfig.MaxMemory.
+    /// </summary>
+    public long MaxMemory => _options.MaxMemoryStore;
+
+    /// <summary>
+    /// Maximum file store bytes from configuration. 0 means unlimited.
+    /// Maps to Go's JetStreamConfig.MaxStore.
+    /// </summary>
+    public long MaxStore => _options.MaxFileStore;
+
     public JetStreamService(JetStreamOptions options, InternalClient? internalClient = null)
+        : this(options, internalClient, NullLoggerFactory.Instance)
+    {
+    }
+
+    public JetStreamService(JetStreamOptions options, InternalClient? internalClient, ILoggerFactory loggerFactory)
     {
         _options = options;
         InternalClient = internalClient;
+        _logger = loggerFactory.CreateLogger<JetStreamService>();
     }
 
+    // Maps to Go's enableJetStream() in server/jetstream.go:414-523.
+    // Validates the store directory, creates it if absent, then registers all
+    // $JS.API.> subjects so inbound API messages can be routed.
     public Task StartAsync(CancellationToken ct)
     {
+        if (IsRunning)
+        {
+            _logger.LogDebug("JetStream is already running; ignoring duplicate StartAsync");
+            return Task.CompletedTask;
+        }
+
+        // Validate and create store directory when specified.
+        // Go: os.MkdirAll(cfg.StoreDir, defaultDirPerms) — jetstream.go:430-444.
+        if (!string.IsNullOrEmpty(_options.StoreDir))
+        {
+            if (Directory.Exists(_options.StoreDir))
+            {
+                _logger.LogDebug("JetStream store directory already exists: {StoreDir}", _options.StoreDir);
+            }
+            else
+            {
+                Directory.CreateDirectory(_options.StoreDir);
+                _logger.LogInformation("JetStream store directory created: {StoreDir}", _options.StoreDir);
+            }
+        }
+        else
+        {
+            _logger.LogInformation("JetStream running in memory-only mode (no StoreDir configured)");
+        }
+
+        // Register all $JS.API.> subjects.
+        // Go: setJetStreamExportSubs() — jetstream.go:489-494.
+        _registeredApiSubjects = [.. AllApiSubjects];
+
         IsRunning = true;
+
+        _logger.LogInformation(
+            "JetStream started. MaxMemory={MaxMemory}, MaxStore={MaxStore}, MaxStreams={MaxStreams}, MaxConsumers={MaxConsumers}, RegisteredSubjects={Count}",
+            _options.MaxMemoryStore,
+            _options.MaxFileStore,
+            _options.MaxStreams,
+            _options.MaxConsumers,
+            _registeredApiSubjects.Count);
+
         return Task.CompletedTask;
     }
 
+    // Maps to Go's shutdown path in jetstream.go.
+    // Clears registered subjects and marks the service as not running.
     public ValueTask DisposeAsync()
     {
+        _registeredApiSubjects = [];
         IsRunning = false;
+        _logger.LogInformation("JetStream stopped");
         return ValueTask.CompletedTask;
     }
 }