Merge alarm-fallback cleanup: metrics snapshot/reason, SQL prune, teardown, doc drift

Implements the actionable deferred items from pending.md (B1-B5, C6-C7):
- B1/B2 metrics: provider-switch count in snapshot + bounded reason enum
- B5: drop dead primitive branch from AlarmAttributesSql
- B3/B4 worker: UnAdvise only advised handles (+Dispose tests); remove dead field
- C6/C7: doc clarifications and design-doc superseded notes

Verified: gateway tests on macOS, net48/x86 worker suite (318 passed) on windev.

CLAUDE.md

@@ -100,7 +100,7 @@ When source code changes, build and test the affected component before reporting
 ## Design Sources To Consult Before Non-Trivial Changes
 
 - `gateway.md` — top-level architecture, command/event surface, IPC envelope, STA thread model, fault handling.
-- `glauth.md` — local LDAP server (GLAuth on `localhost:3893`, base DN `dc=zb,dc=local`) used for dev authn. Pre-provisioned users (`admin/admin123`, `readonly/readonly123`, etc.) and the role→capability mapping live there.
+- `glauth.md` — shared GLAuth LDAP server (`10.100.0.35:3893`, base DN `dc=zb,dc=local`, source of truth `scadaproj/infra/glauth/`) used for dev authn. Dashboard test users (`multi-role`/`password` = Administrator, `gw-viewer`/`password` = Viewer) and the role→capability mapping live there.
 - `docs/DesignDecisions.md` — v1 choices (MXAccess COM target `LMXProxyServerClass` from `C:\Program Files (x86)\ArchestrA\Framework\Bin\ArchestrA.MXAccess.dll`, API-key-in-SQLite auth, fail-fast event backpressure, etc.).
 - `docs/GatewayProcessDesign.md`, `docs/MxAccessWorkerInstanceDesign.md`, `docs/WorkerFrameProtocol.md`, `docs/WorkerProcessLauncher.md` — detailed component designs.
 - `docs/GatewayConfiguration.md` — full `MxGateway:*` options bound by `GatewayOptions` and validated at startup by `GatewayOptionsValidator`.

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Cli/CliArguments.cs

@@ -44,7 +44,6 @@ internal sealed class CliArguments
 
     /// <summary>Returns whether the named flag was present in the arguments.</summary>
     /// <param name="name">The flag name (without '--' prefix).</param>
-    /// <returns>True if the flag was present; otherwise false.</returns>
     public bool HasFlag(string name)
     {
         return _flags.Contains(name);
@@ -52,7 +51,6 @@ internal sealed class CliArguments
 
     /// <summary>Returns the value for a named argument, or <c>null</c> if absent.</summary>
     /// <param name="name">The argument name (without '--' prefix).</param>
-    /// <returns>The argument value, or null if the argument was not provided.</returns>
     public string? GetOptional(string name)
     {
         return _values.TryGetValue(name, out string? value)
@@ -62,7 +60,6 @@ internal sealed class CliArguments
 
     /// <summary>Returns the value for a required named argument, or throws if absent.</summary>
     /// <param name="name">The argument name (without '--' prefix).</param>
-    /// <returns>The argument value.</returns>
     public string GetRequired(string name)
     {
         string? value = GetOptional(name);
@@ -77,7 +74,6 @@ internal sealed class CliArguments
     /// <summary>Parses and returns an int32 argument, or the default value if absent.</summary>
     /// <param name="name">The argument name (without '--' prefix).</param>
     /// <param name="defaultValue">The default value if the argument is absent; if <c>null</c>, the argument is required.</param>
-    /// <returns>The parsed int32 value, or the default if absent.</returns>
     public int GetInt32(string name, int? defaultValue = null)
     {
         string? value = GetOptional(name);
@@ -97,7 +93,6 @@ internal sealed class CliArguments
     /// <summary>Parses and returns a uint32 argument, or the default value if absent.</summary>
     /// <param name="name">The argument name (without '--' prefix).</param>
     /// <param name="defaultValue">The default value if the argument is absent.</param>
-    /// <returns>The parsed uint32 value, or the default if absent.</returns>
     public uint GetUInt32(string name, uint defaultValue)
     {
         string? value = GetOptional(name);
@@ -109,7 +104,6 @@ internal sealed class CliArguments
     /// <summary>Parses and returns a uint64 argument, or the default value if absent.</summary>
     /// <param name="name">The argument name (without '--' prefix).</param>
     /// <param name="defaultValue">The default value if the argument is absent.</param>
-    /// <returns>The parsed uint64 value, or the default if absent.</returns>
     public ulong GetUInt64(string name, ulong defaultValue)
     {
         string? value = GetOptional(name);
@@ -121,7 +115,6 @@ internal sealed class CliArguments
     /// <summary>Parses and returns a TimeSpan argument, or the default value if absent. Supports "ms", "s", and standard TimeSpan format.</summary>
     /// <param name="name">The argument name (without '--' prefix).</param>
     /// <param name="defaultValue">The default value if the argument is absent.</param>
-    /// <returns>The parsed TimeSpan value, or the default if absent.</returns>
     public TimeSpan GetDuration(string name, TimeSpan defaultValue)
     {
         string? value = GetOptional(name);

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Cli/MxGatewayCliClientAdapter.cs

@@ -100,8 +100,7 @@ internal sealed class MxGatewayCliClientAdapter : IMxGatewayCliClient
         return _galaxyClient.Value.WatchDeployEventsRawAsync(request, cancellationToken);
     }
 
-    /// <summary>Disposes the galaxy client (if created) and the underlying gateway client.</summary>
+    /// <inheritdoc />
-    /// <returns>A value task that completes when both clients are disposed.</returns>
     public async ValueTask DisposeAsync()
     {
         if (_galaxyClient.IsValueCreated)

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Cli/MxGatewayCliSecretRedactor.cs

@@ -6,7 +6,6 @@ internal static class MxGatewayCliSecretRedactor
     /// <summary>Replaces occurrences of the API key in the value with a redacted placeholder.</summary>
     /// <param name="value">The message text to redact.</param>
     /// <param name="apiKey">The API key to remove; no redaction if null or empty.</param>
-    /// <returns>The message text with any API key occurrence replaced by <c>[redacted]</c>.</returns>
     public static string Redact(string value, string? apiKey)
     {
         if (string.IsNullOrEmpty(value) || string.IsNullOrEmpty(apiKey))

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Cli/MxGatewayClientCli.cs

@@ -22,7 +22,6 @@ public static class MxGatewayClientCli
     /// <param name="args">Command-line arguments (command name followed by options).</param>
     /// <param name="standardOutput">TextWriter for command output.</param>
     /// <param name="standardError">TextWriter for error messages.</param>
-    /// <returns>The process exit code (0 for success, 1 for error).</returns>
     public static int Run(
         string[] args,
         TextWriter standardOutput,
@@ -39,7 +38,6 @@ public static class MxGatewayClientCli
     /// <param name="standardError">TextWriter for error messages.</param>
     /// <param name="clientFactory">Optional factory to create the gateway client; defaults to MxGatewayClient.Create.</param>
     /// <param name="standardInput">Optional TextReader for batch-mode stdin; defaults to <see cref="Console.In"/>.</param>
-    /// <returns>A task that resolves to the process exit code (0 for success, 1 for error).</returns>
     public static Task<int> RunAsync(
         string[] args,
         TextWriter standardOutput,

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/BrowseChildrenSmokeTests.cs

@@ -14,7 +14,6 @@ public sealed class BrowseChildrenSmokeTests
     /// Verifies that BrowseChildren returns a non-zero cache sequence and
     /// a consistent children/child-has-children count from a live gateway.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact(Skip = "Set MXGATEWAY_API_KEY and MXGATEWAY_ENDPOINT to enable.")]
     public async Task BrowseChildren_LiveGateway_ReturnsRootsWithCacheSequence()
     {

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/FakeGalaxyRepositoryTransport.cs

@@ -8,10 +8,14 @@ namespace ZB.MOM.WW.MxGateway.Client.Tests;
 /// </summary>
 internal sealed class FakeGalaxyRepositoryTransport(MxGatewayClientOptions options) : IGalaxyRepositoryClientTransport
 {
-    /// <inheritdoc />
+    /// <summary>
+    /// Gets the gateway client options.
+    /// </summary>
     public MxGatewayClientOptions Options { get; } = options;
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Gets the raw gRPC client; always null for the fake.
+    /// </summary>
     public GalaxyRepository.GalaxyRepositoryClient? RawClient => null;
 
     /// <summary>
@@ -62,7 +66,11 @@ internal sealed class FakeGalaxyRepositoryTransport(MxGatewayClientOptions optio
     /// </summary>
     public Queue<Exception> DiscoverHierarchyExceptions { get; } = new();
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the request and either throws a queued exception or returns the configured reply.
+    /// </summary>
+    /// <param name="request">The TestConnectionRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<TestConnectionReply> TestConnectionAsync(
         TestConnectionRequest request,
         CallOptions callOptions)
@@ -76,7 +84,11 @@ internal sealed class FakeGalaxyRepositoryTransport(MxGatewayClientOptions optio
         return Task.FromResult(TestConnectionReply);
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the request and either throws a queued exception or returns the configured reply.
+    /// </summary>
+    /// <param name="request">The GetLastDeployTimeRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<GetLastDeployTimeReply> GetLastDeployTimeAsync(
         GetLastDeployTimeRequest request,
         CallOptions callOptions)
@@ -90,7 +102,11 @@ internal sealed class FakeGalaxyRepositoryTransport(MxGatewayClientOptions optio
         return Task.FromResult(GetLastDeployTimeReply);
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the request and either throws a queued exception or returns the configured reply.
+    /// </summary>
+    /// <param name="request">The DiscoverHierarchyRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<DiscoverHierarchyReply> DiscoverHierarchyAsync(
         DiscoverHierarchyRequest request,
         CallOptions callOptions)
@@ -119,7 +135,11 @@ internal sealed class FakeGalaxyRepositoryTransport(MxGatewayClientOptions optio
     /// <summary>Queue of exceptions to throw from BrowseChildren; dequeued in FIFO order.</summary>
     public Queue<Exception> BrowseChildrenExceptions { get; } = new();
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the request and either throws a queued exception or returns the configured reply.
+    /// </summary>
+    /// <param name="request">The BrowseChildrenRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<BrowseChildrenReply> BrowseChildrenAsync(
         BrowseChildrenRequest request,
         CallOptions callOptions)
@@ -157,7 +177,11 @@ internal sealed class FakeGalaxyRepositoryTransport(MxGatewayClientOptions optio
     /// </summary>
     public Func<CancellationToken, Task>? WatchDeployEventsBeforeYield { get; set; }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the request and streams events, checking for queued exceptions and calling WatchDeployEventsBeforeYield before each event.
+    /// </summary>
+    /// <param name="request">The WatchDeployEventsRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public async IAsyncEnumerable<DeployEvent> WatchDeployEventsAsync(
         WatchDeployEventsRequest request,
         CallOptions callOptions)

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/FakeGatewayTransport.cs

@@ -11,10 +11,14 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
     private readonly Queue<MxCommandReply> _invokeReplies = new();
     private readonly List<MxEvent> _events = [];
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Gets the gateway client options.
+    /// </summary>
     public MxGatewayClientOptions Options { get; } = options;
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Gets null, since this is a test fake without a real gRPC client.
+    /// </summary>
     public MxAccessGateway.MxAccessGatewayClient? RawClient => null;
 
     /// <summary>
@@ -98,7 +102,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
     /// </summary>
     public Queue<Exception> InvokeExceptions { get; } = new();
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Verifies that the OpenSessionAsync call is recorded and returns the configured reply.
+    /// </summary>
+    /// <param name="request">The OpenSessionRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<OpenSessionReply> OpenSessionAsync(
         OpenSessionRequest request,
         CallOptions callOptions)
@@ -112,7 +120,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         return Task.FromResult(OpenSessionReply);
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Verifies that the CloseSessionAsync call is recorded and returns the configured reply.
+    /// </summary>
+    /// <param name="request">The CloseSessionRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<CloseSessionReply> CloseSessionAsync(
         CloseSessionRequest request,
         CallOptions callOptions)
@@ -126,7 +138,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         return Task.FromResult(CloseSessionReply);
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Verifies that the InvokeAsync call is recorded and returns the next enqueued reply.
+    /// </summary>
+    /// <param name="request">The MxCommandRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<MxCommandReply> InvokeAsync(
         MxCommandRequest request,
         CallOptions callOptions)
@@ -140,7 +156,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         return Task.FromResult(_invokeReplies.Dequeue());
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Verifies that the StreamEventsAsync call is recorded and yields all enqueued events.
+    /// </summary>
+    /// <param name="request">The StreamEventsRequest to process.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public async IAsyncEnumerable<MxEvent> StreamEventsAsync(
         StreamEventsRequest request,
         CallOptions callOptions)
@@ -173,7 +193,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         _events.Add(gatewayEvent);
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the acknowledge call and returns the next enqueued reply (or default).
+    /// </summary>
+    /// <param name="request">The acknowledge alarm request.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public Task<AcknowledgeAlarmReply> AcknowledgeAlarmAsync(
         AcknowledgeAlarmRequest request,
         CallOptions callOptions)
@@ -194,7 +218,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
             });
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the query call and yields each enqueued snapshot.
+    /// </summary>
+    /// <param name="request">The query active alarms request.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public async IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
         QueryActiveAlarmsRequest request,
         CallOptions callOptions)
@@ -223,7 +251,11 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         _activeAlarmSnapshots.Add(snapshot);
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Records the stream-alarms call and yields each enqueued feed message.
+    /// </summary>
+    /// <param name="request">The stream alarms request.</param>
+    /// <param name="callOptions">Call options specifying RPC behavior.</param>
     public async IAsyncEnumerable<AlarmFeedMessage> StreamAlarmsAsync(
         StreamAlarmsRequest request,
         CallOptions callOptions)

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/GalaxyRepositoryClientTests.cs

@@ -9,7 +9,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that TestConnectionAsync attaches the API key in request metadata and returns the Ok flag.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task TestConnectionAsync_AttachesApiKeyMetadataAndReturnsOkFlag()
     {
@@ -28,7 +27,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that TestConnectionAsync returns false when the server reports NotOk.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task TestConnectionAsync_ReturnsFalseWhenServerReportsNotOk()
     {
@@ -44,7 +42,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that GetLastDeployTimeAsync returns null when the server reports not present.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task GetLastDeployTimeAsync_ReturnsNullWhenNotPresent()
     {
@@ -61,7 +58,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that GetLastDeployTimeAsync returns the timestamp when the server reports it present.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task GetLastDeployTimeAsync_ReturnsTimestampWhenPresent()
     {
@@ -83,7 +79,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that DiscoverHierarchyAsync returns the objects from the server reply.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task DiscoverHierarchyAsync_ReturnsObjectsFromReply()
     {
@@ -146,7 +141,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that DiscoverHierarchyAsync propagates cancellation tokens to the transport.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task DiscoverHierarchyAsync_PropagatesCancellationToTransport()
     {
@@ -167,7 +161,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that TestConnectionAsync retries on transient gRPC failures.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task DiscoverHierarchyAsync_WithRepeatedPageToken_ThrowsProtocolError()
     {
@@ -191,7 +184,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that DiscoverHierarchyAsync maps typed filter options correctly to the request.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task DiscoverHierarchyAsync_WithOptions_MapsTypedFilters()
     {
@@ -226,7 +218,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that TestConnectionAsync retries on transient gRPC failures.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task TestConnectionAsync_RetriesOnTransientGrpcFailure()
     {
@@ -244,7 +235,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that DiscoverHierarchyAsync retries on transient gRPC failures.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task DiscoverHierarchyAsync_RetriesOnTransientGrpcFailure()
     {
@@ -261,7 +251,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that WatchDeployEventsAsync delivers the bootstrap event.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WatchDeployEventsAsync_DeliversBootstrapEvent()
     {
@@ -298,7 +287,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that WatchDeployEventsAsync delivers multiple events in order.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WatchDeployEventsAsync_DeliversMultipleEventsInOrder()
     {
@@ -337,7 +325,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that WatchDeployEventsAsync stops iteration cleanly when cancelled.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WatchDeployEventsAsync_CancellationStopsIterationCleanly()
     {
@@ -382,7 +369,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that WatchDeployEventsAsync throws ObjectDisposedException after the client is disposed.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WatchDeployEventsAsync_ThrowsAfterDisposal()
     {
@@ -398,7 +384,6 @@ public sealed class GalaxyRepositoryClientTests
     /// <summary>
     /// Verifies that TestConnectionAsync throws ObjectDisposedException after the client is disposed.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task TestConnectionAsync_ThrowsAfterDisposal()
     {

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/LazyBrowseNodeTests.cs

@@ -12,7 +12,6 @@ public sealed class LazyBrowseNodeTests
     /// Verifies that calling BrowseAsync with no parent returns the root nodes
     /// from the first BrowseChildren reply and surfaces the per-child has-children hint.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Browse_NoParent_ReturnsRoots()
     {
@@ -37,7 +36,6 @@ public sealed class LazyBrowseNodeTests
     /// <summary>
     /// Verifies that ExpandAsync populates Children and marks the node expanded after one RPC.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Expand_PopulatesChildrenAndMarksExpanded()
     {
@@ -64,7 +62,6 @@ public sealed class LazyBrowseNodeTests
     /// <summary>
     /// Verifies that a second ExpandAsync call is a no-op and issues no additional RPC.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Expand_CalledTwice_NoSecondRpc()
     {
@@ -89,7 +86,6 @@ public sealed class LazyBrowseNodeTests
     /// <summary>
     /// Verifies that an RPC failure (NotFound) during expand is wrapped in MxGatewayException.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Expand_UnknownParent_ThrowsMxGatewayException()
     {
@@ -117,7 +113,6 @@ public sealed class LazyBrowseNodeTests
     /// <summary>
     /// Verifies that ExpandAsync drains multi-page sibling replies and forwards the page token.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Expand_MultiPageSiblings_GathersAllPages()
     {
@@ -152,7 +147,6 @@ public sealed class LazyBrowseNodeTests
     /// <summary>
     /// Verifies that ten concurrent ExpandAsync calls issue exactly one RPC, not ten.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Expand_CalledConcurrently_OnlyFiresOneRpc()
     {
@@ -184,7 +178,6 @@ public sealed class LazyBrowseNodeTests
     /// <summary>
     /// Verifies that BrowseChildrenOptions filter fields are forwarded to the BrowseChildren request.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Browse_WithFilter_ForwardsToRequest()
     {

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/MxGatewayClientAlarmsTests.cs

@@ -12,7 +12,6 @@ namespace ZB.MOM.WW.MxGateway.Client.Tests;
 public sealed class MxGatewayClientAlarmsTests
 {
     /// <summary>AcknowledgeAlarmAsync records request and returns reply.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task AcknowledgeAlarmAsync_RecordsRequestShapeAndReturnsReply()
     {
@@ -49,7 +48,6 @@ public sealed class MxGatewayClientAlarmsTests
     }
 
     /// <summary>AcknowledgeAlarmAsync honors cancellation.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task AcknowledgeAlarmAsync_HonorsCancellation()
     {
@@ -74,7 +72,6 @@ public sealed class MxGatewayClientAlarmsTests
     }
 
     /// <summary>AcknowledgeAlarmAsync maps unauthenticated RPC exception to typed exception.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task AcknowledgeAlarmAsync_MapsUnauthenticated_RpcException_ToTypedException()
     {
@@ -100,7 +97,6 @@ public sealed class MxGatewayClientAlarmsTests
     }
 
     /// <summary>QueryActiveAlarmsAsync streams enqueued snapshots.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task QueryActiveAlarmsAsync_StreamsEnqueuedSnapshots()
     {
@@ -126,7 +122,6 @@ public sealed class MxGatewayClientAlarmsTests
     }
 
     /// <summary>QueryActiveAlarmsAsync passes filter prefix.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task QueryActiveAlarmsAsync_PassesFilterPrefix()
     {
@@ -147,7 +142,6 @@ public sealed class MxGatewayClientAlarmsTests
     }
 
     /// <summary>QueryActiveAlarmsAsync honors cancellation during enumeration.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task QueryActiveAlarmsAsync_HonorsCancellationDuringEnumeration()
     {

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/MxGatewayClientCliTests.cs

@@ -24,7 +24,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that the version command with --json flag prints JSON protocol versions.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_VersionJson_PrintsJsonProtocolVersions()
     {
@@ -39,7 +38,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that the write command builds a write request and prints JSON reply.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_Write_BuildsWriteCommandAndPrintsJsonReply()
     {
@@ -85,7 +83,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that error output redacts sensitive API key values.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_ErrorOutput_RedactsApiKey()
     {
@@ -110,7 +107,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that stream-events with max-events limit stops output in non-JSON format.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_StreamEvents_WithMaxEventsStopsNonJsonOutput()
     {
@@ -153,7 +149,6 @@ public sealed class MxGatewayClientCliTests
 
 
     /// <summary>Verifies that stream-alarms with --max-events stops output and distinguishes payload cases.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_StreamAlarms_WithMaxEventsStopsAndDistinguishesPayloadCases()
     {
@@ -193,7 +188,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that acknowledge-alarm builds a request and prints the JSON reply.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_AcknowledgeAlarm_BuildsRequestAndPrintsJsonReply()
     {
@@ -236,7 +230,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that smoke command closes opened session when a command fails.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_Smoke_WhenCommandFails_ClosesOpenedSession()
     {
@@ -268,7 +261,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that galaxy-test-connection command prints JSON reply.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_GalaxyTestConnection_PrintsJsonReply()
     {
@@ -299,7 +291,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that galaxy-discover command prints hierarchy summary.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_GalaxyDiscover_PrintsHierarchySummary()
     {
@@ -370,7 +361,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that galaxy-watch command prints text output for deploy events.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_GalaxyWatch_PrintsTextOutputForEvents()
     {
@@ -425,7 +415,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that galaxy-watch with --json emits one JSON object per event.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_GalaxyWatch_JsonEmitsOneObjectPerEvent()
     {
@@ -461,7 +450,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that batch mode dispatches a single version command and emits the EOR sentinel.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_Batch_DispatchesVersionAndWritesEndOfRecord()
     {
@@ -488,7 +476,6 @@ public sealed class MxGatewayClientCliTests
     }
 
     /// <summary>Verifies that batch mode routes per-command errors to stdout as JSON between EOR markers.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_Batch_WritesErrorsToStdoutAsJson()
     {
@@ -533,7 +520,6 @@ public sealed class MxGatewayClientCliTests
     /// against exit code 0.
     /// </summary>
     /// <param name="command">The alarm subcommand to validate (e.g. "stream-alarms", "acknowledge-alarm").</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Theory]
     [InlineData("stream-alarms")]
     [InlineData("acknowledge-alarm")]
@@ -588,7 +574,6 @@ public sealed class MxGatewayClientCliTests
     /// against a zero server handle. The fix must fail loudly with a
     /// descriptive <see cref="MxGatewayException"/>.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_BenchReadBulk_WhenRegisterReplyMissingTypedPayload_FailsLoudly()
     {
@@ -639,7 +624,6 @@ public sealed class MxGatewayClientCliTests
     /// kept spinning until <c>--duration-seconds</c> elapsed. After the fix
     /// the bench must exit promptly when the supplied token cancels.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RunAsync_BenchReadBulk_WhenSteadyStateLoopReceivesCancellation_ExitsPromptly()
     {
@@ -734,7 +718,6 @@ public sealed class MxGatewayClientCliTests
     /// to ~49.7 days. The fix must reject negatives with a clear error.
     /// </summary>
     /// <param name="command">The bulk-read subcommand to validate (e.g. "read-bulk", "bench-read-bulk").</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Theory]
     [InlineData("read-bulk")]
     [InlineData("bench-read-bulk")]
@@ -897,8 +880,7 @@ public sealed class MxGatewayClientCliTests
         /// <summary>Optional per-call handler that overrides queue-based behaviour.</summary>
         public Func<MxCommandRequest, CancellationToken, Task<MxCommandReply>>? InvokeHandler { get; init; }
 
-        /// <summary>Releases resources held by the fake CLI client.</summary>
+        /// <inheritdoc />
-        /// <returns>A completed value task.</returns>
         public ValueTask DisposeAsync()
         {
             return ValueTask.CompletedTask;

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/MxGatewayClientSessionTests.cs

@@ -7,7 +7,6 @@ namespace ZB.MOM.WW.MxGateway.Client.Tests;
 public sealed class MxGatewayClientSessionTests
 {
     /// <summary>Verifies that open session attaches API key metadata and cancellation token.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task OpenSessionRawAsync_AttachesApiKeyMetadataAndCancellation()
     {
@@ -23,7 +22,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that open session returns a session with the raw open reply.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task OpenSessionAsync_ReturnsSessionWithRawOpenReply()
     {
@@ -39,7 +37,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that register builds a register command and returns server handle.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RegisterAsync_BuildsRegisterCommandAndReturnsServerHandle()
     {
@@ -65,7 +62,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that add item 2 builds a command with the specified context.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task AddItem2Async_BuildsAddItem2CommandWithContext()
     {
@@ -91,7 +87,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that write raw builds a write command with the raw value.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WriteRawAsync_BuildsWriteCommandWithRawValue()
     {
@@ -123,7 +118,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that write 2 raw builds a write 2 command with value and timestamp.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Write2RawAsync_BuildsWrite2CommandWithValueAndTimestamp()
     {
@@ -152,7 +146,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that subscribe bulk builds one command and returns per-item results.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task SubscribeBulkAsync_BuildsOneBulkCommandAndReturnsPerItemResults()
     {
@@ -192,7 +185,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that stream events yields events in the order received from the gateway.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task StreamEventsAsync_YieldsEventsInGatewayOrder()
     {
@@ -224,7 +216,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that close is explicit and idempotent.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task CloseAsync_IsExplicitAndIdempotent()
     {
@@ -241,7 +232,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that invoke retries safe diagnostic commands on transient RPC failure.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task InvokeAsync_RetriesSafeDiagnosticCommandOnTransientGrpcFailure()
     {
@@ -266,7 +256,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that open session does not retry on transient RPC failure.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task OpenSessionAsync_DoesNotRetryTransientGrpcFailure()
     {
@@ -280,7 +269,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that invoke does not retry write commands on transient RPC failure.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task InvokeAsync_DoesNotRetryWriteCommand()
     {
@@ -296,7 +284,6 @@ public sealed class MxGatewayClientSessionTests
     }
 
     /// <summary>Verifies that invoke helpers pass cancellation token to the transport.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task InvokeHelpers_PassCancellationTokenToTransport()
     {

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/MxGatewayGeneratedContractTests.cs

@@ -3,7 +3,6 @@ namespace ZB.MOM.WW.MxGateway.Client.Tests;
 public sealed class MxGatewayGeneratedContractTests
 {
     /// <summary>Verifies that the generated gRPC client can be instantiated from the client factory.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task GeneratedGrpcClient_CanBeConstructedFromClientFactory()
     {

clients/dotnet/ZB.MOM.WW.MxGateway.Client/GalaxyRepositoryClient.cs

@@ -337,9 +337,6 @@ public sealed class GalaxyRepositoryClient : IAsyncDisposable
             cancellationToken);
     }
 
-    /// <summary>Builds a <see cref="BrowseChildrenRequest"/> from the provided options.</summary>
-    /// <param name="options">Browse children options to convert.</param>
-    /// <returns>The constructed request message.</returns>
     internal static BrowseChildrenRequest BuildBrowseChildrenRequest(BrowseChildrenOptions options)
     {
         ArgumentNullException.ThrowIfNull(options);
@@ -427,7 +424,6 @@ public sealed class GalaxyRepositoryClient : IAsyncDisposable
     /// <summary>
     /// Closes the gRPC channel and releases resources.
     /// </summary>
-    /// <returns>A task that represents the asynchronous dispose operation.</returns>
     public ValueTask DisposeAsync()
     {
         if (_disposed)
@@ -497,9 +493,6 @@ public sealed class GalaxyRepositoryClient : IAsyncDisposable
     private static HttpMessageHandler CreateHttpHandler(MxGatewayClientOptions options) =>
         CreateHttpHandlerForTests(options);
 
-    /// <summary>Creates an <see cref="HttpMessageHandler"/> configured from the provided options for test use.</summary>
-    /// <param name="options">Client options used to configure TLS and timeouts.</param>
-    /// <returns>The configured HTTP message handler.</returns>
     internal static SocketsHttpHandler CreateHttpHandlerForTests(MxGatewayClientOptions options)
     {
         SocketsHttpHandler handler = new()

clients/dotnet/ZB.MOM.WW.MxGateway.Client/GrpcGalaxyRepositoryClientTransport.cs

@@ -10,7 +10,9 @@ internal sealed class GrpcGalaxyRepositoryClientTransport(
     MxGatewayClientOptions options,
     GalaxyRepository.GalaxyRepositoryClient rawClient) : IGalaxyRepositoryClientTransport
 {
-    /// <inheritdoc />
+    /// <summary>
+    /// Gets the gateway client options.
+    /// </summary>
     public MxGatewayClientOptions Options { get; } = options;
 
     /// <summary>
@@ -89,11 +91,7 @@ internal sealed class GrpcGalaxyRepositoryClientTransport(
         }
     }
 
-    /// <summary>Streams deploy events from the Galaxy Repository, using an explicit cancellation token that overrides the call options token when provided.</summary>
+    /// <inheritdoc />
-    /// <param name="request">The watch deploy events request.</param>
-    /// <param name="callOptions">Call options for the underlying gRPC call.</param>
-    /// <param name="cancellationToken">Optional cancellation token; takes precedence over the token in <paramref name="callOptions"/> when cancellable.</param>
-    /// <returns>An async enumerable of deploy events.</returns>
     public async IAsyncEnumerable<DeployEvent> WatchDeployEventsAsync(
         WatchDeployEventsRequest request,
         CallOptions callOptions,

clients/dotnet/ZB.MOM.WW.MxGateway.Client/GrpcMxGatewayClientTransport.cs

@@ -10,7 +10,9 @@ internal sealed class GrpcMxGatewayClientTransport(
     MxGatewayClientOptions options,
     MxAccessGateway.MxAccessGatewayClient rawClient) : IMxGatewayClientTransport
 {
-    /// <inheritdoc />
+    /// <summary>
+    /// Gets the gateway client options.
+    /// </summary>
     public MxGatewayClientOptions Options { get; } = options;
 
     /// <summary>
@@ -72,11 +74,7 @@ internal sealed class GrpcMxGatewayClientTransport(
         }
     }
 
-    /// <summary>Streams MXAccess events from the gateway, forwarding an explicit cancellation token to the stream reader.</summary>
+    /// <inheritdoc />
-    /// <param name="request">The stream events request.</param>
-    /// <param name="callOptions">gRPC call options.</param>
-    /// <param name="cancellationToken">Token to cancel the streaming enumeration.</param>
-    /// <returns>An async enumerable of MXAccess events.</returns>
     public async IAsyncEnumerable<MxEvent> StreamEventsAsync(
         StreamEventsRequest request,
         CallOptions callOptions,
@@ -135,11 +133,7 @@ internal sealed class GrpcMxGatewayClientTransport(
         }
     }
 
-    /// <summary>Queries active alarms from the gateway, forwarding an explicit cancellation token to the stream reader.</summary>
+    /// <inheritdoc />
-    /// <param name="request">The query active alarms request.</param>
-    /// <param name="callOptions">gRPC call options.</param>
-    /// <param name="cancellationToken">Token to cancel the streaming enumeration.</param>
-    /// <returns>An async enumerable of active alarm snapshots.</returns>
     public async IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
         QueryActiveAlarmsRequest request,
         CallOptions callOptions,
@@ -181,11 +175,7 @@ internal sealed class GrpcMxGatewayClientTransport(
         return QueryActiveAlarmsAsync(request, callOptions);
     }
 
-    /// <summary>Streams alarm feed messages from the gateway, forwarding an explicit cancellation token to the stream reader.</summary>
+    /// <inheritdoc />
-    /// <param name="request">The stream alarms request.</param>
-    /// <param name="callOptions">gRPC call options.</param>
-    /// <param name="cancellationToken">Token to cancel the streaming enumeration.</param>
-    /// <returns>An async enumerable of alarm feed messages.</returns>
     public async IAsyncEnumerable<AlarmFeedMessage> StreamAlarmsAsync(
         StreamAlarmsRequest request,
         CallOptions callOptions,

clients/dotnet/ZB.MOM.WW.MxGateway.Client/IGalaxyRepositoryClientTransport.cs

@@ -15,7 +15,6 @@ internal interface IGalaxyRepositoryClientTransport
     /// <summary>Tests the connection to the Galaxy Repository server.</summary>
     /// <param name="request">The test connection request.</param>
     /// <param name="callOptions">gRPC call options (timeout, cancellation, etc.).</param>
-    /// <returns>A task that resolves to the test connection reply.</returns>
     Task<TestConnectionReply> TestConnectionAsync(
         TestConnectionRequest request,
         CallOptions callOptions);
@@ -23,7 +22,6 @@ internal interface IGalaxyRepositoryClientTransport
     /// <summary>Gets the last deploy time from the Galaxy Repository server.</summary>
     /// <param name="request">The get last deploy time request.</param>
     /// <param name="callOptions">gRPC call options (timeout, cancellation, etc.).</param>
-    /// <returns>A task that resolves to the last deploy time reply.</returns>
     Task<GetLastDeployTimeReply> GetLastDeployTimeAsync(
         GetLastDeployTimeRequest request,
         CallOptions callOptions);
@@ -31,7 +29,6 @@ internal interface IGalaxyRepositoryClientTransport
     /// <summary>Discovers the object hierarchy in the Galaxy Repository.</summary>
     /// <param name="request">The discover hierarchy request.</param>
     /// <param name="callOptions">gRPC call options (timeout, cancellation, etc.).</param>
-    /// <returns>A task that resolves to the hierarchy discovery reply.</returns>
     Task<DiscoverHierarchyReply> DiscoverHierarchyAsync(
         DiscoverHierarchyRequest request,
         CallOptions callOptions);
@@ -39,7 +36,6 @@ internal interface IGalaxyRepositoryClientTransport
     /// <summary>Returns direct children of a parent in the Galaxy hierarchy.</summary>
     /// <param name="request">The browse children request.</param>
     /// <param name="callOptions">gRPC call options (timeout, cancellation, etc.).</param>
-    /// <returns>A task that resolves to the browse children reply.</returns>
     Task<BrowseChildrenReply> BrowseChildrenAsync(
         BrowseChildrenRequest request,
         CallOptions callOptions);
@@ -47,7 +43,6 @@ internal interface IGalaxyRepositoryClientTransport
     /// <summary>Watches for deployment events from the Galaxy Repository server.</summary>
     /// <param name="request">The watch deploy events request.</param>
     /// <param name="callOptions">gRPC call options (timeout, cancellation, etc.).</param>
-    /// <returns>An async enumerable of deploy events.</returns>
     IAsyncEnumerable<DeployEvent> WatchDeployEventsAsync(
         WatchDeployEventsRequest request,
         CallOptions callOptions);

clients/dotnet/ZB.MOM.WW.MxGateway.Client/LazyBrowseNode.cs

@@ -16,11 +16,6 @@ public sealed class LazyBrowseNode
     private readonly SemaphoreSlim _expandLock = new(1, 1);
     private bool _isExpanded;
 
