fix(server): start event bus processor for manual wiring

Ensure MainEventBusProcessor.ensureStarted() starts manually constructed processors, and call it from DefaultRequestHandler.create(...). This prevents manually wired integrations from leaving events stuck on the main event bus.

Add a regression test for the manual wiring path that returns a Message response.

This fixes a2aproject#995

Author: 014-code

server-common/src/main/java/org/a2aproject/sdk/server/events/MainEventBusProcessor.java

@@ -158,23 +158,31 @@ int pushNotificationChainCount() {
 
     @SuppressWarnings("NullAway.Init")
     @PostConstruct
-    void start() {
+    synchronized void start() {
+        if (processorThread != null) {
+            LOGGER.debug("MainEventBusProcessor already started");
+            return;
+        }
+        running = true;
         processorThread = new Thread(this, "MainEventBusProcessor");
         processorThread.setDaemon(true); // Allow JVM to exit even if this thread is running
         processorThread.start();
         LOGGER.info("MainEventBusProcessor started");
     }
 
     /**
-     * No-op method to force CDI proxy resolution and ensure @PostConstruct has been called.
-     * Called by MainEventBusProcessorInitializer during application startup.
+     * Ensures the background processor thread has been started.
+     * <p>
+     * In CDI runtimes, this forces proxy resolution and {@link PostConstruct}. For manual
+     * wiring, this starts the processor directly.
+     * </p>
      */
     public void ensureStarted() {
-        // Method intentionally empty - just forces proxy resolution
+        start();
     }
 
     @PreDestroy
-    void stop() {
+    synchronized void stop() {
         LOGGER.info("MainEventBusProcessor stopping...");
         running = false;
         if (processorThread != null) {

server-common/src/test/java/org/a2aproject/sdk/server/requesthandlers/DefaultRequestHandlerTest.java

@@ -186,6 +186,41 @@ void testInitConfigReadsBlockingTimeouts() {
         assertEquals(7, handler.reconciliationTimeoutSeconds);
     }
 
+    @Test
+    void testCreateStartsManuallyConstructedMainEventBusProcessor() throws Exception {
+        InMemoryTaskStore manualTaskStore = new InMemoryTaskStore();
+        PushNotificationConfigStore manualPushConfigStore = new InMemoryPushNotificationConfigStore();
+        MainEventBus manualMainEventBus = new MainEventBus();
+        InMemoryQueueManager manualQueueManager = new InMemoryQueueManager(manualTaskStore, manualMainEventBus);
+        MainEventBusProcessor manualProcessor = new MainEventBusProcessor(
+            manualMainEventBus, manualTaskStore, NOOP_PUSHNOTIFICATION_SENDER, manualQueueManager);
+
+        try {
+            AgentExecutor manualAgentExecutor = new AgentExecutor() {
+                @Override
+                public void execute(RequestContext context, AgentEmitter agentEmitter) {
+                    agentEmitter.sendMessage("manual lifecycle response");
+                }
+
+                @Override
+                public void cancel(RequestContext context, AgentEmitter agentEmitter) {
+                    throw new AssertionError("Cancel should not be invoked");
+                }
+            };
+            RequestHandler manualRequestHandler = DefaultRequestHandler.create(
+                manualAgentExecutor, manualTaskStore, manualQueueManager, manualPushConfigStore,
+                manualProcessor, internalExecutor, internalExecutor);
+
+            EventKind eventKind = manualRequestHandler.onMessageSend(
+                MessageSendParams.builder().message(MESSAGE).build(), NULL_CONTEXT);
+
+            assertInstanceOf(Message.class, eventKind);
+            assertEquals(Message.Role.ROLE_AGENT, ((Message) eventKind).role());
+        } finally {
+            EventQueueUtil.stop(manualProcessor);
+        }
+    }
+
     /**
      * Test 1: Non-streaming AUTH_REQUIRED returns immediately while agent continues.
      * Verifies: