Merge branch 'fix/gwc-26-27-alarm-attach'

# Conflicts:
#	archreview/2026-07-12/remediation/00-tracking.md
#	archreview/2026-07-12/remediation/10-gateway-core.md

src/ZB.MOM.WW.MxGateway.Server/Sessions/GatewaySession.cs

@@ -548,10 +548,37 @@ public sealed class GatewaySession
     ///     <c>MaxEventSubscribersPerSession</c> accounting and out of the single-subscriber
     ///     overflow-fault path, so a slow alarm reconcile can never fault the session — it only
     ///     disconnects this internal subscriber.
+    ///     <para>
+    ///         Gated on readiness exactly like <see cref="AttachEventSubscriber"/>: attaching
+    ///         before the session and its worker are <c>Ready</c> throws
+    ///         <see cref="SessionManagerException"/> with
+    ///         <see cref="SessionManagerErrorCode.SessionNotReady"/>.
+    ///     </para>
     /// </remarks>
     /// <returns>The internal subscriber's lease; dispose it to unregister.</returns>
+    /// <exception cref="SessionManagerException">
+    ///     The session or its worker client is not <c>Ready</c>.
+    /// </exception>
     public IEventSubscriberLease AttachInternalEventSubscriber()
     {
+        // Readiness gate, mirroring AttachEventSubscriber (GWC-27). It must run BEFORE
+        // EnsureDistributorCreated: a premature attach would construct the distributor and start
+        // its pump against a not-yet-Ready worker, the pump source would throw SessionNotReady,
+        // PumpAsync would complete every subscriber with that error and latch _completed, and
+        // _eventDistributorStarted is never reset — so the session would reach Ready with
+        // permanently dead event streaming, silently, for the rest of its life. Failing loudly
+        // here keeps that state unreachable. The check is under _syncRoot and the distributor
+        // calls stay outside it, matching AttachEventSubscriber's lock discipline.
+        lock (_syncRoot)
+        {
+            if (_state != SessionState.Ready || _workerClient?.State != WorkerClientState.Ready)
+            {
+                throw new SessionManagerException(
+                    SessionManagerErrorCode.SessionNotReady,
+                    $"Session {SessionId} is not ready for event streaming. Current state is {_state}.");
+            }
+        }
+
         // Same sequence StartDashboardMirror uses: create the distributor (claiming the pump
         // start if we are first), register the internal subscriber BEFORE the pump starts so a
         // subscriber is always present at pump start, then start the pump if requested.

src/ZB.MOM.WW.MxGateway.Server/Sessions/ISessionManager.cs

@@ -43,18 +43,6 @@ public interface ISessionManager
         string sessionId,
         CancellationToken cancellationToken);
 
-    /// <summary>
-    ///     Reads mapped events for the central alarm monitor by attaching an internal
-    ///     (non-counted) distributor subscriber, so the alarm feed shares the one worker-event
-    ///     pump instead of opening a second raw drain of the single worker event channel.
-    /// </summary>
-    /// <param name="sessionId">Identifier of the session.</param>
-    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>The mapped <see cref="MxEvent"/>s fanned by the session's distributor.</returns>
-    IAsyncEnumerable<MxEvent> ReadAlarmEventsAsync(
-        string sessionId,
-        CancellationToken cancellationToken);
-
     /// <summary>Closes a session and terminates its worker process.</summary>
     /// <param name="sessionId">Identifier of the session to close.</param>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>

src/ZB.MOM.WW.MxGateway.Server/Sessions/SessionManager.cs

@@ -1,5 +1,4 @@
 using System.Diagnostics.CodeAnalysis;
-using System.Runtime.CompilerServices;
 using System.Security.Cryptography;
 using Google.Protobuf.WellKnownTypes;
 using Microsoft.Extensions.Logging;
@@ -191,22 +190,6 @@ public sealed class SessionManager : ISessionManager
         return session.ReadEventsAsync(cancellationToken);
     }
 
-    /// <inheritdoc />
-    public async IAsyncEnumerable<MxEvent> ReadAlarmEventsAsync(
-        string sessionId,
-        [EnumeratorCancellation] CancellationToken cancellationToken)
-    {
-        GatewaySession session = GetRequiredSession(sessionId);
-        using IEventSubscriberLease lease = session.AttachInternalEventSubscriber();
-
-        await foreach (MxEvent mxEvent in lease.Reader
-            .ReadAllAsync(cancellationToken)
-            .ConfigureAwait(false))
-        {
-            yield return mxEvent;
-        }
-    }
-
     /// <inheritdoc />
     public async Task<SessionCloseResult> CloseSessionAsync(
         string sessionId,