[Bug]: Chat Conversation Fails with 10 Pydantic Validation Errors (Agent Card Retrieval Works) - Possible Version Incompatibility

### What happened?

I started the agent server using the URL: https://github.com/a2aproject/a2a-samples/tree/main/samples/java/custom_java_impl/server. The Agent card can be retrieved normally, but there is an issue during the chat conversation. Could this be due to version incompatibility?

The error prompt is as follows:
```json
{
"error": "Failed to send message: 10 validation errors for SendStreamingMessageResponse\nJSONRPCErrorResponse.error\n Field required [type=missing, input_value={'id': '566f5596-f4f9-4ad...455Z'}, 'final': False}}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.Task.contextId\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.Message.messageId\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.Message.parts\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.Message.role\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.TaskStatusUpdateEvent.contextId\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.TaskStatusUpdateEvent.taskId\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.TaskArtifactUpdateEvent.artifact\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.TaskArtifactUpdateEvent.contextId\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing\nSendStreamingMessageSuccessResponse.result.TaskArtifactUpdateEvent.taskId\n Field required [type=missing, input_value={'id': 'c9da416d-41c2-4ac...9455Z'}, 'final': False}, input_type=dict]\n For further information visit https://errors.pydantic.dev/2.11/v/missing",
"id": "msg-1763167497720-mcbdi3sgz"
}
```

### Relevant log output

```shell

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

The error indicates Pydantic validation failures in the SendStreamingMessageResponse schema. Start by examining the A2A protocol definitions for the response structure, likely in TypeScript types or OpenAPI specs. Compare the server's actual JSON output against the expected schema. Look for missing required fields like 'error', 'contextId', 'messageId', 'parts', 'role', 'taskId', and 'artifact'. Check version compatibility between the Java server and the inspector's validation expectations.

Scritto dal modello di indicizzazione a partire dal testo della issue.