fix: Use parts instead of content for gRPC Message object as per a2aproject/A2A#1100

Fixes #355

Author: fjuma

client/transport/rest/src/test/java/io/a2a/client/transport/rest/JsonRestMessages.java

@@ -13,7 +13,7 @@ public class JsonRestMessages {
                   "messageId": "message-1234",
                   "contextId": "context-1234",
                   "role": "ROLE_USER",
-                  "content": [{
+                  "parts": [{
                     "text": "tell me a joke"
                   }],
                   "metadata": {
@@ -35,7 +35,7 @@ public class JsonRestMessages {
                     "contextId": "context-1234",
                     "taskId": "9b511af4-b27c-47fa-aecf-2a93c08a44f8",
                     "role": "ROLE_USER",
-                    "content": [
+                    "parts": [
                       {
                         "text": "tell me a joke"
                       }
@@ -81,7 +81,7 @@ public class JsonRestMessages {
               "history": [
                {
                 "role": "ROLE_USER",
-                "content": [
+                "parts": [
                  {
                   "text": "tell me a joke"
                  },
@@ -624,7 +624,7 @@ public class JsonRestMessages {
             {
               "message": {
                 "role": "ROLE_USER",
-                "content": [
+                "parts": [
                   {
                     "text": "tell me some jokes"
                   }

transport/grpc/src/test/java/io/a2a/transport/grpc/handler/GrpcHandlerTest.java

@@ -63,7 +63,7 @@ public class GrpcHandlerTest extends AbstractA2ARequestHandlerTest {
             .setContextId(AbstractA2ARequestHandlerTest.MINIMAL_TASK.getContextId())
             .setMessageId(AbstractA2ARequestHandlerTest.MESSAGE.getMessageId())
             .setRole(Role.ROLE_AGENT)
-            .addContent(Part.newBuilder().setText(((TextPart) AbstractA2ARequestHandlerTest.MESSAGE.getParts().get(0)).getText()).build())
+            .addParts(Part.newBuilder().setText(((TextPart) AbstractA2ARequestHandlerTest.MESSAGE.getParts().get(0)).getText()).build())
             .setMetadata(Struct.newBuilder().build())
             .build();
 

transport/rest/src/test/java/io/a2a/transport/rest/handler/RestHandlerTest.java

@@ -63,7 +63,7 @@ public void testSendMessage() throws InvalidProtocolBufferException {
                   "messageId": "message-1234",
                   "contextId": "context-1234",
                   "role": "ROLE_USER",
-                  "content": [{
+                  "parts": [{
                     "text": "tell me a joke"
                   }],
                   "metadata": {
@@ -103,7 +103,7 @@ public void testSendMessageWrongValueBody() {
                           "messageId": "message-1234",
                           "contextId": "context-1234",
                           "role": "user",
-                          "content": [{
+                          "parts": [{
                             "text": "tell me a joke"
                           }],
                           "metadata": {
@@ -170,7 +170,7 @@ public void testSendStreamingMessageSuccess() {
             {
               "message": {
                 "role": "ROLE_USER",
-                "content": [
+                "parts": [
                   {
                     "text": "tell me some jokes"
                   }
@@ -200,7 +200,7 @@ public void testSendStreamingMessageNotSupported() {
             {
                 "contextId": "ctx123",
                 "role": "ROLE_USER",
-                "content": [{
+                "parts": [{
                     "text": "Hello"
                 }]
             }
@@ -341,7 +341,7 @@ public void testStreamingDoesNotBlockMainThread() throws Exception {
             {
               "message": {
                 "role": "ROLE_USER",
-                "content": [
+                "parts": [
                   {
                     "text": "tell me some jokes"
                   }