-    /// <summary>Initializes a new instance of <see cref="LazyBrowseNode"/>.</summary>
-    /// <param name="client">The repository client used to fetch children.</param>
-    /// <param name="object">The underlying Galaxy object for this node.</param>
-    /// <param name="hasChildrenHint">True when the server reports the node has at least one matching descendant.</param>
-    /// <param name="options">Options controlling child browse behavior.</param>
     internal LazyBrowseNode(
         GalaxyRepositoryClient client,
         GalaxyObject @object,
@@ -54,7 +49,6 @@ public sealed class LazyBrowseNode
     ///     (after the first completes) return immediately.
     /// </remarks>
     /// <param name="cancellationToken">Token to observe for cancellation.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task ExpandAsync(CancellationToken cancellationToken = default)
     {
         if (_isExpanded)

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxCommandReplyExtensions.cs

@@ -7,7 +7,6 @@ public static class MxCommandReplyExtensions
 {
     /// <summary>Validates that the reply has a successful protocol status (Ok or MxAccessFailure), throwing a gateway exception if not.</summary>
     /// <param name="reply">The command reply to check.</param>
-    /// <returns>The same <paramref name="reply"/> for fluent chaining when validation passes.</returns>
     public static MxCommandReply EnsureProtocolSuccess(this MxCommandReply reply)
     {
         ArgumentNullException.ThrowIfNull(reply);
@@ -25,7 +24,6 @@ public static class MxCommandReplyExtensions
 
     /// <summary>Validates that the reply indicates MXAccess success (no HResult or status failures), throwing MxAccessException if not.</summary>
     /// <param name="reply">The command reply to check.</param>
-    /// <returns>The same <paramref name="reply"/> for fluent chaining when validation passes.</returns>
     public static MxCommandReply EnsureMxAccessSuccess(this MxCommandReply reply)
     {
         ArgumentNullException.ThrowIfNull(reply);

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxGatewayClient.cs

@@ -249,7 +249,6 @@ public sealed class MxGatewayClient : IAsyncDisposable
     /// <summary>
     /// Disposes the client and releases all resources.
     /// </summary>
-    /// <returns>A task that represents the asynchronous dispose operation.</returns>
     public ValueTask DisposeAsync()
     {
         if (_disposed)
@@ -319,9 +318,6 @@ public sealed class MxGatewayClient : IAsyncDisposable
     private static HttpMessageHandler CreateHttpHandler(MxGatewayClientOptions options) =>
         CreateHttpHandlerForTests(options);
 
-    /// <summary>Creates an <see cref="HttpMessageHandler"/> configured from the provided options for test use.</summary>
-    /// <param name="options">Client options used to configure TLS and timeouts.</param>
-    /// <returns>The configured HTTP message handler.</returns>
     internal static SocketsHttpHandler CreateHttpHandlerForTests(MxGatewayClientOptions options)
     {
         SocketsHttpHandler handler = new()

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxGatewayClientRetryPolicy.cs

@@ -12,7 +12,6 @@ internal static class MxGatewayClientRetryPolicy
     /// <summary>Creates a Polly ResiliencePipeline that retries transient gRPC failures with exponential backoff.</summary>
     /// <param name="options">Retry configuration (max attempts, delay bounds, jitter).</param>
     /// <param name="logger">Optional logger for retry diagnostics.</param>
-    /// <returns>A configured <see cref="ResiliencePipeline"/> with exponential-backoff retry.</returns>
     public static ResiliencePipeline Create(
         MxGatewayClientRetryOptions options,
         ILogger? logger)
@@ -43,7 +42,6 @@ internal static class MxGatewayClientRetryPolicy
 
     /// <summary>Returns whether a command kind is eligible for automatic retry on transient failures.</summary>
     /// <param name="kind">The command kind to check.</param>
-    /// <returns><see langword="true"/> if the command kind is safe to retry; otherwise <see langword="false"/>.</returns>
     public static bool IsRetryableCommand(MxCommandKind kind)
     {
         return kind is MxCommandKind.Ping

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxGatewaySession.cs

@@ -211,7 +211,6 @@ public sealed class MxGatewaySession : IAsyncDisposable
     /// <param name="serverHandle">The ServerHandle from register.</param>
     /// <param name="itemHandle">The ItemHandle from add-item.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task AdviseAsync(
         int serverHandle,
         int itemHandle,
@@ -253,7 +252,6 @@ public sealed class MxGatewaySession : IAsyncDisposable
     /// <param name="serverHandle">The ServerHandle from register.</param>
     /// <param name="itemHandle">The ItemHandle from add-item.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task UnAdviseAsync(
         int serverHandle,
         int itemHandle,
@@ -295,7 +293,6 @@ public sealed class MxGatewaySession : IAsyncDisposable
     /// <param name="serverHandle">The ServerHandle from register.</param>
     /// <param name="itemHandle">The ItemHandle from add-item.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task RemoveItemAsync(
         int serverHandle,
         int itemHandle,
@@ -678,7 +675,6 @@ public sealed class MxGatewaySession : IAsyncDisposable
     /// <param name="value">The value to write.</param>
     /// <param name="userId">User ID context for the write.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task WriteAsync(
         int serverHandle,
         int itemHandle,
@@ -733,7 +729,6 @@ public sealed class MxGatewaySession : IAsyncDisposable
     /// <param name="timestampValue">The timestamp to write with the value.</param>
     /// <param name="userId">User ID context for the write.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task Write2Async(
         int serverHandle,
         int itemHandle,
@@ -826,7 +821,6 @@ public sealed class MxGatewaySession : IAsyncDisposable
     /// <summary>
     /// Closes the session and releases resources.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async ValueTask DisposeAsync()
     {
         await CloseAsync().ConfigureAwait(false);

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxStatusProxyExtensions.cs

@@ -7,7 +7,6 @@ public static class MxStatusProxyExtensions
 {
     /// <summary>Returns whether the status indicates success (success flag set and category is Ok).</summary>
     /// <param name="status">The status to check.</param>
-    /// <returns><c>true</c> if the status is successful; <c>false</c> otherwise.</returns>
     public static bool IsSuccess(this MxStatusProxy status)
     {
         ArgumentNullException.ThrowIfNull(status);
@@ -18,7 +17,6 @@ public static class MxStatusProxyExtensions
 
     /// <summary>Returns a formatted summary of the status for diagnostic output.</summary>
     /// <param name="status">The status to summarize.</param>
-    /// <returns>A human-readable string combining category, source, detail, and diagnostic text.</returns>
     public static string ToDiagnosticSummary(this MxStatusProxy status)
     {
         ArgumentNullException.ThrowIfNull(status);

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxValueExtensions.cs

@@ -14,7 +14,6 @@ public static class MxValueExtensions
     /// Converts a boolean value to an MxValue with MxDataType.Boolean.
     /// </summary>
     /// <param name="value">Scalar boolean value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Boolean</c>.</returns>
     public static MxValue ToMxValue(this bool value)
     {
         return new MxValue
@@ -29,7 +28,6 @@ public static class MxValueExtensions
     /// Converts a 32-bit integer value to an MxValue with MxDataType.Integer.
     /// </summary>
     /// <param name="value">32-bit integer value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Integer</c>.</returns>
     public static MxValue ToMxValue(this int value)
     {
         return new MxValue
@@ -44,7 +42,6 @@ public static class MxValueExtensions
     /// Converts a 64-bit integer value to an MxValue with MxDataType.Integer.
     /// </summary>
     /// <param name="value">64-bit integer value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Integer</c>.</returns>
     public static MxValue ToMxValue(this long value)
     {
         return new MxValue
@@ -59,7 +56,6 @@ public static class MxValueExtensions
     /// Converts a single-precision floating-point value to an MxValue with MxDataType.Float.
     /// </summary>
     /// <param name="value">Single-precision floating-point value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Float</c>.</returns>
     public static MxValue ToMxValue(this float value)
     {
         return new MxValue
@@ -74,7 +70,6 @@ public static class MxValueExtensions
     /// Converts a double-precision floating-point value to an MxValue with MxDataType.Double.
     /// </summary>
     /// <param name="value">Double-precision floating-point value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Double</c>.</returns>
     public static MxValue ToMxValue(this double value)
     {
         return new MxValue
@@ -89,7 +84,6 @@ public static class MxValueExtensions
     /// Converts a string value to an MxValue with MxDataType.String.
     /// </summary>
     /// <param name="value">String value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.String</c>.</returns>
     public static MxValue ToMxValue(this string value)
     {
         ArgumentNullException.ThrowIfNull(value);
@@ -106,7 +100,6 @@ public static class MxValueExtensions
     /// Converts a DateTimeOffset value to an MxValue with MxDataType.Time.
     /// </summary>
     /// <param name="value">DateTimeOffset value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Time</c>.</returns>
     public static MxValue ToMxValue(this DateTimeOffset value)
     {
         return new MxValue
@@ -121,7 +114,6 @@ public static class MxValueExtensions
     /// Converts a DateTime value to an MxValue with MxDataType.Time.
     /// </summary>
     /// <param name="value">DateTime value to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Time</c>.</returns>
     public static MxValue ToMxValue(this DateTime value)
     {
         return new DateTimeOffset(
@@ -135,7 +127,6 @@ public static class MxValueExtensions
     /// Converts a boolean array to an MxValue with MxDataType.Boolean.
     /// </summary>
     /// <param name="values">Array of boolean values to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Boolean</c> and an array payload.</returns>
     public static MxValue ToMxValue(this IReadOnlyList<bool> values)
     {
         ArgumentNullException.ThrowIfNull(values);
@@ -154,7 +145,6 @@ public static class MxValueExtensions
     /// Converts a 32-bit integer array to an MxValue with MxDataType.Integer.
     /// </summary>
     /// <param name="values">Array of 32-bit integer values to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Integer</c> and an array payload.</returns>
     public static MxValue ToMxValue(this IReadOnlyList<int> values)
     {
         ArgumentNullException.ThrowIfNull(values);
@@ -173,7 +163,6 @@ public static class MxValueExtensions
     /// Converts a 64-bit integer array to an MxValue with MxDataType.Integer.
     /// </summary>
     /// <param name="values">Array of 64-bit integer values to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Integer</c> and an array payload.</returns>
     public static MxValue ToMxValue(this IReadOnlyList<long> values)
     {
         ArgumentNullException.ThrowIfNull(values);
@@ -192,7 +181,6 @@ public static class MxValueExtensions
     /// Converts a single-precision floating-point array to an MxValue with MxDataType.Float.
     /// </summary>
     /// <param name="values">Array of single-precision floating-point values to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Float</c> and an array payload.</returns>
     public static MxValue ToMxValue(this IReadOnlyList<float> values)
     {
         ArgumentNullException.ThrowIfNull(values);
@@ -211,7 +199,6 @@ public static class MxValueExtensions
     /// Converts a double-precision floating-point array to an MxValue with MxDataType.Double.
     /// </summary>
     /// <param name="values">Array of double-precision floating-point values to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Double</c> and an array payload.</returns>
     public static MxValue ToMxValue(this IReadOnlyList<double> values)
     {
         ArgumentNullException.ThrowIfNull(values);
@@ -230,7 +217,6 @@ public static class MxValueExtensions
     /// Converts a string array to an MxValue with MxDataType.String.
     /// </summary>
     /// <param name="values">Array of string values to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.String</c> and an array payload.</returns>
     public static MxValue ToMxValue(this IReadOnlyList<string> values)
     {
         ArgumentNullException.ThrowIfNull(values);
@@ -249,7 +235,6 @@ public static class MxValueExtensions
     /// Converts a DateTimeOffset array to an MxValue with MxDataType.Time.
     /// </summary>
     /// <param name="values">Array of DateTimeOffset values to wrap.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Time</c> and an array payload.</returns>
     public static MxValue ToMxValue(this IReadOnlyList<DateTimeOffset> values)
     {
         ArgumentNullException.ThrowIfNull(values);
@@ -268,7 +253,6 @@ public static class MxValueExtensions
     /// Gets the projection kind (field name) of the given MxValue's current oneof value.
     /// </summary>
     /// <param name="value">The MxValue whose oneof projection kind is returned.</param>
-    /// <returns>The JSON field name of the active oneof case, or <c>"nullValue"</c>/<c>"unspecified"</c> for null/unset values.</returns>
     public static string GetProjectionKind(this MxValue value)
     {
         ArgumentNullException.ThrowIfNull(value);
@@ -292,7 +276,6 @@ public static class MxValueExtensions
     /// Converts an MxValue to a CLR object; returns the boxed value or null for null MxValues.
     /// </summary>
     /// <param name="value">The MxValue to convert.</param>
-    /// <returns>The boxed CLR value, or null if the MxValue represents a null.</returns>
     public static object? ToClrValue(this MxValue value)
     {
         ArgumentNullException.ThrowIfNull(value);
@@ -316,7 +299,6 @@ public static class MxValueExtensions
     /// Converts an MxArray to a CLR array; returns null if the array does not have a known element type.
     /// </summary>
     /// <param name="array">The MxArray to convert.</param>
-    /// <returns>A CLR array of the appropriate element type, or null for unknown element types.</returns>
     public static object? ToClrArrayValue(this MxArray array)
     {
         ArgumentNullException.ThrowIfNull(array);
@@ -346,7 +328,6 @@ public static class MxValueExtensions
     /// <param name="variantType">Variant type string (e.g., "VT_BSTR").</param>
     /// <param name="rawDiagnostic">Diagnostic string describing the raw value.</param>
     /// <param name="rawDataType">Optional MXAccess data type override.</param>
-    /// <returns>An <see cref="MxValue"/> with <c>MxDataType.Unknown</c> and the raw byte payload.</returns>
     public static MxValue ToRawMxValue(
         byte[] value,
         string variantType,

docs/AlarmClientDiscovery.md

@@ -790,3 +790,159 @@ Post-ack transition: kind=Clear …
 
 10s cadence held throughout; full proto fields populated correctly;
 ack registered server-side without errors.
+
+## Subtag-monitoring fallback provider
+
+When the wnwrap alarm-manager source fails, the gateway worker switches to
+`SubtagAlarmConsumer` — a synthetic alarm source that advises each alarm
+attribute's subtags via the existing MXAccess `AddItem`/`Advise` pipeline and
+derives alarm transitions from the resulting value-change stream. This is a
+non-parity, degraded-mode source; every transition and snapshot it produces
+carries `degraded = true`.
+
+### Watch-list discovery
+
+`GatewayAlarmMonitor` resolves the subtag watch-list at subscribe time by
+calling `IAlarmWatchListResolver.GetAlarmAttributesAsync`. The resolver merges:
+
+1. Galaxy Repository SQL (`GetAlarmAttributesAsync`) — objects that have alarm
+   extensions in the configured area.
+2. Config overrides — `IncludeAttributes` adds explicit entries;
+   `ExcludeAttributes` removes Repository-derived ones. The config list takes
+   effect even when `UseGalaxyRepository` is `false`.
+
+The resolved list is a set of `AlarmSubtagTarget` messages sent to the worker
+inside `SubscribeAlarmsCommand.watch_list`. Each target carries the composed
+MXAccess item addresses for the `InAlarm`, `Acked`, `AckMsg`, and `Priority`
+subtags (confirmed AVEVA `AlarmExtension` field names, verified against the live
+ZB Galaxy `attribute_definition` rows). The gateway re-runs discovery on its
+reconcile cadence and pushes an updated watch-list when the model changes.
+
+Each target's canonical `AlarmFullReference` is composed as
+`Galaxy!{area}.{reference}` (literal `Galaxy` provider). The `{area}` is the
+alarm object's **real Galaxy area** — discovered per object via
+`gobject.area_gobject_id` (`GetAlarmAttributesAsync` projects it as `area_name`)
+— so the synthesized reference's group matches exactly the area the native
+alarmmgr (wnwrap) emits for the same alarm (e.g. `TestMachine_001` in `TestArea`
+yields `Galaxy!TestArea.TestMachine_001.TestAlarm001`). The configured
+`Discovery.Area` / `DefaultArea` is **only** the fallback for explicit
+`IncludeAttributes` entries, which carry no discovered area.
+
+### Subtag advise and `LmxSubtagAlarmSource`
+
+`LmxSubtagAlarmSource` (implements `ISubtagAlarmSource`) owns a separate
+`LMXProxyServerClass` instance on the worker STA — it does not share the
+session's main MXAccess object. For each watch-list target it calls
+`AddItem`/`Advise` on the configured subtag addresses. When a subtag value
+changes, it raises `ValueChanged` on the STA and `SubtagAlarmConsumer`
+forwards it to `SubtagAlarmStateMachine`.
+
+`PollOnce()` on the subtag consumer is a no-op — the path is event-driven
+through `Advise`, not poll-driven.
+
+### Synthesis rules
+
+`SubtagAlarmStateMachine` tracks `(active, acked)` per watch-list entry and
+emits `MxAlarmTransitionEvent` records on change:
+
+| Subtag change | Emitted transition | Notes |
+|---|---|---|
+| `InAlarm` false → true | Raise (`UNACK_ALM`) | `original_raise_timestamp` = first observed active time for this episode |
+| `Acked` false → true, while `InAlarm` | Acknowledge (`ACK_ALM`) | `AckedDuringEpisode` latch set |
+| `InAlarm` true → false | Clear | `AckRtn` if `AckedDuringEpisode` is set, else `UnackRtn` |
+| `Acked` true → false, while `InAlarm` | (none) | Latch is NOT cleared; the episode retains its acknowledged status at clear |
+
+The `AckedDuringEpisode` latch addresses out-of-order subtag delivery:
+MXAccess does not guarantee the `Acked = false` update arrives before the
+`InAlarm = false` update. The latch ensures a clear always emits `ACK_RTN`
+when the alarm was acknowledged at any point during the active episode.
+
+`SnapshotActive()` returns one `MxAlarmSnapshotRecord` per currently-active
+alarm. State mapping:
+
+- `InAlarm && !Acked` → `UNACK_ALM`
+- `InAlarm && Acked` → `ACK_ALM`
+- `!InAlarm` → not included in the snapshot
+
+### Synthetic GUID
+
+The alarmmgr provider supplies a native GUID per alarm record. The subtag
+provider has no native GUID. `SubtagAlarmConsumer` derives a deterministic
+GUID by hashing `alarm_full_reference` (via `SyntheticAlarmGuid.ForReference`).
+The same reference always produces the same GUID within a session, so
+GUID-based ack routing resolves correctly. The GUID is not stable across
+different alarm references or gateway restarts in the sense of matching any
+AVEVA-internal GUID.
+
+### Acknowledge in subtag mode
+
+`AlarmDispatcher` routes ack calls by active provider mode:
+
+- **Alarm-manager mode:** `AlarmAckByName` on `wwAlarmConsumerClass` (unchanged).
+- **Subtag mode:** `SubtagAlarmConsumer.AcknowledgeByName` resolves the
+  watch-list entry's `ack_comment_subtag` and issues a `Write(comment)` on
+  the STA via `LmxSubtagAlarmSource`. Writing the `AckMsg` subtag performs
+  the acknowledge in AVEVA (`AckMsg` is the confirmed `AlarmExtension` ack-comment
+  write target).
+
+If the alarm has no writable ack-comment subtag (`AckComment` config key is
+empty, or the entry's `ack_comment_subtag` field is empty), the ack call
+returns a failure code that the gateway surfaces as `FailedPrecondition`.
+`AcknowledgeByGuid` maps the synthetic GUID back to its reference via an
+internal dictionary, then calls the same write path.
+
+`SubtagAlarmConsumer.Subscribe` advises the ack-comment subtag alongside the
+observed ones (active/acked/priority). This is required: MXAccess rejects a
+write to an item that has been added but not advised with `E_INVALIDARG`
+("Value does not fall within the expected range"). Advising it at subscribe
+time makes it an active item so the later ack write succeeds — its value
+changes carry no transition (the state machine ignores unmapped addresses).
+
+### Live validation
+
+The subtag path was validated against live MXAccess on the dev rig
+(`DESKTOP-6JL3KKO`, Galaxy `DEV`, `TestMachine_001.TestAlarm001`):
+
+- `…​.InAlarm` → `True` (Boolean), `…​.Acked` → `False` (Boolean),
+  `…​.Priority` → `500` (Int32), `…​.AckMsg` → string — confirming the field
+  names **and** the runtime reference shape `<Object>.<AlarmAttr>.<field>`
+  with **no** intermediate alarm-condition segment.
+- `AcknowledgeByName` (AckMsg write) returned `0` once the ack-comment subtag
+  was advised — confirming the ack-by-comment-write mechanism end to end.
+
+### Fidelity limitations
+
+The following fields are not available or have lower quality in subtag mode:
+
+| Field | Subtag-mode behavior |
+|-------|---------------------|
+| `alarm_guid` | Synthetic deterministic GUID from `alarm_full_reference`; not an AVEVA-native GUID |
+| `original_raise_timestamp` | First observed `active = true` time; no AVEVA-native raise time |
+| `transition_timestamp` | `OnDataChange` source timestamp from MXAccess |
+| `severity` | From priority subtag if advised; 0 otherwise |
+| `category` / `description` | Not populated (no subtag for these) |
+| `current_value` / `limit_value` | Not populated unless corresponding subtags are in the watch-list |
+| `alarm_type_name` | Not populated |
+| `operator_user` / `operator_comment` | Not populated on synthesized raise/clear transitions |
+| `retrigger` transition | Not synthesized (no re-alarm counter subtag is observed) |
+
+Every transition and snapshot record carries `degraded = true` and
+`source_provider = ALARM_PROVIDER_MODE_SUBTAG`. Clients that require full
+fidelity must wait for failback to the alarm manager.
+
+### Provider mode reflection
+
+When `FailoverAlarmConsumer` switches between providers, it raises
+`ProviderModeChanged`. `AlarmDispatcher` enqueues an
+`OnAlarmProviderModeChangedEvent` (carried as an `MxEvent`), which the
+gateway receives and reflects into:
+
+- `AlarmFeedMessage.provider_status` emitted to every `StreamAlarms`
+  subscriber.
+- The `/hubs/alarms` SignalR hub for the dashboard.
+- Metrics: `mxgateway.alarms.provider_mode` gauge and
+  `mxgateway.alarms.provider_switches` counter.
+
+On every switch `GatewayAlarmMonitor` also forces a reconcile
+(`QueryActiveAlarms`) against the now-active provider so the gateway cache
+reflects the post-switch state without a spurious raise/clear storm.

docs/DesignDecisions.md

@@ -411,6 +411,58 @@ a per-channel skip-verify hook:
 See [Gateway Configuration — Automatic self-signed certificate](./GatewayConfiguration.md#automatic-self-signed-certificate)
 and the per-client READMEs for the as-built behavior.
 
+## Alarm-Manager to Subtag Fallback
+
+Decision: add a second alarm provider (subtag monitoring) that the worker
+activates automatically when the native wnwrap alarm manager fails, and fails
+back to automatically when the manager recovers.
+
+### Worker-side synthesis
+
+Synthesis of alarm transitions from subtag value changes happens entirely in
+the worker (`SubtagAlarmConsumer` / `SubtagAlarmStateMachine`). The gateway
+still forwards only events the worker emits and synthesizes nothing itself.
+This satisfies the parity rule even though the subtag path is inherently
+non-parity: the parity rule governs where synthesis lives, not whether
+synthesis is permitted when the native source is unavailable.
+
+### Degraded is explicit
+
+Every subtag-mode transition carries `degraded = true` on the
+`OnAlarmTransitionEvent` and `ActiveAlarmSnapshot` proto messages, and the
+`AlarmFeedMessage` feed carries an `AlarmProviderStatus` payload on stream
+open and on every switch. No client can mistake a subtag-mode alarm for an
+authoritative alarmmgr record. Subtag mode has lower fidelity: synthetic
+deterministic GUID (SHA-derived from the alarm reference), best-effort
+original-raise timestamp, narrower field set. Clients that need full fidelity
+must wait for failback.
+
+### Failover trigger
+
+The failover trigger is N consecutive wnwrap COM failures — a `COMException`
+thrown by `Subscribe` or `PollOnce`, or a failure HRESULT from
+`GetXmlCurrentAlarms2`. A single poll failure does not trigger a switch; the
+threshold (default 3, floored at 1) guards against transient COM hiccups. The
+counter resets on any clean poll so a flapping provider does not permanently
+latch in subtag mode.
+
+### Acknowledge via ack-comment write
+
+In subtag mode, `AcknowledgeAlarm` writes the operator comment to the alarm
+attribute's ack-comment subtag (`Fallback:Subtags:AckComment`). The write
+performs the native ack in AVEVA. This differs from alarmmgr mode, where
+`AlarmAckByName` on `wwAlarmConsumerClass` is called directly. The `AckComment`
+subtag name is empty by default; configuring it is required for ack to work in
+subtag mode. The exact AVEVA subtag names are not hard-coded — the `Subtags`
+config block exists precisely so names are not guessed without validation
+against the live MXAccess attribute set.
+
+### Related documentation
+
+- [Gateway Configuration — Alarm Fallback options](./GatewayConfiguration.md#alarm-fallback-options)
+- [Alarm Client Discovery — Subtag provider](./AlarmClientDiscovery.md)
+- [gRPC Contract — provider_status and degraded fields](./Grpc.md)
+
 ## Later Revisit Items
 
 These are explicit post-v1 revisit items, not open blockers:

docs/GatewayConfiguration.md

@@ -148,6 +148,7 @@ the affected stream while the MXAccess session remains active.
 | `MxGateway:Dashboard:Enabled` | `true` | Enables Blazor Server dashboard route mapping. The dashboard mounts at the host root (`/`); there is no separate path-base prefix. |
 | `MxGateway:Dashboard:AllowAnonymousLocalhost` | `true` | Allows loopback dashboard requests to bypass the dashboard cookie requirement for local development. Remote requests still require dashboard authentication. |
 | `MxGateway:Dashboard:RequireHttpsCookie` | `true` | Sets the dashboard auth cookie's secure policy. `true` keeps `CookieSecurePolicy.Always` — the cookie is only sent over HTTPS, which matches a production HTTPS deployment. Set to `false` for plain-HTTP dev deployments to use `CookieSecurePolicy.SameAsRequest`; the cookie is still flagged Secure on HTTPS requests, but it can round-trip over HTTP. Browsers drop Secure cookies set over HTTP from non-localhost hosts, so leaving this `true` while serving the dashboard over plain HTTP will break login from any remote browser. |
+| `MxGateway:Dashboard:CookieName` | `MxGatewayDashboard` | Dashboard auth cookie name. Leave unset (null/blank) to use the default. Override it to give a distinct name to a gateway that shares a hostname with another gateway instance: browser cookies are scoped by host+path but **not** by port, so two instances on the same host would otherwise clobber each other's dashboard session under a shared cookie name. Changing it signs out existing dashboard sessions on next deploy. |
 | `MxGateway:Dashboard:SnapshotIntervalMilliseconds` | `1000` | Dashboard snapshot refresh interval used by the snapshot SignalR hub and the pages that subscribe to it. |
 | `MxGateway:Dashboard:RecentFaultLimit` | `100` | Maximum number of fault summaries projected into each dashboard snapshot. |
 | `MxGateway:Dashboard:RecentSessionLimit` | `200` | Maximum number of session summaries projected into each dashboard snapshot. |
@@ -229,6 +230,75 @@ behavior.
 The alarm monitor is independent of client sessions: `AcknowledgeAlarm` and
 `StreamAlarms` are session-less RPCs served by the monitor.
 
+### Alarm fallback options
+
+The `Fallback` sub-section controls how the alarm feed selects between the
+native wnwrap alarm-manager provider and the subtag-monitoring fallback.
+
+| Option | Default | Description |
+|--------|---------|-------------|
+| `MxGateway:Alarms:Fallback:Mode` | `Auto` | Provider selection mode. `Auto` uses the alarm manager as primary and fails over to subtag monitoring after consecutive COM failures, then fails back automatically. `ForceAlarmManager` disables failover. `ForceSubtag` forces subtag monitoring on from startup. Values are case-insensitive. |
+| `MxGateway:Alarms:Fallback:ConsecutiveFailureThreshold` | `3` | Number of consecutive wnwrap COM failures (`COMException` or failure HRESULT from `Subscribe` / `GetXmlCurrentAlarms2`) before the monitor switches to subtag mode. Floored at 1. |
+| `MxGateway:Alarms:Fallback:FailbackProbeIntervalSeconds` | `30` | While in subtag mode, how often (in seconds) the monitor probes the wnwrap provider to detect recovery. Floored at 1. |
+| `MxGateway:Alarms:Fallback:FailbackStableProbes` | `3` | Number of consecutive clean wnwrap probes required before the monitor switches back to the alarm manager. Floored at 1. |
+| `MxGateway:Alarms:Fallback:Discovery:UseGalaxyRepository` | `true` | When `true`, the monitor queries the Galaxy Repository SQL database to build the subtag watch-list for the configured area. |
+| `MxGateway:Alarms:Fallback:Discovery:Area` | _(empty)_ | Galaxy area to scope the Repository query to. Falls back to `MxGateway:Alarms:DefaultArea` when empty. Ignored when `UseGalaxyRepository` is `false`. This area is **not** used to compose a Repository-derived alarm's canonical `Galaxy!{area}.{reference}`: each discovered alarm uses its object's real Galaxy area (discovered via `gobject.area_gobject_id`), so the reference's group matches what the native alarmmgr emits. `Discovery:Area` / `DefaultArea` is used as the composition area only for explicit `IncludeAttributes` entries, which carry no discovered area. |
+| `MxGateway:Alarms:Fallback:Discovery:IncludeAttributes` | _(empty)_ | Explicit MXAccess attribute paths to add to the subtag watch-list, supplementing (or replacing, when `UseGalaxyRepository` is `false`) the Repository-derived list. |
+| `MxGateway:Alarms:Fallback:Discovery:ExcludeAttributes` | _(empty)_ | Attribute paths to remove from the Repository-derived watch-list. Ignored when `UseGalaxyRepository` is `false`. |
+| `MxGateway:Alarms:Fallback:Subtags:Active` | `InAlarm` | Subtag name for the in-alarm boolean. Confirmed AVEVA `AlarmExtension` field name. |
+| `MxGateway:Alarms:Fallback:Subtags:Acked` | `Acked` | Subtag name for the acknowledged boolean. Confirmed AVEVA `AlarmExtension` field name. |
+| `MxGateway:Alarms:Fallback:Subtags:AckComment` | `AckMsg` | Subtag name for the acknowledgement comment write target. Writing this subtag performs the acknowledge in AVEVA. Confirmed AVEVA `AlarmExtension` field name. When empty, the ack-comment write path is disabled. |
+| `MxGateway:Alarms:Fallback:Subtags:Priority` | `Priority` | Subtag name for the alarm priority / severity value. Confirmed AVEVA `AlarmExtension` field name. |
+
+Validation rules:
+
+- `Mode` must be `Auto`, `ForceAlarmManager`, or `ForceSubtag` (case-insensitive).
+- `Mode = ForceSubtag` with both `UseGalaxyRepository = false` and an empty
+  `IncludeAttributes` list produces a startup validation warning: the subtag
+  provider has no attributes to advise.
+- `ConsecutiveFailureThreshold`, `FailbackProbeIntervalSeconds`, and
+  `FailbackStableProbes` are floored at 1 by `GatewayOptionsValidator`.
+
+Full example with non-default fallback settings:
+
+```json
+{
+  "MxGateway": {
+    "Alarms": {
+      "Enabled": true,
+      "SubscriptionExpression": "\\\\SCADA01\\Galaxy!PlantArea",
+      "DefaultArea": "PlantArea",
+      "ReconcileIntervalSeconds": 30,
+      "Fallback": {
+        "Mode": "Auto",
+        "ConsecutiveFailureThreshold": 3,
+        "FailbackProbeIntervalSeconds": 30,
+        "FailbackStableProbes": 3,
+        "Discovery": {
+          "UseGalaxyRepository": true,
+          "Area": "",
+          "IncludeAttributes": [],
+          "ExcludeAttributes": []
+        },
+        "Subtags": {
+          "Active": "InAlarm",
+          "Acked": "Acked",
+          "AckComment": "AckMsg",
+          "Priority": "Priority"
+        }
+      }
+    }
+  }
+}
+```
+
+The defaults (`InAlarm`/`Acked`/`AckMsg`/`Priority`) are the confirmed AVEVA
+`AlarmExtension` primitive field names, verified by querying the live ZB Galaxy
+`attribute_definition` rows. The `Subtags` block exists so names can be
+overridden without a code change if a site's alarm template uses different
+attribute names. See `docs/AlarmClientDiscovery.md` for the synthesis rules that
+depend on these names.
+
 ## Host Endpoints and Transport Security (Kestrel)
 
 The listening endpoints are **not** part of the `MxGateway` section. The gateway

docs/Grpc.md

@@ -94,6 +94,73 @@ Carrying the enqueue timestamp into the worker layer is what lets queue-wait tim
 
 `StreamAlarms` is a server-streaming, **session-less** RPC that attaches to the gateway's central alarm feed. The handler delegates to `IGatewayAlarmService.StreamAsync`. The stream opens with one `AlarmFeedMessage` carrying an `active_alarm` per currently-active alarm (the ConditionRefresh snapshot), then a single `snapshot_complete`, then a `transition` for every subsequent raise / acknowledge / clear. It is served by the always-on `GatewayAlarmMonitor`, which owns a single gateway-managed worker session and fans out to every attached client — clients no longer open a session of their own. `alarm_filter_prefix`, when set, scopes the stream to a sub-tree.
 
