feat: mark a2a module as experimental

a2a/src/main/java/com/google/adk/a2a/A2AClient.java

@@ -22,7 +22,12 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-/** A thin HTTP client for interacting with an A2A-compliant agent endpoint. */
+/**
+ * A thin HTTP client for interacting with an A2A-compliant agent endpoint.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 public final class A2AClient {
 
   private static final Logger logger = LoggerFactory.getLogger(A2AClient.class);

a2a/src/main/java/com/google/adk/a2a/A2ASendMessageExecutor.java

@@ -29,7 +29,12 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-/** Shared SendMessage execution between HTTP service and other integrations. */
+/**
+ * Shared SendMessage execution between HTTP service and other integrations.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 public final class A2ASendMessageExecutor {
   private static final Logger logger = LoggerFactory.getLogger(A2ASendMessageExecutor.class);
 

a2a/src/main/java/com/google/adk/a2a/RemoteA2AAgent.java

@@ -46,6 +46,9 @@
  *   <li>A2A message conversion and error handling
  *   <li>Session state management across requests
  * </ul>
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
  */
 public class RemoteA2AAgent extends BaseAgent {
 

a2a/src/main/java/com/google/adk/a2a/converters/ConversationPreprocessor.java

@@ -20,6 +20,9 @@
  *
  * <p>This mirrors the Python A2A implementation where the in-flight user message is maintained
  * separately from the persisted transcript.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
  */
 public final class ConversationPreprocessor {
 

a2a/src/main/java/com/google/adk/a2a/converters/EventConverter.java

@@ -13,7 +13,12 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-/** Converter for ADK Events to A2A Messages. */
+/**
+ * Converter for ADK Events to A2A Messages.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 public final class EventConverter {
   private static final Logger logger = LoggerFactory.getLogger(EventConverter.class);
 

a2a/src/main/java/com/google/adk/a2a/converters/PartConverter.java

@@ -20,7 +20,12 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-/** Utility class for converting between Google GenAI Parts and A2A DataParts. */
+/**
+ * Utility class for converting between Google GenAI Parts and A2A DataParts.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 public final class PartConverter {
   private static final Logger logger = LoggerFactory.getLogger(PartConverter.class);
   private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

a2a/src/main/java/com/google/adk/a2a/converters/RequestConverter.java

@@ -18,6 +18,9 @@
 /**
  * rfe Converter for A2A Messages to ADK Events. This is used on the A2A service side to convert
  * incoming A2A requests to ADK Events.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
  */
 public final class RequestConverter {
   private static final Logger logger = LoggerFactory.getLogger(RequestConverter.class);

a2a/src/main/java/com/google/adk/a2a/converters/ResponseConverter.java

@@ -16,7 +16,12 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-/** Utility for converting ADK events to A2A spec messages (and back). */
+/**
+ * Utility for converting ADK events to A2A spec messages (and back).
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 public final class ResponseConverter {
   private static final Logger logger = LoggerFactory.getLogger(ResponseConverter.class);
 

a2a/webservice/src/main/java/com/google/adk/webservice/A2ARemoteApplication.java

@@ -4,7 +4,12 @@
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.context.annotation.Import;
 
-/** Entry point for the standalone Spring Boot A2A service. */
+/**
+ * Entry point for the standalone Spring Boot A2A service.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 @SpringBootApplication
 @Import(A2ARemoteConfiguration.class)
 public class A2ARemoteApplication {

a2a/webservice/src/main/java/com/google/adk/webservice/A2ARemoteConfiguration.java

@@ -23,6 +23,9 @@
  *       directly.
  *   <li>Add optional remote-proxy wiring for cases where no local agent bean is available.
  * </ul>
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
  */
 @Configuration
 @ComponentScan(basePackages = "com.google.adk.webservice")

a2a/webservice/src/main/java/com/google/adk/webservice/A2ARemoteController.java

@@ -9,7 +9,12 @@
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 
-/** REST controller exposing an A2A-compliant JSON-RPC endpoint backed by a local ADK runner. */
+/**
+ * REST controller exposing an A2A-compliant JSON-RPC endpoint backed by a local ADK runner.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 @RestController
 @RequestMapping("/a2a/remote")
 public class A2ARemoteController {

a2a/webservice/src/main/java/com/google/adk/webservice/A2ARemoteService.java

@@ -13,7 +13,12 @@
 import org.slf4j.LoggerFactory;
 import org.springframework.stereotype.Service;
 
-/** Core service that bridges the A2A JSON-RPC sendMessage API to a local ADK runner. */
+/**
+ * Core service that bridges the A2A JSON-RPC sendMessage API to a local ADK runner.
+ *
+ * @apiNote **EXPERIMENTAL:** Subject to change, rename, or removal in any future patch release. Do
+ *     not use in production code.
+ */
 @Service
 public class A2ARemoteService {