[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

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