PR 4.1 — ITagDiscovery via GalaxyRepositoryClient + AlarmRefBuilder

Browse path online. GalaxyDriver now implements ITagDiscovery against the
gateway's GalaxyRepositoryClient (PR 0.1's mxaccessgw browse RPC) and feeds
the address-space builder one folder per gobject + one variable per dynamic
attribute, with alarm-bearing attributes carrying all five sub-attribute refs
the server-level AlarmConditionService (PR 2.2) needs.

Files:
- Browse/IGalaxyHierarchySource.cs — driver-side seam between the discoverer
  and the gateway. Test fakes return canned hierarchies so the discoverer's
  translation logic is exercised without a real gRPC channel.
- Browse/GatewayGalaxyHierarchySource.cs — production wrapper around
  GalaxyRepositoryClient.DiscoverHierarchyAsync (paged internally).
- Browse/GalaxyDiscoverer.cs — translates GalaxyObject → IAddressSpaceBuilder
  calls. Browse name = contained_name (falls back to tag_name); full
  reference = attr.full_tag_reference when set, else tag_name + "." +
  attribute_name. Skips objects/attributes with empty identity.
- Browse/DataTypeMap.cs — mx_data_type → DriverDataType (port from legacy
  GalaxyProxyDriver.MapDataType, same fallback to String for unknown codes).
- Browse/SecurityMap.cs — security_classification → SecurityClassification
  (port from legacy GalaxyProxyDriver.MapSecurity).
- Browse/AlarmRefBuilder.cs — populates the five sub-attribute refs by
  Galaxy convention (.InAlarm/.Priority/.DescAttrName/.Acked/.AckMsg). The
  same convention the legacy GalaxyAlarmTracker hard-coded; concentrated
  here so PR 2.2's service receives complete AlarmConditionInfo rows.

GalaxyDriver:
- Added internal ctor accepting IGalaxyHierarchySource? for test injection.
  Default lazily builds GatewayGalaxyHierarchySource around a
  GalaxyRepositoryClient constructed from options on first DiscoverAsync.
- Owned GalaxyRepositoryClient disposed in Dispose.
- ApiKey resolution is currently a passthrough of ApiKeySecretRef — PR 4.W
  (or follow-up) wires DPAPI-backed secret resolution.

csproj: path-based ProjectReference to mxaccessgw (the user is shipping
that repo on a parallel track; both repos sit side-by-side on the dev box).
Tests project also references MxGateway.Contracts directly to construct
GalaxyObject / GalaxyAttribute fixtures.

Tests: 10 new in Browse/GalaxyDiscovererTests.cs covering folder-per-object,
variable-per-attribute, full-ref defaulting + gw-supplied override, browse-
name fallback, every metadata field propagation, alarm sub-attribute ref
population, non-alarm rows skip MarkAsAlarmCondition, empty-identity skips,
empty-attribute-name skips, end-to-end through GalaxyDriver.DiscoverAsync.
20 total Galaxy tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs

@@ -1,6 +1,8 @@
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
+using MxGateway.Client;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Browse;
 using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Config;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy;
@@ -20,12 +22,19 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy;
 ///     <see cref="GalaxyDriverFactoryExtensions"/> registers under driver-type name
 ///     "GalaxyMxGateway" so both paths can be live simultaneously during parity testing.
 /// </remarks>
-public sealed class GalaxyDriver : IDriver, IDisposable
+public sealed class GalaxyDriver : IDriver, ITagDiscovery, IDisposable
 {
     private readonly string _driverInstanceId;
     private readonly GalaxyDriverOptions _options;
     private readonly ILogger<GalaxyDriver> _logger;
 
+    // PR 4.1 — IGalaxyHierarchySource is the test seam for browse. When null, the driver
+    // lazily builds a GatewayGalaxyHierarchySource around a GalaxyRepositoryClient on
+    // first DiscoverAsync. Tests inject a fake source via the internal ctor to exercise
+    // GalaxyDiscoverer's translation logic without a real gRPC channel.
+    private IGalaxyHierarchySource? _hierarchySource;
+    private GalaxyRepositoryClient? _ownedRepositoryClient;
+
     private DriverHealth _health = new(DriverState.Unknown, null, null);
     private bool _disposed;
 
