From: Anderson A. Giacomolli <agiacomolli@gmail.com>
Date: Fri, 6 Nov 2026 23:19:46 +0000 (-0300)
Subject: Run the turns of an agent in a loop
X-Git-Url: http://git.giacomolli.uk/onechat/commitdiff_plain/5da3ea038d1e9f9a2634d5ab137aef6989a3a789?ds=inline

Run the turns of an agent in a loop

A user message goes to the log when it comes and wakes the loop. A turn
waits until every build is done, so the view holds the summaries of the
messages before it. Its first request holds the prompt, the six tools,
and one user message with the view, the date and time of the turn, and
each new message whole. The view leaves out the leaf lines of the new
messages, but it keeps every other line, also the replies that came
after a message that waited.

The loop runs the tool calls of each response and sends their results
back until a response has no tool call. Each later request begins with
the whole previous input, then the output items with the encrypted
reasoning and without their ids, because the calls do not store them,
then the tool results. So each request of a turn begins with all of the
one before it. User messages that come during a turn join the next
request after the tool results, and a message that comes during the
final request starts a new turn. Replies, tool calls, and results go to
the log as they happen, and the reasoning never does.

An interrupt cancels the turn and kills a running tool. A failed call
ends the turn without a retry, and its messages stay in the log, so a
lasting failure does not repeat. Only a failed log write stops the loop.

The prompt gets a paragraph on persistent mode: a reply with no tool
call ends the turn, a question in the middle of a task does not end the
task, and "continue" resumes the latest unfinished task.

Issue: 5daf23e
---

diff --git a/memory.go b/memory.go
index 792fe21..d7fff4e 100644
--- a/memory.go
+++ b/memory.go
@@ -543,6 +543,15 @@ func (m *Memory) View() string {
 	return m.chat.Render()
 }
 
+// ViewWithout returns the chat view without the leaf lines of the messages in
+// skip.
+func (m *Memory) ViewWithout(skip map[int]bool) string {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	return m.chat.RenderWithout(skip)
+}
+
 // Len returns the number of messages in the log.
 func (m *Memory) Len() int {
 	m.mutex.Lock()
diff --git a/prompt.go b/prompt.go
index b536a36..373aab6 100644
--- a/prompt.go
+++ b/prompt.go
@@ -26,7 +26,8 @@ const (
 // word. The reference design names its own agent, so promptText has the name of
 // the agent and the kind reply in its place. It describes only what OneChat can
 // do, so it leaves out the spec text on images, subagents, computers, and
-// background tasks. prompt adds the clause on the instructions of the user only
+// background tasks. Its paragraph on persistent mode tells the model that a
+// final answer ends the turn. prompt adds the clause on the instructions of the user only
 // when there are instructions. It holds no date and no state, so turns and
 // compactions share its prompt cache.
 const promptText = `You are {name}, an AI agent that works for one user in a single chat that never
@@ -72,6 +73,13 @@ say in your reply what you learned that will matter later.
 
 Messages the user sends while you work reach you between tool calls.
 
+You are in persistent mode: a reply with no tool call is your final answer, and
+it ends your turn. You act again only when the user writes. So keep going until
+the user's task is done, or until only the user can unblock it. Answer a
+question asked in the middle of a task, then go on with the task in the same
+turn. When the user says "continue", resume the latest unfinished task from the
+view.
+
 # Compactions
 
