feat(chat,seahorse): persist and display model_name across history (#2897)

* feat(chat,seahorse): persist and display model_name across history

* test(seahorse): fix lint regressions in repair coverage

* fix(pico): preserve model_name in live updates

* fix(pico): preserve model_name through live stream wrappers

pkg/channels/interfaces.go

@@ -20,6 +20,17 @@ type MessageEditor interface {
 	EditMessage(ctx context.Context, chatID string, messageID string, content string) error
 }
 
+// MessageEditorWithPayload extends MessageEditor for channels that can update
+// structured message metadata in addition to plain text content.
+type MessageEditorWithPayload interface {
+	EditMessageWithPayload(
+		ctx context.Context,
+		chatID string,
+		messageID string,
+		payload map[string]any,
+	) error
+}
+
 // MessageDeleter — channels that can delete a message by ID.
 type MessageDeleter interface {
 	DeleteMessage(ctx context.Context, chatID string, messageID string) error

pkg/channels/manager.go

@@ -191,6 +191,19 @@ func outboundMessageBypassesPlaceholderEdit(msg bus.OutboundMessage) bool {
 	return strings.EqualFold(kind, "thought") || strings.EqualFold(kind, "tool_calls")
 }
 
+func outboundMessageEditPayload(msg bus.OutboundMessage, content string) map[string]any {
+	payload := map[string]any{
+		"content": content,
+	}
+	if len(msg.Context.Raw) == 0 {
+		return payload
+	}
+	if modelName := strings.TrimSpace(msg.Context.Raw["model_name"]); modelName != "" {
+		payload["model_name"] = modelName
+	}
+	return payload
+}
+
 func outboundMediaChannel(msg bus.OutboundMediaMessage) string {
 	return msg.Context.Channel
 }
@@ -394,7 +407,16 @@ func (m *Manager) preSend(ctx context.Context, name string, msg bus.OutboundMess
 					if deleter, ok := ch.(MessageDeleter); ok {
 						deleter.DeleteMessage(ctx, chatID, entry.id) // best effort
 					} else if editor, ok := ch.(MessageEditor); ok {
-						editor.EditMessage(ctx, chatID, entry.id, msg.Content) // fallback
+						if payloadEditor, ok := ch.(MessageEditorWithPayload); ok {
+							_ = payloadEditor.EditMessageWithPayload(
+								ctx,
+								chatID,
+								entry.id,
+								outboundMessageEditPayload(msg, msg.Content),
+							)
+						} else {
+							editor.EditMessage(ctx, chatID, entry.id, msg.Content) // fallback
+						}
 					}
 				}
 			}
@@ -446,7 +468,18 @@ func (m *Manager) preSend(ctx context.Context, name string, msg bus.OutboundMess
 					trackedContent = prepareToolFeedbackMessageContent(ch, msg.Content)
 					content = InitialAnimatedToolFeedbackContent(trackedContent)
 				}
-				if err := editor.EditMessage(ctx, chatID, entry.id, content); err == nil {
+				err := func() error {
+					if payloadEditor, ok := ch.(MessageEditorWithPayload); ok {
+						return payloadEditor.EditMessageWithPayload(
+							ctx,
+							chatID,
+							entry.id,
+							outboundMessageEditPayload(msg, content),
+						)
+					}
+					return editor.EditMessage(ctx, chatID, entry.id, content)
+				}()
+				if err == nil {
 					trackedChatID := trackedToolFeedbackMessageChatID(ch, chatID, &msg.Context)
 					if tracker, ok := ch.(toolFeedbackMessageTracker); ok && isToolFeedback {
 						tracker.RecordToolFeedbackMessage(trackedChatID, entry.id, trackedContent)
@@ -643,6 +676,18 @@ func reasoningStreamerFrom(streamer bus.Streamer) bus.ReasoningStreamer {
 	return nil
 }
 