+#### Provider status on the alarm feed
+
+`AlarmFeedMessage` has a fourth `payload` case, `provider_status`, carrying
+an `AlarmProviderStatus` message:
+
+```protobuf
+message AlarmProviderStatus {
+  AlarmProviderMode mode = 1;
+  bool degraded = 2;       // true whenever mode == SUBTAG
+  string reason = 3;       // human-readable switch reason
+  google.protobuf.Timestamp since = 4;
+}
+```
+
+The gateway emits `provider_status` once when a client first subscribes
+(immediately after the initial snapshot and before the first live transition)
+and again on every failover or failback. A late-joining client therefore
+always learns the current provider mode without waiting for the next switch.
+
+`AlarmProviderMode` is an enum with three values:
+
+| Value | Meaning |
+|-------|---------|
+| `ALARM_PROVIDER_MODE_UNSPECIFIED` (0) | Default / unset |
+| `ALARM_PROVIDER_MODE_ALARMMGR` (1) | Native wnwrap alarm-manager source |
+| `ALARM_PROVIDER_MODE_SUBTAG` (2) | Subtag-monitoring fallback (degraded) |
+
+#### Degraded and source-provider fields on transitions and snapshots
+
+`OnAlarmTransitionEvent` and `ActiveAlarmSnapshot` both carry two new fields:
+
+- `bool degraded` (field 14) — `true` when the record came from the subtag
+  fallback, not the native alarmmgr.
+- `AlarmProviderMode source_provider` (field 15) — which provider produced
+  this record (`ALARMMGR` or `SUBTAG`).
+
+Both fields are proto3 defaults (`false` / `UNSPECIFIED`) in alarmmgr mode,
+so existing clients that do not read them continue to function without change.
+Clients that care about provenance — for example, an OPC UA server that
+applies different quality flags to degraded alarms — should inspect `degraded`
+before consuming the transition.
+
+Subtag-mode records are a non-parity source. They carry synthetic GUIDs,
+best-effort timestamps, and reduced field coverage. See
+`docs/AlarmClientDiscovery.md` for the full fidelity table.
+
+#### Provider-mode-changed event
+
+The worker emits `OnAlarmProviderModeChangedEvent` (family
+`MX_EVENT_FAMILY_ON_ALARM_PROVIDER_MODE_CHANGED`) on each switch between
+providers:
+
+```protobuf
+message OnAlarmProviderModeChangedEvent {
+  AlarmProviderMode mode = 1;
+  string reason = 2;
+  int32 hresult = 3;  // COM HRESULT that triggered failover; 0 on failback
+  google.protobuf.Timestamp at = 4;
+}
+```
+
+This event arrives on the `StreamEvents` stream of the alarm monitor's
+internal gateway session (not on client sessions). `GatewayAlarmMonitor`
+consumes it and reflects the new mode into the `StreamAlarms` feed's
+`provider_status`, the dashboard hub, and metrics. Client sessions do not
+receive this event directly.
+
 ## Validation Rules
 
 `MxAccessGrpcRequestValidator` rejects requests with `StatusCode.InvalidArgument` before any session work happens. The rules are intentionally narrow — anything that requires session state (for example, "session does not exist") is left for `ISessionManager` so the validator can stay synchronous and side-effect free.

docs/plans/2026-06-13-alarm-subtag-fallback-design.md

@@ -0,0 +1,316 @@
+# Alarm Subtag-Monitoring Fallback — Design
+
+**Date:** 2026-06-13
+**Status:** Superseded by implementation (merged to `main`). This is the original
+brainstorming design; a few details below were refined during implementation —
+see the inline **Superseded** notes. The shipped behaviour is documented in
+`docs/AlarmClientDiscovery.md`, the client READMEs, and the contracts.
+**Branch:** `feat/alarm-subtag-fallback`
+
+## Problem
+
+The gateway's central alarm feed (`GatewayAlarmMonitor` → worker
+`WnWrapAlarmConsumer`) depends on the AVEVA wnwrap COM consumer
+(`WNWRAPCONSUMERLib.wwAlarmConsumerClass`), which polls `GetXmlCurrentAlarms2`
+on the worker STA. That provider can fail at the COM boundary (the older
+`aaAlarmManagedClient` crashed on FILETIME marshaling; wnwrap can still return
+failure HRESULTs or throw `COMException`). When it does, the gateway loses all
+alarm visibility.
+
+This design adds a **second alarm source** — direct monitoring of each alarm
+attribute's subtags (`.active`, `.acked`, …) via the existing MXAccess
+`AddItem`/`Advise` pipeline — and **fails over to it automatically when the
+wnwrap provider breaks, then fails back automatically when it recovers**. The
+subtag source can also be forced on by config.
+
+## Decisions (locked during brainstorming)
+
+| Decision | Choice |
+|---|---|
+| Failover model | **Auto-failover + auto-failback** (both directions, runtime) |
+| Watch-list source | **Galaxy Repository SQL discovery + config override** |
+| Acknowledge in subtag mode | **Write the operator comment to the alarm's ack-comment subtag** (the write performs the ack) |
+| Failure signal | **N consecutive wnwrap COM failures** (Subscribe / `GetXmlCurrentAlarms2` throws or returns a failure HRESULT) |
+| Degraded-state visibility | **Both** — explicit field in the gRPC contract **and** dashboard + metrics |
+| Synthesis location | **Worker-side** (`Approach A`) — keeps the parity rule "the gateway forwards only events the worker emits; it never synthesizes events" |
+
+## Core principle
+
+Subtag monitoring is, by definition, a **non-parity, lower-fidelity** alarm
+source: it synthesizes alarm transitions from raw data changes, has no native
+alarm GUID, no native original-raise timestamp, and a narrower field set. Per
+`CLAUDE.md`, synthesizing events is allowed only as an explicit opt-in
+non-parity mode. This design satisfies that by (a) doing the synthesis **inside
+the worker** (so the gateway still only forwards worker-emitted events) and
+(b) marking every degraded event and the whole feed as degraded so no client
+mistakes it for the authoritative alarmmgr feed.
+
+## Architecture
+
+```
+                          GATEWAY (.NET 10, x64)
+  ┌─────────────────────────────────────────────────────────────────┐
+  │ GatewayAlarmMonitor (BackgroundService)                           │
+  │  • resolves watch-list: Galaxy Repository SQL + config override   │
+  │  • arms the worker with the watch-list at subscribe time          │
+  │  • consumes AlarmProviderModeChanged → reflects mode into feed,   │
+  │    /hubs/alarms dashboard hub, and metrics                        │
+  │  • forces a cache reconcile (QueryActiveAlarms) on every switch   │
+  └───────────────────────────────┬───────────────────────────────────┘
+                                   │ IPC (WorkerEnvelope frames)
+                                   │  · SubscribeAlarms{ watch_list, failover cfg }
+                                   │  · AlarmProviderModeChanged{ mode, reason, hresult }
+                                   │  · OnAlarmTransitionEvent (degraded flag set in subtag mode)
+                                   ▼
+                          WORKER (.NET FW 4.8, x86, STA)
+  ┌─────────────────────────────────────────────────────────────────┐
+  │ AlarmDispatcher → FailoverAlarmConsumer : IMxAccessAlarmConsumer  │
+  │   ├─ primary : WnWrapAlarmConsumer   (wnwrap COM poll, unchanged) │
+  │   └─ standby : SubtagAlarmConsumer   (AddItem/Advise on subtags)  │
+  │                                                                   │
+  │  FailoverAlarmConsumer owns the state machine:                    │
+  │   PrimaryActive ──(N consecutive wnwrap COM failures)──▶ Degraded │
+  │   Degraded ──(M consecutive clean wnwrap probe polls)──▶ Primary  │
+  │   on each switch: snapshot the now-active provider, hand off      │
+  └─────────────────────────────────────────────────────────────────┘
+```
+
+The failover state machine lives **worker-local** so the switch is instant — no
+IPC round-trip at the moment alarmmgr dies. The gateway *arms* the standby
+consumer up front (passes the watch-list at subscribe time) so it is ready
+before it is ever needed.
+
+## Components
+
+### Worker (`src/ZB.MOM.WW.MxGateway.Worker/MxAccess/`)
+
+**`SubtagAlarmConsumer : IMxAccessAlarmConsumer` (new)** — the standby provider.
+
+- On `Subscribe`, instead of wnwrap registration it `AddItem`/`Advise`s the
+  configured subtags for each watch-list entry on the existing STA (reuses the
+  worker's item-subscription machinery). Per attribute it advises at minimum
+  `.active` and `.acked`; optionally `.priority`/severity, `.descr`, value/limit
+  if present.
+- Converts each `OnDataChange` into the same `MxAlarmTransitionEvent` the wnwrap
+  consumer emits, via the synthesis rules below, and raises
+  `AlarmTransitionEmitted`. Marks each as **degraded**.
+- `SnapshotActiveAlarms()` returns the currently-active set computed from
+  last-known subtag values.
+- `AcknowledgeByName(...)` resolves the watch-list entry's ack-comment subtag and
+  issues a `Write(comment)` on the STA. `AcknowledgeByGuid(...)` maps the
+  synthetic GUID (see below) back to a reference, then does the same. If the
+  attribute exposes no writable ack-comment subtag, returns a failure code that
+  the gateway surfaces as `FailedPrecondition`.
+- `PollOnce()` is a no-op (subtag mode is event-driven via Advise).
+
+**`FailoverAlarmConsumer : IMxAccessAlarmConsumer` (new)** — composite + state
+machine. Owns the wnwrap consumer (primary) and the subtag consumer (standby),
+forwards `AlarmTransitionEmitted` from whichever child is active, and raises a
+new `ProviderModeChanged` event on every switch.
+
+- **Failure counting:** wraps `Subscribe`/`PollOnce` on the primary; a thrown
+  `COMException` or a failure HRESULT increments a consecutive-failure counter,
+  reset to zero on any clean poll.
+- **Failover** (`PrimaryActive → Degraded`): at `ConsecutiveFailureThreshold`
+  (default 3), ensures the standby is subscribed (it was armed at startup), sets
+  active = standby, snapshots the standby's active set for hand-off, and emits
+  `ProviderModeChanged(SUBTAG, reason, hresult)`.
+- **Failback probe** (`Degraded → PrimaryActive`): while degraded, every
+  `FailbackProbeIntervalSeconds` (default 30) it re-attempts wnwrap
+  `Subscribe`+`PollOnce` on the STA. After `FailbackStableProbes` (default 3)
+  consecutive clean polls it switches active = primary, returns the standby to
+  standby, and emits `ProviderModeChanged(ALARMMGR, "recovered")`.
+- **Hand-off:** on every switch it takes `SnapshotActiveAlarms()` from the
+  now-active provider so the gateway can reconcile and avoid spurious
+  raise/clear storms.
+
+**`AlarmDispatcher` / `MxAccessAlarmEventSink` / `AlarmCommandHandler`
+(changed, minimal)** — `AlarmDispatcher` holds a `FailoverAlarmConsumer` instead
+of a bare `WnWrapAlarmConsumer`; it subscribes to `ProviderModeChanged` and
+enqueues a mode-changed worker event. The ack path routes by active mode (native
+wnwrap ack in alarmmgr mode; ack-comment write in subtag mode), but that routing
+is entirely inside the consumer — the dispatcher just calls
+`AcknowledgeByName`/`AcknowledgeByGuid`.
+
+### Gateway (`src/ZB.MOM.WW.MxGateway.Server/`)
+
+**Galaxy Repository discovery (new query)** — alongside the existing GR SQL
+browse RPCs, a query "attributes that have alarms configured, with their
+ack-comment subtag and area", scoped to the configured area. Merged with the
+config override (explicit includes/excludes). Produces the watch-list of
+`AlarmSubtagTarget`s.
+
+**`GatewayAlarmMonitor` (changed)** — resolves the watch-list at subscribe time
+and passes it to the worker; consumes `AlarmProviderModeChanged` and reflects
+the current provider mode into (a) the `AlarmFeedMessage` provider-status,
+(b) the `/hubs/alarms` dashboard hub, and (c) metrics; forces a reconcile
+(`QueryActiveAlarms`) on every switch. Re-runs discovery on its existing
+reconcile cadence and pushes an updated watch-list when the model changes.
+
+**`AlarmsOptions` (extended)** — new `Fallback` sub-section (below).
+
+### Contract (`src/ZB.MOM.WW.MxGateway.Contracts/Protos/`)
+
+**`mxaccess_gateway.proto`:**
+
+- `enum AlarmProviderMode { ALARM_PROVIDER_MODE_UNSPECIFIED = 0; ALARMMGR = 1; SUBTAG = 2; }`
+- New `AlarmFeedMessage` oneof case `AlarmProviderStatus provider_status`,
+  carrying `{ AlarmProviderMode mode; bool degraded; string reason;
+  google.protobuf.Timestamp since; }`. Emitted on stream open and on every
+  change so a late-joining client immediately learns the mode.
+- Add `bool degraded` + `AlarmProviderMode source_provider` to
+  `OnAlarmTransitionEvent` **and** `ActiveAlarmSnapshot`, so per-item provenance
+  is visible even mid-stream. All additions are new field numbers — backward
+  compatible; existing clients ignore them and keep seeing alarms.
+
+**`mxaccess_worker.proto`:**
+
+> **Superseded:** these additions shipped in `mxaccess_gateway.proto`, not
+> `mxaccess_worker.proto` — the worker imports the gateway proto and the alarm
+> commands/events live there (`AlarmSubtagTarget`,
+> `OnAlarmProviderModeChangedEvent`, the extended subscribe command).
+
+- Extend the alarm-subscribe command with: `AlarmProviderMode forced_mode`
+  (`UNSPECIFIED` = auto), `int32 consecutive_failure_threshold`,
+  `int32 failback_probe_interval_seconds`, `int32 failback_stable_probes`, and
+  `repeated AlarmSubtagTarget watch_list`, where `AlarmSubtagTarget =
+  { string alarm_full_reference; string source_object_reference;
+  string active_subtag; string acked_subtag; string ack_comment_subtag;
+  string priority_subtag; }`.
+- New worker→gateway event `AlarmProviderModeChanged { AlarmProviderMode mode;
+  string reason; int32 hresult; google.protobuf.Timestamp at; }`.
+
+> Generated code under `Generated/` and `clients/*/generated*/` is rebuilt from
+> these `.proto` files — never hand-edited. Every generated client touched by
+> the contract is rebuilt per the source-update workflow.
+
+## Data flow
+
+### Subtag synthesis rules
+
+`SubtagAlarmConsumer` keeps last-known `(active, acked)` per watch-list entry and
+emits transitions on change:
+
+| Subtag change | Emitted transition | Notes |
+|---|---|---|
+| `active` false → true | `RAISE` (state `UNACK_ALM`) | `original_raise_timestamp` = first-observed active time |
+| `acked` false → true while `active` | `ACKNOWLEDGE` | `operator_user`/`operator_comment` from ack-comment subtag if advised |
+| `active` true → false | `CLEAR` | maps to `AckRtn` if acked at clear, else `UnackRtn` |
+| `active` stays true, re-alarm | `RETRIGGER` | **only** if a re-alarm counter subtag exists; otherwise not synthesized (documented limitation) |
+
+Snapshot state mapping for `ActiveAlarmSnapshot.current_state`:
+`active && !acked → ACTIVE`, `active && acked → ACTIVE_ACKED`,
+`!active → INACTIVE`.
+
+Field degradation in subtag mode:
+- `alarm_full_reference` — from the watch-list entry (stable, drives ack-by-ref).
+- Synthetic, deterministic GUID derived by hashing `alarm_full_reference` so
+  GUID-based ack still resolves; flagged `degraded = true`.
+- `severity` — from the priority subtag if advised, else 0.
+- `original_raise_timestamp` — first-observed active time (best effort).
+- `transition_timestamp` — the `OnDataChange` timestamp.
+- `category`/`description`/`current_value`/`limit_value` — populated only if the
+  corresponding subtag is advised; otherwise empty.
+
+### Acknowledge
+
+`AcknowledgeAlarm`/`AcknowledgeAlarmByName` are unchanged at the RPC surface.
+`AlarmDispatcher` routes by active provider mode:
+- **alarmmgr mode:** native wnwrap `AlarmAckByName`/`AlarmAckByGUID` (unchanged).
+- **subtag mode:** resolve the target's `ack_comment_subtag`, `Write` the
+  operator comment via the existing worker write path on the STA. No writable
+  ack-comment subtag → `FailedPrecondition`.
+
+### Provider-mode reflection
+
+Worker `AlarmProviderModeChanged` → `GatewayAlarmMonitor` → (a) emit/refresh
+`AlarmFeedMessage.provider_status` to every `StreamAlarms` subscriber, (b) push
+to `/hubs/alarms`, (c) update metrics, (d) force a reconcile.
+
+## Error handling
+
+- **Both providers down** (subtag advise also failing): the monitor stays
+  faulted and keeps retrying both; acknowledge returns `Unavailable`. No silent
+  data loss — the feed reports degraded with reason.
+- **Empty watch-list in subtag mode** (GR SQL unavailable, no config override):
+  log + metric `alarm_fallback_watchlist_empty`; the feed reports degraded +
+  empty; the gateway keeps re-running discovery on its reconcile cadence and
+  pushes an updated watch-list when one becomes available.
+- **Switch hand-off:** every switch snapshots the now-active provider and
+  reconciles against the gateway cache to avoid a raise/clear storm.
+- **STA affinity:** all subtag advise/write and wnwrap probe calls run on the
+  worker STA (reuse the existing affinity guard) to satisfy
+  `ThreadingModel=Apartment`.
+
+### Metrics
+
+- `mxgateway_alarm_provider_mode` (gauge: 1 = alarmmgr, 2 = subtag)
+- `mxgateway_alarm_provider_switch_total{from,to,reason}` (counter)
+- `mxgateway_alarm_fallback_watchlist_size` (gauge)
+
+> **Superseded:** the shipped meter names are `mxgateway.alarms.provider_mode`
+> (gauge) and `mxgateway.alarms.provider_switches{from,to,reason}` (counter,
+> `reason` bounded to `failover`/`failback`/`unknown`). The watch-list-size /
+> watch-list-empty gauges were not implemented; an empty watch-list is surfaced
+> via a warning log and the feed's degraded `ProviderStatus` instead.
+
+## Configuration
+
+```jsonc
+"MxGateway": {
+  "Alarms": {
+    "Enabled": true,
+    "SubscriptionExpression": "\\\\DESKTOP-6JL3KKO\\Galaxy!DEV",
+    "DefaultArea": "DEV",
+    "ReconcileIntervalSeconds": 30,
+    "Fallback": {
+      "Mode": "Auto",                      // Auto | ForceAlarmManager | ForceSubtag
+      "ConsecutiveFailureThreshold": 3,
+      "FailbackProbeIntervalSeconds": 30,
+      "FailbackStableProbes": 3,
+      "Discovery": {
+        "UseGalaxyRepository": true,
+        "Area": "",                        // defaults to Alarms.DefaultArea
+        "IncludeAttributes": [],           // explicit additions
+        "ExcludeAttributes": []
+      },
+      "Subtags": {
+        "Active": "active",
+        "Acked": "acked",
+        "AckComment": "",                  // verified against MXAccess analysis
+        "Priority": "priority"
+      }
+    }
+  }
+}
+```
+
+`GatewayOptionsValidator` additions: `Mode = ForceSubtag` with empty discovery
+result and no explicit `IncludeAttributes` → startup validation warning;
+threshold/interval/probe values floored at sane minimums.
+
+## Open item to confirm during implementation
+
+The exact AVEVA subtag names (`.active`, `.acked`, the ack-comment attribute,
+priority) must be confirmed against the MXAccess analysis project
+(`C:\Users\dohertj2\Desktop\mxaccess`, `docs/MXAccess-Public-API.md`) and the
+live Galaxy before wiring `SubtagAlarmConsumer`. The config `Subtags` block
+exists precisely so the resolved names are not hard-coded.
+
+## Testing
+
+| Layer | Tests |
+|---|---|
+| Worker unit (`MxGateway.Worker.Tests`, x86) | `SubtagAlarmConsumer` synthesis — feed `OnDataChange` sequences, assert raise/ack/clear transitions, snapshot states, degraded flag, synthetic-GUID stability, ack-comment write routing |
+| Worker unit | `FailoverAlarmConsumer` state machine — fake wnwrap throwing after K polls: assert switch at threshold, failback after stable probes, `ProviderModeChanged` emitted, no duplicate transitions across switch (hand-off reconcile) |
+| Gateway unit (`MxGateway.Tests`, fake worker) | discovery + config-override merge; `GatewayAlarmMonitor` reflects mode into feed + hub; metrics increment on switch |
+| Contract | proto round-trip for new fields; existing alarm tests unchanged (alarmmgr-mode regression — parity preserved) |
+| Live (opt-in, `MXGATEWAY_RUN_LIVE_MXACCESS_TESTS=1`) | real subtag advise + ack-comment write against a live alarm; GR SQL discovery query against the `ZB` DB (gated like existing GR tests) |
+
+## Docs to update in the same change
+
+`gateway.md` (alarm provider section), `docs/DesignDecisions.md` (record the
+fallback decision), `docs/GatewayConfiguration.md` (the `Fallback` block),
+`docs/AlarmClientDiscovery.md` (subtag provider + synthesis rules),
+`docs/Grpc.md` (the new `provider_status` / `degraded` fields), and any client
+READMEs whose generated alarm types gain fields.