 You write {name}'s memory: one step of the tree, compressing one message into a
diff --git a/turn.go b/turn.go
new file mode 100644
index 0000000..76f524e
--- /dev/null
+++ b/turn.go
@@ -0,0 +1,373 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+)
+
+// modelClient sends model calls.
+type modelClient interface {
+	Create(ctx context.Context, request Request) (Response, error)
+}
+
+// Event tells the clients what the agent does as it happens. Kind is the kind
+// of a logged message (user, reply, tool, echo), or one of busy, idle, and
+// error. ID is the ID of a logged message.
+type Event struct {
+	Kind string `json:"kind"`
+	ID   int    `json:"id,omitempty"`
+	Text string `json:"text,omitempty"`
+}
+
+// loop runs the turns of one agent. A user message goes to the log when it
+// comes, and it wakes the loop. A turn waits until every message before it is
+// summarized. Then its first request holds the prompt, the tools, and the
+// input of turnInput. The loop runs the tool calls of each response and sends
+// their results back, until a response has no tool call: the final answer.
+//
+// Each later request of a turn begins with the whole input of the request
+// before it, then its output items, then the tool results. The output items
+// hold the reasoning with its encrypted content, because the calls do not
+// store it. So each request begins with all of the previous one and reads it
+// from the prompt cache. User messages that come during a turn join the next
+// request after the tool results. The replies, the tool calls, and the results
+// go to the log as they happen. The thoughts never do.
+type loop struct {
+	agent  *Agent
+	memory *Memory
+	client modelClient
+	tools  *toolbox
+	clock  func() time.Time
+	notify func(Event)
+	wake   chan struct{}
+
+	mutex   sync.Mutex
+	pending []Message
+	cancel  context.CancelFunc
+}
+
+// functionCall holds the fields of a function call output item.
+type functionCall struct {
+	Type      string `json:"type"`
+	Name      string `json:"name"`
+	Arguments string `json:"arguments"`
+	CallID    string `json:"call_id"`
+}
+
+// functionCallOutput is the input item with the result of a function call.
+type functionCallOutput struct {
+	Type   string `json:"type"`
+	CallID string `json:"call_id"`
+	Output string `json:"output"`
+}
+
+// newLoop returns the loop of agent with its memory. Its calls go through
+// client, and notify gets each event. The clock gives the date of a turn.
+func newLoop(agent *Agent, memory *Memory, client modelClient, clock func() time.Time, notify func(Event)) *loop {
+	l := &loop{
+		agent:  agent,
+		memory: memory,
+		client: client,
+		clock:  clock,
+		notify: notify,
+		wake:   make(chan struct{}, 1),
+	}
+
+	l.tools = &toolbox{
+		log:     l,
+		chat:    memory,
+		workdir: agent.config.Workdir,
+	}
+
+	return l
+}
+
+// Submit logs a user message and wakes the loop. The message joins the next
+// request: the first one of a new turn, or the next one of a running turn.
+func (l *loop) Submit(text string) (Message, error) {
+	message, err := l.Append("user", text)
+	if err != nil {
+		return Message{}, err
+	}
+
+	l.mutex.Lock()
+	l.pending = append(l.pending, message)
+	l.mutex.Unlock()
+
+	select {
+	case l.wake <- struct{}{}:
+	default:
+	}
+
+	return message, nil
+}
+
+// Interrupt ends the running turn. A running tool is killed, and the turn sends
+// no further request.
+func (l *loop) Interrupt() bool {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	if l.cancel == nil {
+		return false
+	}
+
+	l.cancel()
+
+	return true
+}
+
+// Append logs a message and tells the clients. The toolbox logs its calls and
+// results through it.
+func (l *loop) Append(kind, text string) (Message, error) {
+	message, err := l.memory.Append(kind, text)
+	if err != nil {
+		return Message{}, err
+	}
+
+	l.notify(Event{
+		Kind: kind,
+		ID:   message.ID,
+		Text: text,
+	})
+
+	return message, nil
+}
+
