Adjust SSE for jsonrpc

Author: kabir

reference/jsonrpc/src/main/java/io/a2a/server/apps/quarkus/A2AServerRoutes.java

@@ -784,7 +784,14 @@ public void onNext(String sseEvent) {
                         if (headers.get(CONTENT_TYPE) == null) {
                             headers.set(CONTENT_TYPE, SERVER_SENT_EVENTS);
                         }
+                        // Additional SSE headers to prevent buffering
+                        headers.set("Cache-Control", "no-cache");
+                        headers.set("X-Accel-Buffering", "no");  // Disable nginx buffering
                         response.setChunked(true);
+
+                        // CRITICAL: Disable write queue max size to prevent buffering
+                        // Vert.x buffers writes by default - we need immediate flushing for SSE
+                        response.setWriteQueueMaxSize(1);  // Force immediate flush
                     }
 
                     // Write SSE-formatted string to response

server-common/src/main/java/io/a2a/server/events/EventConsumer.java

@@ -242,6 +242,12 @@ public Flow.Publisher<EventQueueItem> consumeAll() {
                                     boolean writeCompleted = finalEventWriteLatch.await(2, TimeUnit.SECONDS);
                                     if (writeCompleted) {
                                         LOGGER.debug("Final event write confirmed via backpressure signal");
+                                        // Additional safety delay: backpressure callback is shared across all events,
+                                        // so it might fire for a previous event after we set the flag. Also, even
+                                        // with setWriteQueueMaxSize(1), Vert.x may have additional buffering.
+                                        // 50ms ensures the final event is truly transmitted to the network.
+                                        Thread.sleep(50);
+                                        LOGGER.debug("Safety buffer flush delay completed");
                                     } else {
                                         LOGGER.warn("Timeout waiting for final event write confirmation - proceeding anyway");
                                     }