fix(notifications): deterministic lowest-Id SMTP config selection (+ multi-row warning); atomic OAuth2 token cache entry

Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj

src/ZB.MOM.WW.ScadaBridge.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs

@@ -73,12 +73,22 @@ public sealed class EmailNotificationDeliveryAdapter : INotificationDeliveryAdap
         }
 
         var smtpConfigs = await _repository.GetAllSmtpConfigurationsAsync(cancellationToken);
-        var smtpConfig = smtpConfigs.FirstOrDefault();
+        // Deterministic pick: the lowest-Id row wins regardless of repository order,
+        // so every node/attempt agrees on the same configuration (arch-review S7).
+        var smtpConfig = smtpConfigs.OrderBy(c => c.Id).FirstOrDefault();
         if (smtpConfig == null)
         {
             return DeliveryOutcome.Permanent("No SMTP configuration available");
         }
 
+        if (smtpConfigs.Count > 1)
+        {
+            _logger.LogWarning(
+                "Multiple SMTP configurations exist; using the lowest-Id row ({Id}). "
+                + "Enforce a single row or delete extras.",
+                smtpConfig.Id);
+        }
+
         // An unknown TLS mode is a configuration error that retrying cannot fix —
         // surface it as a permanent failure (SMTP TLS validation policy).
         SmtpTlsMode tlsMode;

src/ZB.MOM.WW.ScadaBridge.NotificationOutbox/NotificationOutboxActor.cs

@@ -437,7 +437,7 @@ public class NotificationOutboxActor : ReceiveActor, IWithTimers
     }
 
     /// <summary>
-    /// Resolves the SMTP-derived retry policy from the first SMTP configuration row. When no
+    /// Resolves the SMTP-derived retry policy from the lowest-Id SMTP configuration row. When no
     /// SMTP configuration exists, falls back to the conservative default constants — delivery
     /// itself will permanently fail in that case, so the policy only acts as a guard.
     /// </summary>
@@ -445,12 +445,22 @@ public class NotificationOutboxActor : ReceiveActor, IWithTimers
         INotificationRepository notificationRepository)
     {
         var configurations = await notificationRepository.GetAllSmtpConfigurationsAsync();
-        var configuration = configurations.Count > 0 ? configurations[0] : null;
+        // Deterministic pick: the lowest-Id row wins regardless of repository order, so the
+        // retry policy resolves the same way the delivery adapter selects its config (S7).
+        var configuration = configurations.OrderBy(c => c.Id).FirstOrDefault();
         if (configuration is null)
         {
             return new RetryPolicy(FallbackMaxRetries, FallbackRetryDelay);
         }
 
+        if (configurations.Count > 1)
+        {
+            _logger.LogWarning(
+                "Multiple SMTP configurations exist; using the lowest-Id row ({Id}). "
+                + "Enforce a single row or delete extras.",
+                configuration.Id);
+        }
+
         return ClampRetryPolicy(
             nameof(SmtpConfiguration), configuration.MaxRetries, configuration.RetryDelay);
     }