test(integration): harden B8 live assertions (ArchestrAUserToId user_id, bootstrap arrival, split guard)

Fix 1 (Important): assert ArchestrAUserToId Ok-path payload carries a non-zero user_id, mirroring the AuthenticateUser pattern.
Fix 2 (Important): assert bootstrapBufferedEvents > 0 before the residual return so the "empty NoData bootstrap arrives" claim is verified, not just assumed.
Fix 3 (Minor): change SplitLiveItemForBuffered guard from lastDot <= 0 to lastDot < 0 so a leading-dot reference ".TestInt" (lastDot==0) is not mis-handled as undotted.

src/ZB.MOM.WW.MxGateway.IntegrationTests/WorkerLiveMxAccessSmokeTests.cs

@@ -660,6 +660,14 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
             Assert.True(
                 userToIdReply.ProtocolStatus.Code is ProtocolStatusCode.Ok or ProtocolStatusCode.MxaccessFailure,
                 $"ArchestrAUserToId must surface a real MXAccess outcome, got {userToIdReply.ProtocolStatus.Code}.");
+            if (userToIdReply.ProtocolStatus.Code == ProtocolStatusCode.Ok)
+            {
+                // On the dev rig ArchestrAUserToId with a valid GUID resolves to user_id=1.
+                // Don't pin the exact id (provider-dependent) — just prove the Ok path carried
+                // a usable non-zero ArchestrA user id through the reply payload.
+                Assert.NotNull(userToIdReply.ArchestraUserToId);
+                Assert.NotEqual(0, userToIdReply.ArchestraUserToId.UserId);
+            }
 
             // Suspend / Activate against the advised item. The dev-rig TestInt item class
             // may not be suspendable (MXAccess returns 0x80070057 / E_INVALIDARG for a
@@ -848,6 +856,13 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
                     + $"was observed within {IntegrationTestEnvironment.LiveMxAccessEventTimeout}. Live "
                     + "§3.2 multi-sample conversion remains unverified (rig object logic may not drive "
                     + "buffered samples on demand).");
+
+                // The residual claim ("empty NoData bootstrap arrives and converts without crashing")
+                // is only meaningful if at least one OnBufferedDataChange event arrived. Assert that
+                // the buffered subscription registered and the worker's event plumbing fired at all.
+                Assert.True(
+                    bootstrapBufferedEvents > 0,
+                    "No OnBufferedDataChange event arrived at all after Advise; the buffered subscription may not have registered.");
                 return;
             }
 
@@ -1416,7 +1431,7 @@ public sealed class WorkerLiveMxAccessSmokeTests(ITestOutputHelper output)
     private static (string Item, string Context) SplitLiveItemForBuffered(string liveItem)
     {
         int lastDot = liveItem.LastIndexOf('.');
-        if (lastDot <= 0 || lastDot >= liveItem.Length - 1)
+        if (lastDot < 0 || lastDot >= liveItem.Length - 1)
         {
             return (liveItem, string.Empty);
         }