docs/plans/2026-06-13-alarm-subtag-fallback.md

@@ -0,0 +1,860 @@
+# Alarm Subtag-Monitoring Fallback — Implementation Plan
+
+> **For Claude:** REQUIRED SUB-SKILL: Use superpowers-extended-cc:executing-plans (or subagent-driven-development) to implement this plan task-by-task.
+
+**Goal:** Add a second alarm source — direct MXAccess subtag monitoring — that the gateway auto-fails-over to when the wnwrap alarmmgr provider breaks, auto-fails-back to when it recovers, and can be forced on by config.
+
+**Architecture:** Worker-side synthesis (parity rule preserved). A new `SubtagAlarmConsumer` (own `LMXProxyServerClass`, `AddItem`/`Advise` on alarm subtags) and a `FailoverAlarmConsumer` composite (state machine over the wnwrap primary + subtag standby) both implement the existing `IMxAccessAlarmConsumer` seam. The gateway resolves the subtag watch-list (Galaxy Repository SQL + config override), arms the worker at subscribe time, and reflects the live provider mode into the gRPC alarm feed, the dashboard hub, and metrics.
+
+**Tech Stack:** .NET 10 (gateway, x64) + .NET Framework 4.8 (worker, x86, STA), protobuf/gRPC, `Microsoft.Data.SqlClient` (Galaxy Repository), SignalR (dashboard), `System.Diagnostics.Metrics`, xUnit (plain `Assert`, no FluentAssertions).
+
+**Design source:** `docs/plans/2026-06-13-alarm-subtag-fallback-design.md`
+
+**Branch:** `feat/alarm-subtag-fallback` (already created)
+
+---
+
+## Conventions for every task
+
+- **TDD:** write the failing test, run it red, implement, run it green, commit.
+- **xUnit, plain `Assert.*`**, naming `Subject_Condition_Expected`. Worker fakes are sealed private nested classes that raise events.
+- **Build/test commands:**
+  - Contracts regen: `dotnet build src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj`
+  - Gateway: `dotnet build src/ZB.MOM.WW.MxGateway.Server` ; `dotnet test src/ZB.MOM.WW.MxGateway.Tests/ZB.MOM.WW.MxGateway.Tests.csproj`
+  - Worker (x86): `dotnet build src/ZB.MOM.WW.MxGateway.Worker/ZB.MOM.WW.MxGateway.Worker.csproj -p:Platform=x86` ; `dotnet test src/ZB.MOM.WW.MxGateway.Worker.Tests/ZB.MOM.WW.MxGateway.Worker.Tests.csproj -p:Platform=x86`
+  - Single test: append `--filter FullyQualifiedName~<ClassOrMethod>`
+- **Build is strict:** `TreatWarningsAsErrors=true`, nullable enabled. Add XML doc comments on public members (the repo runs a doc checker).
+- **Generated code** under `Generated/` is never hand-edited — rebuild the contracts project to regenerate.
+- **Namespaces:** worker MxAccess types live in `ZB.MOM.WW.MxGateway.Worker.MxAccess`; proto C# types in `ZB.MOM.WW.MxGateway.Contracts.Proto`.
+
+---
+
+## Phase 0 — Contracts
+
+### Task 1: Worker proto — subtag watch-list, failover config, provider-mode enum
+
+**Classification:** high-risk
+**Estimated implement time:** ~4 min
+**Parallelizable with:** none (Task 2 imports these types)
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto` (real `SubscribeAlarmsCommand` at ~line 324; `MxCommand` references it at 123-125)
+
+> **CORRECTION (execution):** The alarm command messages and `MxCommand` live in **`mxaccess_gateway.proto`**, not the worker proto. `mxaccess_worker.proto` *imports* the gateway proto (`WorkerCommand.command` is `mxaccess_gateway.v1.MxCommand`), so the gateway proto is the base and the worker proto needs **no** change. `AlarmProviderMode` and the new types are added to the gateway proto and are visible to worker code as `mxaccess_gateway.v1` types. Tasks 1 and 2 are executed as a single combined edit on this one file.
+
+**Step 1: Add the enum and messages.** In `mxaccess_gateway.proto`, extend the existing `SubscribeAlarmsCommand` message (line 324) and add the new types after it:
+
+```protobuf
+// Provider selection / current provider for the alarm feed. Defined here in
+// the worker contract because the worker SubscribeAlarmsCommand references it;
+// mxaccess_gateway.proto imports this file and reuses the same enum.
+enum AlarmProviderMode {
+  ALARM_PROVIDER_MODE_UNSPECIFIED = 0;  // auto: alarmmgr primary, subtag fallback
+  ALARM_PROVIDER_MODE_ALARMMGR = 1;
+  ALARM_PROVIDER_MODE_SUBTAG = 2;
+}
+
+message SubscribeAlarmsCommand {
+  string subscription_expression = 1;  // existing field — keep
+  // UNSPECIFIED = auto-failover/failback. ALARMMGR/SUBTAG force one provider.
+  AlarmProviderMode forced_mode = 2;
+  // Subtag watch-list resolved by the gateway (GR SQL + config). Empty in pure
+  // alarmmgr mode; in subtag mode it bounds what the consumer can observe.
+  repeated AlarmSubtagTarget watch_list = 3;
+  AlarmFailoverConfig failover = 4;
+}
+
+// One alarm attribute the subtag consumer advises. Addresses are full MXAccess
+// item references the worker passes straight to AddItem.
+message AlarmSubtagTarget {
+  string alarm_full_reference = 1;     // e.g. "Galaxy!Area.Tank01.Level.HiHi"
+  string source_object_reference = 2;  // e.g. "Tank01"
+  string active_subtag = 3;            // item address of the in-alarm boolean
+  string acked_subtag = 4;             // item address of the acknowledged boolean
+  string ack_comment_subtag = 5;       // writable ack-comment attribute (ack write target)
+  string priority_subtag = 6;          // optional severity source; empty if absent
+}
+
+message AlarmFailoverConfig {
+  int32 consecutive_failure_threshold = 1;   // wnwrap COM failures before switching (>=1)
+  int32 failback_probe_interval_seconds = 2; // probe cadence while degraded (>=1)
+  int32 failback_stable_probes = 3;          // clean probes before switching back (>=1)
+}
+```
+
+`UnsubscribeAlarmsCommand` and `AcknowledgeAlarmCommand` are unchanged.
+
+**Step 2: Regenerate & verify it compiles.**
+Run: `dotnet build src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj`
+Expected: build succeeds; generated `AlarmProviderMode`, `AlarmSubtagTarget`, `AlarmFailoverConfig` types appear.
+
+**Step 3: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_worker.proto
+git commit -m "contracts(worker): subtag watch-list + failover config + AlarmProviderMode"
+```
+
+---
+
+### Task 2: Gateway proto — provider status on the feed, degraded provenance, mode-changed event
+
+**Classification:** high-risk
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none (depends on Task 1; Task 3 tests both)
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto` (`OnAlarmTransitionEvent` ~719-771, `ActiveAlarmSnapshot` ~783-803, `AlarmFeedMessage` ~860-870, `MxEvent` family enum + body oneof, `MxEventFamily` enum)
+
+**Step 1: Add degraded provenance to the two alarm payloads.** Append to `OnAlarmTransitionEvent` (next free field 14):
+
+```protobuf
+  // True when this transition came from the subtag-monitoring fallback rather
+  // than the native alarmmgr provider — i.e. it was synthesized from data
+  // changes and carries reduced fidelity (synthetic GUID, no native raise time).
+  bool degraded = 14;
+  // Which provider produced this transition.
+  AlarmProviderMode source_provider = 15;
+```
+
+Append the identical two fields to `ActiveAlarmSnapshot` (next free field 14):
+```protobuf
+  bool degraded = 14;
+  AlarmProviderMode source_provider = 15;
+```
+
+**Step 2: Add provider status to the feed oneof.** Add a new oneof case to `AlarmFeedMessage` (next free field 4) and a new message:
+
+```protobuf
+message AlarmFeedMessage {
+  oneof payload {
+    ActiveAlarmSnapshot active_alarm = 1;
+    bool snapshot_complete = 2;
+    OnAlarmTransitionEvent transition = 3;
+    // Provider-mode status. Emitted once on stream open and again on every
+    // failover/failback so late joiners learn the current mode immediately.
+    AlarmProviderStatus provider_status = 4;
+  }
+}
+
+message AlarmProviderStatus {
+  AlarmProviderMode mode = 1;
+  bool degraded = 2;            // true whenever mode == SUBTAG
+  string reason = 3;            // human-readable switch reason
+  google.protobuf.Timestamp since = 4;
+}
+```
+
+**Step 3: Add the worker→gateway mode-changed event to `MxEvent`.** Find the `MxEventFamily` enum and the `MxEvent` body oneof. Add a family member and a body message + oneof case (use the next free family value and the next free `MxEvent` body field number — check the file):
+
+```protobuf
+// in MxEventFamily enum:
+  MX_EVENT_FAMILY_ON_ALARM_PROVIDER_MODE_CHANGED = <next>;
+
+// new message near OnAlarmTransitionEvent:
+message OnAlarmProviderModeChangedEvent {
+  AlarmProviderMode mode = 1;
+  string reason = 2;
+  int32 hresult = 3;   // COM HRESULT that triggered failover; 0 on failback
+  google.protobuf.Timestamp at = 4;
+}
+
+// in MxEvent body oneof:
+  OnAlarmProviderModeChangedEvent on_alarm_provider_mode_changed = <next>;
+```
+
+`AlarmProviderMode` is defined in `mxaccess_worker.proto`; confirm `mxaccess_gateway.proto` already has `import "mxaccess_worker.proto";` (it references `SubscribeAlarmsCommand`, so it does) and reference the enum unqualified or via its package as the existing references do.
+
+**Step 4: Regenerate & verify.**
+Run: `dotnet build src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj`
+Expected: build succeeds.
+
+**Step 5: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto
+git commit -m "contracts(gateway): AlarmProviderStatus feed case, degraded provenance, mode-changed event"
+```
+
+---
+
+### Task 3: Proto round-trip tests for the new alarm fields
+
+**Classification:** small
+**Estimated implement time:** ~3 min
+**Parallelizable with:** none (depends on Tasks 1-2)
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Tests/Contracts/ProtobufContractRoundTripTests.cs`
+
+**Step 1: Add tests** mirroring the existing `Event_RoundTripsOnAlarmTransitionWithFullPayload` style:
+
+```csharp
+[Fact]
+public void Feed_RoundTripsProviderStatus()
+{
+    var since = Timestamp.FromDateTime(new DateTime(2026, 6, 13, 9, 0, 0, DateTimeKind.Utc));
+    var original = new AlarmFeedMessage
+    {
+        ProviderStatus = new AlarmProviderStatus
+        {
+            Mode = AlarmProviderMode.Subtag,
+            Degraded = true,
+            Reason = "wnwrap poll failed 3x (HRESULT 0x80004005)",
+            Since = since,
+        },
+    };
+
+    var parsed = AlarmFeedMessage.Parser.ParseFrom(original.ToByteArray());
+
+    Assert.Equal(original, parsed);
+    Assert.Equal(AlarmFeedMessage.PayloadOneofCase.ProviderStatus, parsed.PayloadCase);
+    Assert.True(parsed.ProviderStatus.Degraded);
+    Assert.Equal(AlarmProviderMode.Subtag, parsed.ProviderStatus.Mode);
+}
+
+[Fact]
+public void Transition_RoundTripsDegradedProvenance()
+{
+    var t = new OnAlarmTransitionEvent
+    {
+        AlarmFullReference = "Galaxy!Area.Tank01.Level.HiHi",
+        TransitionKind = AlarmTransitionKind.Raise,
+        Degraded = true,
+        SourceProvider = AlarmProviderMode.Subtag,
+    };
+
+    var parsed = OnAlarmTransitionEvent.Parser.ParseFrom(t.ToByteArray());
+
+    Assert.True(parsed.Degraded);
+    Assert.Equal(AlarmProviderMode.Subtag, parsed.SourceProvider);
+}
+```
+
+**Step 2: Run red→green.**
+Run: `dotnet test src/ZB.MOM.WW.MxGateway.Tests/ZB.MOM.WW.MxGateway.Tests.csproj --filter FullyQualifiedName~ProtobufContractRoundTripTests`
+Expected: PASS.
+
+**Step 3: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Tests/Contracts/ProtobufContractRoundTripTests.cs
+git commit -m "test(contracts): round-trip provider status + degraded provenance"
+```
+
+---
+
+## Phase 1 — Worker: subtag consumer + failover
+
+### Task 4: Subtag value-source abstraction + synthesis state holder
+
+**Classification:** standard
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none (Task 5 builds on it)
+
+A testable seam so synthesis logic is unit-tested without COM. The COM wiring lands in Task 6.
+
+**Files:**
+- Create: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/ISubtagAlarmSource.cs`
+- Create: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SubtagAlarmStateMachine.cs`
+- Test: `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SubtagAlarmStateMachineTests.cs`
+
+**Step 1: Define the source abstraction.** `ISubtagAlarmSource` advises subtag addresses and raises a normalized value-change callback on the STA:
+
+```csharp
+namespace ZB.MOM.WW.MxGateway.Worker.MxAccess;
+
+/// <summary>A change in one advised subtag value, normalized off the COM boundary.</summary>
+public sealed class SubtagValueChange
+{
+    /// <summary>The full item address that changed (matches an AlarmSubtagTarget subtag).</summary>
+    public string ItemAddress { get; init; } = string.Empty;
+    /// <summary>The new value (boolean for .active/.acked, numeric for priority).</summary>
+    public object? Value { get; init; }
+    /// <summary>The change timestamp in UTC.</summary>
+    public DateTime TimestampUtc { get; init; }
+}
+
+/// <summary>
+///     Advises a set of MXAccess subtag addresses and surfaces value changes.
+///     The production implementation (Task 6) owns its own LMXProxyServerClass;
+///     tests substitute a fake that pushes <see cref="SubtagValueChange"/>s.
+/// </summary>
+public interface ISubtagAlarmSource : IDisposable
+{
+    /// <summary>Raised on the STA when an advised subtag's value changes.</summary>
+    event EventHandler<SubtagValueChange>? ValueChanged;
+
+    /// <summary>Advises every subtag in the supplied addresses; idempotent per address.</summary>
+    void Advise(IReadOnlyCollection<string> itemAddresses);
+
+    /// <summary>Writes a value to an item address (used for the ack-comment write).</summary>
+    void Write(string itemAddress, object? value);
+}
+```
+
+**Step 2: Write the state-machine tests first.** `SubtagAlarmStateMachine` maps `(active, acked)` changes per target to `MxAlarmTransitionEvent`s. Test the four core transitions:
+
+```csharp
+namespace ZB.MOM.WW.MxGateway.Worker.Tests.MxAccess;
+
+public sealed class SubtagAlarmStateMachineTests
+{
+    private static AlarmSubtagTarget Target() => new()
+    {
+        AlarmFullReference = "Galaxy!Area.Tank01.Level.HiHi",
+        SourceObjectReference = "Tank01",
+        ActiveSubtag = "Tank01.Level.HiHi.active",
+        AckedSubtag = "Tank01.Level.HiHi.acked",
+        AckCommentSubtag = "Tank01.Level.HiHi.ackmsg",
+    };
+
+    [Fact]
+    public void ActiveFalseToTrue_EmitsRaise_FlaggedDegraded()
+    {
+        var sm = new SubtagAlarmStateMachine(new[] { Target() });
+        var ts = new DateTime(2026, 6, 13, 9, 0, 0, DateTimeKind.Utc);
+
+        var events = sm.Apply("Tank01.Level.HiHi.active", true, ts);
+
+        var e = Assert.Single(events);
+        Assert.Equal(MxAlarmStateKind.UnackAlm, e.Record.State);
+        Assert.Equal(MxAlarmStateKind.Unspecified, e.PreviousState);
+        Assert.Equal("Tank01.Level.HiHi", e.Record.TagName); // reference minus provider/area
+    }
+
+    [Fact]
+    public void AckedTrueWhileActive_EmitsAckTransition()
+    {
+        var sm = new SubtagAlarmStateMachine(new[] { Target() });
+        var ts = new DateTime(2026, 6, 13, 9, 0, 0, DateTimeKind.Utc);
+        sm.Apply("Tank01.Level.HiHi.active", true, ts);
+
+        var events = sm.Apply("Tank01.Level.HiHi.acked", true, ts.AddSeconds(5));
+
+        var e = Assert.Single(events);
+        Assert.Equal(MxAlarmStateKind.AckAlm, e.Record.State);
+        Assert.Equal(MxAlarmStateKind.UnackAlm, e.PreviousState);
+    }
+
+    [Fact]
+    public void ActiveTrueToFalse_WhileUnacked_EmitsUnackRtn()
+    {
+        var sm = new SubtagAlarmStateMachine(new[] { Target() });
+        var ts = new DateTime(2026, 6, 13, 9, 0, 0, DateTimeKind.Utc);
+        sm.Apply("Tank01.Level.HiHi.active", true, ts);
+
+        var events = sm.Apply("Tank01.Level.HiHi.active", false, ts.AddSeconds(10));
+
+        var e = Assert.Single(events);
+        Assert.Equal(MxAlarmStateKind.UnackRtn, e.Record.State);
+    }
+
+    [Fact]
+    public void Snapshot_ReflectsActiveAndAckedState()
+    {
+        var sm = new SubtagAlarmStateMachine(new[] { Target() });
+        var ts = new DateTime(2026, 6, 13, 9, 0, 0, DateTimeKind.Utc);
+        sm.Apply("Tank01.Level.HiHi.active", true, ts);
+        sm.Apply("Tank01.Level.HiHi.acked", true, ts);
+
+        var snap = Assert.Single(sm.SnapshotActive());
+        Assert.Equal(MxAlarmStateKind.AckAlm, snap.State);
+    }
+}
+```
+
+Run: `dotnet test ...Worker.Tests... -p:Platform=x86 --filter FullyQualifiedName~SubtagAlarmStateMachineTests` → FAIL (type missing).
+
+**Step 3: Implement `SubtagAlarmStateMachine`.** Build an address→target index (active/acked/priority/comment addresses), hold per-reference `(bool active, bool acked, DateTime firstRaiseUtc, int priority)`, and emit on change:
+- active `false→true` ⇒ `UnackAlm`, set `firstRaiseUtc`, `PreviousState` from prior state.
+- acked `false→true` while active ⇒ `AckAlm`.
+- active `true→false` ⇒ `AckRtn` if currently acked else `UnackRtn`; then reset acked.
+- priority change ⇒ update stored priority, no transition.
+- `TagName` = `alarm_full_reference` with any `Provider!Area.` prefix stripped (match `WnWrapAlarmConsumer`'s reference shape so `GatewayAlarmMonitor` keys align). Set `ProviderName`, `Group`, `Priority`, `AlarmComment` from the target/last values. Mark a `Degraded`/source flag (carried via a new field — see Task 5 wiring).
+- `SnapshotActive()` returns `MxAlarmSnapshotRecord` for references whose active is true.
+
+**Step 4: Run green.** Expected: PASS.
+
+**Step 5: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Worker/MxAccess/ISubtagAlarmSource.cs \
+        src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SubtagAlarmStateMachine.cs \
+        src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SubtagAlarmStateMachineTests.cs
+git commit -m "worker(alarms): subtag value-source seam + synthesis state machine"
+```
+
+---
+
+### Task 5: `SubtagAlarmConsumer` over the source seam (no COM yet)
+
+**Classification:** standard
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none (depends on Task 4)
+
+**Files:**
+- Create: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SubtagAlarmConsumer.cs`
+- Test: `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SubtagAlarmConsumerTests.cs`
+
+**Step 1: Test with a fake `ISubtagAlarmSource`.** Drive value changes through the source, assert `AlarmTransitionEmitted` fires with synthesized records and that ack writes the comment to the ack-comment subtag:
+
+```csharp
+public sealed class SubtagAlarmConsumerTests
+{
+    private sealed class FakeSource : ISubtagAlarmSource
+    {
+        public event EventHandler<SubtagValueChange>? ValueChanged;
+        public List<string> Advised { get; } = new();
+        public (string Address, object? Value)? LastWrite { get; private set; }
+        public void Advise(IReadOnlyCollection<string> a) => Advised.AddRange(a);
+        public void Write(string a, object? v) => LastWrite = (a, v);
+        public void Raise(string addr, object? val, DateTime ts) =>
+            ValueChanged?.Invoke(this, new SubtagValueChange { ItemAddress = addr, Value = val, TimestampUtc = ts });
+        public void Dispose() { }
+    }
+
+    private static AlarmSubtagTarget Target() => new()
+    {
+        AlarmFullReference = "Galaxy!Area.Tank01.Level.HiHi",
+        ActiveSubtag = "Tank01.Level.HiHi.active",
+        AckedSubtag = "Tank01.Level.HiHi.acked",
+        AckCommentSubtag = "Tank01.Level.HiHi.ackmsg",
+    };
+
+    [Fact]
+    public void Subscribe_AdvisesAllSubtags()
+    {
+        var src = new FakeSource();
+        using var c = new SubtagAlarmConsumer(src, new[] { Target() });
+        c.Subscribe("ignored-in-subtag-mode");
+        Assert.Contains("Tank01.Level.HiHi.active", src.Advised);
+        Assert.Contains("Tank01.Level.HiHi.acked", src.Advised);
+    }
+
+    [Fact]
+    public void ValueChange_RaisesSynthesizedTransition()
+    {
+        var src = new FakeSource();
+        using var c = new SubtagAlarmConsumer(src, new[] { Target() });
+        c.Subscribe("x");
+        MxAlarmTransitionEvent? seen = null;
+        c.AlarmTransitionEmitted += (_, e) => seen = e;
+
+        src.Raise("Tank01.Level.HiHi.active", true, new DateTime(2026, 6, 13, 9, 0, 0, DateTimeKind.Utc));
+
+        Assert.NotNull(seen);
+        Assert.Equal(MxAlarmStateKind.UnackAlm, seen!.Record.State);
+    }
+
+    [Fact]
+    public void AcknowledgeByName_WritesCommentToAckCommentSubtag()
+    {
+        var src = new FakeSource();
+        using var c = new SubtagAlarmConsumer(src, new[] { Target() });
+        c.Subscribe("x");
+
+        int rc = c.AcknowledgeByName("Tank01.Level.HiHi", "Galaxy", "Area",
+            "ack from HMI", "op1", "node", "dom", "Op One");
+
+        Assert.Equal(0, rc);
+        Assert.Equal(("Tank01.Level.HiHi.ackmsg", (object?)"ack from HMI"), src.LastWrite);
+    }
+}
+```
+
+**Step 2: Implement `SubtagAlarmConsumer : IMxAccessAlarmConsumer`.**
+- Constructor `(ISubtagAlarmSource source, IReadOnlyList<AlarmSubtagTarget> watchList)`; build a `SubtagAlarmStateMachine`; index `alarm_full_reference`→target for ack routing.
+- `Subscribe(_)`: call `source.Advise(<all subtag addresses>)`; subscribe to `source.ValueChanged`, feed each into the state machine, and re-raise each produced `MxAlarmTransitionEvent` via `AlarmTransitionEmitted` (mark degraded).
+- `AcknowledgeByName(alarmName, …, comment, …)`: resolve the target by reference; if no `AckCommentSubtag`, return a non-zero failure code; else `source.Write(target.AckCommentSubtag, comment)` and return 0.
+- `AcknowledgeByGuid(guid, …)`: map the synthetic GUID (deterministic hash of reference — see Task 8 helper, or a local copy) back to a reference, then delegate to the name path; unknown GUID ⇒ non-zero.
+- `SnapshotActiveAlarms()`: from the state machine.
+- `PollOnce()`: no-op.
+- `Dispose()`: unsubscribe + dispose source.
+
+**Step 3: Run green.** `dotnet test ...Worker.Tests... -p:Platform=x86 --filter FullyQualifiedName~SubtagAlarmConsumerTests`.
+
+**Step 4: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SubtagAlarmConsumer.cs \
+        src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SubtagAlarmConsumerTests.cs
+git commit -m "worker(alarms): SubtagAlarmConsumer synthesizing transitions over the source seam"
+```
+
+---
+
+### Task 6: COM-backed `LmxSubtagAlarmSource` (own LMXProxyServerClass)
+
+**Classification:** high-risk
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none
+
+The only piece that touches live COM. Like `WnWrapAlarmConsumer`, it owns its own MXAccess server object so the subtag source is self-contained and isolated from the session's item pipeline. Logic stays thin (advise/write/marshal); real verification is the live smoke test in Task 17.
+
+**Files:**
+- Create: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/LmxSubtagAlarmSource.cs`
+- Test: `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/LmxSubtagAlarmSourceTests.cs` (constructor/guard tests only; COM path is live-gated)
+
+**Step 1: Implement `LmxSubtagAlarmSource : ISubtagAlarmSource`.**
+- Own an `LMXProxyServerClass` (reuse the worker's `IMxAccessServer`/`MxAccessComServer` wrapper + `IMxAccessComObjectFactory` so it is fakeable; constructor takes the factory).
+- `Advise(addresses)`: `RegisterServer` (topic) once; per address `AddItem`→`itemHandle`, `Advise`, and record `itemHandle→address`. Subscribe to the proxy's `OnDataChange`; in the handler, look up the address by `phItemHandle`, normalize `pvItemValue` (VARIANT→bool/double) and `pftItemTimeStamp`→UTC, and raise `ValueChanged`. All calls run on the STA (the worker STA pumps messages, so `OnDataChange` delivers).
+- `Write(address, value)`: resolve/create the item handle, `server.Write(serverHandle, itemHandle, value, userId: 0)`.
+- `Dispose()`: `UnAdvise`/`RemoveItem`/`Unregister`/release COM.
+
+**Step 2: Tests** — only the non-COM guards (null factory throws; `Write` before `Advise` resolves a handle or throws a clear error). Mark the COM round-trip `[LiveMxAccessFact]` and `Skip` per the `AlarmsLiveSmokeTests` precedent.
+
+**Step 3: Build x86 + run unit tests.**
+`dotnet build src/ZB.MOM.WW.MxGateway.Worker/ZB.MOM.WW.MxGateway.Worker.csproj -p:Platform=x86`
+`dotnet test ...Worker.Tests... -p:Platform=x86 --filter FullyQualifiedName~LmxSubtagAlarmSourceTests`
+
+**Step 4: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Worker/MxAccess/LmxSubtagAlarmSource.cs \
+        src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/LmxSubtagAlarmSourceTests.cs
+git commit -m "worker(alarms): COM-backed LmxSubtagAlarmSource advising alarm subtags"
+```
+
+---
+
+### Task 7: `FailoverAlarmConsumer` state machine
+
+**Classification:** high-risk
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none (depends on Task 5)
+
+**Files:**
+- Create: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/FailoverAlarmConsumer.cs`
+- Create: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmProviderModeChange.cs` (small EventArgs)
+- Test: `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/FailoverAlarmConsumerTests.cs`
+
+**Step 1: Test the switch/failback with a fake primary that throws.**
+
+```csharp
+public sealed class FailoverAlarmConsumerTests
+{
+    private sealed class FlakyPrimary : IMxAccessAlarmConsumer
+    {
+        public event EventHandler<MxAlarmTransitionEvent>? AlarmTransitionEmitted;
+        public int PollsUntilHeal = int.MaxValue;   // becomes healthy after N polls while degraded
+        public bool ThrowOnPoll = true;
+        private int _polls;
+        public void Subscribe(string s) { if (ThrowOnPoll) throw new COMException("boom", unchecked((int)0x80004005)); }
+        public void PollOnce()
+        {
+            _polls++;
+            if (ThrowOnPoll && _polls < PollsUntilHeal) throw new COMException("boom", unchecked((int)0x80004005));
+        }
+        public int AcknowledgeByGuid(Guid g, string c, string a, string b, string d, string e) => 0;
+        public int AcknowledgeByName(string n, string p, string gr, string c, string a, string b, string d, string e) => 0;
+        public IReadOnlyList<MxAlarmSnapshotRecord> SnapshotActiveAlarms() => Array.Empty<MxAlarmSnapshotRecord>();
+        public void Dispose() { }
+    }
+
+    private sealed class StubStandby : IMxAccessAlarmConsumer { /* records Subscribe, no-op rest */ }
+
+    [Fact]
+    public void Primary_FailsThresholdTimes_SwitchesToSubtagAndEmitsModeChange()
+    {
+        var primary = new FlakyPrimary();
+        var standby = new StubStandby();
+        using var c = new FailoverAlarmConsumer(primary, standby,
+            new FailoverSettings(threshold: 3, probeIntervalSeconds: 30, stableProbes: 3));
+        AlarmProviderModeChange? change = null;
+        c.ProviderModeChanged += (_, e) => change = e;
+
+        c.Subscribe("\\\\host\\Galaxy!Area");     // primary.Subscribe throws -> counts as failure 1
+        c.PollOnce();                              // failure 2
+        c.PollOnce();                              // failure 3 -> switch
+
+        Assert.NotNull(change);
+        Assert.Equal(AlarmProviderMode.Subtag, change!.Mode);
+    }
+
+    [Fact]
+    public void WhileDegraded_PrimaryHeals_FailsBackAfterStableProbes()
+    {
+        var primary = new FlakyPrimary { PollsUntilHeal = 0 }; // will heal once we stop throwing
+        var standby = new StubStandby();
+        using var c = new FailoverAlarmConsumer(primary, standby,
+            new FailoverSettings(threshold: 1, probeIntervalSeconds: 0, stableProbes: 2));
+        var modes = new List<AlarmProviderMode>();
+        c.ProviderModeChanged += (_, e) => modes.Add(e.Mode);
+
+        c.Subscribe("x");          // failure -> switch to subtag
+        primary.ThrowOnPoll = false;
+        c.ProbeOnce();             // clean probe 1
+        c.ProbeOnce();             // clean probe 2 -> failback
+
+        Assert.Equal(AlarmProviderMode.Subtag, modes[0]);
+        Assert.Equal(AlarmProviderMode.Alarmmgr, modes[^1]);
+    }
+}
+```
+
+**Step 2: Implement.**
+- `record FailoverSettings(int threshold, int probeIntervalSeconds, int stableProbes)`; `AlarmProviderModeChange : EventArgs { AlarmProviderMode Mode; string Reason; int HResult; DateTime AtUtc; }`.
+- Constructor `(IMxAccessAlarmConsumer primary, IMxAccessAlarmConsumer standby, FailoverSettings settings)`; forced-mode variants handled in Task 9 wiring (forced ⇒ skip the other consumer).
+- Forward `AlarmTransitionEmitted` from the **active** child only (swap the subscription on switch).
+- Wrap `Subscribe`/`PollOnce` on the primary: on `COMException` (or a failure HRESULT) while `PrimaryActive`, increment a counter; at `threshold`, ensure standby `Subscribe`d, set active=standby, snapshot standby for hand-off, raise `ProviderModeChanged(Subtag, reason, hresult, now)`. Reset counter on any clean primary poll.
+- `ProbeOnce()` (driven by the poll loop while degraded, gated by `probeIntervalSeconds`): try primary `Subscribe`+`PollOnce`; count consecutive clean probes; at `stableProbes`, set active=primary, return standby to standby, raise `ProviderModeChanged(Alarmmgr, "recovered", 0, now)`.
+- `Acknowledge*` / `SnapshotActiveAlarms` delegate to the **active** child.
+- `PollOnce()` drives the active child's poll, and—while degraded—also drives the failback probe cadence.
+
+**Step 3: Run green** (x86 filter `FailoverAlarmConsumerTests`).
+
+**Step 4: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Worker/MxAccess/FailoverAlarmConsumer.cs \
+        src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmProviderModeChange.cs \
+        src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/FailoverAlarmConsumerTests.cs
+git commit -m "worker(alarms): FailoverAlarmConsumer auto-failover/failback state machine"
+```
+
+---
+
+### Task 8: Synthetic-GUID helper + degraded flag on the event sink path
+
+**Classification:** standard
+**Estimated implement time:** ~4 min
+**Parallelizable with:** Task 9
+
+Carry `degraded` + `source_provider` from the worker synthesis into the emitted `OnAlarmTransitionEvent`.
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAlarmSnapshot.cs` (add `bool Degraded`)
+- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessAlarmEventSink.cs` (`EnqueueTransition` carries degraded)
+- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessEventMapper.cs` (`CreateOnAlarmTransition` sets `Degraded`/`SourceProvider`)
+- Create: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SyntheticAlarmGuid.cs`
+- Test: add cases to `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmDispatcherTests.cs` and a new `SyntheticAlarmGuidTests.cs`
+
+**Step 1: `SyntheticAlarmGuid.ForReference(string reference)`** — deterministic GUID from a stable hash (e.g. MD5 of the UTF-8 reference → `new Guid(bytes)`), so subtag-mode acks resolve by GUID. Test determinism + difference:
+
+```csharp
+[Fact] public void SameReference_SameGuid() =>
+    Assert.Equal(SyntheticAlarmGuid.ForReference("A.B.C"), SyntheticAlarmGuid.ForReference("A.B.C"));
+[Fact] public void DifferentReference_DifferentGuid() =>
+    Assert.NotEqual(SyntheticAlarmGuid.ForReference("A.B.C"), SyntheticAlarmGuid.ForReference("A.B.D"));
+```
+
+**Step 2: Thread `degraded`** through `MxAlarmSnapshotRecord.Degraded`, `EnqueueTransition(... bool degraded)`, and `CreateOnAlarmTransition(... bool degraded, AlarmProviderMode sourceProvider)`. Default `degraded=false`, `sourceProvider=Alarmmgr` so the wnwrap path is unchanged (regression: existing `AlarmDispatcherTests` still pass with `Degraded=false`).
+
+**Step 3: Tests** — extend `AlarmDispatcherTests` with a subtag-style transition asserting `body.Degraded == true` and `SourceProvider == Subtag`.
+
+**Step 4: Build x86 + run** worker tests for `AlarmDispatcherTests`, `SyntheticAlarmGuidTests`.
+
+**Step 5: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAlarmSnapshot.cs \
+        src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessAlarmEventSink.cs \
+        src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessEventMapper.cs \
+        src/ZB.MOM.WW.MxGateway.Worker/MxAccess/SyntheticAlarmGuid.cs \
+        src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/
+git commit -m "worker(alarms): synthetic GUID + degraded provenance on emitted transitions"
+```
+
+---
+
+### Task 9: Wire watch-list + failover config through `AlarmCommandHandler`; emit mode-changed event
+
+**Classification:** high-risk
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none (depends on Tasks 5, 7, 8)
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmCommandHandler.cs`
+- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/IAlarmCommandHandler.cs`
+- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessCommandExecutor.cs` (`ExecuteSubscribeAlarms`, ~lines 588-616)
+- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessStaSession.cs` (consumer factory wiring; mode-change → event queue)
+- Test: `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/AlarmCommandHandlerTests.cs` (extend or create)
+
+**Step 1: Carry the subscribe payload.** Change the alarm subscribe entry point from `Subscribe(string subscription)` to `Subscribe(SubscribeAlarmsCommand command)` (the command now has `ForcedMode`, `WatchList`, `Failover`). In `AlarmCommandHandler.Subscribe`:
+- Build the active provider per `ForcedMode`:
+  - `ALARMMGR` ⇒ `WnWrapAlarmConsumer` only.
+  - `SUBTAG` ⇒ `SubtagAlarmConsumer(new LmxSubtagAlarmSource(factory), watchList)` only.
+  - `UNSPECIFIED` ⇒ `FailoverAlarmConsumer(primary: wnwrap, standby: subtag, settings-from-Failover)`.
+- Use the existing `consumerFactory` seam but widen it to `Func<SubscribeAlarmsCommand, IMxAccessAlarmConsumer>` so tests inject fakes and production builds the failover composite. Subscribe to `FailoverAlarmConsumer.ProviderModeChanged` and enqueue an `OnAlarmProviderModeChangedEvent` MxEvent via the event queue (new mapper method `CreateOnAlarmProviderModeChanged`).
+
+**Step 2: Executor + STA wiring.** `ExecuteSubscribeAlarms` passes the full `SubscribeAlarmsCommand` (not just the expression). In `MxAccessStaSession`, the `alarmCommandHandlerFactory` must give the handler access to the `IMxAccessComObjectFactory` so the subtag source can create its own proxy server on the STA; keep the `EnsureOnAlarmConsumerThread` affinity guard on every path.
+
+**Step 3: Test** — fake consumer factory; assert that a `SUBTAG` forced command builds the subtag consumer and advises; that an auto command building a fake failover composite, when it raises `ProviderModeChanged`, enqueues an `OnAlarmProviderModeChangedEvent` on the queue.
+
+**Step 4: Build x86 + worker tests.**
+
+**Step 5: Commit.**
+```bash
+git add src/ZB.MOM.WW.MxGateway.Worker/MxAccess/ src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/
+git commit -m "worker(alarms): route watch-list/failover config; emit provider-mode-changed event"
+```
+
+---
+
+## Phase 2 — Gateway: discovery, options, monitor, metrics, dashboard
+
+### Task 10: `AlarmsOptions.Fallback` + validation
+
+**Classification:** standard
+**Estimated implement time:** ~4 min
+**Parallelizable with:** Task 11, Task 13
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Server/Configuration/AlarmsOptions.cs`
+- Create: `src/ZB.MOM.WW.MxGateway.Server/Configuration/AlarmFallbackOptions.cs`
+- Modify: `src/ZB.MOM.WW.MxGateway.Server/Configuration/GatewayOptionsValidator.cs` (`ValidateAlarms`, ~lines 234-258)
+- Test: `src/ZB.MOM.WW.MxGateway.Tests/Configuration/GatewayOptionsValidatorTests.cs` (extend)
+
+**Step 1:** Add `AlarmFallbackOptions Fallback { get; init; } = new();` to `AlarmsOptions`. `AlarmFallbackOptions`: `string Mode = "Auto"` (`Auto|ForceAlarmManager|ForceSubtag`), `int ConsecutiveFailureThreshold = 3`, `int FailbackProbeIntervalSeconds = 30`, `int FailbackStableProbes = 3`, a `Discovery` sub-object (`bool UseGalaxyRepository = true`, `string Area = ""`, `string[] IncludeAttributes = []`, `string[] ExcludeAttributes = []`), and a `Subtags` sub-object (`Active="active"`, `Acked="acked"`, `AckComment=""`, `Priority="priority"`).
+
+**Step 2:** In `ValidateAlarms`, when `Enabled` and `Mode == "ForceSubtag"` and `Discovery.UseGalaxyRepository == false` and `IncludeAttributes` empty ⇒ add a validation error ("ForceSubtag requires Galaxy Repository discovery or an explicit IncludeAttributes list"). Floor the three numeric values at 1. Validate `Mode` is one of the three literals.
+
+**Step 3-5:** Test the new validation cases (red→green), build the server, commit.
+
+---
+
+### Task 11: Galaxy Repository "alarm attributes" discovery query
+
+**Classification:** standard
+**Estimated implement time:** ~5 min
+**Parallelizable with:** Task 10, Task 13
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyRepository.cs` (add `GetAlarmAttributesAsync` + SQL constant, following `GetAttributesAsync` ~lines 86-115 and `AttributesSql` ~line 176)
+- Modify: `src/ZB.MOM.WW.MxGateway.Server/Galaxy/IGalaxyRepository.cs`
+- Create: `src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyAlarmAttributeRow.cs`
+- Test: `src/ZB.MOM.WW.MxGateway.Tests/Galaxy/` (projection unit test; live SQL gated)
+
+**Step 1:** `GalaxyAlarmAttributeRow { string FullTagReference; string SourceObjectReference; string AckCommentSubtag; }` (and any priority subtag). `GetAlarmAttributesAsync` reuses the existing `is_alarm` detection (the `AlarmExtension` primitive join already in `AttributesSql`) filtered to `is_alarm = 1`, projecting the alarm reference + its ack-comment attribute. Follow the exact `SqlConnection`/`SqlCommand`/`SqlDataReader` pattern from `GetAttributesAsync`.
+
+**Step 2:** Unit-test the row→`AlarmSubtagTarget` mapping (a pure mapper function); gate any live-DB test like the existing Galaxy live tests (or `Skip` with a note, matching `AlarmsLiveSmokeTests`).
+
+**Step 3-5:** red→green, build server, commit.
+
+---
+
+### Task 12: Watch-list resolver (GR SQL + config override → `AlarmSubtagTarget[]`)
+
+**Classification:** standard
+**Estimated implement time:** ~4 min
+**Parallelizable with:** none (depends on Tasks 10, 11)
+
+**Files:**
+- Create: `src/ZB.MOM.WW.MxGateway.Server/Alarms/AlarmWatchListResolver.cs`
+- Create: `src/ZB.MOM.WW.MxGateway.Server/Alarms/IAlarmWatchListResolver.cs`
+- Test: `src/ZB.MOM.WW.MxGateway.Tests/Alarms/AlarmWatchListResolverTests.cs`
+
+**Step 1: Test the merge** with a fake `IGalaxyRepository`:
+- discovery rows + `IncludeAttributes` are unioned; `ExcludeAttributes` removed; each becomes an `AlarmSubtagTarget` with `.active`/`.acked`/`.ackmsg` addresses composed from the configured `Subtags` names (`<reference>.<Active>`, etc.); empty config subtag names fall back to defaults; GR unavailable + no includes ⇒ empty list + a logged warning flag.
+
+**Step 2: Implement** `ResolveAsync(AlarmsOptions, CancellationToken) → IReadOnlyList<AlarmSubtagTarget>`.
+
+**Step 3-5:** red→green, build, commit.
+
+---
+
+### Task 13: Gateway metrics — provider-mode gauge + switch counter
+
+**Classification:** small
+**Estimated implement time:** ~3 min
+**Parallelizable with:** Task 10, Task 11
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Server/Metrics/GatewayMetrics.cs` (ctor ~lines 55-79; add counter + observable gauge following the existing pattern)
+- Test: `src/ZB.MOM.WW.MxGateway.Tests/Metrics/GatewayMetricsTests.cs` (if present; else assert via a `MeterListener`)
+
+**Step 1:** Add `mxgateway.alarms.provider_switches` counter (tagged `from`,`to`,`reason`) and `mxgateway.alarms.provider_mode` observable gauge (1=alarmmgr, 2=subtag), plus `AlarmProviderSwitched(int from, int to, string reason)` and a private `GetAlarmProviderMode()` (lock on `_syncRoot` like the others).
+
+**Step 2-4:** test, build, commit.
+
+---
+
+### Task 14: `GatewayAlarmMonitor` — arm watch-list, reflect provider mode, reconcile on switch
+
+**Classification:** high-risk
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none (depends on Tasks 9, 12, 13)
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Server/Alarms/GatewayAlarmMonitor.cs` (ctor ~41-49; `SubscribeAlarmsAsync` ~210-233; event-drain loop; `StreamAsync` ~386-434)
+- Test: `src/ZB.MOM.WW.MxGateway.Tests/Alarms/GatewayAlarmMonitorProviderModeTests.cs` (new, using `FakeWorkerHarness`)
+
+**Step 1:** Inject `IAlarmWatchListResolver` and `GatewayMetrics`. In `SubscribeAlarmsAsync`, resolve the watch-list and build the `SubscribeAlarmsCommand` with `ForcedMode` (from `Fallback.Mode`), `WatchList`, and `Failover` populated from options — instead of the bare `{ SubscriptionExpression }`.
+
+**Step 2:** In the worker-event drain path, handle `OnAlarmProviderModeChangedEvent`: update a `_providerStatus` field (mode/degraded/reason/since), `Broadcast(new AlarmFeedMessage { ProviderStatus = … })` to every subscriber, call `metrics.AlarmProviderSwitched(...)`, and force a `ReconcileAsync` so the cache re-seeds from the now-active provider (avoids raise/clear storms).
+
+**Step 3:** In `StreamAsync`, emit the current `provider_status` as the **first** message (before the snapshot) so a late joiner immediately knows the mode.
+
+**Step 4: Test** — stand up the monitor with `FakeWorkerHarness`; emit an `OnAlarmProviderModeChangedEvent(Subtag)`; assert a `StreamAsync` subscriber receives a `ProviderStatus{ Mode=Subtag, Degraded=true }` and that the switch counter incremented. Also assert a transition emitted in subtag mode flows through with `Degraded=true`.
+
+**Step 5:** build server, run the new test, commit.
+
+---
+
+### Task 15: Dashboard — push provider status to `/hubs/alarms` + UI indicator
+
+**Classification:** standard
+**Estimated implement time:** ~5 min
+**Parallelizable with:** none (depends on Task 14)
+
+**Files:**
+- Modify: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/Hubs/AlarmsHubPublisher.cs` (forward `ProviderStatus` messages — they already flow through `StreamAsync`, so confirm the existing `SendAsync(AlarmMessage, message)` carries them; add a dedicated `"ProviderModeChanged"` client method if the dashboard needs a distinct channel)
+- Modify: the alarms dashboard page/component (Bootstrap-only badge: green "alarmmgr" / amber "degraded — subtag") — find under `src/ZB.MOM.WW.MxGateway.Server/Dashboard/`
+- Test: `src/ZB.MOM.WW.MxGateway.Tests/` dashboard model test (e.g. a `DashboardAlarmProviderStatus.FromFeed` mapper, mirroring `DashboardActiveAlarm.FromSnapshot`)
+
+**Constraint:** Bootstrap CSS/JS only — no MudBlazor/Radzen/FluentUI.
+
+**Steps:** TDD the model mapper, wire the publisher + badge, build, commit.
+
+---
+
+## Phase 3 — Integration, docs, live smoke
+
+### Task 16: End-to-end fake-worker failover test
+
+**Classification:** standard
+**Estimated implement time:** ~5 min
+**Parallelizable with:** Task 18
+
+**Files:**
+- Test: `src/ZB.MOM.WW.MxGateway.Tests/Alarms/AlarmFailoverEndToEndTests.cs`
+
+Drive the full gateway path with `FakeWorkerHarness`: subscribe (assert the `SubscribeAlarmsCommand` carries a watch-list), emit a wnwrap-style transition (assert `Degraded=false`), emit `OnAlarmProviderModeChangedEvent(Subtag)`, emit a synthesized transition (assert `Degraded=true`, `SourceProvider=Subtag`), then `OnAlarmProviderModeChangedEvent(Alarmmgr)` and assert the feed reports recovery. Build, run, commit.
+
+---
+
+### Task 17: Live subtag smoke test (opt-in)
+
+**Classification:** small
+**Estimated implement time:** ~4 min
+**Parallelizable with:** Task 18
+
+**Files:**
+- Test: `src/ZB.MOM.WW.MxGateway.IntegrationTests/...AlarmSubtagLiveSmokeTests.cs` (or the worker live suite)
+
+A `[LiveMxAccessFact]`, `Skip`-by-default test (per `AlarmsLiveSmokeTests` precedent) that, against a live Galaxy + alarm flip script: advises the real `.active`/`.acked` subtags via `LmxSubtagAlarmSource`, asserts a synthesized raise/clear, and performs an ack via the ack-comment write. Document the exact subtag names discovered (resolves the design's open item). Commit.
+
+---
+
+### Task 18: Documentation
+
+**Classification:** trivial
+**Estimated implement time:** ~5 min
+**Parallelizable with:** Task 16, Task 17
+
+**Files:**
+- Modify: `gateway.md` (alarm provider section: dual provider + auto-failover/failback)
+- Modify: `docs/DesignDecisions.md` (record the fallback decision + parity rationale)
+- Modify: `docs/GatewayConfiguration.md` (the `MxGateway:Alarms:Fallback` block)
+- Modify: `docs/AlarmClientDiscovery.md` (subtag provider, synthesis rules, ack-comment write)
+- Modify: `docs/Grpc.md` (new `provider_status` feed case + `degraded`/`source_provider` fields)
+
+Follow `StyleGuide.md` (PascalCase filenames, present tense, explain *why*). No code; commit.
+
+---
+
+## Execution order & parallelism summary
+
+- **Serial spine:** 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8/9 → 10/11 → 12 → 13 → 14 → 15 → 16 → 17/18.
+- **Parallelizable clusters:** {8, 9 partially}, {10, 11, 13}, {16, 17, 18}.
+- **High-risk tasks** (full review chain): 1, 2, 6, 7, 9, 14. **Standard:** 4, 5, 8, 10, 11, 12, 15, 16. **Small/trivial:** 3, 13, 17, 18.
+
+## Risk notes for the executor
+
+- **Field-number collisions:** Task 2 must read the live `MxEvent`/`MxEventFamily` numbers before adding — the agent map gave alarm-payload maxima but not `MxEvent`'s. Verify before editing.
+- **STA discipline:** every COM call in `LmxSubtagAlarmSource` and every consumer swap runs on the worker STA; keep the `EnsureOnAlarmConsumerThread` guard. The worker STA already pumps Windows messages, which is required for the subtag `OnDataChange` to deliver.
+- **Parity regression:** alarmmgr-mode output must be byte-for-byte unchanged. Existing `AlarmDispatcherTests` and `ProtobufContractRoundTripTests` are the guardrail — they must stay green with `Degraded=false` defaults.
+- **Subtag names unverified:** the design leaves exact AVEVA subtag names (`.active`, `.acked`, ack-comment) to confirm against `C:\Users\dohertj2\Desktop\mxaccess` + a live Galaxy (Task 17). The config `Subtags` block exists so names are not hard-coded.

docs/plans/2026-06-13-alarm-subtag-fallback.md.tasks.json

@@ -0,0 +1,147 @@
+{
+  "planPath": "docs/plans/2026-06-13-alarm-subtag-fallback.md",
+  "tasks": [
+    {
+      "id": 54,
+      "subject": "Task 1: Worker proto \u2014 watch-list, failover config, AlarmProviderMode",
+      "status": "completed"
+    },
+    {
+      "id": 55,
+      "subject": "Task 2: Gateway proto \u2014 provider status, degraded provenance, mode-changed event",
+      "status": "completed",
+      "blockedBy": [
+        54
+      ]
+    },
+    {
+      "id": 56,
+      "subject": "Task 3: Proto round-trip tests for new alarm fields",
+      "status": "completed",
+      "blockedBy": [
+        54,
+        55
+      ]
+    },
+    {
+      "id": 57,
+      "subject": "Task 4: Subtag value-source abstraction + synthesis state machine",
+      "status": "completed",
+      "blockedBy": [
+        54
+      ]
+    },
+    {
+      "id": 58,
+      "subject": "Task 5: SubtagAlarmConsumer over the source seam",
+      "status": "completed",
+      "blockedBy": [
+        57
+      ]
+    },
+    {
+      "id": 59,
+      "subject": "Task 6: COM-backed LmxSubtagAlarmSource",
+      "status": "completed",
+      "blockedBy": [
+        57
+      ]
+    },
+    {
+      "id": 60,
+      "subject": "Task 7: FailoverAlarmConsumer state machine",
+      "status": "completed",
+      "blockedBy": [
+        58
+      ]
+    },
+    {
+      "id": 61,
+      "subject": "Task 8: Synthetic GUID + degraded flag on event sink path",
+      "status": "completed",
+      "blockedBy": [
+        55
+      ]
+    },
+    {
+      "id": 62,
+      "subject": "Task 9: Wire watch-list/failover through AlarmCommandHandler; emit mode-changed",
+      "status": "completed",
+      "blockedBy": [
+        58,
+        60,
+        61
+      ]
+    },
+    {
+      "id": 63,
+      "subject": "Task 10: AlarmsOptions.Fallback + validation",
+      "status": "completed"
+    },
+    {
+      "id": 64,
+      "subject": "Task 11: Galaxy Repository alarm-attributes discovery query",
+      "status": "completed"
+    },
+    {
+      "id": 65,
+      "subject": "Task 12: Watch-list resolver (GR SQL + config override)",
+      "status": "completed",
+      "blockedBy": [
+        54,
+        63,
+        64
+      ]
+    },
+    {
+      "id": 66,
+      "subject": "Task 13: Metrics \u2014 provider-mode gauge + switch counter",
+      "status": "completed"
+    },
+    {
+      "id": 67,
+      "subject": "Task 14: GatewayAlarmMonitor \u2014 arm watch-list, reflect mode, reconcile on switch",
+      "status": "completed",
+      "blockedBy": [
+        55,
+        62,
+        65,
+        66
+      ]
+    },
+    {
+      "id": 68,
+      "subject": "Task 15: Dashboard \u2014 push provider status + UI badge",
+      "status": "completed",
+      "blockedBy": [
+        67
+      ]
+    },
+    {
+      "id": 69,
+      "subject": "Task 16: End-to-end fake-worker failover test",
+      "status": "completed",
+      "blockedBy": [
+        67
+      ]
+    },
+    {
+      "id": 70,
+      "subject": "Task 17: Live subtag smoke test (opt-in)",
+      "status": "completed",
+      "blockedBy": [
+        59,
+        62
+      ]
+    },
+    {
+      "id": 71,
+      "subject": "Task 18: Documentation",
+      "status": "completed",
+      "blockedBy": [
+        67
+      ]
+    }
+  ],
+  "lastUpdated": "2026-06-13T13:30:00Z"
+}

gateway.md

@@ -143,6 +143,63 @@ session if the worker faults. Gated by `MxGateway:Alarms:Enabled` — see
 `docs/DesignDecisions.md` for why this reverses the v1 single-subscriber rule
 for the alarm subsystem.
 