+type modelNameStreamer interface {
+	SetModelName(modelName string)
+}
+
+func setStreamerModelName(streamer any, modelName string) {
+	setter, ok := streamer.(modelNameStreamer)
+	if !ok {
+		return
+	}
+	setter.SetModelName(modelName)
+}
+
 // splitMarkerStreamer turns accumulated streaming text containing
 // MessageSplitMarker into separate channel stream messages.
 type splitMarkerStreamer struct {
@@ -654,6 +699,7 @@ type splitMarkerStreamer struct {
 	finalized      bool
 	onFinalize     func(context.Context, string)
 	clearMarker    func()
+	modelName      string
 }
 
 func (s *splitMarkerStreamer) Update(ctx context.Context, content string) error {
@@ -682,6 +728,7 @@ func (s *splitMarkerStreamer) UpdateReasoning(ctx context.Context, content strin
 	if s.reasoning == nil {
 		return nil
 	}
+	setStreamerModelName(s.reasoning, s.modelName)
 	return s.reasoning.UpdateReasoning(ctx, content)
 }
 
@@ -691,9 +738,18 @@ func (s *splitMarkerStreamer) FinalizeReasoning(ctx context.Context, content str
 	if s.reasoning == nil {
 		return nil
 	}
+	setStreamerModelName(s.reasoning, s.modelName)
 	return s.reasoning.FinalizeReasoning(ctx, content)
 }
 
+func (s *splitMarkerStreamer) SetModelName(modelName string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.modelName = strings.TrimSpace(modelName)
+	setStreamerModelName(s.current, s.modelName)
+	setStreamerModelName(s.reasoning, s.modelName)
+}
+
 func (s *splitMarkerStreamer) Cancel(ctx context.Context) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -772,6 +828,7 @@ func (s *splitMarkerStreamer) ensureCurrentLocked(ctx context.Context) error {
 		return err
 	}
 	s.current = streamer
+	setStreamerModelName(s.current, s.modelName)
 	return nil
 }
 
@@ -856,6 +913,10 @@ func (s *finalizeHookStreamer) FinalizeReasoning(ctx context.Context, content st
 	return nil
 }
 
+func (s *finalizeHookStreamer) SetModelName(modelName string) {
+	setStreamerModelName(s.Streamer, strings.TrimSpace(modelName))
+}
+
 func (s *finalizeHookStreamer) runFinalizeHook(ctx context.Context, content string) {
 	if s.onFinalize != nil {
 		s.onFinalize(ctx, content)

pkg/channels/manager_test.go

@@ -142,11 +142,21 @@ func (m *mockReasoningStreamer) FinalizeReasoning(_ context.Context, content str
 	return nil
 }
 
+type modelTrackingReasoningStreamer struct {
+	mockReasoningStreamer
+	modelNames []string
+}
+
+func (m *modelTrackingReasoningStreamer) SetModelName(modelName string) {
+	m.modelNames = append(m.modelNames, strings.TrimSpace(modelName))
+}
+
 type recordingStreamSegment struct {
 	updates       []string
 	finals        []string
 	finalUsage    *bus.ContextUsage
 	canceledCount int
+	modelNames    []string
 }
 
 func (s *recordingStreamSegment) Update(_ context.Context, content string) error {
@@ -168,6 +178,10 @@ func (s *recordingStreamSegment) Cancel(context.Context) {
 	s.canceledCount++
 }
 
+func (s *recordingStreamSegment) SetModelName(modelName string) {
+	s.modelNames = append(s.modelNames, strings.TrimSpace(modelName))
+}
+
 type mockStreamingChannel struct {
 	mockMessageEditor
 	streamer        Streamer
@@ -2068,6 +2082,42 @@ func TestGetStreamer_PreservesReasoningStreamer(t *testing.T) {
 	}
 }
 