+// Flush makes the log durable.
+func (l *loop) Flush(ctx context.Context) error {
+	return l.memory.Flush(ctx)
+}
+
+// Run runs a turn each time user messages wait, until ctx ends. It returns the
+// error of a failed log write, which stops the agent.
+func (l *loop) Run(ctx context.Context) error {
+	for {
+		for l.waiting() {
+			err := l.turn(ctx)
+			if err != nil {
+				return err
+			}
+		}
+
+		select {
+		case <-l.wake:
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+	}
+}
+
+// waiting tells if user messages wait for a request.
+func (l *loop) waiting() bool {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	return len(l.pending) > 0
+}
+
+// take returns the user messages that wait for a request, and removes them.
+func (l *loop) take() []Message {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	messages := l.pending
+	l.pending = nil
+
+	return messages
+}
+
+// turn runs one turn. A failed or interrupted model call ends the turn and
+// tells the clients. The messages of the turn stay in the log and the view, and
+// the next turn starts only with a new message, so a lasting failure such as a
+// needed login does not repeat. Only a failed log write is an error of turn.
+func (l *loop) turn(ctx context.Context) error {
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	l.mutex.Lock()
+	l.cancel = cancel
+	l.mutex.Unlock()
+
+	defer func() {
+		l.mutex.Lock()
+		l.cancel = nil
+		l.mutex.Unlock()
+	}()
+
+	l.notify(Event{
+		Kind: "busy",
+	})
+
+	err := l.chain(ctx)
+	if err != nil && !errors.Is(err, errLogWrite) {
+		l.notify(Event{
+			Kind: "error",
+			Text: turnError(ctx, err),
+		})
+
+		err = nil
+	}
+
+	l.notify(Event{
+		Kind: "idle",
+	})
+
+	return err
+}
+
+// errLogWrite marks an error of a log write, which ends the loop.
+var errLogWrite = errors.New("log write failed")
+
+// chain runs the request chain of a turn until the final answer.
+func (l *loop) chain(ctx context.Context) error {
+	messages := l.take()
+	if len(messages) == 0 {
+		return nil
+	}
+
+	err := l.memory.Wait(ctx)
+	if err != nil {
+		return err
+	}
+
+	instructions, err := l.agent.Prompt()
+	if err != nil {
+		return err
+	}
+
+	skip := make(map[int]bool, len(messages))
+	for _, message := range messages {
+		skip[message.ID] = true
+	}
+
+	input := turnInput(l.memory.ViewWithout(skip), l.state(), messages)
+	for {
+		response, err := l.client.Create(ctx, Request{
+			Model:        l.agent.config.Model,
+			Effort:       l.agent.config.Effort,
+			Instructions: instructions,
+			Tools:        agentTools(),
+			Input:        input,
+		})
+		if err != nil {
+			return err
+		}
+
+		input, err = l.handle(ctx, input, response)
+		if err != nil {
+			return err
+		}
+
+		if len(input) == 0 {
+			return nil
+		}
+	}
+}
+
+// handle logs the replies of response and runs its tool calls. It returns the
+// input of the next request: input, the output items, the tool results, and
+// the user messages that came in the meantime. After the final answer it
+// returns no input.
+func (l *loop) handle(ctx context.Context, input []any, response Response) ([]any, error) {
+	var outputs []any
+	for _, raw := range response.Output {
+		item, err := inputItem(raw)
+		if err != nil {
+			return nil, err
+		}
+
+		input = append(input, item)
+
+		var call functionCall
+		err = json.Unmarshal(raw, &call)
+		if err != nil {
+			return nil, fmt.Errorf("decode output item: %w", err)
+		}
+
+		switch call.Type {
+		case "message":
+			text, err := outputText([]json.RawMessage{raw})
+			if err != nil {
+				return nil, err
+			}
+
+			text = strings.TrimSpace(text)
+			if text == "" {
+				continue
+			}
+
+			_, err = l.Append("reply", text)
+			if err != nil {
+				return nil, fmt.Errorf("%w: %w", errLogWrite, err)
+			}
+		case "function_call":
+			output, err := l.tools.Call(ctx, call.Name, call.Arguments)
+			if err != nil {
+				return nil, fmt.Errorf("%w: %w", errLogWrite, err)
+			}
+
+			outputs = append(outputs, functionCallOutput{