+### Alarm providers and failover
+
+The alarm feed has two providers, both implemented worker-side:
+
+- **Alarm manager (primary):** `WnWrapAlarmConsumer` polls
+  `wwAlarmConsumerClass.GetXmlCurrentAlarms2` on the worker STA. This is the
+  authoritative native source.
+- **Subtag monitoring (standby):** `SubtagAlarmConsumer` advises each alarm
+  attribute's subtags (`.active`, `.acked`, optionally `.priority`) via the
+  existing `AddItem`/`Advise` pipeline through `LmxSubtagAlarmSource` and
+  synthesizes alarm transitions with `SubtagAlarmStateMachine`. This is a
+  non-parity, lower-fidelity source — synthetic GUIDs, no native raise
+  timestamps, narrower fields.
+
+`FailoverAlarmConsumer` wraps both and owns the state machine:
+
+- **Auto-failover:** after `ConsecutiveFailureThreshold` (default 3)
+  consecutive wnwrap COM failures — `Subscribe` or `PollOnce` throws or
+  returns a failure HRESULT — it activates the standby. The standby is armed
+  (subscribed and adviseing) from the start so its state is warm at the moment
+  of switch.
+- **Auto-failback:** while degraded, every `FailbackProbeIntervalSeconds`
+  (default 30) it re-probes the still-subscribed primary. After
+  `FailbackStableProbes` (default 3) consecutive clean polls it switches back
+  to the alarm manager.
+- **On every switch:** the consumer snapshots the now-active provider and
+  emits `OnAlarmProviderModeChangedEvent` so the gateway can reconcile its
+  cache without a raise/clear storm.
+
+Synthesis is worker-side. This preserves the parity rule — the gateway
+forwards only events the worker emits and never synthesizes transitions
+itself. The synthesis rules are documented in
+`docs/AlarmClientDiscovery.md`.
+
+**Acknowledge in subtag mode:** the ack-by-name path writes the operator
+comment to the alarm attribute's ack-comment subtag. The write performs the
+ack. If the attribute has no writable ack-comment subtag configured, the RPC
+returns `FailedPrecondition`. In alarm-manager mode, `AlarmAckByName` is
+used as before.
+
+**Degraded state visibility:** every subtag-mode transition carries
+`degraded = true` and `source_provider = ALARM_PROVIDER_MODE_SUBTAG` on the
+`OnAlarmTransitionEvent` and `ActiveAlarmSnapshot` proto fields. The
+`AlarmFeedMessage` feed emits an `AlarmProviderStatus` message (the
+`provider_status` oneof case) on stream open and on every switch. The
+dashboard shows a Bootstrap badge (green for alarm manager, amber when
+degraded). Metrics: `mxgateway.alarms.provider_mode` gauge (1 = alarmmgr,
+2 = subtag) and `mxgateway.alarms.provider_switches` counter.
+
+Forced modes are available via `MxGateway:Alarms:Fallback:Mode`:
+`ForceAlarmManager` disables failover; `ForceSubtag` forces the standby
+on from startup; `Auto` (default) enables failover and failback. Watch-list
+discovery for the subtag provider uses Galaxy Repository SQL with config
+overrides. See `docs/GatewayConfiguration.md` for the full `Fallback` option
+block and `docs/AlarmClientDiscovery.md` for synthesis rules and fidelity
+limitations.
+
 Dashboard authentication is LDAP-backed (distinct from the API-key model on
 the gRPC API). `/login` accepts username and password in a form body, binds
 against `MxGateway:Ldap`, maps the user's LDAP groups to `Admin` or `Viewer`

glauth.md

@@ -1,27 +1,36 @@
 # GLAuth — LDAP authn reference for mxaccessgw
 
-GLAuth is a lightweight LDAP server installed on this dev box at
+> **UPDATED 2026-06-04 — mxaccessgw no longer uses a per-box GLAuth at `C:\publish\glauth`.
-`C:\publish\glauth\` and run as a Windows service via NSSM. It already
+> Dev/test LDAP is now the SHARED GLAuth on `10.100.0.35:3893` (`dc=zb,dc=local`);
-backs the LmxOpcUa OPC UA server's UserName-token authn and the LmxOpcUa
+> the single source of truth is `scadaproj/infra/glauth/` (`config.toml` + `README`).
-Admin UI's cookie login; this doc captures everything mxaccessgw needs
+> The localhost/NSSM/`glauth.cfg` procedures below are RETIRED, kept for reference/rollback.**
-to consume the same directory so a single set of dev credentials covers
-both stacks.
 
-The authoritative copy of LmxOpcUa's reference lives at
+GLAuth is a lightweight LDAP server. It already backs all three sister apps (MxAccessGateway,
-`C:\publish\glauth\auth.md`. This doc is a redistilled view tailored to
+OtOpcUa, ScadaBridge) through a **shared container** (`zb-shared-glauth`) running on the Linux
-mxaccessgw — what users + groups are already provisioned, how to bind
+docker host at **`10.100.0.35:3893`**. This doc captures everything mxaccessgw needs to consume
-against them, and what's needed to add a gw-specific role.
+that directory so a single set of dev credentials covers all stacks.
+
+~~GLAuth is installed on this dev box at `C:\publish\glauth\` and run as a Windows service via
+NSSM.~~ *(RETIRED — the per-box Windows service has been stopped and set to Manual startup;
+kept only as a rollback option. Do not edit or restart it for new work.)*
+
+The single source of truth for the shared GLAuth is
+**`~/Desktop/scadaproj/infra/glauth/config.toml`** (deploy/verify runbook:
+`scadaproj/infra/glauth/README.md`). This doc is a redistilled view tailored to mxaccessgw —
+what users + groups are provisioned, how to bind against them, and what's needed to add a
+gw-specific role.
 
 ## Connection details
 
 | Setting | Value |
 |---|---|
 | Protocol | LDAP (unencrypted) |
-| Host | `localhost` |
+| Host | **`10.100.0.35`** (shared docker host — ~~`localhost`~~ retired) |
 | Port | `3893` |
-| LDAPS | disabled in dev (set `[ldaps]` block to enable) |
+| LDAPS | disabled in dev (`Transport=None`, `AllowInsecure=true`) |
 | Base DN | `dc=zb,dc=local` |
 | Bind DN format | `cn={username},dc=zb,dc=local` |
+| Service account DN | `cn=serviceaccount,dc=zb,dc=local` / `serviceaccount123` |
 | Group OU | `ou=<groupname>,ou=groups,dc=zb,dc=local` |
 | Failed-bind throttle | 3 fails → 10-minute IP lockout (per `[behaviors]`) |
 
@@ -59,13 +68,13 @@ For mxaccessgw dev, `admin` covers every gw-side capability test;
 `readonly` is the right "negative" case for proving Browse-OK /
 Write-denied.
 
-The gateway dashboard adds one role beyond this LmxOpcUa taxonomy:
+The gateway dashboard uses two gateway-specific groups beyond the LmxOpcUa taxonomy:
-`GwAdmin`. `LdapOptions.RequiredGroup` defaults to `GwAdmin`, so the
+`GwAdmin` (gid 5610 → role `Administrator`) and `GwReader` (gid 5611 → role `Viewer`).
-dashboard login and `DashboardLdapLiveTests` require `admin` to be a
+These are already provisioned in the shared `scadaproj/infra/glauth/config.toml`.
-member of a `GwAdmin` group. `GwAdmin` is **not** in the baseline
+The dashboard test users are **`multi-role`/`password`** (Administrator) and
-GLAuth config — it must be provisioned before dashboard authn or the
+**`gw-viewer`/`password`** (Viewer). `LdapOptions.RequiredGroup` defaults to `GwAdmin`.
-LDAP live tests work. See [Provisioning the GwAdmin
+See [Provisioning the GwAdmin group](#provisioning-the-gwadmin-group) below for the
-group](#provisioning-the-gwadmin-group) below.
+(now-retired) per-box procedure and for the shared-config equivalent.
 
 > **Dashboard role value (Task 1.7):** the LDAP `GwAdmin` group now maps to
 > the canonical dashboard role **`Administrator`** (was `Admin`); `GwReader`
@@ -118,7 +127,7 @@ record:
 ```yaml
 ldap:
   enabled: true
-  server: localhost
+  server: 10.100.0.35     # shared GLAuth on docker host (was localhost)
   port: 3893
   useTls: false
   allowInsecureLdap: true       # dev only
@@ -143,13 +152,29 @@ look that up in `groupToRole`.
 
 ## Provisioning the GwAdmin group
 
+> **UPDATED 2026-06-04 — RETIRED per-box procedure.** `GwAdmin` (gid 5610) and `GwReader`
+> (gid 5611) are already present in the shared GLAuth. To add or modify users/groups,
+> edit **`~/Desktop/scadaproj/infra/glauth/config.toml`** on host `10.100.0.35` and run:
+>
+> ```bash
+> cd ~/Desktop/scadaproj/infra/glauth
+> docker compose up -d --force-recreate
+> ```
+>
+> The per-box `C:\publish\glauth\glauth.cfg` + NSSM procedure below is kept for
+> rollback reference only — do not use it for new provisioning.
+
 `GwAdmin` is the gateway-specific dashboard-admin role. It is the
 default `LdapOptions.RequiredGroup`, so the dashboard cookie login and
 `DashboardLdapLiveTests` (`MXGATEWAY_RUN_LIVE_LDAP_TESTS=1`) reject
-`admin` until a `GwAdmin` group exists and `admin` is a member.
+logins unless the user is a member of `GwAdmin`.
-GLAuth's baseline config ships only the five LmxOpcUa role groups, so
+The `GwAdmin` (gid 5610) and `GwReader` (gid 5611) groups already exist in the shared
-`GwAdmin` must be added to GLAuth rather than run from a separate LDAP
+config at `scadaproj/infra/glauth/config.toml`. Dashboard test users are
-server:
+`multi-role`/`password` (Administrator) and `gw-viewer`/`password` (Viewer).
+
+---
+
+**RETIRED — per-box provisioning (reference/rollback only):**
 
 1. Edit `C:\publish\glauth\glauth.cfg`
 2. Append the group:
@@ -199,15 +224,16 @@ echo -n "yourpassword" | openssl dgst -sha256
 
 ## Quick verification
 
-From mxaccessgw's dev box, prove the directory is reachable:
+From mxaccessgw's dev box, prove the shared directory is reachable:
 
 ```powershell
 # Plain bind via PowerShell + System.DirectoryServices.Protocols
-$ldap = New-Object System.DirectoryServices.Protocols.LdapConnection("localhost:3893")
+# (shared GLAuth on 10.100.0.35 — was localhost, now the docker host)
+$ldap = New-Object System.DirectoryServices.Protocols.LdapConnection("10.100.0.35:3893")
 $ldap.AuthType = [System.DirectoryServices.Protocols.AuthType]::Basic
 $ldap.SessionOptions.ProtocolVersion = 3
 $ldap.SessionOptions.SecureSocketLayer = $false
-$cred = New-Object System.Net.NetworkCredential("cn=admin,dc=zb,dc=local","admin123")
+$cred = New-Object System.Net.NetworkCredential("cn=multi-role,dc=zb,dc=local","password")
 $ldap.Bind($cred)
 "Bind OK"
 ```
@@ -215,17 +241,32 @@ $ldap.Bind($cred)
 Or via `ldapsearch` if you have OpenLDAP CLI tools:
 
 ```bash
-ldapsearch -x -H ldap://localhost:3893 \
+ldapsearch -x -H ldap://10.100.0.35:3893 \
-  -D "cn=admin,dc=zb,dc=local" -w admin123 \
+  -D "cn=serviceaccount,dc=zb,dc=local" -w serviceaccount123 \
-  -b "dc=zb,dc=local" "(uid=admin)"
+  -b "dc=zb,dc=local" "(uid=multi-role)"
 ```
 
-The response should list `admin`'s entry with `memberOf` populated for
+The response should list `multi-role`'s entry with `memberOf` including
-all five role groups — plus `GwAdmin` once the gateway-specific group
+`ou=GwAdmin,ou=groups,dc=zb,dc=local`.
-is provisioned.
 
 ## Service management
 
+> **RETIRED — per-box NSSM service (reference/rollback only).** The shared GLAuth is
+> managed via `docker compose` on `10.100.0.35` (`scadaproj/infra/glauth/`). The
+> Windows NSSM `GLAuth` service on the dev box has been stopped and set to
+> `StartupType=Manual`; only restart it if you need to roll back to a local directory.
+>
+> **Active (shared) management:**
+> ```bash
+> ssh 10.100.0.35
+> cd ~/Desktop/scadaproj/infra/glauth
+> docker compose ps                      # check container status
+> docker compose up -d --force-recreate  # apply config.toml changes
+> docker compose logs -f                 # tail logs
+> ```
+
+**RETIRED — per-box NSSM commands (rollback reference):**
+
 ```powershell
 # Status / start / stop / restart
 nssm status  GLAuth
@@ -259,7 +300,7 @@ applies to mxaccessgw verbatim. Keys that change:
 
 | Field | GLAuth dev value | AD production value |
 |---|---|---|
-| `Server` | `localhost` | a domain controller FQDN, or the domain itself |
+| `Server` | `10.100.0.35` (shared docker host) | a domain controller FQDN, or the domain itself |
 | `Port` | `3893` | `636` (LDAPS) — AD increasingly rejects plain bind under LDAP-signing enforcement |
 | `UseTls` | `false` | `true` |
 | `AllowInsecureLdap` | `true` | `false` |
@@ -275,12 +316,12 @@ add a `tokenGroups` query as an enhancement.
 
 ## Security notes for production
 
-- **Plaintext passwords in `glauth.cfg` are dev-only.** The config is
+- **Plaintext passwords in `config.toml` are dev-only.** The shared config is in
-  unencrypted on disk; anyone with read access to `C:\publish\glauth\`
+  `scadaproj/infra/glauth/config.toml` (unencrypted); restrict filesystem access on
-  can SHA256-rainbow-table the entries. Treat the dev creds as
+  `10.100.0.35` accordingly. Treat the dev creds as throwaway. Production LDAP is Active
-  throwaway. Production LDAP is Active Directory.
+  Directory. *(The retired per-box `C:\publish\glauth\glauth.cfg` has the same caveat.)*
 - The 3-fail / 10-minute lockout is per source IP, not per user — a
   shared NAT can lock out a whole office. Tunable in `[behaviors]`.
 - LDAPS isn't enabled in dev; binding sends passwords cleartext on the
-  wire. Fine for `localhost`, never expose port 3893 off-box without
+  wire. The shared GLAuth listens only on the LAN (`10.100.0.35`); never
-  enabling TLS first.
+  expose port 3893 externally without enabling TLS first.

src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto

@@ -315,6 +315,14 @@ message SubscribeBulkCommand {
   repeated string tag_addresses = 2;
 }
 
+// Provider selection / current provider for the alarm feed. UNSPECIFIED on a
+// SubscribeAlarmsCommand means auto: alarmmgr primary with subtag fallback.
+enum AlarmProviderMode {
+  ALARM_PROVIDER_MODE_UNSPECIFIED = 0;
+  ALARM_PROVIDER_MODE_ALARMMGR = 1;
+  ALARM_PROVIDER_MODE_SUBTAG = 2;
+}
+
 // Subscribe the worker's alarm consumer to an AVEVA alarm provider.
 // Subscription expression follows the canonical
 // `\\<machine>\Galaxy!<area>` format (literal "Galaxy" provider). The
@@ -323,6 +331,12 @@ message SubscribeBulkCommand {
 // SubscribeAlarms to reconfigure).
 message SubscribeAlarmsCommand {
   string subscription_expression = 1;
+  // UNSPECIFIED = auto-failover/failback. ALARMMGR/SUBTAG force one provider.
+  AlarmProviderMode forced_mode = 2;
+  // Subtag watch-list resolved by the gateway (GR SQL + config). Empty in pure
+  // alarmmgr mode; in subtag mode it bounds what the consumer can observe.
+  repeated AlarmSubtagTarget watch_list = 3;
+  AlarmFailoverConfig failover = 4;
 }
 
 // Tear down the worker's alarm consumer. No-op if no subscription is
@@ -330,6 +344,23 @@ message SubscribeAlarmsCommand {
 message UnsubscribeAlarmsCommand {
 }
 
+// One alarm attribute the subtag fallback consumer advises. Addresses are full
+// MXAccess item references the worker passes straight to AddItem.
+message AlarmSubtagTarget {
+  string alarm_full_reference = 1;     // e.g. "Galaxy!Area.Tank01.Level.HiHi"
+  string source_object_reference = 2;  // e.g. "Tank01"
+  string active_subtag = 3;            // item address of the in-alarm boolean
+  string acked_subtag = 4;             // item address of the acknowledged boolean
+  string ack_comment_subtag = 5;       // writable ack-comment attribute (ack write target)
+  string priority_subtag = 6;          // optional severity source; empty if absent
+}
+
+message AlarmFailoverConfig {
+  int32 consecutive_failure_threshold = 1;   // wnwrap COM failures before switching (>=1)
+  int32 failback_probe_interval_seconds = 2; // probe cadence while degraded (>=1)
+  int32 failback_stable_probes = 3;          // clean probes before switching back (>=1)
+}
+
 // Acknowledge a single alarm by its GUID. Operator identity fields are
 // recorded atomically with the ack transition in the alarm-history log.
 // The reply's hresult / native_status surfaces AVEVA's
@@ -684,6 +715,7 @@ message MxEvent {
     OperationCompleteEvent operation_complete = 22;
     OnBufferedDataChangeEvent on_buffered_data_change = 23;
     OnAlarmTransitionEvent on_alarm_transition = 24;
+    OnAlarmProviderModeChangedEvent on_alarm_provider_mode_changed = 25;
   }
 }
 
@@ -694,6 +726,7 @@ enum MxEventFamily {
   MX_EVENT_FAMILY_OPERATION_COMPLETE = 3;
   MX_EVENT_FAMILY_ON_BUFFERED_DATA_CHANGE = 4;
   MX_EVENT_FAMILY_ON_ALARM_TRANSITION = 5;
+  MX_EVENT_FAMILY_ON_ALARM_PROVIDER_MODE_CHANGED = 6;
 }
 
 message OnDataChangeEvent {
@@ -768,6 +801,20 @@ message OnAlarmTransitionEvent {
   // Limit/threshold value that triggered the transition for limit alarms.
   // Optional; populated for AnalogLimitAlarm-family transitions.
   MxValue limit_value = 13;
+
+  // True when this transition came from the subtag-monitoring fallback rather
+  // than the native alarmmgr provider — synthesized from data changes, reduced
+  // fidelity (synthetic GUID, no native raise time).
+  bool degraded = 14;
+  // Which provider produced this transition.
+  AlarmProviderMode source_provider = 15;
+}
+
+message OnAlarmProviderModeChangedEvent {
+  AlarmProviderMode mode = 1;
+  string reason = 2;
+  int32 hresult = 3;   // COM HRESULT that triggered failover; 0 on failback
+  google.protobuf.Timestamp at = 4;
 }
 
 enum AlarmTransitionKind {
@@ -800,6 +847,8 @@ message ActiveAlarmSnapshot {
   string operator_comment = 11;
   MxValue current_value = 12;
   MxValue limit_value = 13;
+  bool degraded = 14;
+  AlarmProviderMode source_provider = 15;
 }
 
 enum AlarmConditionState {
@@ -866,9 +915,19 @@ message AlarmFeedMessage {
     bool snapshot_complete = 2;
     // A live alarm state change (raise / acknowledge / clear).
     OnAlarmTransitionEvent transition = 3;
+    // Provider-mode status. Emitted once on stream open and again on every
+    // failover/failback so late joiners learn the current mode immediately.
+    AlarmProviderStatus provider_status = 4;
   }
 }
 
+message AlarmProviderStatus {
+  AlarmProviderMode mode = 1;
+  bool degraded = 2;            // true whenever mode == SUBTAG
+  string reason = 3;            // human-readable switch reason
+  google.protobuf.Timestamp since = 4;
+}
+
 message MxStatusProxy {
   // Mirrors the `success` member of the MXAccess MXSTATUS_PROXY struct
   // (a 16-bit signed value in the COM struct, widened to int32 on the

src/ZB.MOM.WW.MxGateway.IntegrationTests/DashboardLdapLiveTests.cs

@@ -14,7 +14,6 @@ namespace ZB.MOM.WW.MxGateway.IntegrationTests;
 public sealed class DashboardLdapLiveTests
 {
     /// <summary>Verifies that an admin user in the GwAdmin group authenticates successfully.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveLdapFact]
     public async Task AuthenticateAsync_AdminInGwAdminGroup_Succeeds()
     {
@@ -43,7 +42,6 @@ public sealed class DashboardLdapLiveTests
     }
 
     /// <summary>Verifies that a readonly user without GwAdmin group fails to authenticate.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveLdapFact]
     public async Task AuthenticateAsync_ReadOnlyUserMissingGwAdminGroup_Fails()
     {
@@ -60,7 +58,6 @@ public sealed class DashboardLdapLiveTests
     }
 
     /// <summary>Verifies that authentication with wrong password fails without leaking the password.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveLdapFact]
     public async Task AuthenticateAsync_AdminWithWrongPassword_FailsWithoutLeakingPassword()
     {
@@ -80,7 +77,6 @@ public sealed class DashboardLdapLiveTests
     }
 
     /// <summary>Verifies that authentication with unknown username fails.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveLdapFact]
     public async Task AuthenticateAsync_UnknownUsername_Fails()
     {
@@ -98,7 +94,6 @@ public sealed class DashboardLdapLiveTests
     }
 
     /// <summary>Verifies that authentication fails gracefully when the server is unreachable.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveLdapFact]
     public async Task AuthenticateAsync_ServerUnreachable_FailsWithoutThrowing()
     {

src/ZB.MOM.WW.MxGateway.IntegrationTests/Galaxy/GalaxyRepositoryLiveTests.cs

@@ -7,7 +7,6 @@ namespace ZB.MOM.WW.MxGateway.IntegrationTests.Galaxy;
 public sealed class GalaxyRepositoryLiveTests
 {
     /// <summary>Verifies that the Galaxy Repository can establish a live connection to the ZB database.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveGalaxyRepositoryFact]
     public async Task TestConnection_AgainstZb_Succeeds()
     {
@@ -19,7 +18,6 @@ public sealed class GalaxyRepositoryLiveTests
     }
 
     /// <summary>Verifies that the last deploy time can be retrieved from the ZB database.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveGalaxyRepositoryFact]
     public async Task GetLastDeployTime_AgainstZb_ReturnsTimestamp()
     {
@@ -31,7 +29,6 @@ public sealed class GalaxyRepositoryLiveTests
     }
 
     /// <summary>Verifies that the hierarchy can be retrieved from the ZB database.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveGalaxyRepositoryFact]
     public async Task GetHierarchy_AgainstZb_ReturnsObjects()
     {
@@ -49,7 +46,6 @@ public sealed class GalaxyRepositoryLiveTests
     }
 
     /// <summary>Verifies that object attributes can be retrieved from the ZB database.</summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveGalaxyRepositoryFact]
     public async Task GetAttributes_AgainstZb_ReturnsAtLeastOneAttribute()
     {

src/ZB.MOM.WW.MxGateway.IntegrationTests/WorkerLiveMxAccessSmokeTests.cs

@@ -30,7 +30,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     /// <summary>
     /// Verifies that a gateway session can register, add item, advise, and stream events from live MXAccess.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveMxAccessFact]
     public async Task GatewaySession_WithLiveWorker_RegistersAdvisesStreamsDataAndCloses()
     {
@@ -120,7 +119,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     /// and that the worker emits a matching <see cref="MxEventFamily.OnWriteComplete"/> event
     /// — the proof of round-trip the cross-language client e2e runner relies on.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveMxAccessFact]
     public async Task GatewaySession_WithLiveWorker_WritesValueToAdvisedItem()
     {
@@ -237,7 +235,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     /// Verifies that an AddItem against an invalid server handle surfaces the MXAccess failure
     /// without faulting the gateway transport, exercising the invalid-handle parity path.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveMxAccessFact]
     public async Task GatewaySession_WithLiveWorker_InvalidHandleCommand_SurfacesFailureWithoutTransportFault()
     {
@@ -296,7 +293,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     /// OnDataChange events for the un-advised item. Exercises the lifecycle-ordering
     /// parity CLAUDE.md singles out as a "do not synthesize" rule.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveMxAccessFact]
     public async Task GatewaySession_WithLiveWorker_UnadviseRemoveItemUnregister_TeardownOrderingParity()
     {
@@ -441,7 +437,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     /// parity surface the gateway must not "fix" — the test asserts the reply kind and
     /// protocol status, not a fabricated outcome.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveMxAccessFact]
     public async Task GatewaySession_WithLiveWorker_WriteSecured_AuthenticatedRoundTripParity()
     {
@@ -573,7 +568,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     /// must observe the abnormal exit, transition the session, and surface a non-empty
     /// fault description rather than hanging or crashing.
     /// </summary>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     [LiveMxAccessFact]
     public async Task GatewaySession_WithLiveWorker_AbnormalWorkerExit_MarksSessionFaulted()
     {
@@ -1120,7 +1114,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
         /// </summary>
         /// <param name="sessionId">The session identifier.</param>
         /// <param name="session">The session if found; otherwise null.</param>
-        /// <returns>True if the session was found; otherwise false.</returns>
         public bool TryGetSession(string sessionId, [MaybeNullWhen(false)] out GatewaySession session)
         {
             return _registry.TryGet(sessionId, out session);
@@ -1129,7 +1122,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
         /// <summary>
         /// Disposes the fixture resources and closes all sessions.
         /// </summary>
-        /// <returns>A task that represents the asynchronous dispose operation.</returns>
         public async ValueTask DisposeAsync()
         {
             foreach (GatewaySession session in _registry.Snapshot())
@@ -1200,7 +1192,6 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
         /// Records the message and signals any pending waiter.
         /// </summary>
         /// <param name="message">The message to write.</param>
-        /// <returns>A task that represents the asynchronous operation.</returns>
         public Task WriteAsync(T message)
         {
             lock (syncRoot)
@@ -1383,9 +1374,7 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
             return workerProcess;
         }
 
-        /// <summary>Waits for all recorded worker processes to exit within the specified timeout.</summary>
+        /// <inheritdoc />
-        /// <param name="timeout">Maximum time to wait for each process to exit.</param>
-        /// <returns>A task that represents the asynchronous operation.</returns>
         public async Task WaitForProcessesAsync(TimeSpan timeout)
         {
             foreach (TestWorkerProcess process in processes)
@@ -1465,7 +1454,7 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
             process.Kill(entireProcessTree);
         }
 
-        /// <summary>Releases the wrapped process resources.</summary>
+        /// <inheritdoc />
         public void Dispose()
         {
             process.Dispose();
@@ -1477,15 +1466,13 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     /// </summary>
     private sealed class TestOutputLoggerProvider(ITestOutputHelper output) : ILoggerProvider
     {
-        /// <summary>Creates a logger that writes to the test output helper for the given category.</summary>
+        /// <inheritdoc />
-        /// <param name="categoryName">The logger category name.</param>
-        /// <returns>A logger that forwards to the test output helper.</returns>
         public ILogger CreateLogger(string categoryName)
         {
             return new TestOutputLogger(output, categoryName);
         }
 
-        /// <summary>Releases resources held by the provider (no-op for this test double).</summary>
+        /// <inheritdoc />
         public void Dispose()
         {
         }
@@ -1498,31 +1485,20 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
         ITestOutputHelper output,
         string categoryName) : ILogger
     {
-        /// <summary>Begins a log scope; returns null as this test logger does not support scopes.</summary>
+        /// <inheritdoc />
-        /// <param name="state">The state object for the scope.</param>
-        /// <typeparam name="TState">The type of the state object.</typeparam>
-        /// <returns>Always null.</returns>
         public IDisposable? BeginScope<TState>(TState state)
             where TState : notnull
         {
             return null;
         }
 
-        /// <summary>Returns true for log levels at or above <see cref="LogLevel.Information"/>.</summary>
+        /// <inheritdoc />
-        /// <param name="logLevel">The log level to check.</param>
-        /// <returns>True if the log level is enabled.</returns>
         public bool IsEnabled(LogLevel logLevel)
         {
             return logLevel >= LogLevel.Information;
         }
 
-        /// <summary>Writes a log entry to the test output helper.</summary>
+        /// <inheritdoc />
-        /// <param name="logLevel">The log level.</param>
-        /// <param name="eventId">The event identifier.</param>
-        /// <param name="state">The state object to log.</param>
-        /// <param name="exception">Optional exception associated with the log entry.</param>
-        /// <param name="formatter">Function to format the state and exception into a string.</param>
-        /// <typeparam name="TState">The type of the state object.</typeparam>
         public void Log<TState>(
             LogLevel logLevel,
             EventId eventId,

src/ZB.MOM.WW.MxGateway.Server/Alarms/AlarmWatchListResolver.cs

@@ -0,0 +1,178 @@
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+using ZB.MOM.WW.MxGateway.Server.Configuration;
+using ZB.MOM.WW.MxGateway.Server.Galaxy;
+
+namespace ZB.MOM.WW.MxGateway.Server.Alarms;
+
+/// <summary>
+///     Default <see cref="IAlarmWatchListResolver"/>. Merges Galaxy Repository
+///     alarm-attribute discovery with the configured include/exclude overrides
+///     and composes the per-attribute subtag item addresses from the configured
+///     subtag names.
+/// </summary>
+// NOTE: The exact subtag names and the canonical AlarmFullReference shape
+// ("Galaxy!{area}.{reference}") are validated against a live Galaxy in the
+// Task 17 live smoke test. The config Subtags block exists precisely so these
+// names are not hard-coded here. The {area} is the alarm object's REAL Galaxy
+// area discovered via gobject.area_gobject_id (the alarm group the native
+// alarmmgr emits), giving exact reference parity with wnwrap. The configured
+// Discovery.Area/DefaultArea is only the fallback for explicit IncludeAttributes
+// entries, which carry no discovered area.
+public sealed class AlarmWatchListResolver : IAlarmWatchListResolver
+{
+    private const string ProviderLiteral = "Galaxy";
+    private const string DefaultActiveSubtag = "InAlarm";
+    private const string DefaultAckedSubtag = "Acked";
+
+    private readonly IGalaxyRepository _repository;
+    private readonly ILogger<AlarmWatchListResolver> _logger;
+
+    /// <summary>Initializes the watch-list resolver.</summary>
+    /// <param name="repository">Galaxy Repository used for alarm-attribute discovery.</param>
+    /// <param name="logger">Diagnostic logger.</param>
+    public AlarmWatchListResolver(
+        IGalaxyRepository repository,
+        ILogger<AlarmWatchListResolver> logger)
+    {
+        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    /// <inheritdoc />
+    public async Task<IReadOnlyList<AlarmSubtagTarget>> ResolveAsync(
+        AlarmsOptions options,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+
+        AlarmDiscoveryOptions discovery = options.Fallback.Discovery;
+
+        // Config fallback area used only for explicit IncludeAttributes entries (which
+        // carry no discovered area): discovery area, else the default area (may be empty).
+        string configFallbackArea = string.IsNullOrEmpty(discovery.Area) ? options.DefaultArea : discovery.Area;
+
+        // 1. Build the ordered, de-duplicated attribute reference set.
+        //    Each entry carries the reference, the source-object reference, and the
+        //    per-entry area used to compose the canonical reference. GR rows contribute
+        //    the object's real Galaxy area; config includes contribute the config
+        //    fallback area (Discovery.Area else DefaultArea).
+        List<(string Reference, string SourceObject, string Area)> ordered = [];
+        HashSet<string> seen = new(StringComparer.OrdinalIgnoreCase);
+
+        if (discovery.UseGalaxyRepository)
+        {
+            List<GalaxyAlarmAttributeRow> rows;
+            try
+            {
+                rows = await _repository.GetAlarmAttributesAsync(cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception ex)
+            {
+                // Discovery being unavailable must not crash the resolver: log and
+                // continue with an empty discovery set. The caller decides what to
+                // do with the (possibly config-only) result.
+                _logger.LogWarning(
+                    ex,
+                    "Galaxy Repository alarm-attribute discovery failed; continuing with configuration-only watch-list.");
+                rows = [];
+            }
+
+            foreach (GalaxyAlarmAttributeRow row in rows)
+            {
+                if (string.IsNullOrEmpty(row.FullTagReference) || !seen.Add(row.FullTagReference))
+                {
+                    continue;
+                }
+
+                ordered.Add((row.FullTagReference, row.SourceObjectReference, row.Area));
+            }
+        }
+
+        foreach (string include in discovery.IncludeAttributes)
+        {
+            if (string.IsNullOrEmpty(include) || !seen.Add(include))
+            {
+                continue;
+            }
+
+            ordered.Add((include, DeriveSourceObject(include), configFallbackArea));
+        }
+
+        // Remove excluded references (case-insensitive), but only when GR discovery
+        // is active. ExcludeAttributes is documented as "Ignored when
+        // UseGalaxyRepository is false" (AlarmDiscoveryOptions.ExcludeAttributes).
+        // Whitespace-only entries are skipped, consistent with the include guard above.
+        if (discovery.UseGalaxyRepository)
+        {
+            HashSet<string> excluded = new(
+                discovery.ExcludeAttributes.Where(e => !string.IsNullOrWhiteSpace(e)),
+                StringComparer.OrdinalIgnoreCase);
+            if (excluded.Count > 0)
+            {
+                ordered.RemoveAll(e => excluded.Contains(e.Reference));
+            }
+        }
+
+        // 2. Resolve subtag names with safe fallbacks.
+        string active = string.IsNullOrEmpty(options.Fallback.Subtags.Active)
+            ? DefaultActiveSubtag
+            : options.Fallback.Subtags.Active;
+        string acked = string.IsNullOrEmpty(options.Fallback.Subtags.Acked)
+            ? DefaultAckedSubtag
+            : options.Fallback.Subtags.Acked;
+        string priority = options.Fallback.Subtags.Priority;
+        string ackComment = options.Fallback.Subtags.AckComment;
+
+        // 3. Compose one target per reference, using the PER-ENTRY area: the GR row's
+        //    real Galaxy area (matching the alarmmgr group), or the config fallback for
+        //    explicit includes.
+        List<AlarmSubtagTarget> targets = new(ordered.Count);
+        foreach ((string reference, string sourceObject, string area) in ordered)
+        {
+            targets.Add(new AlarmSubtagTarget
+            {
+                AlarmFullReference = ComposeFullReference(area, reference),
+                SourceObjectReference = sourceObject,
+                ActiveSubtag = $"{reference}.{active}",
+                AckedSubtag = $"{reference}.{acked}",
+                PrioritySubtag = string.IsNullOrEmpty(priority) ? string.Empty : $"{reference}.{priority}",
+                AckCommentSubtag = string.IsNullOrEmpty(ackComment) ? string.Empty : $"{reference}.{ackComment}",
+            });
+        }
+
+        // 4. Report the resolved count; warn when subtag mode was expected to cover
+        //    something (GR enabled, or explicit includes were configured) but resolved
+        //    to nothing. Only emit the Debug line when there is at least one target,
+        //    to avoid a confusing "0 target(s)" noise line.
+        if (targets.Count == 0 && (discovery.UseGalaxyRepository || discovery.IncludeAttributes.Length > 0))
+        {
+            _logger.LogWarning(
+                "Alarm subtag watch-list resolved to zero targets; subtag-polling fallback will cover no alarms.");
+        }
+        else if (targets.Count > 0)
+        {
+            _logger.LogDebug("Resolved alarm subtag watch-list with {TargetCount} target(s).", targets.Count);
+        }
+
+        return targets;
+    }
+
+    /// <summary>
+    ///     Derives the source-object reference for a configuration entry: the
+    ///     substring before the first '.', or the whole string when there is no dot.
+    /// </summary>
+    private static string DeriveSourceObject(string reference)
+    {
+        int dot = reference.IndexOf('.', StringComparison.Ordinal);
+        return dot < 0 ? reference : reference[..dot];
+    }
+
+    /// <summary>
+    ///     Composes the canonical alarm full reference: <c>Galaxy!{area}.{reference}</c>
+    ///     when an area is set, otherwise <c>Galaxy!{reference}</c>.
+    /// </summary>
+    private static string ComposeFullReference(string area, string reference) =>
+        string.IsNullOrEmpty(area)
+            ? $"{ProviderLiteral}!{reference}"
+            : $"{ProviderLiteral}!{area}.{reference}";
+}

src/ZB.MOM.WW.MxGateway.Server/Alarms/AlarmsServiceCollectionExtensions.cs

@@ -13,6 +13,7 @@ public static class AlarmsServiceCollectionExtensions
     /// <returns>The service collection for chaining.</returns>
     public static IServiceCollection AddGatewayAlarms(this IServiceCollection services)
     {
+        services.AddSingleton<IAlarmWatchListResolver, AlarmWatchListResolver>();
         services.AddSingleton<GatewayAlarmMonitor>();
         services.AddSingleton<IGatewayAlarmService>(provider => provider.GetRequiredService<GatewayAlarmMonitor>());
         services.AddHostedService(provider => provider.GetRequiredService<GatewayAlarmMonitor>());

src/ZB.MOM.WW.MxGateway.Server/Alarms/GatewayAlarmMonitor.cs

@@ -1,7 +1,9 @@
 using System.Threading.Channels;
+using Google.Protobuf.WellKnownTypes;
 using Microsoft.Extensions.Options;
 using ZB.MOM.WW.MxGateway.Contracts.Proto;
 using ZB.MOM.WW.MxGateway.Server.Configuration;
+using ZB.MOM.WW.MxGateway.Server.Metrics;
 using ZB.MOM.WW.MxGateway.Server.Sessions;
 
 namespace ZB.MOM.WW.MxGateway.Server.Alarms;
@@ -23,6 +25,8 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
     private static readonly TimeSpan StartupGrace = TimeSpan.FromSeconds(2);
 
     private readonly ISessionManager _sessionManager;
+    private readonly IAlarmWatchListResolver _watchListResolver;
+    private readonly GatewayMetrics _metrics;
     private readonly AlarmsOptions _options;
     private readonly ILogger<GatewayAlarmMonitor> _logger;
 