+func TestGetStreamer_PreservesModelNameSetter(t *testing.T) {
+	m := newTestManager()
+	inner := &modelTrackingReasoningStreamer{}
+	ch := &mockStreamingChannel{
+		streamer: inner,
+	}
+	m.channels["test"] = ch
+
+	streamer, ok := m.GetStreamer(context.Background(), "test", "123", "")
+	if !ok {
+		t.Fatal("expected streamer to be available")
+	}
+	setter, ok := streamer.(interface{ SetModelName(modelName string) })
+	if !ok {
+		t.Fatal("manager-wrapped streamer should preserve SetModelName")
+	}
+	setter.SetModelName("gpt-5.4")
+	if err := streamer.Update(context.Background(), "hello"); err != nil {
+		t.Fatalf("Update() error = %v", err)
+	}
+	reasoningStreamer, ok := streamer.(bus.ReasoningStreamer)
+	if !ok {
+		t.Fatal("manager-wrapped streamer should preserve ReasoningStreamer")
+	}
+	setter.SetModelName("gpt-5.4")
+	if err := reasoningStreamer.UpdateReasoning(context.Background(), "thinking"); err != nil {
+		t.Fatalf("UpdateReasoning() error = %v", err)
+	}
+	if len(inner.modelNames) != 2 {
+		t.Fatalf("model name calls = %v, want 2 forwarded calls", inner.modelNames)
+	}
+	if inner.modelNames[0] != "gpt-5.4" || inner.modelNames[1] != "gpt-5.4" {
+		t.Fatalf("model name calls = %v, want both forwarded as gpt-5.4", inner.modelNames)
+	}
+}
+
 func TestGetStreamer_SplitOnMarkerStreamsSeparateSegments(t *testing.T) {
 	m := newTestManager()
 	m.config = &config.Config{
@@ -2188,6 +2238,58 @@ func TestGetStreamer_SplitOnMarkerKeepsReasoningOnInitialStreamer(t *testing.T)
 	}
 }
 
+func TestGetStreamer_SplitOnMarkerPreservesModelNameSetter(t *testing.T) {
+	m := newTestManager()
+	m.config = &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				SplitOnMarker: true,
+			},
+		},
+	}
+
+	initial := &modelTrackingReasoningStreamer{}
+	next := &recordingStreamSegment{}
+	callCount := 0
+	ch := &mockStreamingChannel{
+		beginStreamFn: func(context.Context, string) (Streamer, error) {
+			callCount++
+			if callCount == 1 {
+				return initial, nil
+			}
+			return next, nil
+		},
+	}
+	m.channels["test"] = ch
+
+	streamer, ok := m.GetStreamer(context.Background(), "test", "123", "")
+	if !ok {
+		t.Fatal("expected streamer to be available")
+	}
+	setter, ok := streamer.(interface{ SetModelName(modelName string) })
+	if !ok {
+		t.Fatal("split streamer should preserve SetModelName")
+	}
+	setter.SetModelName("gpt-5.4-mini")
+	if err := streamer.Update(context.Background(), "hello<|[SPLIT]|>world"); err != nil {
+		t.Fatalf("Update() error = %v", err)
+	}
+	reasoningStreamer, ok := streamer.(bus.ReasoningStreamer)
+	if !ok {
+		t.Fatal("split streamer should preserve ReasoningStreamer")
+	}
+	if err := reasoningStreamer.UpdateReasoning(context.Background(), "thinking"); err != nil {
+		t.Fatalf("UpdateReasoning() error = %v", err)
+	}
+
+	if len(initial.modelNames) == 0 || initial.modelNames[0] != "gpt-5.4-mini" {
+		t.Fatalf("initial model names = %v, want forwarded gpt-5.4-mini", initial.modelNames)
+	}
+	if len(next.modelNames) == 0 || next.modelNames[0] != "gpt-5.4-mini" {
+		t.Fatalf("next model names = %v, want forwarded gpt-5.4-mini", next.modelNames)
+	}
+}
+
 func TestGetStreamer_FinalizeSeparateMessagesClearsTrackedToolFeedback(t *testing.T) {
 	m := newTestManager()
 	m.config = &config.Config{

