llmagent: a task agent that finishes with a null result never returns it to the coordinator #1738

package llmagent_test

import (
	"testing"

	"google.golang.org/genai"

	"google.golang.org/adk/v2/agent"
	"google.golang.org/adk/v2/agent/llmagent"
	"google.golang.org/adk/v2/model"
	"google.golang.org/adk/v2/runner"
	"google.golang.org/adk/v2/session"
)

func fcTurn(id, name string, args map[string]any) *model.LLMResponse {
	return &model.LLMResponse{Content: &genai.Content{Role: "model", Parts: []*genai.Part{{
		FunctionCall: &genai.FunctionCall{ID: id, Name: name, Args: args},
	}}}}
}

// A task agent whose OutputSchema is a nullable string finishes with null.
// The delegation should close (the coordinator receives a FunctionResponse).
func TestReproNullableTaskResultClosesDelegation(t *testing.T) {
	taskLLM := &scriptedLLM{turns: []*model.LLMResponse{
		fcTurn("finish-1", "finish_task", map[string]any{"result": nil}),
		// Only consumed if the null call is rejected and the model retries.
		fcTurn("finish-2", "finish_task", map[string]any{"result": "retry-value"}),
	}}
	task, err := llmagent.New(llmagent.Config{
		Name: "doer", Description: "d", Model: taskLLM, Mode: llmagent.ModeTask,
		OutputSchema: &genai.Schema{Type: genai.TypeString, Nullable: genai.Ptr(true)},
	})
	if err != nil {
		t.Fatal(err)
	}
	coordLLM := &scriptedLLM{turns: []*model.LLMResponse{
		fcTurn("fc-1", "doer", map[string]any{"request": "x"}),
		{Content: &genai.Content{Role: "model", Parts: []*genai.Part{genai.NewPartFromText("coordinator resumed")}}},
	}}
	coord, err := llmagent.New(llmagent.Config{Name: "coord", Model: coordLLM, Mode: llmagent.ModeChat, SubAgents: []agent.Agent{task}})
	if err != nil {
		t.Fatal(err)
	}
	svc := session.InMemoryService()
	if _, err := svc.Create(t.Context(), &session.CreateRequest{AppName: "app", UserID: "u", SessionID: "s"}); err != nil {
		t.Fatal(err)
	}
	r, err := runner.New(runner.Config{Agent: coord, SessionService: svc, AppName: "app"})
	if err != nil {
		t.Fatal(err)
	}
	var delegationFR *genai.FunctionResponse
	for ev, err := range r.Run(t.Context(), "u", "s", genai.NewContentFromText("go", "user"), agent.RunConfig{}) {
		if err != nil {
			t.Fatalf("run: %v", err)
		}
		if ev.Content == nil {
			continue
		}
		for _, p := range ev.Content.Parts {
			if p.FunctionCall != nil {
				t.Logf("author=%s FC %s args=%v", ev.Author, p.FunctionCall.Name, p.FunctionCall.Args)
			}
			if p.FunctionResponse != nil {
				t.Logf("author=%s FR %s resp=%v", ev.Author, p.FunctionResponse.Name, p.FunctionResponse.Response)
				if p.FunctionResponse.Name == "doer" {
					delegationFR = p.FunctionResponse
				}
			}
			if p.Text != "" {
				t.Logf("author=%s text=%q", ev.Author, p.Text)
			}
		}
	}
	t.Logf("coordinator LLM calls=%d task LLM calls=%d", coordLLM.callIdx, taskLLM.callIdx)
	if delegationFR == nil {
		t.Errorf("no FunctionResponse closed the delegation to doer")
	}
}