@@ -30,20 +34,34 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
     private readonly Dictionary<string, ActiveAlarmSnapshot> _alarms = new(StringComparer.Ordinal);
     private readonly List<Subscriber> _subscribers = [];
 
+    // Current provider status (mode + degraded + reason + since), guarded by _sync.
+    // Initialized to the alarm-manager, not-degraded baseline so a late joiner sees
+    // a sensible status even before any OnAlarmProviderModeChanged event arrives.
+    private AlarmProviderMode _providerMode = AlarmProviderMode.Alarmmgr;
+    private bool _providerDegraded;
+    private string _providerReason = string.Empty;
+    private DateTimeOffset _providerSince = DateTimeOffset.UtcNow;
+
     private volatile GatewayAlarmMonitorState _state = GatewayAlarmMonitorState.Disabled;
     private volatile string? _lastError;
     private GatewaySession? _session;
 
     /// <summary>Initializes the gateway alarm monitor.</summary>
     /// <param name="sessionManager">Gateway session manager.</param>
+    /// <param name="watchListResolver">Resolver for the subtag-fallback watch-list.</param>
+    /// <param name="metrics">Gateway metrics sink.</param>
     /// <param name="options">Gateway options carrying the alarm configuration.</param>
     /// <param name="logger">Diagnostic logger.</param>
     public GatewayAlarmMonitor(
         ISessionManager sessionManager,
+        IAlarmWatchListResolver watchListResolver,
+        GatewayMetrics metrics,
         IOptions<GatewayOptions> options,
         ILogger<GatewayAlarmMonitor> logger)
     {
         _sessionManager = sessionManager ?? throw new ArgumentNullException(nameof(sessionManager));
+        _watchListResolver = watchListResolver ?? throw new ArgumentNullException(nameof(watchListResolver));
+        _metrics = metrics ?? throw new ArgumentNullException(nameof(metrics));
         _options = (options ?? throw new ArgumentNullException(nameof(options))).Value.Alarms;
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
     }
@@ -139,6 +157,20 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
     private async Task RunMonitorAsync(string subscription, CancellationToken stoppingToken)
     {
         _state = GatewayAlarmMonitorState.Starting;
+        lock (_sync)
+        {
+            // Re-baseline the provider status for this lifecycle so a restarted
+            // monitor advertises alarm-manager/not-degraded until told otherwise.
+            _providerMode = AlarmProviderMode.Alarmmgr;
+            _providerDegraded = false;
+            _providerReason = string.Empty;
+            _providerSince = DateTimeOffset.UtcNow;
+        }
+
+        // Align the observable gauge with the Alarmmgr baseline without recording
+        // a switch — the gauge was 0 (unknown) from construction until now.
+        _metrics.SetAlarmProviderMode(ModeToInt(AlarmProviderMode.Alarmmgr));
+
         GatewaySession session = await _sessionManager.OpenSessionAsync(
                 new SessionOpenRequest(BackendName, MonitorClientName, Guid.NewGuid().ToString("N"), CommandTimeout: null),
                 MonitorClientName,
@@ -173,6 +205,15 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
                     {
                         ApplyTransition(mxEvent.OnAlarmTransition);
                     }
+                    else if (mxEvent is { BodyCase: MxEvent.BodyOneofCase.OnAlarmProviderModeChanged }
+                        && mxEvent.OnAlarmProviderModeChanged is not null)
+                    {
+                        await ApplyProviderModeChangeAsync(
+                                session.SessionId,
+                                mxEvent.OnAlarmProviderModeChanged,
+                                linked.Token)
+                            .ConfigureAwait(false);
+                    }
                 }
             }
             finally
@@ -209,6 +250,29 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
 
     private async Task SubscribeAlarmsAsync(string sessionId, string subscription, CancellationToken cancellationToken)
     {
+        IReadOnlyList<AlarmSubtagTarget> watchList = await _watchListResolver
+            .ResolveAsync(_options, cancellationToken)
+            .ConfigureAwait(false);
+
+        AlarmProviderMode forcedMode = MapForcedMode(_options.Fallback.Mode);
+
+        // When the forced mode is Unspecified (the "Auto" case) and the resolved
+        // watch-list is empty — the common alarmmgr-only deployment — the command
+        // is identical-in-effect to the historical SubscribeAlarms (wnwrap only):
+        // the worker builds the wnwrap consumer and no subtag watch-list.
+        SubscribeAlarmsCommand command = new()
+        {
+            SubscriptionExpression = subscription,
+            ForcedMode = forcedMode,
+            Failover = new AlarmFailoverConfig
+            {
+                ConsecutiveFailureThreshold = _options.Fallback.ConsecutiveFailureThreshold,
+                FailbackProbeIntervalSeconds = _options.Fallback.FailbackProbeIntervalSeconds,
+                FailbackStableProbes = _options.Fallback.FailbackStableProbes,
+            },
+        };
+        command.WatchList.AddRange(watchList);
+
         WorkerCommandReply reply = await _sessionManager.InvokeAsync(
                 sessionId,
                 new WorkerCommand
@@ -216,7 +280,7 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
                     Command = new MxCommand
                     {
                         Kind = MxCommandKind.SubscribeAlarms,
-                        SubscribeAlarms = new SubscribeAlarmsCommand { SubscriptionExpression = subscription },
+                        SubscribeAlarms = command,
                     },
                 },
                 cancellationToken)
@@ -310,6 +374,104 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
         }
     }
 
+    // Handles the worker's provider-mode-change event: updates the stored provider
+    // status, broadcasts it to every subscriber (provider status is global, not
+    // alarm-scoped), records the switch metric, and forces a cache reconcile so the
+    // active-alarm set reflects whatever the new mode reports.
+    private async Task ApplyProviderModeChangeAsync(
+        string sessionId,
+        OnAlarmProviderModeChangedEvent change,
+        CancellationToken cancellationToken)
+    {
+        AlarmProviderMode toMode = change.Mode;
+        string reason = change.Reason ?? string.Empty;
+
+        AlarmProviderStatus status;
+        int fromModeInt;
+        lock (_sync)
+        {
+            fromModeInt = ModeToInt(_providerMode);
+            _providerMode = toMode;
+            _providerDegraded = toMode == AlarmProviderMode.Subtag;
+            _providerReason = reason;
+            _providerSince = DateTimeOffset.UtcNow;
+            status = BuildProviderStatus();
+            BroadcastToAll(new AlarmFeedMessage { ProviderStatus = status });
+        }
+
+        AlarmProviderSwitchReason switchReason = toMode switch
+        {
+            AlarmProviderMode.Subtag => AlarmProviderSwitchReason.Failover,
+            AlarmProviderMode.Alarmmgr => AlarmProviderSwitchReason.Failback,
+            _ => AlarmProviderSwitchReason.Unknown,
+        };
+        _metrics.AlarmProviderSwitched(fromModeInt, ModeToInt(toMode), switchReason);
+
+        _logger.LogInformation(
+            "Alarm provider mode changed to {Mode} (degraded={Degraded}): {Reason}",
+            toMode,
+            status.Degraded,
+            reason);
+
+        try
+        {
+            // Intentionally awaited OUTSIDE _sync: ReconcileAsync acquires _sync itself,
+            // so holding it across the await here would deadlock. Subscribers therefore
+            // see the ProviderStatus push (above) slightly before the cache is re-seeded
+            // by the reconcile — an accepted brief inconsistency.
+            await ReconcileAsync(sessionId, cancellationToken).ConfigureAwait(false);
+        }
+        catch (OperationCanceledException)
+        {
+            throw;
+        }
+        catch (Exception exception)
+        {
+            _logger.LogDebug(
+                exception,
+                "Reconcile after alarm provider mode change failed; keeping the current cache.");
+        }
+    }
+
+    // Caller holds _sync. Builds an AlarmProviderStatus snapshot of the current state.
+    private AlarmProviderStatus BuildProviderStatus()
+    {
+        return new AlarmProviderStatus
+        {
+            Mode = _providerMode,
+            Degraded = _providerDegraded,
+            Reason = _providerReason,
+            Since = Timestamp.FromDateTimeOffset(_providerSince),
+        };
+    }
+
+    // Maps the configured fallback mode string to the forced provider mode the
+    // worker honours. Case-insensitive; anything other than the two force values
+    // (including the default "Auto") yields Unspecified ("let the worker decide").
+    private static AlarmProviderMode MapForcedMode(string? mode)
+    {
+        if (string.Equals(mode, "ForceAlarmManager", StringComparison.OrdinalIgnoreCase))
+        {
+            return AlarmProviderMode.Alarmmgr;
+        }
+
+        if (string.Equals(mode, "ForceSubtag", StringComparison.OrdinalIgnoreCase))
+        {
+            return AlarmProviderMode.Subtag;
+        }
+
+        return AlarmProviderMode.Unspecified;
+    }
+
+    // Maps the provider-mode enum to the integer the metric expects
+    // (alarmmgr=1, subtag=2, unknown/unspecified=0).
+    private static int ModeToInt(AlarmProviderMode mode) => mode switch
+    {
+        AlarmProviderMode.Alarmmgr => 1,
+        AlarmProviderMode.Subtag => 2,
+        _ => 0,
+    };
+
     // Replaces the cache with the worker's authoritative snapshot, broadcasting
     // a synthetic transition for any alarm the live stream missed.
     private void ApplyReconcile(IEnumerable<ActiveAlarmSnapshot> snapshots)
@@ -374,6 +536,23 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
         }
     }
 
+    // Caller holds _sync. Pushes a feed message to every subscriber regardless of
+    // its alarm-filter prefix. Used for provider-status messages, which are global
+    // rather than scoped to a single alarm reference.
+    private void BroadcastToAll(AlarmFeedMessage message)
+    {
+        for (int index = _subscribers.Count - 1; index >= 0; index--)
+        {
+            Subscriber subscriber = _subscribers[index];
+            if (!subscriber.Channel.Writer.TryWrite(message))
+            {
+                subscriber.Channel.Writer.TryComplete(new InvalidOperationException(
+                    "Alarm feed subscriber fell behind and was dropped; reconnect to re-snapshot."));
+                _subscribers.RemoveAt(index);
+            }
+        }
+    }
+
     private void ClearCache()
     {
         lock (_sync)
@@ -398,11 +577,14 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
         Subscriber subscriber = new(channel, prefix);
 
         ActiveAlarmSnapshot[] snapshot;
+        AlarmProviderStatus providerStatus;
         lock (_sync)
         {
-            // Register before snapshotting under the same lock so no transition
+            // Register before snapshotting under the same lock so neither a
-            // can slip between the snapshot and the live stream.
+            // transition nor a provider-mode change can slip between the snapshot
+            // and the live stream.
             _subscribers.Add(subscriber);
+            providerStatus = BuildProviderStatus();
             snapshot = _alarms.Values
                 .Where(alarm => prefix.Length == 0
                     || alarm.AlarmFullReference.StartsWith(prefix, StringComparison.Ordinal))
@@ -412,6 +594,10 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
 
         try
         {
+            // Emit the current provider status first so a late joiner immediately
+            // learns the mode (and whether the feed is degraded) before any alarms.
+            yield return new AlarmFeedMessage { ProviderStatus = providerStatus };
+
             foreach (ActiveAlarmSnapshot alarm in snapshot)
             {
                 yield return new AlarmFeedMessage { ActiveAlarm = alarm };
@@ -624,6 +810,8 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
             Description = transition.Description,
             OperatorUser = transition.OperatorUser,
             OperatorComment = transition.OperatorComment,
+            Degraded = transition.Degraded,
+            SourceProvider = transition.SourceProvider,
         };
         if (transition.OriginalRaiseTimestamp is not null)
         {
@@ -660,6 +848,8 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
             Description = snapshot.Description,
             OperatorUser = snapshot.OperatorUser,
             OperatorComment = snapshot.OperatorComment,
+            Degraded = snapshot.Degraded,
+            SourceProvider = snapshot.SourceProvider,
         };
         if (snapshot.OriginalRaiseTimestamp is not null)
         {
@@ -688,7 +878,6 @@ public sealed class GatewayAlarmMonitor : BackgroundService, IGatewayAlarmServic
 
         /// <summary>Determines whether the alarm reference matches this subscriber's filter.</summary>
         /// <param name="reference">The alarm reference to match.</param>
-        /// <returns>True if the reference starts with this subscriber's prefix or no prefix is set.</returns>
         public bool Matches(string reference)
         {
             return prefix.Length == 0 || reference.StartsWith(prefix, StringComparison.Ordinal);

src/ZB.MOM.WW.MxGateway.Server/Alarms/IAlarmWatchListResolver.cs

@@ -0,0 +1,30 @@
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+using ZB.MOM.WW.MxGateway.Server.Configuration;
+
+namespace ZB.MOM.WW.MxGateway.Server.Alarms;
+
+/// <summary>
+///     Resolves the subtag watch-list the gateway sends to the worker when the
+///     central alarm monitor operates in subtag-polling fallback mode. Merges
+///     Galaxy Repository alarm-attribute discovery with the configured
+///     include/exclude overrides and composes the per-attribute subtag item
+///     addresses from the configured subtag names.
+/// </summary>
+public interface IAlarmWatchListResolver
+{
+    /// <summary>
+    ///     Builds the subtag watch-list for the supplied alarm configuration.
+    /// </summary>
+    /// <param name="options">Alarm configuration carrying discovery and subtag-name settings.</param>
+    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
+    /// <returns>
+    ///     The resolved <see cref="AlarmSubtagTarget"/> watch-list, possibly empty.
+    ///     Discovery being unavailable never throws — it yields an empty (or
+    ///     config-only) list and the caller decides what to do with it. Cancellation
+    ///     is the one exception: a triggered <paramref name="cancellationToken"/>
+    ///     still propagates an <see cref="OperationCanceledException"/>.
+    /// </returns>
+    Task<IReadOnlyList<AlarmSubtagTarget>> ResolveAsync(
+        AlarmsOptions options,
+        CancellationToken cancellationToken = default);
+}

src/ZB.MOM.WW.MxGateway.Server/Alarms/IGatewayAlarmService.cs

@@ -46,7 +46,6 @@ public interface IGatewayAlarmService
     /// </summary>
     /// <param name="alarmFilterPrefix">Optional alarm-reference prefix scoping the feed.</param>
     /// <param name="cancellationToken">Token that ends the subscription.</param>
-    /// <returns>An async enumerable of alarm feed messages.</returns>
     IAsyncEnumerable<AlarmFeedMessage> StreamAsync(
         string? alarmFilterPrefix,
         CancellationToken cancellationToken);
@@ -58,7 +57,6 @@ public interface IGatewayAlarmService
     /// </summary>
     /// <param name="request">The acknowledge request.</param>
     /// <param name="cancellationToken">Token to cancel the call.</param>
-    /// <returns>A task that resolves to the acknowledge reply.</returns>
     Task<AcknowledgeAlarmReply> AcknowledgeAsync(
         AcknowledgeAlarmRequest request,
         CancellationToken cancellationToken);

src/ZB.MOM.WW.MxGateway.Server/Configuration/AlarmFallbackOptions.cs

@@ -0,0 +1,131 @@
+namespace ZB.MOM.WW.MxGateway.Server.Configuration;
+
+/// <summary>
+///     Controls how the central alarm monitor selects between the MXAccess
+///     alarm-manager subscription and the subtag-polling fallback, and
+///     governs the failure-detection thresholds used when switching.
+/// </summary>
+public sealed class AlarmFallbackOptions
+{
+    /// <summary>
+    ///     Selects the operating mode for the alarm-manager ↔ subtag fallback
+    ///     mechanism. Accepted values (case-insensitive):
+    ///     <list type="bullet">
+    ///         <item><c>Auto</c> — use the alarm manager; switch to subtag polling
+    ///         automatically when <see cref="ConsecutiveFailureThreshold"/> failures
+    ///         are detected, and probe for failback.</item>
+    ///         <item><c>ForceAlarmManager</c> — always use the alarm manager;
+    ///         never fall back.</item>
+    ///         <item><c>ForceSubtag</c> — always use subtag polling;
+    ///         never try the alarm manager.</item>
+    ///     </list>
+    ///     Default is <c>Auto</c>.
+    /// </summary>
+    public string Mode { get; init; } = "Auto";
+
+    /// <summary>
+    ///     Number of consecutive alarm-manager failures before the monitor
+    ///     switches to subtag-polling fallback. Must be at least 1. Default 3.
+    /// </summary>
+    public int ConsecutiveFailureThreshold { get; init; } = 3;
+
+    /// <summary>
+    ///     How often (in seconds) the monitor sends a probe to the alarm manager
+    ///     while operating in subtag-polling fallback mode, to detect recovery.
+    ///     Must be at least 1. Default 30.
+    /// </summary>
+    public int FailbackProbeIntervalSeconds { get; init; } = 30;
+
+    /// <summary>
+    ///     Number of consecutive successful probes required before the monitor
+    ///     considers the alarm manager recovered and switches back. Must be at
+    ///     least 1. Default 3.
+    /// </summary>
+    public int FailbackStableProbes { get; init; } = 3;
+
+    /// <summary>
+    ///     Controls how the monitor discovers the set of objects to poll when
+    ///     operating in subtag-polling fallback mode.
+    /// </summary>
+    public AlarmDiscoveryOptions Discovery { get; init; } = new();
+
+    /// <summary>
+    ///     Configures the subtag names the monitor reads when polling alarm state
+    ///     in subtag-fallback mode.
+    /// </summary>
+    public AlarmSubtagNameOptions Subtags { get; init; } = new();
+}
+
+/// <summary>
+///     Governs how the alarm monitor discovers objects to include in subtag-polling
+///     fallback mode. Either the Galaxy Repository query (when
+///     <see cref="UseGalaxyRepository"/> is <c>true</c>) or an explicit
+///     <see cref="IncludeAttributes"/> list must be supplied when
+///     <c>MxGateway:Alarms:Fallback:Mode</c> is <c>ForceSubtag</c>.
+/// </summary>
+public sealed class AlarmDiscoveryOptions
+{
+    /// <summary>
+    ///     When <c>true</c> the monitor queries the Galaxy Repository SQL database
+    ///     to enumerate alarm objects for the configured area. Default <c>true</c>.
+    /// </summary>
+    public bool UseGalaxyRepository { get; init; } = true;
+
+    /// <summary>
+    ///     Galaxy area to scope the Repository query to. When empty the monitor
+    ///     falls back to <see cref="AlarmsOptions.DefaultArea"/>. Ignored when
+    ///     <see cref="UseGalaxyRepository"/> is <c>false</c>.
+    /// </summary>
+    public string Area { get; init; } = string.Empty;
+
+    /// <summary>
+    ///     Explicit list of MXAccess attribute paths to include in subtag polling,
+    ///     supplementing (or replacing, when <see cref="UseGalaxyRepository"/> is
+    ///     <c>false</c>) the Repository-derived list. Default empty.
+    /// </summary>
+    public string[] IncludeAttributes { get; init; } = Array.Empty<string>();
+
+    /// <summary>
+    ///     Attribute paths to exclude from the Repository-derived poll list.
+    ///     Ignored when <see cref="UseGalaxyRepository"/> is <c>false</c>.
+    ///     Default empty.
+    /// </summary>
+    public string[] ExcludeAttributes { get; init; } = Array.Empty<string>();
+}
+
+/// <summary>
+///     Configures the subtag names read by the alarm monitor when it is operating
+///     in subtag-polling fallback mode. Names are matched against MXAccess item
+///     handles; validation against the live MXAccess attribute list occurs at
+///     runtime, not at startup.
+///     Defaults are the confirmed AVEVA <c>AlarmExtension</c> primitive field names,
+///     verified against the live ZB Galaxy <c>attribute_definition</c> rows.
+/// </summary>
+public sealed class AlarmSubtagNameOptions
+{
+    /// <summary>
+    ///     Subtag name for the in-alarm boolean. Confirmed AVEVA <c>AlarmExtension</c>
+    ///     field name. Default <c>InAlarm</c>.
+    /// </summary>
+    public string Active { get; init; } = "InAlarm";
+
+    /// <summary>
+    ///     Subtag name for the acknowledged boolean. Confirmed AVEVA <c>AlarmExtension</c>
+    ///     field name. Default <c>Acked</c>.
+    /// </summary>
+    public string Acked { get; init; } = "Acked";
+
+    /// <summary>
+    ///     Subtag name for the acknowledgement comment write target. Writing this subtag
+    ///     performs the acknowledge in AVEVA. Confirmed AVEVA <c>AlarmExtension</c>
+    ///     field name. When empty the ack-comment write path is disabled.
+    ///     Default <c>AckMsg</c>.
+    /// </summary>
+    public string AckComment { get; init; } = "AckMsg";
+
+    /// <summary>
+    ///     Subtag name for the alarm priority / severity. Confirmed AVEVA
+    ///     <c>AlarmExtension</c> field name. Default <c>Priority</c>.
+    /// </summary>
+    public string Priority { get; init; } = "Priority";
+}

src/ZB.MOM.WW.MxGateway.Server/Configuration/AlarmsOptions.cs

@@ -45,4 +45,12 @@ public sealed class AlarmsOptions
     ///     the monitor floors it at 5 seconds.
     /// </summary>
     public int ReconcileIntervalSeconds { get; init; } = 30;
+
+    /// <summary>
+    ///     Configuration for the alarm-manager ↔ subtag fallback mechanism:
+    ///     operating mode, failure-detection thresholds, discovery, and subtag
+    ///     names. Defaults (Mode = "Auto") preserve behaviour when the section is
+    ///     omitted from configuration.
+    /// </summary>
+    public AlarmFallbackOptions Fallback { get; init; } = new();
 }

src/ZB.MOM.WW.MxGateway.Server/Configuration/DashboardOptions.cs

@@ -21,6 +21,17 @@ public sealed class DashboardOptions
     /// </summary>
     public bool RequireHttpsCookie { get; init; } = true;
 
+    /// <summary>
+    /// Dashboard auth cookie name. When null/blank (the default) the canonical
+    /// <see cref="ZB.MOM.WW.MxGateway.Server.Dashboard.DashboardAuthenticationDefaults.CookieName"/>
+    /// is used. Override it (<c>MxGateway:Dashboard:CookieName</c>) to give a distinct name to a
+    /// gateway that shares a hostname with another gateway instance — browser cookies are scoped
+    /// by host+path but NOT by port, so two instances on the same host would otherwise clobber
+    /// each other's dashboard session under a shared cookie name. Changing this signs out
+    /// existing dashboard sessions on next deploy.
+    /// </summary>
+    public string? CookieName { get; init; }
+
     /// <summary>Gets the dashboard snapshot update interval in milliseconds.</summary>
     public int SnapshotIntervalMilliseconds { get; init; } = 1_000;
 

src/ZB.MOM.WW.MxGateway.Server/Configuration/GatewayOptionsValidator.cs

@@ -9,7 +9,11 @@ public sealed class GatewayOptionsValidator : OptionsValidatorBase<GatewayOption
     private const int MinimumMaxMessageBytes = 1024;
     private const int MaximumMaxMessageBytes = 256 * 1024 * 1024;
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Validates gateway configuration options.
+    /// </summary>
+    /// <param name="builder">The accumulator to record failures on.</param>
+    /// <param name="options">Gateway options to validate.</param>
     protected override void Validate(ValidationBuilder builder, GatewayOptions options)
     {
         ValidateAuthentication(options.Authentication, builder);
@@ -227,6 +231,8 @@ public sealed class GatewayOptionsValidator : OptionsValidatorBase<GatewayOption
             builder);
     }
 
+    private static readonly string[] ValidAlarmFallbackModes = ["Auto", "ForceAlarmManager", "ForceSubtag"];
+
     private static void ValidateAlarms(AlarmsOptions options, ValidationBuilder builder)
     {
         if (!options.Enabled)
@@ -251,6 +257,46 @@ public sealed class GatewayOptionsValidator : OptionsValidatorBase<GatewayOption
             builder.Add(
                 @"MxGateway:Alarms:SubscriptionExpression must start with '\\' (canonical \\<host>\Galaxy!<area> shape).");
         }
+
+        ValidateAlarmFallback(options.Fallback, builder);
+    }
+
+    private static void ValidateAlarmFallback(AlarmFallbackOptions fallback, ValidationBuilder builder)
+    {
+        // Validate Mode is one of the recognised values (case-insensitive).
+        bool modeValid = Array.Exists(
+            ValidAlarmFallbackModes,
+            m => string.Equals(m, fallback.Mode, StringComparison.OrdinalIgnoreCase));
+
+        if (!modeValid)
+        {
+            builder.Add(
+                $"MxGateway:Alarms:Fallback:Mode must be one of: {string.Join(", ", ValidAlarmFallbackModes)} (was '{fallback.Mode}').");
+        }
+
+        // ForceSubtag requires either Galaxy Repository discovery or an explicit IncludeAttributes list.
+        if (modeValid
+            && string.Equals(fallback.Mode, "ForceSubtag", StringComparison.OrdinalIgnoreCase)
+            && !fallback.Discovery.UseGalaxyRepository
+            && fallback.Discovery.IncludeAttributes.Length == 0)
+        {
+            builder.Add(
+                "MxGateway:Alarms:Fallback ForceSubtag requires Galaxy Repository discovery or a non-empty Discovery:IncludeAttributes list.");
+        }
+
+        // Floor validation: numeric thresholds must be at least 1.
+        AddIfNotPositive(
+            fallback.ConsecutiveFailureThreshold,
+            "MxGateway:Alarms:Fallback:ConsecutiveFailureThreshold must be greater than zero.",
+            builder);
+        AddIfNotPositive(
+            fallback.FailbackProbeIntervalSeconds,
+            "MxGateway:Alarms:Fallback:FailbackProbeIntervalSeconds must be greater than zero.",
+            builder);
+        AddIfNotPositive(
+            fallback.FailbackStableProbes,
+            "MxGateway:Alarms:Fallback:FailbackStableProbes must be greater than zero.",
+            builder);
     }
 
     private const int MinimumCertValidityYears = 1;

src/ZB.MOM.WW.MxGateway.Server/Configuration/IGatewayConfigurationProvider.cs

@@ -8,6 +8,5 @@ public interface IGatewayConfigurationProvider
     /// <summary>
     /// Returns the validated and effective gateway configuration.
     /// </summary>
-    /// <returns>The <see cref="EffectiveGatewayConfiguration"/> with validated defaults applied.</returns>
     EffectiveGatewayConfiguration GetEffectiveConfiguration();
 }

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/DashboardPageBase.cs

@@ -38,8 +38,7 @@ public abstract class DashboardPageBase : ComponentBase, IAsyncDisposable
         await ConnectHubAsync().ConfigureAwait(false);
     }
 
-    /// <summary>Disposes the SignalR hub connection and suppresses finalization.</summary>
+    /// <inheritdoc />
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async ValueTask DisposeAsync()
     {
         if (_hub is not null)

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/Pages/AlarmsPage.razor

@@ -1,7 +1,10 @@
 @page "/alarms"
 @implements IAsyncDisposable
+@using Microsoft.AspNetCore.SignalR.Client
+@using ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs
 @inject IDashboardLiveDataService LiveData
 @inject IOptions<GatewayOptions> GatewayOptions
+@inject DashboardHubConnectionFactory HubFactory
 
 <PageTitle>Dashboard Alarms</PageTitle>
 
@@ -10,6 +13,12 @@
         <h1>Alarms</h1>
         <div class="text-secondary">@HeaderLine()</div>
     </div>
+    <div class="d-flex align-items-center gap-2">
+        <span class="badge @_providerStatus.BadgeCssClass"
+              title="@ProviderStatusTitle()">
+            @_providerStatus.Label
+        </span>
+    </div>
 </div>
 
 @if (!GatewayOptions.Value.Alarms.Enabled)
@@ -163,10 +172,44 @@
     private readonly CancellationTokenSource _cts = new();
     private Task? _pollTask;
 
+    private DashboardAlarmProviderStatus _providerStatus = DashboardAlarmProviderStatus.Healthy;
+    private HubConnection? _alarmsHub;
+
     /// <inheritdoc />
     protected override void OnInitialized()
     {
         _pollTask = PollLoopAsync();
+        _ = AttachAlarmsHubAsync();
+    }
+
+    private string? ProviderStatusTitle()
+    {
+        return _providerStatus.IsDegraded && !string.IsNullOrWhiteSpace(_providerStatus.Reason)
+            ? _providerStatus.Reason
+            : null;
+    }
+
+    private async Task AttachAlarmsHubAsync()
+    {
+        _alarmsHub = HubFactory.Create("/hubs/alarms");
+        _alarmsHub.On<AlarmFeedMessage>(AlarmsHub.AlarmMessage, async message =>
+        {
+            if (message.PayloadCase == AlarmFeedMessage.PayloadOneofCase.ProviderStatus)
+            {
+                _providerStatus = DashboardAlarmProviderStatus.FromFeed(message);
+                await InvokeAsync(StateHasChanged).ConfigureAwait(false);
+            }
+        });
+
+        try
+        {
+            await _alarmsHub.StartAsync(_cts.Token).ConfigureAwait(false);
+        }
+        catch
+        {
+            // The badge is best-effort; it stays at the healthy default until
+            // the hub reconnects and delivers a fresh provider-status message.
+        }
     }
 
     private string HeaderLine()
@@ -268,6 +311,19 @@
     public async ValueTask DisposeAsync()
     {
         await _cts.CancelAsync();
+
+        if (_alarmsHub is not null)
+        {
+            try
+            {
+                await _alarmsHub.DisposeAsync();
+            }
+            catch
+            {
+                // Disposal-time errors are best-effort.
+            }
+        }
+
         if (_pollTask is not null)
         {
             try

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/Pages/Login.razor

@@ -6,13 +6,19 @@
    cookie scheme's LoginPath="/login" redirect lands here for unauthenticated users.
 