pkg/channels/pico/pico.go

@@ -325,6 +325,9 @@ func (c *PicoChannel) Send(ctx context.Context, msg bus.OutboundMessage) ([]stri
 		PayloadKeyContent: content,
 		"message_id":      msgID,
 	}
+	if modelName := strings.TrimSpace(msg.Context.Raw[PayloadKeyModelName]); modelName != "" {
+		payload[PayloadKeyModelName] = modelName
+	}
 	switch {
 	case isThought:
 		payload[PayloadKeyKind] = MessageKindThought
@@ -359,6 +362,15 @@ func (c *PicoChannel) EditMessage(ctx context.Context, chatID string, messageID
 	return c.editMessage(ctx, chatID, messageID, content, nil)
 }
 
+func (c *PicoChannel) EditMessageWithPayload(
+	ctx context.Context,
+	chatID string,
+	messageID string,
+	payload map[string]any,
+) error {
+	return c.editMessagePayload(ctx, chatID, messageID, payload, nil)
+}
+
 // DeleteMessage implements channels.MessageDeleter.
 func (c *PicoChannel) DeleteMessage(ctx context.Context, chatID string, messageID string) error {
 	outMsg := newMessage(TypeMessageDelete, map[string]any{
@@ -419,14 +431,23 @@ func (c *PicoChannel) finalizeTrackedToolFeedbackMessage(
 	ctx context.Context,
 	chatID string,
 	content string,
-	editFn func(context.Context, string, string, string, *bus.ContextUsage) error,
+	editFn func(context.Context, string, string, map[string]any, *bus.ContextUsage) error,
+	payload map[string]any,
 	contextUsage *bus.ContextUsage,
 ) ([]string, bool) {
 	msgID, baseContent, ok := c.takeToolFeedbackMessage(chatID)
 	if !ok || editFn == nil {
 		return nil, false
 	}
-	if err := editFn(ctx, chatID, msgID, content, contextUsage); err != nil {
+	if payload == nil {
+		payload = map[string]any{
+			PayloadKeyContent: content,
+		}
+	}
+	if _, ok := payload[PayloadKeyContent]; !ok {
+		payload[PayloadKeyContent] = content
+	}
+	if err := editFn(ctx, chatID, msgID, payload, contextUsage); err != nil {
 		c.RecordToolFeedbackMessage(chatID, msgID, baseContent)
 		return nil, false
 	}
@@ -437,7 +458,20 @@ func (c *PicoChannel) FinalizeToolFeedbackMessage(ctx context.Context, msg bus.O
 	if !outboundMessageFinalizesTrackedToolFeedback(msg) {
 		return nil, false
 	}
-	return c.finalizeTrackedToolFeedbackMessage(ctx, msg.ChatID, msg.Content, c.editMessage, msg.ContextUsage)
+	payload := map[string]any{
+		PayloadKeyContent: msg.Content,
+	}
+	if modelName := strings.TrimSpace(msg.Context.Raw[PayloadKeyModelName]); modelName != "" {
+		payload[PayloadKeyModelName] = modelName
+	}
+	return c.finalizeTrackedToolFeedbackMessage(
+		ctx,
+		msg.ChatID,
+		msg.Content,
+		c.editMessagePayload,
+		payload,
+		msg.ContextUsage,
+	)
 }
 
 // StartTyping implements channels.TypingCapable.
@@ -496,6 +530,7 @@ func (c *PicoChannel) BeginStream(ctx context.Context, chatID string) (channels.
 type picoStreamer struct {
 	channel          *PicoChannel
 	chatID           string
+	modelName        string
 	messageID        string
 	reasoningID      string
 	throttleInterval time.Duration
@@ -509,6 +544,15 @@ type picoStreamer struct {
 	mu               sync.Mutex
 }
 
