Create an appropriate buffer with the size that accommodates signal f…

…rame payload (#537)

runtime/engine/src/main/java/io/aklivity/zilla/runtime/engine/internal/registry/DispatchAgent.java

@@ -310,7 +310,7 @@ public DispatchAgent(
         this.timerWheel = new DeadlineTimerWheel(MILLISECONDS, currentTimeMillis(), 512, 1024);
         this.tasksByTimerId = new Long2ObjectHashMap<>();
         this.futuresById = new Long2ObjectHashMap<>();
-        this.signaler = new ElektronSignaler(executor);
+        this.signaler = new ElektronSignaler(executor, Math.max(config.bufferSlotCapacity(), 512));
 
         this.poller = new Poller();
 
@@ -1672,9 +1672,10 @@ public Affinity resolveAffinity(
         return affinity;
     }
 
-    private static SignalFW.Builder newSignalRW()
+    private static SignalFW.Builder newSignalRW(
+        int capacity)
     {
-        MutableDirectBuffer buffer = new UnsafeBuffer(new byte[512]);
+        MutableDirectBuffer buffer = new UnsafeBuffer(new byte[capacity]);
         return new SignalFW.Builder().wrap(buffer, 0, buffer.capacity());
     }
 
@@ -1691,16 +1692,18 @@ private Int2ObjectHashMap<MessageConsumer>[] initDispatcher()
 
     private final class ElektronSignaler implements Signaler
     {
-        private final ThreadLocal<SignalFW.Builder> signalRW = withInitial(DispatchAgent::newSignalRW);
+        private final ThreadLocal<SignalFW.Builder> signalRW;
 
         private final ExecutorService executorService;
 
         private long nextFutureId;
 
         private ElektronSignaler(
-            ExecutorService executorService)
+            ExecutorService executorService,
+            int slotCapacity)
         {
             this.executorService = executorService;
+            signalRW = withInitial(() -> newSignalRW(slotCapacity));
         }
 
         public void executeTaskAt(