How to do a long-running tool call that does not require client input?

[sushicw]

I have a case where I want to create a custom Agent that can take a while to process. When someone calls the agent (via SendMessage over A2A) I do not want to block: instead, I want to immediately return a task with TASK_STATE_SUBMITTED or TASK_STATE_WORKING.

Long running function tool support comes close: https://google.github.io/adk-docs/tools-custom/function-tools/#long-run-tool . However, this results in TASK_STATE_INPUT_REQUIRED, even though I don't actually need any user input.

e.g. the closest I've come is something like this:

    agent, err := agent.New(agent.Config{
        Name:        "MyLongRunningAgent",
        Description: "description",
        Run: func(ctx agent.InvocationContext) iter.Seq2[*session.Event, error] {
            return func(yield func(*session.Event, error) bool) {
                // TODO: enqueue the long-running task for processing elsewhere,
                // and return immediately with TASK_STATE_WORKING so the client
                // can poll for progress
                
                // What almost works, except that it gives TASK_STATE_INPUT_REQUIRED
                e := session.NewEvent(ctx.InvocationID())
                e.LLMResponse = model.LLMResponse{
                    Content: &genai.Content{
                        Parts: []*genai.Part{
                            {
                                FunctionCall: &genai.FunctionCall{
                                    ID:   "long_running_task_work",
                                    Name: "long_running_task_work",
                                },
                            },
                        },
                    },
                }
                e.LongRunningToolIDs = []string{"long_running_task_work"}
                yield(e, nil)
            }
        },

If I just emit a placeholder event like a "started" message, without a long running tool ID and corresponding FunctionCall, it's treated as completed (TASK_STATE_COMPLETED). If I just do the long-running work without yielding any initial event, the SendMessage RPC blocks until it finishes.

Is the use-case of a long-running task that does not require user input supported by ADK?
If so, how?
If not, should it be? (And where would be the best place to make that request? Probably filing an issue either in adk-go or adk-python, right?)

[sushicw]

After investigating more, I realized that the blocking-ness is controlled by the client as part of the A2A spec: https://a2a-protocol.org/latest/specification/#322-sendmessageconfiguration

When correctly including configuration in the request with blocking:false and invoking my ADK agent, I do get an immediate return with TASK_STATE_SUBMITTED. No need to represent the internal work as a tool call.