fix(historian-gateway): dispose alarm-write channel at shutdown + ServerHistorian startup diagnostic

Claude-Session: https://claude.ai/code/session_012SDSQ3AcaXqPcBtDESBRii

src/Core/ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian/SqliteStoreAndForwardSink.cs

@@ -732,12 +732,13 @@ public sealed class SqliteStoreAndForwardSink : IAlarmHistorianSink, IDisposable
     /// <summary>Gets the current exponential backoff delay for retry operations.</summary>
     public TimeSpan CurrentBackoff => BackoffLadder[_backoffIndex];
 
-    /// <summary>Disposes the sink and releases all held resources including the drain timer.</summary>
+    /// <summary>Disposes the sink and releases all held resources including the drain timer and the writer.</summary>
     public void Dispose()
     {
         if (_disposed) return;
         _disposed = true;
         _drainTimer?.Dispose();
         _drainGate.Dispose();
+        if (_writer is IDisposable writerDisposable) writerDisposable.Dispose();
     }
 }

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway/GatewayAlarmHistorianWriter.cs

@@ -36,7 +36,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway;
 ///         event forever.
 ///     </para>
 /// </remarks>
-public sealed class GatewayAlarmHistorianWriter : IAlarmHistorianWriter
+public sealed class GatewayAlarmHistorianWriter : IAlarmHistorianWriter, IDisposable
 {
     private readonly IHistorianGatewayClient _client;
     private readonly ILogger<GatewayAlarmHistorianWriter> _logger;
@@ -154,4 +154,11 @@ public sealed class GatewayAlarmHistorianWriter : IAlarmHistorianWriter
         // Unknown/unclassified gRPC code → dead-letter to avoid an infinite drain loop.
         _ => HistorianWriteOutcome.PermanentFail,
     };
+
+    /// <summary>
+    ///     Disposes the underlying gateway client and its gRPC channel. The concrete
+    ///     <see cref="HistorianGatewayClientAdapter"/> implements <see cref="IDisposable"/>; test doubles
+    ///     that only implement <see cref="IAsyncDisposable"/> are safely no-opped by the cast guard.
+    /// </summary>
+    public void Dispose() => (_client as IDisposable)?.Dispose();
 }

src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs

@@ -109,6 +109,8 @@ if (hasDriver)
     var serverHistorianOptions = builder.Configuration
         .GetSection(ServerHistorianOptions.SectionName).Get<ServerHistorianOptions>()
         ?? new ServerHistorianOptions();
+    foreach (var warning in serverHistorianOptions.Validate())
+        Log.Warning("ServerHistorian misconfiguration detected at startup: {Warning}", warning);
     builder.Services.AddAlarmHistorian(
         builder.Configuration,
         (_, sp) => GatewayHistorian.CreateAlarmWriter(serverHistorianOptions, sp));

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests/GatewayAlarmHistorianWriterTests.cs

@@ -199,4 +199,20 @@ public sealed class GatewayAlarmHistorianWriterTests
 
         Assert.Empty(outcomes);
     }
+
+    [Fact]
+    public void Dispose_with_async_only_client_does_not_throw()
+    {
+        // FakeHistorianGatewayClient implements IAsyncDisposable only — not IDisposable.
+        // The `as IDisposable` guard in GatewayAlarmHistorianWriter.Dispose() must safely
+        // no-op rather than throw when the client cannot be cast to IDisposable.
+        var fake = new FakeHistorianGatewayClient();
+        var writer = Writer(fake);
+
+        var ex = Record.Exception(() => ((IDisposable)writer).Dispose());
+
+        Assert.Null(ex);
+        // The Fake is IAsyncDisposable only; the sync Dispose must not call DisposeAsync.
+        Assert.Equal(0, fake.DisposeCallCount);
+    }
 }