fix(siteeventlog): suppress snapshot-resync alarm re-emit + coverage + hardening (review)

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Actors/AlarmActor.cs

@@ -41,6 +41,17 @@ public class AlarmActor : ReceiveActor
     private readonly ISiteHealthCollector? _healthCollector;
     private readonly IServiceProvider? _serviceProvider;
 
+    /// <summary>
+    /// M1.5: the optional site operational-event log, resolved once from
+    /// <see cref="_serviceProvider"/> at construction and cached. The
+    /// registration is process-lifetime (a singleton), so resolving once on
+    /// the actor's own thread is both correct and cheaper than a per-event
+    /// <c>GetService</c> on the hot path. <c>null</c> when no provider was
+    /// supplied (the test/no-logging path) — <see cref="LogAlarmEvent"/> then
+    /// no-ops.
+    /// </summary>
+    private readonly ISiteEventLogger? _siteEventLogger;
+
     /// <summary>
     /// M1.5: priority at or above which a computed-alarm raise is logged as
     /// <c>Error</c> to the site event log; below it, raises log as <c>Warning</c>.
@@ -118,6 +129,9 @@ public class AlarmActor : ReceiveActor
         _logger = logger;
         _healthCollector = healthCollector;
         _serviceProvider = serviceProvider;
+        // M1.5: resolve the optional site event logger once and cache it,
+        // rather than calling GetService on every alarm transition.
+        _siteEventLogger = serviceProvider?.GetService<ISiteEventLogger>();
         _priority = alarmConfig.PriorityLevel;
         _onTriggerScriptName = alarmConfig.OnTriggerScriptCanonicalName;
         _onTriggerCompiledScript = onTriggerCompiledScript;
@@ -323,13 +337,14 @@ public class AlarmActor : ReceiveActor
 
     /// <summary>
     /// M1.5: fire-and-forget an <c>alarm</c> operational event to the optional
-    /// <see cref="ISiteEventLogger"/>. Resolved optionally and never awaited so a
-    /// logging failure cannot affect alarm evaluation (matching the established
+    /// <see cref="ISiteEventLogger"/> (resolved once at construction and cached
+    /// in <see cref="_siteEventLogger"/>). Never awaited so a logging failure
+    /// cannot affect alarm evaluation (matching the established
     /// ScriptActor/ScriptExecutionActor pattern).
     /// </summary>
     private void LogAlarmEvent(string severity, string message)
     {
-        _ = _serviceProvider?.GetService<ISiteEventLogger>()?.LogEventAsync(
+        _ = _siteEventLogger?.LogEventAsync(
             "alarm", severity, _instanceName, $"AlarmActor:{_alarmName}", message);
     }