fix(notifications): SMS adapter short-circuits on first transient — kills duplicate amplification and bounds the dispatch sweep

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

docs/requirements/Component-NotificationService.md

@@ -99,7 +99,7 @@ The `SmsNotificationDeliveryAdapter` delivers notifications to an SMS list via t
 SMS has no BCC mechanism. The adapter sends one Twilio request per recipient and classifies each:
 
 - **All accepted** → `Success`; `ResolvedTargets` is snapshotted with the accepted numbers.
-- **Any transient failure** → `Transient` (the whole notification retries at the fixed interval, then Parks after max-retries). Numbers already accepted on a prior attempt are re-texted on retry — the same "re-send to all" characteristic the Email adapter already has with BCC. (v1 does not track per-recipient state; that is a documented future enhancement.)
+- **Any transient failure** → `Transient` (the whole notification retries at the fixed interval, then Parks after max-retries). Numbers already accepted on a prior attempt are re-texted on retry — the same "re-send to all" characteristic the Email adapter already has with BCC. The recipient loop stops at the **first** transient rather than attempting the remaining recipients: every recipient accepted after the first transient would just be a guaranteed duplicate text on retry, and stopping early also bounds a black-holed endpoint to one request timeout per sweep instead of recipients × timeout. (v1 does not track per-recipient state; that is a documented future enhancement.)
 - **No transient failures, mix of accepted + permanent-bad** → `Success` to the good numbers; permanently-bad numbers are recorded in `LastError`. The notification is not parked if anything got through.
 - **All permanent / no recipients / no SMS config / list-not-found** → `Permanent` (Park).
 

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

@@ -155,17 +155,22 @@ public sealed class SmsNotificationDeliveryAdapter : INotificationDeliveryAdapte
                 httpClient, requestUri, authHeader, smsConfig, hasMessagingService,
                 phone, body, timeoutSeconds, redactSecret, cancellationToken);
 
-            switch (attempt.Class)
+            if (attempt.Class == SmsErrorClass.Transient)
             {
-                case SmsErrorClass.Transient:
-                    firstTransientError ??= attempt.Detail;
+                // Every recipient accepted after the first transient is a guaranteed
+                // duplicate on retry (the whole notification re-sends); stopping here
+                // also bounds a black-holed endpoint to one timeout per sweep.
+                firstTransientError = attempt.Detail;
                 break;
-                case SmsErrorClass.Permanent:
+            }
+
+            if (attempt.Class == SmsErrorClass.Permanent)
+            {
                 permanentlyFailed.Add(phone);
-                    break;
-                default:
+            }
+            else
+            {
                 accepted.Add(phone);
-                    break;
             }
         }
 
@@ -284,6 +289,13 @@ public sealed class SmsNotificationDeliveryAdapter : INotificationDeliveryAdapte
     /// any transient → Transient (whole notification retries); else any
     /// accepted → Success (the permanently-failed numbers are noted, NOT parked); else
     /// (all permanent / zero accepted) → Permanent.
+    /// <para>
+    /// The caller's recipient loop stops at the FIRST transient rather than attempting
+    /// every recipient: every recipient accepted after the first transient is a
+    /// guaranteed duplicate on retry (the whole notification re-sends), so
+    /// <paramref name="accepted"/> and <paramref name="permanentlyFailed"/> only ever
+    /// reflect recipients attempted before that first transient.
+    /// </para>
     /// </summary>
     private DeliveryOutcome RollUp(
         string listName,

tests/ZB.MOM.WW.ScadaBridge.NotificationOutbox.Tests/Delivery/SmsNotificationDeliveryAdapterTests.cs

@@ -299,6 +299,24 @@ public class SmsNotificationDeliveryAdapterTests
         Assert.Equal(DeliveryResult.TransientFailure, outcome.Result);
     }
 
+    [Fact]
+    public async Task MidListTransient_ShortCircuits_RemainingRecipientsNotAttempted()
+    {
+        // Three recipients; the FIRST one comes back transient (500). Every recipient
+        // accepted after a transient is a guaranteed duplicate on retry (the whole
+        // notification re-sends), so the adapter must stop at the first transient
+        // instead of attempting the remaining two.
+        SetupList(phones: new[] { "+15551112222", "+15553334444", "+15555556666" });
+        var handler = ScriptedHttpMessageHandler.ForStatuses(
+            HttpStatusCode.InternalServerError, HttpStatusCode.Created, HttpStatusCode.Created);
+        var adapter = CreateAdapter(handler);
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.TransientFailure, outcome.Result);
+        Assert.Single(handler.Requests);
+    }
+
     [Fact]
     public async Task Deliver_ListNotFound_ReturnsPermanent()
     {