perf(worker): launcher-configurable event queue capacity

src/ZB.MOM.WW.MxGateway.Server/Configuration/GatewayOptionsValidator.cs

@@ -10,6 +10,12 @@ public sealed class GatewayOptionsValidator : OptionsValidatorBase<GatewayOption
     private const int MinimumMaxMessageBytes = 1024;
     private const int MaximumMaxMessageBytes = 256 * 1024 * 1024;
 
+    // Bounds on the worker's outbound event-queue capacity. The floor keeps enough headroom that a
+    // normal subscription burst cannot overflow the queue (an overflow faults the whole session);
+    // the ceiling keeps a mistyped value from committing the x86 worker to an unbounded backlog.
+    private const int MinimumWorkerEventQueueCapacity = 1000;
+    private const int MaximumWorkerEventQueueCapacity = 1_000_000;
+
     // Whether the host is running in the Production environment. Drives the production-only
     // hard-stops (dashboard login disabled, plaintext LDAP transport) that must abort startup
     // rather than merely warn. Non-production hosts keep the permissive dev posture.
@@ -275,6 +281,12 @@ public sealed class GatewayOptionsValidator : OptionsValidatorBase<GatewayOption
                 "MxGateway:Worker:HeartbeatGraceSeconds must be greater than or equal to HeartbeatIntervalSeconds.");
         }
 
+        if (options.EventQueueCapacity is < MinimumWorkerEventQueueCapacity or > MaximumWorkerEventQueueCapacity)
+        {
+            builder.Add(
+                $"MxGateway:Worker:EventQueueCapacity must be between {MinimumWorkerEventQueueCapacity} and {MaximumWorkerEventQueueCapacity}.");
+        }
+
         if (options.MaxMessageBytes is < MinimumMaxMessageBytes or > MaximumMaxMessageBytes)
         {
             builder.Add(