fix: Use deployment CL to load TransportMetadata services if different from TCCL (#263)

I found working on
wildfly-extras/a2a-java-sdk-server-jakarta#26
that in WildFly gRPC happens on a separate thread with its own
classloader. Hence the serviceloader lookup from the default TCCL didn't
work in WildFLy.

Author: kabir

transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpcHandler.java

@@ -380,12 +380,35 @@ private <V> void handleInternalError(StreamObserver<V> responseObserver, Throwab
     private AgentCard getAgentCardInternal() {
         AgentCard agentCard = getAgentCard();
         if (initialised.compareAndSet(false, true)) {
-            // Validate transport configuration
-            AgentCardValidator.validateTransportConfiguration(agentCard);
+            // Validate transport configuration with proper classloader context
+            validateTransportConfigurationWithCorrectClassLoader(agentCard);
         }
         return agentCard;
     }
 
+    private void validateTransportConfigurationWithCorrectClassLoader(AgentCard agentCard) {
+        ClassLoader originalTccl = Thread.currentThread().getContextClassLoader();
+        ClassLoader deploymentCl = getDeploymentClassLoader();
+        boolean switchCl = deploymentCl != null && deploymentCl != originalTccl;
+
+        try {
+            if (switchCl) {
+                // Set TCCL to the classloader that loaded this class, which should have access
+                // to the deployment classpath containing META-INF/services files
+                Thread.currentThread().setContextClassLoader(deploymentCl);
+            }
+            AgentCardValidator.validateTransportConfiguration(agentCard);
+        } finally {
+            if (switchCl) {
+                Thread.currentThread().setContextClassLoader(originalTccl);
+            }
+        }
+    }
+
+    protected ClassLoader getDeploymentClassLoader() {
+        return this.getClass().getClassLoader();
+    }
+
     public static void setStreamingSubscribedRunnable(Runnable runnable) {
         streamingSubscribedRunnable = runnable;
     }