    The card is the shared kit's <LoginCard>: it renders a NATIVE static
-   <form method="post" action="/login"> (username/password + hidden returnUrl). A native
+   <form method="post" action="/auth/login"> (username/password + hidden returnUrl). A native
-   form submit is not a Blazor event, so it reaches the minimal-API POST /login endpoint
+   form submit is not a Blazor event, so it reaches the minimal-API POST /auth/login endpoint
    regardless of this app's InteractiveServer render mode. <AntiforgeryToken/> supplies the
-   token that PostLoginAsync's antiforgery.ValidateRequestAsync checks. *@
+   token that PostLoginAsync's antiforgery.ValidateRequestAsync checks.
+
+   NOTE: the POST target is /auth/login, NOT /login. This @page lives at "/login" and the
+   Razor Components endpoint matches ALL methods, so a POST to /login collided with the
+   minimal-API MapPost("/login") and threw AmbiguousMatchException (HTTP 500). Posting to a
+   distinct /auth/login path (mirroring ScadaBridge) keeps the GET page and POST handler from
+   sharing a route. *@
 @attribute [AllowAnonymous]
 
-<LoginCard Product="MXAccess Gateway" Action="/login" ReturnUrl="@ReturnUrl" Error="@Error">
+<LoginCard Product="MXAccess Gateway" Action="/auth/login" ReturnUrl="@ReturnUrl" Error="@Error">
     <AntiforgeryToken />
 </LoginCard>
 

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardAlarmProviderStatus.cs

@@ -0,0 +1,78 @@
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+
+namespace ZB.MOM.WW.MxGateway.Server.Dashboard;
+
+/// <summary>
+///     Dashboard projection of an <see cref="AlarmProviderStatus" /> message
+///     carried on the alarm feed. Maps the protobuf provider mode / degraded
+///     flag into Bootstrap-only display fields so the Alarms page can render a
+///     status badge without touching protobuf types.
+/// </summary>
+public sealed record DashboardAlarmProviderStatus(
+    AlarmProviderMode Mode,
+    bool IsDegraded,
+    string Label,
+    string BadgeCssClass,
+    string Reason,
+    DateTimeOffset? SinceUtc)
+{
+    /// <summary>Badge label shown when the alarm-manager provider is healthy.</summary>
+    public const string AlarmManagerLabel = "Alarm Manager";
+
+    /// <summary>Badge label shown when the feed has fallen back to subtag monitoring.</summary>
+    public const string DegradedLabel = "Subtag monitoring (degraded)";
+
+    private const string HealthyBadge = "bg-success";
+    private const string DegradedBadge = "bg-warning text-dark";
+
+    /// <summary>
+    ///     The default status assumed before the first provider-status message
+    ///     arrives: healthy alarm-manager mode.
+    /// </summary>
+    public static DashboardAlarmProviderStatus Healthy { get; } = new(
+        Mode: AlarmProviderMode.Alarmmgr,
+        IsDegraded: false,
+        Label: AlarmManagerLabel,
+        BadgeCssClass: HealthyBadge,
+        Reason: string.Empty,
+        SinceUtc: null);
+
+    /// <summary>Projects an alarm-feed provider-status payload into a dashboard badge model.</summary>
+    /// <param name="status">The provider-status payload from an <see cref="AlarmFeedMessage" />.</param>
+    /// <returns>The projected dashboard status.</returns>
+    public static DashboardAlarmProviderStatus FromProviderStatus(AlarmProviderStatus status)
+    {
+        ArgumentNullException.ThrowIfNull(status);
+
+        // Treat the explicit degraded flag and the SUBTAG mode as equivalent;
+        // the contract sets degraded=true whenever mode == SUBTAG, but guard
+        // against either being set independently.
+        bool degraded = status.Degraded || status.Mode == AlarmProviderMode.Subtag;
+
+        return new DashboardAlarmProviderStatus(
+            Mode: status.Mode,
+            IsDegraded: degraded,
+            Label: degraded ? DegradedLabel : AlarmManagerLabel,
+            BadgeCssClass: degraded ? DegradedBadge : HealthyBadge,
+            Reason: status.Reason ?? string.Empty,
+            SinceUtc: status.Since?.ToDateTimeOffset());
+    }
+
+    /// <summary>Projects an alarm-feed message into a dashboard badge model.</summary>
+    /// <param name="message">An alarm-feed message whose payload is a provider status.</param>
+    /// <returns>The projected dashboard status.</returns>
+    /// <exception cref="ArgumentException">The message does not carry a provider-status payload.</exception>
+    public static DashboardAlarmProviderStatus FromFeed(AlarmFeedMessage message)
+    {
+        ArgumentNullException.ThrowIfNull(message);
+
+        if (message.PayloadCase != AlarmFeedMessage.PayloadOneofCase.ProviderStatus)
+        {
+            throw new ArgumentException(
+                "Alarm-feed message does not carry a provider-status payload.",
+                nameof(message));
+        }
+
+        return FromProviderStatus(message.ProviderStatus);
+    }
+}

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardApiKeyAuthorization.cs

@@ -6,7 +6,6 @@ public sealed class DashboardApiKeyAuthorization
 {
     /// <summary>Determines whether the user can manage API keys.</summary>
     /// <param name="user">The authenticated user principal.</param>
-    /// <returns>True if the user is an authenticated admin; otherwise false.</returns>
     public bool CanManage(ClaimsPrincipal user)
     {
         if (user.Identity?.IsAuthenticated != true)

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardApiKeyManagementService.cs

@@ -20,13 +20,17 @@ public sealed class DashboardApiKeyManagementService(
     private const string UnauthorizedMessage = "Sign in with an authorized LDAP account to manage API keys.";
     private const string PepperUnavailableMarker = "pepper unavailable";
 
-    /// <inheritdoc />
+    /// <summary>Determines whether the user can manage API keys.</summary>
+    /// <param name="user">The authenticated user principal.</param>
     public bool CanManage(ClaimsPrincipal user)
     {
         return authorization.CanManage(user);
     }
 
-    /// <inheritdoc />
+    /// <summary>Creates an API key asynchronously.</summary>
+    /// <param name="user">The authenticated user principal.</param>
+    /// <param name="request">The request payload.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public async Task<DashboardApiKeyManagementResult> CreateAsync(
         ClaimsPrincipal user,
         DashboardApiKeyManagementRequest request,
@@ -78,7 +82,10 @@ public sealed class DashboardApiKeyManagementService(
         }
     }
 
-    /// <inheritdoc />
+    /// <summary>Revokes an API key asynchronously.</summary>
+    /// <param name="user">The authenticated user principal.</param>
+    /// <param name="keyId">The API key identifier.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public async Task<DashboardApiKeyManagementResult> RevokeAsync(
         ClaimsPrincipal user,
         string keyId,
@@ -113,7 +120,10 @@ public sealed class DashboardApiKeyManagementService(
             : DashboardApiKeyManagementResult.Fail("API key was not found or is already revoked.");
     }
 
-    /// <inheritdoc />
+    /// <summary>Rotates an API key secret asynchronously.</summary>
+    /// <param name="user">The authenticated user principal.</param>
+    /// <param name="keyId">The API key identifier.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public async Task<DashboardApiKeyManagementResult> RotateAsync(
         ClaimsPrincipal user,
         string keyId,
@@ -160,7 +170,10 @@ public sealed class DashboardApiKeyManagementService(
         }
     }
 
-    /// <inheritdoc />
+    /// <summary>Deletes a revoked API key asynchronously.</summary>
+    /// <param name="user">The authenticated user principal.</param>
+    /// <param name="keyId">The API key identifier.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public async Task<DashboardApiKeyManagementResult> DeleteAsync(
         ClaimsPrincipal user,
         string keyId,

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardAuthenticationResult.cs

@@ -23,7 +23,6 @@ public sealed record DashboardAuthenticationResult(
     /// Creates a successful authentication result.
     /// </summary>
     /// <param name="principal">Authenticated principal.</param>
-    /// <returns>A successful <see cref="DashboardAuthenticationResult"/> wrapping the principal.</returns>
     public static DashboardAuthenticationResult Success(ClaimsPrincipal principal)
     {
         return new DashboardAuthenticationResult(true, principal, null);
@@ -33,7 +32,6 @@ public sealed record DashboardAuthenticationResult(
     /// Creates a failed authentication result.
     /// </summary>
     /// <param name="failureMessage">Diagnostic message describing the failure.</param>
-    /// <returns>A failed <see cref="DashboardAuthenticationResult"/> with the given message.</returns>
     public static DashboardAuthenticationResult Fail(string failureMessage)
     {
         return new DashboardAuthenticationResult(false, null, failureMessage);

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardConnectionStringDisplay.cs

@@ -6,7 +6,6 @@ public static class DashboardConnectionStringDisplay
 {
     /// <summary>Returns a sanitized Galaxy Repository connection string for display.</summary>
     /// <param name="connectionString">The connection string to sanitize.</param>
-    /// <returns>A sanitized connection string with credentials removed, or <c>"[invalid connection string]"</c> if parsing fails.</returns>
     public static string GalaxyRepositoryConnectionString(string connectionString)
     {
         try

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardEndpointRouteBuilderExtensions.cs

@@ -29,8 +29,14 @@ public static class DashboardEndpointRouteBuilderExtensions
         // kit's <LoginCard>. Its [AllowAnonymous] attribute overrides the
         // RequireAuthorization(ViewerPolicy) that MapRazorComponents<App>() applies,
         // so the cookie scheme's LoginPath="/login" redirect resolves for anonymous users.
+        //
+        // The credential POST is mapped to /auth/login, NOT /login. The @page "/login"
+        // Razor Components endpoint matches ALL HTTP methods, so a MapPost("/login") shared
+        // the "/login" route with it and every POST threw AmbiguousMatchException (HTTP 500).
+        // A distinct /auth/login path (as ScadaBridge does) keeps the GET page and the POST
+        // handler on separate routes. The <LoginCard Action="/auth/login"> form posts here.
         endpoints.MapPost(
-                "/login",
+                "/auth/login",
                 (HttpContext httpContext, IAntiforgery antiforgery, IDashboardAuthenticator authenticator) =>
                     PostLoginAsync(httpContext, antiforgery, authenticator))
             .AllowAnonymous()

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardGalaxyProjector.cs

@@ -7,7 +7,6 @@ internal static class DashboardGalaxyProjector
 {
     /// <summary>Projects the cache entry to a dashboard Galaxy summary.</summary>
     /// <param name="entry">The Galaxy hierarchy cache entry.</param>
-    /// <returns>The precomputed <see cref="DashboardGalaxySummary"/> from the cache entry.</returns>
     public static DashboardGalaxySummary Project(GalaxyHierarchyCacheEntry entry)
     {
         return entry.DashboardSummary;

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardGroupRoleMapper.cs

@@ -17,10 +17,7 @@ namespace ZB.MOM.WW.MxGateway.Server.Dashboard;
 public sealed class DashboardGroupRoleMapper(IOptions<GatewayOptions> options)
     : IGroupRoleMapper<string>
 {
-    /// <summary>Maps LDAP group memberships to dashboard roles using the configured group-to-role rules.</summary>
+    /// <inheritdoc />
-    /// <param name="groups">The list of LDAP group names or distinguished names for the authenticated user.</param>
-    /// <param name="ct">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to the role mapping for the supplied groups.</returns>
     public Task<GroupRoleMapping<string>> MapAsync(
         IReadOnlyList<string> groups,
         CancellationToken ct)

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardGroupRoleMapping.cs

@@ -16,7 +16,6 @@ internal static class DashboardGroupRoleMapping
     /// </summary>
     /// <param name="groups">The collection of LDAP groups the user belongs to.</param>
     /// <param name="groupToRole">The mapping from group names to dashboard role names.</param>
-    /// <returns>The distinct set of dashboard roles matched from the user's groups.</returns>
     internal static IReadOnlyList<string> MapGroupsToRoles(
         IEnumerable<string> groups,
         IReadOnlyDictionary<string, string> groupToRole)
@@ -62,7 +61,6 @@ internal static class DashboardGroupRoleMapping
 
     /// <summary>Extracts the first RDN value from a distinguished name.</summary>
     /// <param name="distinguishedName">The LDAP distinguished name.</param>
-    /// <returns>The value portion of the first RDN component, or the full string if no <c>=</c> is found.</returns>
     internal static string ExtractFirstRdnValue(string distinguishedName)
     {
         int equalsIndex = distinguishedName.IndexOf('=');

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardLiveDataService.cs

@@ -192,8 +192,7 @@ public sealed class DashboardLiveDataService : IDashboardLiveDataService, IAsync
         }
     }
 
-    /// <summary>Releases resources and closes the associated gateway session.</summary>
+    /// <inheritdoc />
-    /// <returns>A task that represents the asynchronous dispose operation.</returns>
     public async ValueTask DisposeAsync()
     {
         if (_disposed)

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardServiceCollectionExtensions.cs

@@ -23,7 +23,6 @@ public static class DashboardServiceCollectionExtensions
     /// Application configuration, used to bind the shared LDAP provider's options
     /// from the <c>MxGateway:Ldap</c> section.
     /// </param>
-    /// <returns>The <paramref name="services"/> collection for chaining.</returns>
     public static IServiceCollection AddGatewayDashboard(
         this IServiceCollection services,
         IConfiguration configuration)
@@ -67,6 +66,8 @@ public static class DashboardServiceCollectionExtensions
                 ZbCookieDefaults.Apply(cookieOptions, requireHttps: true, idleTimeout: TimeSpan.FromHours(8));
                 // Cookie name, path, and redirect paths are MxGateway-specific — set after Apply
                 // so they are never overwritten by the shared helper (Apply intentionally skips name).
+                // This is the canonical default; it is overridden per-environment from
+                // DashboardOptions.CookieName by the PostConfigure below.
                 cookieOptions.Cookie.Name = DashboardAuthenticationDefaults.CookieName;
                 cookieOptions.Cookie.Path = "/";
                 cookieOptions.LoginPath = "/login";
@@ -78,13 +79,22 @@ public static class DashboardServiceCollectionExtensions
                 _ => { });
 
         // Honour DashboardOptions.RequireHttpsCookie (default true / Always; set false for dev
-        // HTTP deployments → SameAsRequest). This overrides the Apply default above.
+        // HTTP deployments → SameAsRequest) and the optional per-environment cookie-name
+        // override. Both run after the inline AddCookie config above, so they win.
         services.AddOptions<CookieAuthenticationOptions>(DashboardAuthenticationDefaults.AuthenticationScheme)
             .Configure<IOptions<GatewayOptions>>((cookieOptions, gatewayOptions) =>
             {
                 cookieOptions.Cookie.SecurePolicy = gatewayOptions.Value.Dashboard.RequireHttpsCookie
                     ? CookieSecurePolicy.Always
                     : CookieSecurePolicy.SameAsRequest;
+
+                // Config-driven cookie name (MxGateway:Dashboard:CookieName). Null/blank keeps
+                // the canonical default set above, so a misconfiguration cannot unname the cookie.
+                var cookieName = gatewayOptions.Value.Dashboard.CookieName;
+                if (!string.IsNullOrWhiteSpace(cookieName))
+                {
+                    cookieOptions.Cookie.Name = cookieName;
+                }
             });
 
         services.AddAuthorization(authorization =>

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardSessionAdminResult.cs

@@ -6,7 +6,6 @@ public sealed record DashboardSessionAdminResult(
 {
     /// <summary>Creates a successful result with the given message.</summary>
     /// <param name="message">The result message.</param>
-    /// <returns>A <see cref="DashboardSessionAdminResult"/> with <c>Succeeded</c> set to <c>true</c>.</returns>
     public static DashboardSessionAdminResult Success(string message)
     {
         return new DashboardSessionAdminResult(true, message);
@@ -14,7 +13,6 @@ public sealed record DashboardSessionAdminResult(
 
     /// <summary>Creates a failed result with the given message.</summary>
     /// <param name="message">The result message.</param>
-    /// <returns>A <see cref="DashboardSessionAdminResult"/> with <c>Succeeded</c> set to <c>false</c>.</returns>
     public static DashboardSessionAdminResult Fail(string message)
     {
         return new DashboardSessionAdminResult(false, message);

src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardSnapshotService.cs

@@ -65,7 +65,10 @@ public sealed class DashboardSnapshotService : IDashboardSnapshotService
         _logger = logger ?? NullLogger<DashboardSnapshotService>.Instance;
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Gets a current dashboard snapshot of gateway state.
+    /// </summary>
+    /// <returns>Dashboard snapshot.</returns>
     public DashboardSnapshot GetSnapshot()
     {
         DateTimeOffset generatedAt = _timeProvider.GetUtcNow();
@@ -97,7 +100,11 @@ public sealed class DashboardSnapshotService : IDashboardSnapshotService
             Galaxy: DashboardGalaxyProjector.Project(_galaxyHierarchyCache.Current));
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Watches dashboard snapshots at regular intervals asynchronously.
+    /// </summary>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Async enumerable of dashboard snapshots.</returns>
     public async IAsyncEnumerable<DashboardSnapshot> WatchSnapshotsAsync(
         [EnumeratorCancellation] CancellationToken cancellationToken)
     {

src/ZB.MOM.WW.MxGateway.Server/Dashboard/HubTokenService.cs

@@ -40,7 +40,6 @@ public sealed class HubTokenService
 
     /// <summary>Issues a bearer token carrying the user's identity and roles.</summary>
     /// <param name="user">The claims principal representing the user.</param>
-    /// <returns>The time-limited bearer token string.</returns>
     public string Issue(ClaimsPrincipal user)
     {
         ArgumentNullException.ThrowIfNull(user);
@@ -53,7 +52,6 @@ public sealed class HubTokenService
 
     /// <summary>Validates a token and returns the equivalent claims principal; null when invalid or expired.</summary>
     /// <param name="token">The token string to validate.</param>
-    /// <returns>The claims principal if the token is valid, or null if invalid or expired.</returns>
     public ClaimsPrincipal? Validate(string? token)
     {
         if (string.IsNullOrEmpty(token))

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Hubs/DashboardEventBroadcaster.cs

@@ -14,7 +14,9 @@ public sealed class DashboardEventBroadcaster(
     IHubContext<EventsHub> hubContext,
     ILogger<DashboardEventBroadcaster> logger) : IDashboardEventBroadcaster
 {
-    /// <inheritdoc />
+    /// <summary>Publishes an MX event to connected dashboard clients.</summary>
+    /// <param name="sessionId">The session identifier.</param>
+    /// <param name="mxEvent">The MX event to publish.</param>
     public void Publish(string sessionId, MxEvent mxEvent)
     {
         if (string.IsNullOrEmpty(sessionId) || mxEvent is null)

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Hubs/EventsHub.cs

@@ -49,7 +49,6 @@ public sealed class EventsHub : Hub
     /// dedicated authorization policy applied to the hub method itself.
     /// </remarks>
     /// <param name="sessionId">Session id to subscribe the caller to.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public Task SubscribeSession(string sessionId)
     {
         if (string.IsNullOrWhiteSpace(sessionId))

src/ZB.MOM.WW.MxGateway.Server/Dashboard/IDashboardAuthenticator.cs

@@ -11,7 +11,6 @@ public interface IDashboardAuthenticator
     /// <param name="username">Username to authenticate.</param>
     /// <param name="password">Password to authenticate.</param>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to the authentication result.</returns>
     Task<DashboardAuthenticationResult> AuthenticateAsync(
         string? username,
         string? password,

src/ZB.MOM.WW.MxGateway.Server/Dashboard/IDashboardBrowseService.cs

@@ -12,13 +12,11 @@ public interface IDashboardBrowseService
 {
     /// <summary>Returns root browse nodes (objects with no parent).</summary>
     /// <param name="filter">Filter arguments forwarded to the projector.</param>
-    /// <returns>The root-level browse result.</returns>
     BrowseLevelResult GetRoots(BrowseFilterArgs filter);
 
     /// <summary>Returns the direct children of the given parent gobject id.</summary>
     /// <param name="parentGobjectId">The Galaxy gobject id of the parent to expand.</param>
     /// <param name="filter">Filter arguments forwarded to the projector.</param>
-    /// <returns>The children browse result for the specified parent.</returns>
     BrowseLevelResult GetChildren(int parentGobjectId, BrowseFilterArgs filter);
 
     /// <summary>Current Galaxy cache sequence. Bumps after each successful refresh.</summary>

src/ZB.MOM.WW.MxGateway.Server/Dashboard/IDashboardSnapshotService.cs

@@ -8,13 +8,11 @@ public interface IDashboardSnapshotService
     /// <summary>
     /// Gets the current dashboard snapshot.
     /// </summary>
-    /// <returns>The most recent <see cref="DashboardSnapshot"/>.</returns>
     DashboardSnapshot GetSnapshot();
 
     /// <summary>
     /// Watches for changes to the dashboard state as an async enumerable.
     /// </summary>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>An async sequence of <see cref="DashboardSnapshot"/> values as state changes.</returns>
     IAsyncEnumerable<DashboardSnapshot> WatchSnapshotsAsync(CancellationToken cancellationToken);
 }

src/ZB.MOM.WW.MxGateway.Server/Diagnostics/AuthStoreHealthCheck.cs

@@ -12,15 +12,9 @@ public sealed class AuthStoreHealthCheck : IHealthCheck
 {
     private readonly AuthSqliteConnectionFactory _connectionFactory;
 
-    /// <summary>Initializes a new instance of <see cref="AuthStoreHealthCheck"/> with the given connection factory.</summary>
-    /// <param name="connectionFactory">Factory for opening SQLite connections to the auth store.</param>
     public AuthStoreHealthCheck(AuthSqliteConnectionFactory connectionFactory) =>
         _connectionFactory = connectionFactory ?? throw new ArgumentNullException(nameof(connectionFactory));
 
-    /// <summary>Runs a lightweight connectivity probe against the SQLite authentication store.</summary>
-    /// <param name="context">Health check context supplied by the framework.</param>
-    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to the health check result.</returns>
     public async Task<HealthCheckResult> CheckHealthAsync(
         HealthCheckContext context,
         CancellationToken cancellationToken = default)

src/ZB.MOM.WW.MxGateway.Server/Diagnostics/GatewayLogRedactor.cs

@@ -19,7 +19,6 @@ public static class GatewayLogRedactor
     /// Determines whether a command method bears credentials.
     /// </summary>
     /// <param name="commandMethod">The command method name to check.</param>
-    /// <returns><c>true</c> if the method carries credentials; otherwise <c>false</c>.</returns>
     public static bool IsCredentialBearingCommand(string? commandMethod)
     {
         return commandMethod is not null
@@ -30,7 +29,6 @@ public static class GatewayLogRedactor
     /// Redacts the API key secret portion of a Bearer authorization header.
     /// </summary>
     /// <param name="authorizationHeader">The authorization header value to redact.</param>
-    /// <returns>The header with the secret portion replaced by <see cref="RedactedValue"/>, or the original if no key is detected.</returns>
     public static string? RedactApiKey(string? authorizationHeader)
     {
         if (string.IsNullOrWhiteSpace(authorizationHeader))
@@ -64,7 +62,6 @@ public static class GatewayLogRedactor
     /// Redacts the client identity if it contains an API key.
     /// </summary>
     /// <param name="clientIdentity">The client identity string to redact.</param>
-    /// <returns>The redacted identity string, or the original if no key pattern is found.</returns>
     public static string? RedactClientIdentity(string? clientIdentity)
     {
         if (string.IsNullOrWhiteSpace(clientIdentity))
@@ -83,7 +80,6 @@ public static class GatewayLogRedactor
     /// <param name="commandMethod">The command method name to check for credentials.</param>
     /// <param name="value">The command value to redact.</param>
     /// <param name="valueLoggingEnabled">Whether value logging is enabled.</param>
-    /// <returns>The original value when logging is enabled and the command is not credential-bearing; otherwise <see cref="RedactedValue"/>.</returns>
     public static object? RedactCommandValue(
         string? commandMethod,
         object? value,

src/ZB.MOM.WW.MxGateway.Server/Diagnostics/GatewayLogScope.cs

@@ -8,7 +8,6 @@ public sealed record GatewayLogScope(
     string? ClientIdentity = null)
 {
     /// <summary>Converts the log scope to a dictionary with redacted sensitive fields.</summary>
-    /// <returns>A dictionary of non-null scope properties with sensitive fields redacted.</returns>
     public IReadOnlyDictionary<string, object?> ToDictionary()
     {
         Dictionary<string, object?> values = [];

src/ZB.MOM.WW.MxGateway.Server/Diagnostics/GatewayRequestLoggingMiddlewareExtensions.cs

@@ -19,7 +19,6 @@ public static class GatewayRequestLoggingMiddlewareExtensions
 
     /// <summary>Adds gateway request logging scope middleware that reads correlation headers and redacts sensitive data.</summary>
     /// <param name="app">Application builder.</param>
-    /// <returns>The <paramref name="app"/> instance for chaining.</returns>
     public static IApplicationBuilder UseGatewayRequestLoggingScope(this IApplicationBuilder app)
     {
         ArgumentNullException.ThrowIfNull(app);

src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyAlarmAttributeRow.cs

@@ -0,0 +1,48 @@
+namespace ZB.MOM.WW.MxGateway.Server.Galaxy;
+
+/// <summary>
+///     One alarm-bearing attribute discovered by
+///     <see cref="GalaxyRepository.GetAlarmAttributesAsync"/>: an attribute whose owning
+///     object configures an <c>AlarmExtension</c> primitive (the same
+///     <c>is_alarm</c> detection used by <see cref="GalaxyRepository.GetAttributesAsync"/>).
+///     Used to build the subtag-fallback watch-list.
+/// </summary>
+public sealed class GalaxyAlarmAttributeRow
+{
+    /// <summary>
+    ///     Gets the alarm-bearing attribute reference (e.g. <c>Tank01.Level.HiHi</c>),
+    ///     matching the <c>full_tag_reference</c> projection of
+    ///     <see cref="GalaxyRepository.GetAttributesAsync"/>.
+    /// </summary>
+    public string FullTagReference { get; init; } = string.Empty;
+
+    /// <summary>
+    ///     Gets the owning object reference (e.g. <c>Tank01</c>). This is the Galaxy
+    ///     <c>tag_name</c> — the segment that precedes the first attribute dot in
+    ///     <see cref="FullTagReference"/>.
+    /// </summary>
+    public string SourceObjectReference { get; init; } = string.Empty;
+
+    /// <summary>
+    ///     Gets the owning object's Galaxy area (e.g. <c>TestArea</c>) — the alarm group.
+    ///     <para>
+    ///     Resolved via <c>gobject.area_gobject_id</c> in <c>AlarmAttributesSql</c>. The
+    ///     watch-list resolver composes the canonical <c>Galaxy!{area}.{reference}</c> from
+    ///     this so the synthesized reference's group matches the native alarmmgr (wnwrap)
+    ///     for reference parity. May be <see cref="string.Empty"/> when the object has no
+    ///     area; the resolver then falls back to the configured area.
+    ///     </para>
+    /// </summary>
+    public string Area { get; init; } = string.Empty;
+
+    /// <summary>
+    ///     Gets the writable ack-comment attribute address.
+    ///     <para>
+    ///     The Galaxy Repository schema does not expose an ack-comment subtag address
+    ///     directly, so this is always <see cref="string.Empty"/> here. The watch-list
+    ///     resolver (a later task) composes the concrete address from configuration plus
+    ///     <see cref="SourceObjectReference"/> / <see cref="FullTagReference"/>.
+    ///     </para>
+    /// </summary>
+    public string AckCommentSubtag { get; init; } = string.Empty;
+}

src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyBrowseProjector.cs

@@ -27,7 +27,6 @@ public static class GalaxyBrowseProjector
     /// <param name="browseSubtreeGlobs">Optional API-key browse-subtree constraints.</param>
     /// <param name="offset">Zero-based offset into the filtered child list.</param>
     /// <param name="pageSize">Maximum number of children to return.</param>
-    /// <returns>A page of children with total count and filter signature.</returns>
     public static GalaxyBrowseChildrenResult ProjectChildren(
         GalaxyHierarchyCacheEntry entry,
         BrowseChildrenRequest request,
@@ -72,7 +71,6 @@ public static class GalaxyBrowseProjector
     /// </summary>
     /// <param name="entry">The Galaxy hierarchy cache entry to query.</param>
     /// <param name="request">The browse-children request.</param>
-    /// <returns>The resolved parent gobject id, or 0 for roots.</returns>
     public static int ResolveParentId(GalaxyHierarchyCacheEntry entry, BrowseChildrenRequest request)
     {
         switch (request.ParentCase)
@@ -259,7 +257,6 @@ public static class GalaxyBrowseProjector
     /// <param name="request">The browse-children request.</param>
     /// <param name="browseSubtreeGlobs">Optional API-key browse-subtree constraints.</param>
     /// <param name="parentId">Resolved parent gobject id (0 for roots).</param>
-    /// <returns>A hex-encoded SHA-256 prefix that uniquely identifies the filter combination.</returns>
     public static string ComputeFilterSignature(
         BrowseChildrenRequest request,
         IReadOnlyList<string>? browseSubtreeGlobs,

src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyDeployNotifier.cs

@@ -20,7 +20,9 @@ public sealed class GalaxyDeployNotifier : IGalaxyDeployNotifier
     private readonly ConcurrentDictionary<Guid, Channel<GalaxyDeployEventInfo>> _subscribers = new();
     private GalaxyDeployEventInfo? _latest;
 
-    /// <inheritdoc />
+    /// <summary>
+    /// The most recent deploy event, or null if none has been published.
+    /// </summary>
     public GalaxyDeployEventInfo? Latest => Volatile.Read(ref _latest);
 
     /// <inheritdoc />

src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyGlobMatcher.cs

@@ -46,7 +46,6 @@ public static class GalaxyGlobMatcher
     /// <summary>Determines whether a value matches a glob pattern (with * and ? wildcards).</summary>
     /// <param name="value">The value to test against the glob pattern.</param>
     /// <param name="glob">The glob pattern with * and ? wildcards.</param>
-    /// <returns><see langword="true"/> if the value matches the glob pattern; otherwise <see langword="false"/>.</returns>
     public static bool IsMatch(string value, string glob)
     {
         if (string.IsNullOrWhiteSpace(glob))

src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyHierarchyCache.cs

@@ -54,7 +54,7 @@ public sealed class GalaxyHierarchyCache : IGalaxyHierarchyCache
         _snapshotStore = snapshotStore;
     }
 
-    /// <inheritdoc />
+    /// <summary>Gets the current Galaxy hierarchy cache entry with projected status.</summary>
     public GalaxyHierarchyCacheEntry Current
     {
         get
@@ -74,7 +74,9 @@ public sealed class GalaxyHierarchyCache : IGalaxyHierarchyCache
         }
     }
 
-    /// <inheritdoc />
+    /// <summary>Refreshes the Galaxy hierarchy cache if the deploy time has advanced.</summary>
+    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
+    /// <returns>Asynchronous task representing the refresh operation.</returns>
     public async Task RefreshAsync(CancellationToken cancellationToken)
     {
         await _refreshGate.WaitAsync(cancellationToken).ConfigureAwait(false);
@@ -88,7 +90,9 @@ public sealed class GalaxyHierarchyCache : IGalaxyHierarchyCache
         }
     }
 
-    /// <inheritdoc />
+    /// <summary>Waits for the Galaxy hierarchy cache to complete its first load.</summary>
+    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
+    /// <returns>Asynchronous task representing the wait operation.</returns>
     public Task WaitForFirstLoadAsync(CancellationToken cancellationToken)
     {
         return _firstLoad.Task.WaitAsync(cancellationToken);

src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyHierarchyProjector.cs

@@ -25,7 +25,6 @@ public static class GalaxyHierarchyProjector
     /// <param name="entry">The Galaxy hierarchy cache entry.</param>
     /// <param name="request">The discovery hierarchy request.</param>
     /// <param name="browseSubtreeGlobs">Optional glob patterns to filter browse subtrees.</param>
-    /// <returns>The query result containing matching objects.</returns>
     public static GalaxyHierarchyQueryResult Project(
         GalaxyHierarchyCacheEntry entry,
         DiscoverHierarchyRequest request,
@@ -45,7 +44,6 @@ public static class GalaxyHierarchyProjector
     /// <param name="browseSubtreeGlobs">Optional glob patterns to filter browse subtrees.</param>
     /// <param name="offset">The zero-based offset into the result set.</param>
     /// <param name="pageSize">The maximum number of results to return.</param>
-    /// <returns>The query result containing the requested page of matching objects.</returns>
     public static GalaxyHierarchyQueryResult Project(
         GalaxyHierarchyCacheEntry entry,
         DiscoverHierarchyRequest request,
@@ -133,7 +131,6 @@ public static class GalaxyHierarchyProjector
     /// <summary>Finds an object in the hierarchy by its tag address.</summary>
     /// <param name="entry">The Galaxy hierarchy cache entry.</param>
     /// <param name="tagAddress">The tag address to search for.</param>
-    /// <returns>The matching Galaxy object, or <c>null</c> if not found.</returns>
     public static GalaxyObject? FindObjectForTag(
         GalaxyHierarchyCacheEntry entry,
         string tagAddress)
@@ -151,7 +148,6 @@ public static class GalaxyHierarchyProjector
     /// <summary>Finds an attribute in the hierarchy by its tag address.</summary>
     /// <param name="entry">The Galaxy hierarchy cache entry.</param>
     /// <param name="tagAddress">The tag address to search for.</param>
-    /// <returns>The matching Galaxy attribute, or <c>null</c> if not found.</returns>
     public static GalaxyAttribute? FindAttributeForTag(
         GalaxyHierarchyCacheEntry entry,
         string tagAddress)
@@ -169,7 +165,6 @@ public static class GalaxyHierarchyProjector
     /// <summary>Gets the contained path for an object by its gobject ID.</summary>
     /// <param name="entry">The Galaxy hierarchy cache entry.</param>
     /// <param name="gobjectId">The Galaxy object ID.</param>
-    /// <returns>The contained path string, or an empty string if the object is not found.</returns>
     public static string GetContainedPath(
         GalaxyHierarchyCacheEntry entry,
         int gobjectId)
@@ -287,7 +282,6 @@ public static class GalaxyHierarchyProjector
     /// <summary>Computes a stable filter signature for memoization purposes.</summary>
     /// <param name="request">The discovery hierarchy request.</param>
     /// <param name="browseSubtreeGlobs">Optional glob patterns to filter browse subtrees.</param>
-    /// <returns>A string key that uniquely identifies the combination of filter parameters.</returns>
     public static string ComputeFilterSignature(
         DiscoverHierarchyRequest request,
         IReadOnlyList<string>? browseSubtreeGlobs)

src/ZB.MOM.WW.MxGateway.Server/Galaxy/GalaxyRepository.cs

@@ -15,7 +15,8 @@ namespace ZB.MOM.WW.MxGateway.Server.Galaxy;
 /// </summary>
 public sealed class GalaxyRepository(GalaxyRepositoryOptions options) : IGalaxyRepository
 {
-    /// <inheritdoc />
+    /// <summary>Tests the connection to the Galaxy Repository database.</summary>
+    /// <param name="ct">Token to cancel the asynchronous operation.</param>
     public async Task<bool> TestConnectionAsync(CancellationToken ct = default)
     {
         try
@@ -30,7 +31,8 @@ public sealed class GalaxyRepository(GalaxyRepositoryOptions options) : IGalaxyR
         catch (InvalidOperationException) { return false; }
     }
 
-    /// <inheritdoc />
+    /// <summary>Retrieves the last deployment time from the Galaxy Repository.</summary>
+    /// <param name="ct">Token to cancel the asynchronous operation.</param>
     public async Task<DateTime?> GetLastDeployTimeAsync(CancellationToken ct = default)
     {
         using SqlConnection conn = new(options.ConnectionString);
@@ -41,7 +43,8 @@ public sealed class GalaxyRepository(GalaxyRepositoryOptions options) : IGalaxyR
         return result is DateTime dt ? dt : null;
     }
 
-    /// <inheritdoc />
+    /// <summary>Retrieves the complete hierarchy of Galaxy objects from the repository.</summary>
+    /// <param name="ct">Token to cancel the asynchronous operation.</param>
     public async Task<List<GalaxyHierarchyRow>> GetHierarchyAsync(CancellationToken ct = default)
     {
         List<GalaxyHierarchyRow> rows = new();
@@ -78,7 +81,8 @@ public sealed class GalaxyRepository(GalaxyRepositoryOptions options) : IGalaxyR
         return rows;
     }
 