+				Type:   "function_call_output",
+				CallID: call.CallID,
+				Output: output,
+			})
+		}
+	}
+
+	if len(outputs) == 0 {
+		return nil, nil
+	}
+
+	input = append(input, outputs...)
+	for _, message := range l.take() {
+		input = append(input, userMessage(message.Text))
+	}
+
+	return input, nil
+}
+
+// state returns the per-turn state: the date and time of the turn.
+func (l *loop) state() string {
+	return "Now: " + l.clock().Format("Monday 2006-01-02 15:04 -07:00")
+}
+
+// turnInput returns the input of the first request of a turn: one user message
+// with the view, the per-turn state, and each new message whole. The view
+// leaves out the leaf lines of the new messages, which come whole after it.
+func turnInput(view, state string, messages []Message) []any {
+	parts := []string{view + "\n", state + "\n"}
+	for _, message := range messages {
+		parts = append(parts, message.Text)
+	}
+
+	return []any{userMessage(parts...)}
+}
+
+// inputItem returns an output item as an input item for the next request. The
+// calls do not store their items, so the item goes back whole, without its id.
+func inputItem(raw json.RawMessage) (map[string]any, error) {
+	var item map[string]any
+	err := json.Unmarshal(raw, &item)
+	if err != nil {
+		return nil, fmt.Errorf("decode output item: %w", err)
+	}
+
+	delete(item, "id")
+
+	return item, nil
+}
+
+// turnError returns the text of the error that ended a turn.
+func turnError(ctx context.Context, err error) string {
+	if ctx.Err() != nil {
+		return "interrupted"
+	}
+
+	return err.Error()
+}
diff --git a/turn_test.go b/turn_test.go
new file mode 100644
index 0000000..1b17940
--- /dev/null
+++ b/turn_test.go
@@ -0,0 +1,355 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestTurnRunsToolsUntilTheFinalAnswer(t *testing.T) {
+	server := newFakeResponses(t)
+	server.reply = func(w http.ResponseWriter, call fakeCall) {
+		if call.number == 0 {
+			writeEvents(w, completedEvent([]any{
+				reasoningItem("rs_1", "opaque thought"),
+				functionCallItem("fc_1", "call_1", "shell", `{"command":"echo hi"}`),
+			}, 100, 0, 5))
+
+			return
+		}
+
+		writeEvents(w, completedEvent([]any{messageItem("It said hi.")}, 120, 100, 5))
+	}
+
+	test := newTestLoop(t, server)
+	_, err := test.loop.Submit("Run echo hi.")
+	require.NoError(t, err)
+	test.events.WaitFor(t, "idle", 1)
+	require.Equal(t, 2, server.Calls())
+
+	first := server.Call(0).body
+	second := server.Call(1).body
+	instructions, err := test.agent.Prompt()
+	require.NoError(t, err)
+	require.Equal(t, instructions, first["instructions"])
+	require.Equal(t, test.agent.config.Model, first["model"])
+
+	// The second request begins with the whole first one.
+	firstInput := first["input"].([]any)
+	secondInput := second["input"].([]any)
+	require.Equal(t, firstInput, secondInput[:len(firstInput)])
+	require.Equal(t, []any{
+		map[string]any{"type": "reasoning", "encrypted_content": "opaque thought", "summary": []any{}},
+		map[string]any{"type": "function_call", "call_id": "call_1", "name": "shell", "arguments": `{"command":"echo hi"}`},
+		map[string]any{"type": "function_call_output", "call_id": "call_1", "output": "hi\n"},
+	}, secondInput[len(firstInput):])
+
+	require.Equal(t, []string{
+		"user: Run echo hi.",
+		`tool: shell {"command":"echo hi"}`,
+		"echo: hi\n",
+		"reply: It said hi.",
+	}, test.Log(t))
+	require.Equal(t, []string{"user", "busy", "tool", "echo", "reply", "idle"}, test.events.Kinds())
+}
+
+func TestFirstRequestHoldsTheViewTheStateAndTheMessage(t *testing.T) {
+	server := newFakeResponses(t)
+	test := newTestLoop(t, server)
+	_, err := test.memory.Append("user", "an earlier message")
+	require.NoError(t, err)
+
+	_, err = test.loop.Submit("The new message.")
+	require.NoError(t, err)
+	test.events.WaitFor(t, "idle", 1)
+
+	require.Equal(t, []string{
+		"<chat>\n0+1|user: an earlier message\n</chat>\n",
+		"Now: Thursday 2026-01-01 12:00 +00:00\n",