@@ -33,12 +42,27 @@ public sealed class GalaxyDriver : IDriver, IDisposable
         string driverInstanceId,
         GalaxyDriverOptions options,
         ILogger<GalaxyDriver>? logger = null)
+        : this(driverInstanceId, options, hierarchySource: null, logger)
+    {
+    }
+
+    /// <summary>
+    ///     Test-visible ctor — inject a custom <see cref="IGalaxyHierarchySource"/> so
+    ///     <see cref="DiscoverAsync"/> can be exercised against canned hierarchies without
+    ///     building a real gRPC channel.
+    /// </summary>
+    internal GalaxyDriver(
+        string driverInstanceId,
+        GalaxyDriverOptions options,
+        IGalaxyHierarchySource? hierarchySource,
+        ILogger<GalaxyDriver>? logger = null)
     {
         _driverInstanceId = !string.IsNullOrWhiteSpace(driverInstanceId)
             ? driverInstanceId
             : throw new ArgumentException("Driver instance id required.", nameof(driverInstanceId));
         _options = options ?? throw new ArgumentNullException(nameof(options));
         _logger = logger ?? NullLogger<GalaxyDriver>.Instance;
+        _hierarchySource = hierarchySource;
     }
 
     /// <inheritdoc />
@@ -93,10 +117,52 @@ public sealed class GalaxyDriver : IDriver, IDisposable
     /// <inheritdoc />
     public Task FlushOptionalCachesAsync(CancellationToken cancellationToken) => Task.CompletedTask;
 
+    // ===== ITagDiscovery (PR 4.1) =====
+
+    /// <inheritdoc />
+    public async Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        ArgumentNullException.ThrowIfNull(builder);
+
+        var source = _hierarchySource ??= BuildDefaultHierarchySource();
+        var discoverer = new GalaxyDiscoverer(source);
+        await discoverer.DiscoverAsync(builder, cancellationToken).ConfigureAwait(false);
+    }
+
+    /// <summary>
+    ///     Lazily builds the default <see cref="IGalaxyHierarchySource"/> from
+    ///     <c>_options.Gateway</c>. Owned <see cref="GalaxyRepositoryClient"/> is disposed in
+    ///     <see cref="Dispose"/>. Tests bypass this by injecting their own source via the
+    ///     internal ctor.
+    /// </summary>
+    private IGalaxyHierarchySource BuildDefaultHierarchySource()
+    {
+        var gw = _options.Gateway;
+        var clientOptions = new MxGatewayClientOptions
+        {
+            Endpoint = new Uri(gw.Endpoint, UriKind.Absolute),
+            // PR 4.1 stub: ApiKeySecretRef is currently treated as the literal API key.
+            // PR 4.W (or a follow-up) wires up DPAPI-backed secret resolution.
+            ApiKey = gw.ApiKeySecretRef,
+            UseTls = gw.UseTls,
+            CaCertificatePath = gw.CaCertificatePath,
+            ConnectTimeout = TimeSpan.FromSeconds(gw.ConnectTimeoutSeconds),
+            DefaultCallTimeout = TimeSpan.FromSeconds(gw.DefaultCallTimeoutSeconds),
+            StreamTimeout = gw.StreamTimeoutSeconds > 0
+                ? TimeSpan.FromSeconds(gw.StreamTimeoutSeconds)
+                : null,
+        };
+        _ownedRepositoryClient = GalaxyRepositoryClient.Create(clientOptions);
+        return new GatewayGalaxyHierarchySource(_ownedRepositoryClient);
+    }
+
     public void Dispose()
     {
         if (_disposed) return;
         _disposed = true;
-        // No owned IDisposables until PR 4.2's GalaxyMxSession lands.
+        _ownedRepositoryClient?.DisposeAsync().AsTask().GetAwaiter().GetResult();
+        _ownedRepositoryClient = null;
+        _hierarchySource = null;
     }
 }