-    /// <inheritdoc />
+    /// <summary>Retrieves all attributes for Galaxy objects from the repository.</summary>
+    /// <param name="ct">Token to cancel the asynchronous operation.</param>
     public async Task<List<GalaxyAttributeRow>> GetAttributesAsync(CancellationToken ct = default)
     {
         List<GalaxyAttributeRow> rows = new();
@@ -110,6 +114,64 @@ public sealed class GalaxyRepository(GalaxyRepositoryOptions options) : IGalaxyR
         return rows;
     }
 
+    /// <summary>
+    ///     Retrieves only the alarm-bearing attributes for the subtag-fallback watch-list.
+    ///     Alarm detection is identical to <see cref="GetAttributesAsync"/>: a row is
+    ///     alarm-bearing when its owning object configures an <c>AlarmExtension</c>
+    ///     primitive (the same <c>is_alarm</c> projection, here applied as a SQL filter).
+    /// </summary>
+    /// <param name="ct">Token to cancel the asynchronous operation.</param>
+    public async Task<List<GalaxyAlarmAttributeRow>> GetAlarmAttributesAsync(CancellationToken ct = default)
+    {
+        List<GalaxyAlarmAttributeRow> rows = new();
+
+        using SqlConnection conn = new(options.ConnectionString);
+        await conn.OpenAsync(ct).ConfigureAwait(false);
+
+        using SqlCommand cmd = new(AlarmAttributesSql, conn) { CommandTimeout = options.CommandTimeoutSeconds };
+        using SqlDataReader reader = await cmd.ExecuteReaderAsync(ct).ConfigureAwait(false);
+
+        while (await reader.ReadAsync(ct).ConfigureAwait(false))
+        {
+            rows.Add(MapAlarmRow(
+                fullTagReference: reader.GetString(0),
+                sourceObjectReference: reader.GetString(1),
+                area: reader.GetString(2)));
+        }
+        return rows;
+    }
+
+    /// <summary>
+    ///     Maps a raw alarm-attribute reader row to a <see cref="GalaxyAlarmAttributeRow"/>.
+    ///     <para>
+    ///     <paramref name="sourceObjectReference"/> is the Galaxy <c>tag_name</c> (the
+    ///     owning object), and <paramref name="fullTagReference"/> is
+    ///     <c>tag_name + '.' + attribute_name</c> — the same composition the
+    ///     <c>full_tag_reference</c> projection of <see cref="AttributesSql"/> produces.
+    ///     <see cref="GalaxyAlarmAttributeRow.AckCommentSubtag"/> is left empty here; the
+    ///     schema does not expose an ack-comment address and the watch-list resolver
+    ///     composes it later.
+    ///     </para>
+    ///     <paramref name="area"/> is the owning object's real Galaxy area (its alarm
+    ///     group), resolved via <c>gobject.area_gobject_id</c>; the watch-list resolver
+    ///     composes the canonical reference from it so the synthesized reference's group
+    ///     matches what the native alarmmgr (wnwrap) emits.
+    ///     Exposed internally so the derivation can be unit-tested without a database.
+    /// </summary>
+    /// <param name="fullTagReference">The alarm-bearing attribute reference.</param>
+    /// <param name="sourceObjectReference">The owning object reference (tag name).</param>
+    /// <param name="area">The owning object's Galaxy area (the alarm group).</param>
+    internal static GalaxyAlarmAttributeRow MapAlarmRow(
+        string fullTagReference,
+        string sourceObjectReference,
+        string area) => new()
+        {
+            FullTagReference = fullTagReference,
+            SourceObjectReference = sourceObjectReference,
+            Area = area,
+            AckCommentSubtag = string.Empty,
+        };
+
     private const string HierarchySql = @"
 ;WITH template_chain AS (
     SELECT g.gobject_id AS instance_gobject_id, t.gobject_id AS template_gobject_id,
@@ -244,5 +306,62 @@ SELECT
 FROM ranked r
 LEFT JOIN data_type dt ON dt.mx_data_type = r.mx_data_type
 WHERE r.rn = 1
+ORDER BY r.tag_name, r.attribute_name";
+
+    // Alarm-only discovery for the subtag-fallback watch-list. This reuses the candidate/ranked
+    // CTE shape and the same `AlarmExtension`-based detection as AttributesSql. Unlike
+    // AttributesSql it keeps only the user-attribute (dynamic_attribute) candidate branch: an
+    // alarm anchor is always a user attribute, so the primitive-instance branch AttributesSql
+    // carries would be filtered out here anyway — a row qualifies only when its user attribute
+    // anchors an `AlarmExtension` primitive on the owning object. It projects just what the
+    // watch-list needs — full_tag_reference (tag_name +
+    // '.' + attribute_name, matching AttributesSql) and the owning object's tag_name as
+    // source_object_reference. The array `[]` suffix is intentionally omitted: an
+    // alarm-bearing attribute is a scalar anchor, not an array body. It also projects the
+    // owning object's real Galaxy area (via gobject.area_gobject_id) as area_name so the
+    // watch-list resolver composes a reference whose group matches the native alarmmgr.
+    private const string AlarmAttributesSql = @"
+;WITH deployed_package_chain AS (
+    SELECT g.gobject_id, p.package_id, p.derived_from_package_id, 0 AS depth
+    FROM gobject g
+    INNER JOIN package p ON p.package_id = g.deployed_package_id
+    WHERE g.is_template = 0 AND g.deployed_package_id <> 0
+    UNION ALL
+    SELECT dpc.gobject_id, p.package_id, p.derived_from_package_id, dpc.depth + 1
+    FROM deployed_package_chain dpc
+    INNER JOIN package p ON p.package_id = dpc.derived_from_package_id
+    WHERE dpc.derived_from_package_id <> 0 AND dpc.depth < 10
+),
+candidate AS (
+    SELECT
+        dpc.gobject_id, g.tag_name, da.attribute_name, dpc.depth
+    FROM deployed_package_chain dpc
+    INNER JOIN dynamic_attribute da ON da.package_id = dpc.package_id
+    INNER JOIN gobject g ON g.gobject_id = dpc.gobject_id
+    INNER JOIN template_definition td ON td.template_definition_id = g.template_definition_id
+    WHERE td.category_id IN (1, 3, 4, 10, 11, 13, 17, 24, 26)
+        AND da.attribute_name NOT LIKE '[_]%'
+        AND da.attribute_name NOT LIKE '%.Description'
+        AND da.mx_attribute_category IN (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 24)
+),
+ranked AS (
+    SELECT c.*, ROW_NUMBER() OVER (
+        PARTITION BY c.gobject_id, c.attribute_name ORDER BY c.depth) AS rn
+    FROM candidate c
+)
+SELECT
+    r.tag_name + '.' + r.attribute_name AS full_tag_reference,
+    r.tag_name AS source_object_reference,
+    ISNULL(area.tag_name, '') AS area_name
+FROM ranked r
+INNER JOIN gobject g ON g.gobject_id = r.gobject_id
+LEFT JOIN gobject area ON area.gobject_id = g.area_gobject_id
+WHERE r.rn = 1
+    AND EXISTS (
+        SELECT 1 FROM deployed_package_chain dpc2
+        INNER JOIN primitive_instance pi ON pi.package_id = dpc2.package_id AND pi.primitive_name = r.attribute_name
+        INNER JOIN primitive_definition pd ON pd.primitive_definition_id = pi.primitive_definition_id AND pd.primitive_name = 'AlarmExtension'
+        WHERE dpc2.gobject_id = r.gobject_id
+    )
 ORDER BY r.tag_name, r.attribute_name";
 }

src/ZB.MOM.WW.MxGateway.Server/Galaxy/IGalaxyHierarchyCache.cs

@@ -13,7 +13,6 @@ public interface IGalaxyHierarchyCache
     ///     refresh.
     /// </summary>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     Task RefreshAsync(CancellationToken cancellationToken);
 
     /// <summary>
@@ -22,6 +21,5 @@ public interface IGalaxyHierarchyCache
     ///     very first request after gateway start.
     /// </summary>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     Task WaitForFirstLoadAsync(CancellationToken cancellationToken);
 }

src/ZB.MOM.WW.MxGateway.Server/Galaxy/IGalaxyHierarchySnapshotStore.cs

@@ -13,7 +13,6 @@ public interface IGalaxyHierarchySnapshotStore
     /// </summary>
     /// <param name="snapshot">The browse dataset to persist.</param>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that represents the asynchronous save operation.</returns>
     Task SaveAsync(GalaxyHierarchySnapshot snapshot, CancellationToken cancellationToken);
 
     /// <summary>

src/ZB.MOM.WW.MxGateway.Server/Galaxy/IGalaxyRepository.cs

@@ -14,21 +14,25 @@ public interface IGalaxyRepository
 {
     /// <summary>Tests the connection to the Galaxy Repository database.</summary>
     /// <param name="ct">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to <see langword="true"/> if the connection succeeds; otherwise <see langword="false"/>.</returns>
     Task<bool> TestConnectionAsync(CancellationToken ct = default);
 
     /// <summary>Retrieves the last deployment time from the Galaxy Repository.</summary>
     /// <param name="ct">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to the last deploy time, or <see langword="null"/> if not available.</returns>
     Task<DateTime?> GetLastDeployTimeAsync(CancellationToken ct = default);
 
     /// <summary>Retrieves the complete hierarchy of Galaxy objects from the repository.</summary>
     /// <param name="ct">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to the list of hierarchy rows.</returns>
     Task<List<GalaxyHierarchyRow>> GetHierarchyAsync(CancellationToken ct = default);
 
     /// <summary>Retrieves all attributes for Galaxy objects from the repository.</summary>
     /// <param name="ct">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to the list of attribute rows.</returns>
     Task<List<GalaxyAttributeRow>> GetAttributesAsync(CancellationToken ct = default);
+
+    /// <summary>
+    ///     Retrieves only the alarm-bearing attributes (those whose owning object
+    ///     configures an <c>AlarmExtension</c> primitive) for building the
+    ///     subtag-fallback watch-list.
+    /// </summary>
+    /// <param name="ct">Token to cancel the asynchronous operation.</param>
+    Task<List<GalaxyAlarmAttributeRow>> GetAlarmAttributesAsync(CancellationToken ct = default);
 }

src/ZB.MOM.WW.MxGateway.Server/Grpc/EventStreamService.cs

@@ -18,7 +18,12 @@ public sealed class EventStreamService(
     IDashboardEventBroadcaster dashboardEventBroadcaster,
     ILogger<EventStreamService> logger) : IEventStreamService
 {
-    /// <inheritdoc />
+    /// <summary>
+    /// Streams events from a session to the client asynchronously.
+    /// </summary>
+    /// <param name="request">Stream events request.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Async enumerable of MX events.</returns>
     public async IAsyncEnumerable<MxEvent> StreamEventsAsync(
         StreamEventsRequest request,
         [EnumeratorCancellation] CancellationToken cancellationToken)

src/ZB.MOM.WW.MxGateway.Server/Grpc/GalaxyProtoMapper.cs

@@ -13,7 +13,6 @@ public static class GalaxyProtoMapper
     /// <summary>Maps Galaxy hierarchy and attribute rows to Galaxy object protos.</summary>
     /// <param name="hierarchy">Hierarchy rows from Galaxy Repository.</param>
     /// <param name="attributes">Attribute rows from Galaxy Repository.</param>
-    /// <returns>An enumerable of mapped Galaxy object protos.</returns>
     public static IEnumerable<GalaxyObject> MapHierarchy(
         IReadOnlyList<GalaxyHierarchyRow> hierarchy,
         IReadOnlyList<GalaxyAttributeRow> attributes)
@@ -31,7 +30,6 @@ public static class GalaxyProtoMapper
     /// <summary>Maps a Galaxy hierarchy row to a Galaxy object proto.</summary>
     /// <param name="row">Hierarchy row from Galaxy Repository.</param>
     /// <param name="attributesByGobjectId">Attributes indexed by gobject ID.</param>
-    /// <returns>The mapped Galaxy object proto.</returns>
     public static GalaxyObject MapObject(
         GalaxyHierarchyRow row,
         IReadOnlyDictionary<int, List<GalaxyAttributeRow>> attributesByGobjectId)
@@ -62,7 +60,6 @@ public static class GalaxyProtoMapper
 
     /// <summary>Maps a Galaxy attribute row to a Galaxy attribute proto.</summary>
     /// <param name="row">Attribute row from Galaxy Repository.</param>
-    /// <returns>The mapped Galaxy attribute proto.</returns>
     public static GalaxyAttribute MapAttribute(GalaxyAttributeRow row) => new()
     {
         AttributeName = row.AttributeName,

src/ZB.MOM.WW.MxGateway.Server/Grpc/IEventStreamService.cs

@@ -12,7 +12,6 @@ public interface IEventStreamService
     /// </summary>
     /// <param name="request">Request payload.</param>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>An async enumerable of MXAccess events.</returns>
     IAsyncEnumerable<MxEvent> StreamEventsAsync(
         StreamEventsRequest request,
         CancellationToken cancellationToken);

src/ZB.MOM.WW.MxGateway.Server/Grpc/MxAccessGatewayService.cs

@@ -162,6 +162,15 @@ public sealed class MxAccessGatewayService(
     }
 
     /// <inheritdoc />
+    /// <remarks>
+    ///     Surfaces the public AcknowledgeAlarm RPC. Acknowledgement is
+    ///     session-less: the gateway routes it through the always-on
+    ///     <see cref="IGatewayAlarmService"/> monitor session. An
+    ///     <c>alarm_full_reference</c> that parses as a canonical GUID forwards
+    ///     to <c>AcknowledgeAlarmCommand</c>; a <c>Provider!Group.Tag</c>
+    ///     reference forwards to <c>AcknowledgeAlarmByNameCommand</c>; anything
+    ///     else returns an <c>InvalidRequest</c> diagnostic in the reply.
+    /// </remarks>
     public override async Task<AcknowledgeAlarmReply> AcknowledgeAlarm(
         AcknowledgeAlarmRequest request,
         ServerCallContext context)
@@ -184,6 +193,14 @@ public sealed class MxAccessGatewayService(
     }
 
     /// <inheritdoc />
+    /// <remarks>
+    ///     Surfaces the public StreamAlarms RPC — the session-less central
+    ///     alarm feed. The stream opens with one <c>active_alarm</c> per
+    ///     currently-active alarm, then a single <c>snapshot_complete</c>, then
+    ///     a <c>transition</c> for every subsequent change. Served by the
+    ///     gateway's always-on <see cref="IGatewayAlarmService"/> monitor; any
+    ///     number of clients fan out from the single monitor.
+    /// </remarks>
     public override async Task StreamAlarms(
         StreamAlarmsRequest request,
         IServerStreamWriter<AlarmFeedMessage> responseStream,
@@ -207,6 +224,12 @@ public sealed class MxAccessGatewayService(
     }
 
     /// <inheritdoc />
+    /// <remarks>
+    ///     Snapshot of the active-alarm cache maintained by the gateway's
+    ///     always-on alarm monitor. Streams one <see cref="ActiveAlarmSnapshot"/>
+    ///     per currently-active alarm and completes — no transitions are
+    ///     emitted. Use <c>StreamAlarms</c> for a live transition feed.
+    /// </remarks>
     public override async Task QueryActiveAlarms(
         QueryActiveAlarmsRequest request,
         IServerStreamWriter<ActiveAlarmSnapshot> responseStream,

src/ZB.MOM.WW.MxGateway.Server/Grpc/MxAccessGrpcMapper.cs

@@ -23,7 +23,6 @@ public sealed class MxAccessGrpcMapper
     /// Maps a gRPC MX command request to a worker command.
     /// </summary>
     /// <param name="request">Request payload.</param>
-    /// <returns>The mapped worker command.</returns>
     public WorkerCommand MapCommand(MxCommandRequest request)
     {
         ArgumentNullException.ThrowIfNull(request);
@@ -40,7 +39,6 @@ public sealed class MxAccessGrpcMapper
     /// Maps a worker command reply to a gRPC MX command reply.
     /// </summary>
     /// <param name="reply">Worker command reply.</param>
-    /// <returns>The mapped gRPC command reply.</returns>
     public MxCommandReply MapCommandReply(WorkerCommandReply reply)
     {
         ArgumentNullException.ThrowIfNull(reply);
@@ -60,7 +58,6 @@ public sealed class MxAccessGrpcMapper
     /// Maps a worker event to a gRPC MX event.
     /// </summary>
     /// <param name="workerEvent">Worker event to map.</param>
-    /// <returns>The mapped gRPC MX event.</returns>
     public MxEvent MapEvent(WorkerEvent workerEvent)
     {
         ArgumentNullException.ThrowIfNull(workerEvent);
@@ -76,7 +73,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates an OK protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.Ok"/>.</returns>
     public static ProtocolStatus Ok(string message = "OK")
     {
         return new ProtocolStatus
@@ -90,7 +86,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates an InvalidRequest protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.InvalidRequest"/>.</returns>
     public static ProtocolStatus InvalidRequest(string message)
     {
         return new ProtocolStatus
@@ -104,7 +99,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates a SessionNotFound protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.SessionNotFound"/>.</returns>
     public static ProtocolStatus SessionNotFound(string message)
     {
         return new ProtocolStatus
@@ -118,7 +112,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates a SessionNotReady protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.SessionNotReady"/>.</returns>
     public static ProtocolStatus SessionNotReady(string message)
     {
         return new ProtocolStatus
@@ -132,7 +125,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates a WorkerUnavailable protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.WorkerUnavailable"/>.</returns>
     public static ProtocolStatus WorkerUnavailable(string message)
     {
         return new ProtocolStatus
@@ -146,7 +138,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates a Timeout protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.Timeout"/>.</returns>
     public static ProtocolStatus Timeout(string message)
     {
         return new ProtocolStatus
@@ -160,7 +151,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates a Canceled protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.Canceled"/>.</returns>
     public static ProtocolStatus Canceled(string message)
     {
         return new ProtocolStatus
@@ -174,7 +164,6 @@ public sealed class MxAccessGrpcMapper
     /// Creates a ProtocolViolation protocol status.
     /// </summary>
     /// <param name="message">Status message.</param>
-    /// <returns>A <see cref="ProtocolStatus"/> with code <see cref="ProtocolStatusCode.ProtocolViolation"/>.</returns>
     public static ProtocolStatus ProtocolViolation(string message)
     {
         return new ProtocolStatus

src/ZB.MOM.WW.MxGateway.Server/Metrics/AlarmProviderSwitchReason.cs

@@ -0,0 +1,20 @@
+namespace ZB.MOM.WW.MxGateway.Server.Metrics;
+
+/// <summary>
+///     Bounded classification of an alarm-provider switch, used as the low-cardinality
+///     <c>reason</c> tag on the <c>mxgateway.alarms.provider_switches</c> counter. The
+///     worker supplies a free-text reason (e.g. <c>"primary PollOnce failed"</c>) that
+///     stays in the structured log; only this bounded value reaches the metric tag so the
+///     time series cannot fan out on operation-specific text.
+/// </summary>
+public enum AlarmProviderSwitchReason
+{
+    /// <summary>The switch direction could not be classified.</summary>
+    Unknown = 0,
+
+    /// <summary>Switched from the primary (alarmmgr) provider to the subtag standby — degraded.</summary>
+    Failover = 1,
+
+    /// <summary>Switched back from the subtag standby to the primary (alarmmgr) provider — recovered.</summary>
+    Failback = 2,
+}

src/ZB.MOM.WW.MxGateway.Server/Metrics/GatewayMetrics.cs

@@ -1,5 +1,6 @@
 using System.Collections.Concurrent;
 using System.Diagnostics.Metrics;
+using System.Globalization;
 
 namespace ZB.MOM.WW.MxGateway.Server.Metrics;
 
@@ -22,6 +23,7 @@ public sealed class GatewayMetrics : IDisposable
     private readonly Counter<long> _heartbeatFailuresCounter;
     private readonly Counter<long> _streamDisconnectsCounter;
     private readonly Counter<long> _retryAttemptsCounter;
+    private readonly Counter<long> _alarmProviderSwitchesCounter;
     private readonly Histogram<double> _workerStartupLatencyHistogram;
     private readonly Histogram<double> _commandLatencyHistogram;
     private readonly Histogram<double> _eventStreamSendLatencyHistogram;
@@ -34,6 +36,7 @@ public sealed class GatewayMetrics : IDisposable
     private int _workersRunning;
     private int _workerEventQueueDepth;
     private int _grpcEventStreamQueueDepth;
+    private int _alarmProviderMode;
     private long _sessionsOpened;
     private long _sessionsClosed;
     private long _commandsStarted;
@@ -47,6 +50,7 @@ public sealed class GatewayMetrics : IDisposable
     private long _heartbeatFailures;
     private long _streamDisconnects;
     private long _retryAttempts;
+    private long _alarmProviderSwitches;
     private bool _disposed;
 
     /// <summary>
@@ -68,6 +72,7 @@ public sealed class GatewayMetrics : IDisposable
         _heartbeatFailuresCounter = _meter.CreateCounter<long>("mxgateway.heartbeats.failed");
         _streamDisconnectsCounter = _meter.CreateCounter<long>("mxgateway.grpc.streams.disconnected");
         _retryAttemptsCounter = _meter.CreateCounter<long>("mxgateway.retries.attempted");
+        _alarmProviderSwitchesCounter = _meter.CreateCounter<long>("mxgateway.alarms.provider_switches");
         _workerStartupLatencyHistogram = _meter.CreateHistogram<double>("mxgateway.workers.startup.duration", "s");
         _commandLatencyHistogram = _meter.CreateHistogram<double>("mxgateway.commands.duration", "s");
         _eventStreamSendLatencyHistogram = _meter.CreateHistogram<double>("mxgateway.events.stream_send.duration", "s");
@@ -76,6 +81,7 @@ public sealed class GatewayMetrics : IDisposable
         _meter.CreateObservableGauge("mxgateway.workers.running", GetWorkersRunning);
         _meter.CreateObservableGauge("mxgateway.events.worker_queue.depth", GetWorkerEventQueueDepth);
         _meter.CreateObservableGauge("mxgateway.events.grpc_stream_queue.depth", GetGrpcEventStreamQueueDepth);
+        _meter.CreateObservableGauge("mxgateway.alarms.provider_mode", GetAlarmProviderMode);
     }
 
     /// <summary>
@@ -377,10 +383,44 @@ public sealed class GatewayMetrics : IDisposable
         _retryAttemptsCounter.Add(1, new KeyValuePair<string, object?>("area", area));
     }
 
+    /// <summary>
+    /// Records that the alarm provider switched modes, increments the switch count, and updates the
+    /// current provider mode gauge.
+    /// </summary>
+    /// <param name="fromMode">Provider mode before the switch (1=alarmmgr, 2=subtag, 0=unknown).</param>
+    /// <param name="toMode">Provider mode after the switch (1=alarmmgr, 2=subtag, 0=unknown).</param>
+    /// <param name="reason">Bounded switch classification used as the counter's <c>reason</c> tag.</param>
+    public void AlarmProviderSwitched(int fromMode, int toMode, AlarmProviderSwitchReason reason)
+    {
+        lock (_syncRoot)
+        {
+            _alarmProviderMode = toMode;
+            _alarmProviderSwitches++;
+        }
+
+        _alarmProviderSwitchesCounter.Add(
+            1,
+            new KeyValuePair<string, object?>("from", fromMode.ToString(CultureInfo.InvariantCulture)),
+            new KeyValuePair<string, object?>("to", toMode.ToString(CultureInfo.InvariantCulture)),
+            new KeyValuePair<string, object?>("reason", ReasonTag(reason)));
+    }
+
+    private static string ReasonTag(AlarmProviderSwitchReason reason) => reason switch
+    {
+        AlarmProviderSwitchReason.Failover => "failover",
+        AlarmProviderSwitchReason.Failback => "failback",
+        _ => "unknown",
+    };
+
+    /// <summary>Sets the current alarm provider-mode gauge without recording a switch (e.g. startup baseline).</summary>
+    public void SetAlarmProviderMode(int mode)
+    {
+        lock (_syncRoot) { _alarmProviderMode = mode; }
+    }
+
     /// <summary>
     /// Returns a snapshot of all current metric values.
     /// </summary>
-    /// <returns>A consistent snapshot of the current metric counters and gauges.</returns>
     public GatewayMetricsSnapshot GetSnapshot()
     {
         lock (_syncRoot)
@@ -403,6 +443,7 @@ public sealed class GatewayMetrics : IDisposable
                 HeartbeatFailures: _heartbeatFailures,
                 StreamDisconnects: _streamDisconnects,
                 RetryAttempts: _retryAttempts,
+                AlarmProviderSwitchCount: _alarmProviderSwitches,
                 CommandFailuresByMethod: new Dictionary<string, long>(_commandFailuresByMethod, StringComparer.OrdinalIgnoreCase),
                 EventsByFamily: new Dictionary<string, long>(_eventsByFamily, StringComparer.OrdinalIgnoreCase),
                 EventsBySession: new Dictionary<string, long>(_eventsBySession, StringComparer.Ordinal),
@@ -456,6 +497,14 @@ public sealed class GatewayMetrics : IDisposable
         }
     }
 
+    private int GetAlarmProviderMode()
+    {
+        lock (_syncRoot)
+        {
+            return _alarmProviderMode;
+        }
+    }
+
     private static void Increment(Dictionary<string, long> values, string key)
     {
         values.TryGetValue(key, out long currentValue);

src/ZB.MOM.WW.MxGateway.Server/Metrics/GatewayMetricsSnapshot.cs

@@ -18,6 +18,7 @@ public sealed record GatewayMetricsSnapshot(
     long HeartbeatFailures,
     long StreamDisconnects,
     long RetryAttempts,
+    long AlarmProviderSwitchCount,
     IReadOnlyDictionary<string, long> CommandFailuresByMethod,
     IReadOnlyDictionary<string, long> EventsByFamily,
     IReadOnlyDictionary<string, long> EventsBySession,

src/ZB.MOM.WW.MxGateway.Server/Security/Audit/CanonicalAuditWriter.cs

@@ -19,10 +19,7 @@ public sealed class CanonicalAuditWriter(
     SqliteCanonicalAuditStore store,
     ILogger<CanonicalAuditWriter> logger) : IAuditWriter
 {
-    /// <summary>Persists the audit event to the canonical store; swallows and logs any write failure rather than propagating it.</summary>
+    /// <inheritdoc />
-    /// <param name="auditEvent">The audit event to persist.</param>
-    /// <param name="cancellationToken">Token to observe for cancellation.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task WriteAsync(AuditEvent auditEvent, CancellationToken cancellationToken = default)
     {
         ArgumentNullException.ThrowIfNull(auditEvent);

src/ZB.MOM.WW.MxGateway.Server/Security/Audit/CanonicalForwardingApiKeyAuditStore.cs

@@ -43,10 +43,7 @@ public sealed class CanonicalForwardingApiKeyAuditStore(
     /// <summary>The library's keyless schema-init event type.</summary>
     private const string InitDbEventType = "init-db";
 
-    /// <summary>Converts the library audit entry to a canonical <see cref="AuditEvent"/> and forwards it through the gateway's audit writer.</summary>
+    /// <inheritdoc />
-    /// <param name="entry">The API key audit entry to append.</param>
-    /// <param name="ct">Token to observe for cancellation.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task AppendAsync(ApiKeyAuditEntry entry, CancellationToken ct)
     {
         ArgumentNullException.ThrowIfNull(entry);
@@ -74,10 +71,7 @@ public sealed class CanonicalForwardingApiKeyAuditStore(
         await auditWriter.WriteAsync(auditEvent, ct).ConfigureAwait(false);
     }
 
-    /// <summary>Reads recent audit events from the canonical store and maps them back to library-compatible <see cref="ApiKeyAuditEntry"/> records.</summary>
+    /// <inheritdoc />
-    /// <param name="limit">Maximum number of entries to return.</param>
-    /// <param name="ct">Token to observe for cancellation.</param>
-    /// <returns>A task that resolves to the most recent audit entries, up to <paramref name="limit"/> items.</returns>
     public async Task<IReadOnlyList<ApiKeyAuditEntry>> ListRecentAsync(int limit, CancellationToken ct)
     {
         IReadOnlyList<AuditEvent> events = await store.ListRecentAsync(limit, ct).ConfigureAwait(false);

src/ZB.MOM.WW.MxGateway.Server/Security/Audit/SqliteCanonicalAuditStore.cs

@@ -43,7 +43,6 @@ public sealed class SqliteCanonicalAuditStore(AuthSqliteConnectionFactory connec
     /// <summary>Inserts a canonical audit event into the <c>audit_event</c> table.</summary>
     /// <param name="auditEvent">The canonical event to persist.</param>
     /// <param name="cancellationToken">Token to observe for cancellation.</param>
-    /// <returns>A task that represents the asynchronous operation.</returns>
     public async Task InsertAsync(AuditEvent auditEvent, CancellationToken cancellationToken)
     {
         ArgumentNullException.ThrowIfNull(auditEvent);
@@ -80,7 +79,6 @@ public sealed class SqliteCanonicalAuditStore(AuthSqliteConnectionFactory connec
     /// <summary>Returns the most recent canonical audit events, newest first.</summary>
     /// <param name="limit">Maximum number of events to return.</param>
     /// <param name="cancellationToken">Token to observe for cancellation.</param>
-    /// <returns>A task that resolves to the most recent audit events, up to <paramref name="limit"/>.</returns>
     public async Task<IReadOnlyList<AuditEvent>> ListRecentAsync(int limit, CancellationToken cancellationToken)
     {
         if (limit <= 0)

src/ZB.MOM.WW.MxGateway.Server/Security/Authentication/ApiKeyAdminCliRunner.cs

@@ -26,7 +26,6 @@ public sealed class ApiKeyAdminCliRunner(ApiKeyAdminCommands commands)
     /// <param name="command">API key administration command to execute.</param>
     /// <param name="output">Text writer for command output.</param>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>A task that resolves to the exit code (always 0 on success).</returns>
     public async Task<int> RunAsync(
         ApiKeyAdminCommand command,
         TextWriter output,

src/ZB.MOM.WW.MxGateway.Server/Security/Authentication/ApiKeyAdminParseResult.cs

@@ -6,7 +6,6 @@ public sealed record ApiKeyAdminParseResult(
     string? Error)
 {
     /// <summary>Returns a result indicating the input was not an API key command.</summary>
-    /// <returns>A parse result with <see cref="IsApiKeyCommand"/> set to false.</returns>
     public static ApiKeyAdminParseResult NotApiKeyCommand()
     {
         return new ApiKeyAdminParseResult(false, null, null);
@@ -14,7 +13,6 @@ public sealed record ApiKeyAdminParseResult(
 
     /// <summary>Returns a successful parse result with the parsed API key command.</summary>
     /// <param name="command">Parsed API key administration command.</param>
-    /// <returns>A parse result with <see cref="IsApiKeyCommand"/> set to true and the command populated.</returns>
     public static ApiKeyAdminParseResult Success(ApiKeyAdminCommand command)
     {
         return new ApiKeyAdminParseResult(true, command, null);
@@ -22,7 +20,6 @@ public sealed record ApiKeyAdminParseResult(
 
     /// <summary>Returns a parse result with the specified error message.</summary>
     /// <param name="error">Error message describing the parse failure.</param>
-    /// <returns>A parse result with <see cref="IsApiKeyCommand"/> set to true and the error message populated.</returns>
     public static ApiKeyAdminParseResult Fail(string error)
     {
         return new ApiKeyAdminParseResult(true, null, error);

src/ZB.MOM.WW.MxGateway.Server/Security/Authentication/ApiKeyConstraintSerializer.cs

@@ -12,7 +12,6 @@ public static class ApiKeyConstraintSerializer
 
     /// <summary>Serializes API key constraints to JSON, or returns null if the constraints are empty.</summary>
     /// <param name="constraints">The constraints to serialize.</param>
-    /// <returns>A JSON string representing the constraints, or <see langword="null"/> if empty.</returns>
     public static string? Serialize(ApiKeyConstraints constraints)
     {
         ArgumentNullException.ThrowIfNull(constraints);
@@ -21,7 +20,6 @@ public static class ApiKeyConstraintSerializer
 
     /// <summary>Deserializes API key constraints from JSON, or returns empty constraints if JSON is null or whitespace.</summary>
     /// <param name="json">The JSON string to deserialize.</param>
-    /// <returns>The deserialized <see cref="ApiKeyConstraints"/>, or <see cref="ApiKeyConstraints.Empty"/> when <paramref name="json"/> is null or whitespace.</returns>
     public static ApiKeyConstraints Deserialize(string? json)
     {
         if (string.IsNullOrWhiteSpace(json))

src/ZB.MOM.WW.MxGateway.Server/Security/Authorization/ConstraintEnforcer.cs

@@ -16,7 +16,10 @@ public sealed class ConstraintEnforcer(
     IGalaxyHierarchyCache cache,
     IAuditWriter auditWriter) : IConstraintEnforcer
 {
-    /// <inheritdoc />
+    /// <summary>Checks read constraints on a tag address.</summary>
+    /// <param name="identity">The API key identity to check constraints for.</param>
+    /// <param name="tagAddress">Tag address to validate.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public Task<ConstraintFailure?> CheckReadTagAsync(
         ApiKeyIdentity? identity,
         string tagAddress,
@@ -31,7 +34,12 @@ public sealed class ConstraintEnforcer(
         return Task.FromResult(CheckReadTarget(constraints, tagAddress));
     }
 
-    /// <inheritdoc />
+    /// <summary>Checks read constraints on a server and item handle.</summary>
+    /// <param name="identity">The API key identity to check constraints for.</param>
+    /// <param name="session">The gateway session containing handle registrations.</param>
+    /// <param name="serverHandle">The MXAccess server handle.</param>
+    /// <param name="itemHandle">The MXAccess item handle.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public Task<ConstraintFailure?> CheckReadHandleAsync(
         ApiKeyIdentity? identity,
         GatewaySession session,
@@ -53,7 +61,12 @@ public sealed class ConstraintEnforcer(
         return Task.FromResult(CheckReadTarget(constraints, registration.TagAddress));
     }
 
-    /// <inheritdoc />
+    /// <summary>Checks write constraints on a server and item handle.</summary>
+    /// <param name="identity">The API key identity to check constraints for.</param>
+    /// <param name="session">The gateway session containing handle registrations.</param>
+    /// <param name="serverHandle">The MXAccess server handle.</param>
+    /// <param name="itemHandle">The MXAccess item handle.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public Task<ConstraintFailure?> CheckWriteHandleAsync(
         ApiKeyIdentity? identity,
         GatewaySession session,
@@ -102,7 +115,12 @@ public sealed class ConstraintEnforcer(
         return Task.FromResult<ConstraintFailure?>(null);
     }
 
-    /// <inheritdoc />
+    /// <summary>Records a constraint denial audit entry.</summary>
+    /// <param name="identity">The API key identity that was denied.</param>
+    /// <param name="commandKind">The command type (e.g., read, write).</param>
+    /// <param name="target">The target being accessed (tag address or handle).</param>
+    /// <param name="failure">The constraint failure details.</param>
+    /// <param name="cancellationToken">Token to observe for cancellation.</param>
     public async Task RecordDenialAsync(
         ApiKeyIdentity? identity,
         string commandKind,