+		"The new message.",
+	}, inputParts(t, server.Call(0)))
+}
+
+func TestMessageDuringATurnJoinsTheNextRequest(t *testing.T) {
+	server := newFakeResponses(t)
+	arrived := make(chan struct{})
+	release := make(chan struct{})
+	server.reply = func(w http.ResponseWriter, call fakeCall) {
+		if call.number == 0 {
+			close(arrived)
+			<-release
+			writeEvents(w, completedEvent([]any{functionCallItem("fc_1", "call_1", "date", `{"id":0}`)}, 100, 0, 5))
+
+			return
+		}
+
+		writeEvents(w, completedEvent([]any{messageItem("done")}, 100, 0, 5))
+	}
+
+	test := newTestLoop(t, server)
+	_, err := test.loop.Submit("first")
+	require.NoError(t, err)
+
+	<-arrived
+	_, err = test.loop.Submit("second, during the turn")
+	require.NoError(t, err)
+	close(release)
+
+	test.events.WaitFor(t, "idle", 1)
+	input := server.Call(1).body["input"].([]any)
+	require.Equal(t, map[string]any{
+		"role":    "user",
+		"content": []any{map[string]any{"type": "input_text", "text": "second, during the turn"}},
+	}, input[len(input)-1])
+
+	time.Sleep(50 * time.Millisecond)
+	require.Equal(t, 2, server.Calls())
+	require.Equal(t, 1, test.events.Count("busy"))
+}
+
+func TestMessageDuringTheFinalRequestStartsANewTurn(t *testing.T) {
+	server := newFakeResponses(t)
+	arrived := make(chan struct{})
+	release := make(chan struct{})
+	server.reply = func(w http.ResponseWriter, call fakeCall) {
+		if call.number == 0 {
+			close(arrived)
+			<-release
+		}
+
+		writeEvents(w, completedEvent([]any{messageItem("answer")}, 100, 0, 5))
+	}
+
+	test := newTestLoop(t, server)
+	_, err := test.loop.Submit("first")
+	require.NoError(t, err)
+
+	<-arrived
+	_, err = test.loop.Submit("second")
+	require.NoError(t, err)
+	close(release)
+
+	test.events.WaitFor(t, "idle", 2)
+	require.Equal(t, 2, server.Calls())
+
+	parts := inputParts(t, server.Call(1))
+	require.Equal(t, "second", parts[len(parts)-1])
+	require.Contains(t, parts[0], "|reply: answer\n")
+}
+
+func TestTurnWaitsForTheSummaries(t *testing.T) {
+	server := newFakeResponses(t)
+	summarizer := newFakeSummarizer()
+	summarizer.gate = make(chan struct{})
+	test := newTestLoopWith(t, server, summarizer)
+
+	_, err := test.memory.Append("echo", strings.Repeat("long output ", 100))
+	require.NoError(t, err)
+
+	_, err = test.loop.Submit("go on")
+	require.NoError(t, err)
+
+	time.Sleep(50 * time.Millisecond)
+	require.Equal(t, 0, server.Calls())
+
+	close(summarizer.gate)
+	test.events.WaitFor(t, "idle", 1)
+	require.Equal(t, 1, server.Calls())
+	require.NotContains(t, inputParts(t, server.Call(0))[0], pending)
+}
+
+func TestInterruptEndsTheTurn(t *testing.T) {
+	server := newFakeResponses(t)
+	arrived := make(chan struct{})
+	release := make(chan struct{})
+	server.reply = func(w http.ResponseWriter, call fakeCall) {
+		if call.number == 0 {
+			close(arrived)
+			<-release
+		}
+
+		writeEvents(w, completedEvent([]any{messageItem("answer")}, 100, 0, 5))
+	}
+
+	test := newTestLoop(t, server)
+	_, err := test.loop.Submit("a long task")
+	require.NoError(t, err)
+
+	<-arrived
+	require.True(t, test.loop.Interrupt())
+	test.events.WaitFor(t, "idle", 1)
+	close(release)
+
+	require.Equal(t, "interrupted", test.events.Last("error"))
+	require.Equal(t, []string{"user: a long task"}, test.Log(t))
+	require.False(t, test.loop.Interrupt())
+
+	_, err = test.loop.Submit("again")
+	require.NoError(t, err)
+	test.events.WaitFor(t, "idle", 2)
+	require.Equal(t, "reply: answer", test.Log(t)[2])
+}
+
+func TestFailedCallEndsTheTurnWithoutARetry(t *testing.T) {
+	server := newFakeResponses(t)
+	server.reply = func(w http.ResponseWriter, call fakeCall) {
+		http.Error(w, "busy", http.StatusServiceUnavailable)
+	}
+
+	test := newTestLoop(t, server)
+	_, err := test.loop.Submit("hello")
+	require.NoError(t, err)
+	test.events.WaitFor(t, "idle", 1)
+
+	time.Sleep(50 * time.Millisecond)
+	require.Equal(t, 1, server.Calls())
+	require.Contains(t, test.events.Last("error"), "HTTP 503")
+}
+
