[Redis] Don't update the message to nil in UpdateTaskState

[matino]

Hello,

Usually when sending the final event with status.state = completed, the message is not included in the event.
See https://a2a-protocol.org/latest/specification/#93-streaming-task-execution-sse the last event.

The code in UpdateTaskState does not care if message is nil or not, it sets it anyway:

func (h *taskHandler) UpdateTaskState(
	taskID *string,
	state protocol.TaskState,
	message *protocol.Message,
) error {
	if taskID == nil || *taskID == "" {
		return fmt.Errorf("taskID cannot be nil or empty")
	}

	task, err := h.manager.getTaskInternal(h.ctx, *taskID)
	if err != nil {
		log.Warnf("UpdateTaskState called for non-existent task %s", *taskID)
		return fmt.Errorf("task not found: %s", *taskID)
	}

	// Update task status.
	task.Status = protocol.TaskStatus{
		State:     state,
		Message:   message,
		Timestamp: time.Now().UTC().Format(time.RFC3339),
	}

	// Store updated task.
	if err := h.manager.storeTask(h.ctx, task); err != nil {
		return fmt.Errorf("failed to update task status: %w", err)
	}
        ...
}

WDYT to only update the message if it's not nil? Something like this:

// Update task status.
task.Status = protocol.TaskStatus{
    State:     state,
    Timestamp: time.Now().UTC().Format(time.RFC3339),
}

if message != nil {
    task.Status.Message = message
}

[hyprh]

I think it’s OK to update [the message] even only when it is not nil. And Could you tell me your scenarios of using Status.Message.

[matino]

I'm using AddArtifact event to stream the LLM response chunks, and UpdateTaskState to stream internal notifications.

When stream ends, I'm sending a protocol.Message (to store LLM response in conversion history), followed by UpdateTaskState:

// this triggers storeMessage, which updates the history
taskSubscriber.Send(protocol.StreamingMessageEvent{Result: &finalMessage})

// this updates the task message
taskHandler.UpdateTaskState(taskID, protocol.TaskStateCompleted, &finalMessage)

Not really sure, but maybe I could just simply call like this:

taskHandler.UpdateTaskState(taskID, protocol.TaskStateCompleted, nil)

but then the task message will be set to nil (not sure what are the consequences though).