refactor(sessions): remove the dead ISessionManager.ReadEventsAsync chain

ISessionManager.ReadEventsAsync had zero production call sites: the worker
event channel is drained once by GatewaySession.MapWorkerEventsAsync (the
distributor pump), and every consumer — gRPC subscribers, the dashboard
mirror, the alarm monitor — attaches to the distributor. The interface
member, SessionManager's forwarder, and GatewaySession.ReadEventsAsync are
gone; IWorkerClient/WorkerClient.ReadEventsAsync is untouched, it is the
live worker-channel claim.

No test was removed or rewired: nothing invoked the member through the
interface. Nine ISessionManager test fakes carried a required-member stub
(seven threw NotSupportedException or yielded nothing; EventStreamServiceTests
and GatewaySessionDashboardMirrorTests forwarded to the session; the two
MxAccessGatewayService fakes yielded their Events list) — all nine stubs were
deleted. The MxAccessGatewayService suites' streaming tests already run
through FakeEventStreamService, which reads the same Events list, so their
coverage is unchanged; only the now-inaccurate doc comments on Events /
LastReadEventsSessionId were reworded.

The MapWorkerEventsAsync comment no longer describes a twin to keep in step;
it now states the single-reader claim directly. docs/Sessions.md drops
ReadEventsAsync from the SessionManager member list and from the Run-state
prose. The 2026-08-15 deferred-remediation as-built note records the removal.

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

@@ -765,13 +765,11 @@ public sealed class GatewaySession
     // distributor guarantees a single consumer) and maps each frame to the public MxEvent,
     // preserving worker order. Mirrors the former ProduceEventsAsync mapping exactly.
     //
-    // This deliberately duplicates the three lines of ReadEventsAsync rather than enumerating
-    // it: every worker event crosses this source, and routing it through a second pure
-    // pass-through iterator cost two extra MoveNextAsync state-machine hops per event for no
-    // semantic value. ReadEventsAsync stays for ISessionManager.ReadEventsAsync; keep the two
-    // bodies in step. Only one of them may run per attach — WorkerClient.ReadEventsAsync
-    // single-reader-claims the event channel and throws on a second consumer — and on the
-    // distributor path that one consumer is this method.
+    // This is the session's only reader of the worker event channel: every gateway consumer —
+    // gRPC subscribers, the dashboard mirror, the alarm monitor — attaches to the distributor
+    // this source feeds. WorkerClient.ReadEventsAsync single-reader-claims that channel and
+    // throws on a second consumer, so any future path that drains it directly fails loudly
+    // rather than splitting events.
     private async IAsyncEnumerable<MxEvent> MapWorkerEventsAsync(
         [EnumeratorCancellation] CancellationToken cancellationToken)
     {
@@ -1522,33 +1520,6 @@ public sealed class GatewaySession
             cancellationToken);
     }
 
-    /// <summary>
-    /// Reads events from the worker as an asynchronous enumerable stream.
-    /// </summary>
-    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <remarks>
-    ///     Backs <c>ISessionManager.ReadEventsAsync</c>. The distributor does <em>not</em> come
-    ///     through here — <c>MapWorkerEventsAsync</c> inlines this body to save a per-event
-    ///     iterator hop, so changes made here belong there too. The two are mutually exclusive
-    ///     per attach: <see cref="IWorkerClient.ReadEventsAsync"/> claims the worker event
-    ///     channel for a single reader and throws on the second consumer.
-    /// </remarks>
-    /// <returns>An asynchronous stream of worker events.</returns>
-    public async IAsyncEnumerable<WorkerEvent> ReadEventsAsync(
-        [EnumeratorCancellation] CancellationToken cancellationToken)
-    {
-        IWorkerClient workerClient = await GetReadyWorkerClientAsync(cancellationToken).ConfigureAwait(false);
-        TouchClientActivity(_eventStreaming.TimeProvider.GetUtcNow());
-
-        await foreach (WorkerEvent workerEvent in workerClient
-            .ReadEventsAsync(cancellationToken)
-            .WithCancellation(cancellationToken)
-            .ConfigureAwait(false))
-        {
-            yield return workerEvent;
-        }
-    }
-
     /// <summary>
     /// Closes the session and shuts down the worker process.
     /// </summary>

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

@@ -35,14 +35,6 @@ public interface ISessionManager
         WorkerCommand command,
         CancellationToken cancellationToken);
 
-    /// <summary>Reads events streamed from the worker for the specified session.</summary>
-    /// <param name="sessionId">Identifier of the session.</param>
-    /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
-    /// <returns>Events emitted by the worker.</returns>
-    IAsyncEnumerable<WorkerEvent> ReadEventsAsync(
-        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

@@ -187,16 +187,6 @@ public sealed class SessionManager : ISessionManager
         }
     }
 
-    /// <inheritdoc />
-    public IAsyncEnumerable<WorkerEvent> ReadEventsAsync(
-        string sessionId,
-        CancellationToken cancellationToken)
-    {
-        GatewaySession session = GetRequiredSession(sessionId);
-
-        return session.ReadEventsAsync(cancellationToken);
-    }
-
     /// <inheritdoc />
     public async Task<SessionCloseResult> CloseSessionAsync(
         string sessionId,