+// testLoop is a loop that runs in the background of a test, with its parts.
+type testLoop struct {
+	agent  *Agent
+	memory *Memory
+	loop   *loop
+	events *eventRecorder
+}
+
+// Log returns the logged messages as "kind: text".
+func (l *testLoop) Log(t *testing.T) []string {
+	t.Helper()
+
+	var lines []string
+	for id := range l.memory.Len() {
+		message, err := l.memory.Message(id)
+		require.NoError(t, err)
+
+		lines = append(lines, message.Kind+": "+message.Text)
+	}
+
+	return lines
+}
+
+// eventRecorder keeps the events of a loop.
+type eventRecorder struct {
+	mutex  sync.Mutex
+	events []Event
+}
+
+func (r *eventRecorder) Add(event Event) {
+	r.mutex.Lock()
+	defer r.mutex.Unlock()
+
+	r.events = append(r.events, event)
+}
+
+func (r *eventRecorder) Kinds() []string {
+	r.mutex.Lock()
+	defer r.mutex.Unlock()
+
+	kinds := make([]string, len(r.events))
+	for n, event := range r.events {
+		kinds[n] = event.Kind
+	}
+
+	return kinds
+}
+
+func (r *eventRecorder) Count(kind string) int {
+	count := 0
+	for _, each := range r.Kinds() {
+		if each == kind {
+			count++
+		}
+	}
+
+	return count
+}
+
+// Last returns the text of the last event of kind.
+func (r *eventRecorder) Last(kind string) string {
+	r.mutex.Lock()
+	defer r.mutex.Unlock()
+
+	for n := len(r.events) - 1; n >= 0; n-- {
+		if r.events[n].Kind == kind {
+			return r.events[n].Text
+		}
+	}
+
+	return ""
+}
+
+// WaitFor waits until count events of kind came.
+func (r *eventRecorder) WaitFor(t *testing.T, kind string, count int) {
+	t.Helper()
+
+	require.Eventually(t, func() bool {
+		return r.Count(kind) >= count
+	}, 10*time.Second, time.Millisecond)
+}
+
+func newTestLoop(t *testing.T, server *fakeResponses) *testLoop {
+	t.Helper()
+
+	return newTestLoopWith(t, server, newFakeSummarizer())
+}
+
+// newTestLoopWith returns a running loop on a new agent whose builds use
+// summarizer and whose commands run in a temporary directory.
+func newTestLoopWith(t *testing.T, server *fakeResponses, summarizer Summarizer) *testLoop {
+	t.Helper()
+
+	agent, err := openAgent(t.TempDir())
+	require.NoError(t, err)
+
+	agent.config.Workdir = t.TempDir()
+	clock := newTestClock()
+	memory, err := openMemory(t.Context(), t.TempDir(), clock.Now, summarizer)
+	require.NoError(t, err)
+
+	test := &testLoop{
+		agent:  agent,
+		memory: memory,
+		events: &eventRecorder{},
+	}
+
+	test.loop = newLoop(agent, memory, newTestClient(t, server), clock.Now, test.events.Add)
+	ctx, cancel := context.WithCancel(t.Context())
+	done := make(chan error)
+	go func() {
+		done <- test.loop.Run(ctx)
+	}()
+
+	t.Cleanup(func() {
+		cancel()
+		require.True(t, errors.Is(<-done, context.Canceled))
+		require.NoError(t, memory.Close())
+	})
+
+	return test
+}
+
+func reasoningItem(id, encrypted string) map[string]any {
+	return map[string]any{
+		"type":              "reasoning",
+		"id":                id,
+		"encrypted_content": encrypted,
+		"summary":           []any{},
+	}
+}
+
+func functionCallItem(id, callID, name, arguments string) map[string]any {
+	return map[string]any{
+		"type":      "function_call",
+		"id":        id,
+		"call_id":   callID,
+		"name":      name,
+		"arguments": arguments,
+	}
+}
diff --git a/view.go b/view.go
index 70182d0..8e71eec 100644
--- a/view.go
+++ b/view.go
@@ -280,9 +280,19 @@ func (v *View) lineSize(line nodeKey) int {
 // Render returns the view as the model reads it: one line "id+n|text" for each
 // node inside <chat> tags, with the newlines of the text as spaces.
 func (v *View) Render() string {
+	return v.RenderWithout(nil)
+}
+
+// RenderWithout returns the view as Render does, without the leaf lines of the
+// messages in skip. A line that merges such a message with others stays.
+func (v *View) RenderWithout(skip map[int]bool) string {
 	var text strings.Builder
 	text.WriteString("<chat>\n")
 	for _, line := range v.lines {
+		if line.level == 0 && skip[line.index] {
+			continue
+		}
+
 		v.renderLine(&text, line)
 	}