fix(alarms): truncation-safe transitions; perf: single-pass alarm parse; configurable poll cadence

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessStaSession.cs

@@ -19,7 +19,26 @@ public sealed class MxAccessStaSession : IWorkerRuntimeSession
     internal const string WriteCompletionWaitEnvironmentVariableName =
         "MXGATEWAY_WORKER_WRITE_COMPLETION_WAIT_MS";
 
-    private static readonly TimeSpan AlarmPollInterval = TimeSpan.FromMilliseconds(500);
+    /// <summary>
+    ///     Environment variable the gateway's WorkerProcessLauncher sets from
+    ///     MxGateway:Alarms:PollIntervalMilliseconds. A missing or invalid
+    ///     value falls back to <see cref="DefaultAlarmPollInterval"/>.
+    /// </summary>
+    internal const string AlarmPollIntervalEnvironmentVariableName =
+        "MXGATEWAY_ALARM_POLL_INTERVAL_MS";
+
+    /// <summary>
+    ///     Floor on the resolved alarm poll cadence. Mirrors the gateway-side
+    ///     MxGateway:Alarms:PollIntervalMilliseconds minimum so a value that
+    ///     slipped past validation (or an environment set by hand) still can
+    ///     not starve the STA's command path.
+    /// </summary>
+    internal static readonly TimeSpan MinimumAlarmPollInterval = TimeSpan.FromMilliseconds(100);
+
+    /// <summary>Default alarm poll cadence when the environment says nothing usable.</summary>
+    internal static readonly TimeSpan DefaultAlarmPollInterval = TimeSpan.FromMilliseconds(500);
+
+    private readonly TimeSpan alarmPollInterval = ResolveAlarmPollInterval();
 
     private readonly IMxAccessComObjectFactory factory;
     private readonly IMxAccessEventSink eventSink;
@@ -191,6 +210,31 @@ public sealed class MxAccessStaSession : IWorkerRuntimeSession
                 : MxAccessCommandExecutor.DefaultWriteCompletionTimeout;
     }
 
+    /// <summary>
+    ///     Resolves the alarm poll cadence from the launcher-provided
+    ///     environment variable. A missing, unparseable, or out-of-range value
+    ///     falls back to <see cref="DefaultAlarmPollInterval"/> rather than
+    ///     faulting the worker: an alarm poll that runs at the default cadence
+    ///     is always safe, and a session that refuses to start over a
+    ///     mistyped environment variable is not.
+    /// </summary>
+    /// <returns>The cadence the alarm poll loop waits between polls.</returns>
+    internal static TimeSpan ResolveAlarmPollInterval()
+    {
+        string? value = Environment.GetEnvironmentVariable(AlarmPollIntervalEnvironmentVariableName);
+        if (!int.TryParse(
+                value,
+                System.Globalization.NumberStyles.Integer,
+                System.Globalization.CultureInfo.InvariantCulture,
+                out int milliseconds))
+        {
+            return DefaultAlarmPollInterval;
+        }
+
+        TimeSpan resolved = TimeSpan.FromMilliseconds(milliseconds);
+        return resolved < MinimumAlarmPollInterval ? DefaultAlarmPollInterval : resolved;
+    }
+
     /// <summary>
     /// Starts the MXAccess COM session asynchronously.
     /// </summary>
@@ -274,7 +318,7 @@ public sealed class MxAccessStaSession : IWorkerRuntimeSession
             {
                 try
                 {
-                    await Task.Delay(AlarmPollInterval, cancellationToken).ConfigureAwait(false);
+                    await Task.Delay(alarmPollInterval, cancellationToken).ConfigureAwait(false);
                 }
                 catch (OperationCanceledException)
                 {