fix(client-shared): resolve Low code-review findings (Client.Shared-003,004,009,010,011)

- Client.Shared-003: DefaultSessionAdapter.WriteValueAsync / CallMethodAsync
  guard against null/empty Results and throw ServiceResultException with
  the response's ServiceResult code instead of indexing into a missing
  list.
- Client.Shared-004: DefaultSessionAdapter.CloseAsync / HistoryReadRawAsync
  / HistoryReadAggregateAsync use the Session.*Async overloads and honour
  the caller's CancellationToken.
- Client.Shared-009: AcknowledgeAlarmAsync returns the underlying
  ServiceResultException.StatusCode on failure instead of always Good;
  IOpcUaClientService doc updated to describe the new contract.
- Client.Shared-010: ConnectionSettings.CertificateStorePath defaults to
  empty; DefaultApplicationConfigurationFactory resolves the canonical
  PKI path lazily, so per-failover ConnectionSettings copies don't hit
  the filesystem.
- Client.Shared-011: added the alarm-fallback regression test, extracted
  EndpointSelector as a pure static, and added EndpointSelectorTests
  covering security-mode match, Basic256Sha256 preference, fallback,
  diagnostics, hostname rewrite, and null/empty guards.

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

src/Client/ZB.MOM.WW.OtOpcUa.Client.Shared/Adapters/DefaultSessionAdapter.cs

@@ -73,6 +73,17 @@ internal sealed class DefaultSessionAdapter : ISessionAdapter
 
         var writeCollection = new WriteValueCollection { writeValue };
         var response = await _session.WriteAsync(null, writeCollection, ct);
+        // A malformed or service-level-faulted response can come back with an empty
+        // Results collection alongside a service fault. Surface the service result
+        // (or BadUnexpectedError) rather than letting Results[0] throw
+        // IndexOutOfRangeException upstream.
+        if (response.Results == null || response.Results.Count == 0)
+        {
+            var serviceResult = response.ResponseHeader?.ServiceResult.Code ?? StatusCodes.BadUnexpectedError;
+            throw new ServiceResultException(serviceResult,
+                $"Write response contained no results for node {nodeId}.");
+        }
+
         return response.Results[0];
     }
 
@@ -143,15 +154,18 @@ internal sealed class DefaultSessionAdapter : ISessionAdapter
             if (continuationPoint != null)
                 nodesToRead[0].ContinuationPoint = continuationPoint;
 
-            _session.HistoryRead(
+            // Use the async overload so this method is genuinely asynchronous,
+            // honors the cancellation token, and does not block the caller's thread
+            // (which would block the UI dispatcher for client.ui consumers).
+            var response = await _session.HistoryReadAsync(
                 null,
                 new ExtensionObject(details),
                 TimestampsToReturn.Source,
                 continuationPoint != null,
                 nodesToRead,
-                out var results,
-                out _);
+                ct).ConfigureAwait(false);
 
+            var results = response.Results;
             if (results == null || results.Count == 0)
                 break;
 
@@ -186,15 +200,17 @@ internal sealed class DefaultSessionAdapter : ISessionAdapter
             new HistoryReadValueId { NodeId = nodeId }
         };
 
-        _session.HistoryRead(
+        // Use the async overload so the method honors the cancellation token and
+        // does not block on a synchronous service round-trip.
+        var response = await _session.HistoryReadAsync(
             null,
             new ExtensionObject(details),
             TimestampsToReturn.Source,
             false,
             nodesToRead,
-            out var results,
-            out _);
+            ct).ConfigureAwait(false);
 
+        var results = response.Results;
         var allValues = new List<DataValue>();
 
         if (results != null && results.Count > 0)
@@ -229,7 +245,9 @@ internal sealed class DefaultSessionAdapter : ISessionAdapter
     {
         try
         {
-            if (_session.Connected) _session.Close();
+            // Use the async overload so the caller does not block on the close
+            // service round-trip and the cancellation token is honored.
+            if (_session.Connected) await _session.CloseAsync(ct).ConfigureAwait(false);
         }
         catch (Exception ex)
         {
@@ -270,6 +288,15 @@ internal sealed class DefaultSessionAdapter : ISessionAdapter
             },
             ct);
 
+        // An empty Results collection paired with a service fault must surface as
+        // a ServiceResultException, not an IndexOutOfRangeException from Results[0].
+        if (result.Results == null || result.Results.Count == 0)
+        {
+            var serviceResult = result.ResponseHeader?.ServiceResult.Code ?? StatusCodes.BadUnexpectedError;
+            throw new ServiceResultException(serviceResult,
+                $"Call response contained no results for method {methodId} on {objectId}.");
+        }
+
         var callResult = result.Results[0];
         if (StatusCode.IsBad(callResult.StatusCode))
             throw new ServiceResultException(callResult.StatusCode);