+func (s *picoStreamer) SetModelName(modelName string) {
+	if s == nil {
+		return
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.modelName = strings.TrimSpace(modelName)
+}
+
 func (s *picoStreamer) Update(ctx context.Context, content string) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -613,13 +657,23 @@ func (s *picoStreamer) sendLocked(ctx context.Context, content string, contextUs
 			PayloadKeyContent: content,
 			"message_id":      s.messageID,
 		}
+		if s.modelName != "" {
+			payload[PayloadKeyModelName] = s.modelName
+		}
 		setContextUsagePayload(payload, contextUsage)
 		outMsg := newMessage(TypeMessageCreate, payload)
 		if err := s.channel.broadcastToSession(s.chatID, outMsg); err != nil {
 			return err
 		}
 	} else if content != s.lastContent || contextUsage != nil {
-		if err := s.channel.editMessage(ctx, s.chatID, s.messageID, content, contextUsage); err != nil {
+		payload := map[string]any{
+			PayloadKeyContent: content,
+			"message_id":      s.messageID,
+		}
+		if s.modelName != "" {
+			payload[PayloadKeyModelName] = s.modelName
+		}
+		if err := s.channel.editMessagePayload(ctx, s.chatID, s.messageID, payload, contextUsage); err != nil {
 			return err
 		}
 	}
@@ -642,6 +696,9 @@ func (s *picoStreamer) sendReasoningLocked(ctx context.Context, content string)
 			PayloadKeyKind:    MessageKindThought,
 			PayloadKeyThought: true,
 		}
+		if s.modelName != "" {
+			payload[PayloadKeyModelName] = s.modelName
+		}
 		outMsg := newMessage(TypeMessageCreate, payload)
 		if err := s.channel.broadcastToSession(s.chatID, outMsg); err != nil {
 			return err
@@ -653,6 +710,9 @@ func (s *picoStreamer) sendReasoningLocked(ctx context.Context, content string)
 			PayloadKeyKind:    MessageKindThought,
 			PayloadKeyThought: true,
 		}
+		if s.modelName != "" {
+			payload[PayloadKeyModelName] = s.modelName
+		}
 		outMsg := newMessage(TypeMessageUpdate, payload)
 		if err := s.channel.broadcastToSession(s.chatID, outMsg); err != nil {
 			return err
@@ -744,6 +804,9 @@ func (c *PicoChannel) SendMedia(ctx context.Context, msg bus.OutboundMediaMessag
 		"attachments":     attachments,
 		"message_id":      msgID,
 	})
+	if modelName := strings.TrimSpace(msg.Context.Raw[PayloadKeyModelName]); modelName != "" {
+		outMsg.Payload[PayloadKeyModelName] = modelName
+	}
 
 	if err := c.broadcastToSession(msg.ChatID, outMsg); err != nil {
 		return nil, err
@@ -1358,11 +1421,30 @@ func (c *PicoChannel) editMessage(
 	content string,
 	contextUsage *bus.ContextUsage,
 ) error {
-	payload := map[string]any{
-		"message_id": messageID,
-		"content":    content,
+	return c.editMessagePayload(ctx, chatID, messageID, map[string]any{
+		PayloadKeyContent: content,
+	}, contextUsage)
+}
+
+func (c *PicoChannel) editMessagePayload(
+	ctx context.Context,
+	chatID string,
+	messageID string,
+	payload map[string]any,
+	contextUsage *bus.ContextUsage,
+) error {
+	if payload == nil {
+		payload = map[string]any{}
 	}
-	setContextUsagePayload(payload, contextUsage)
-	outMsg := newMessage(TypeMessageUpdate, payload)
+	normalized := make(map[string]any, len(payload)+1)
+	for key, value := range payload {
+		normalized[key] = value
+	}
+	if _, ok := normalized[PayloadKeyContent]; !ok {
+		normalized[PayloadKeyContent] = ""
+	}
+	normalized["message_id"] = messageID
+	setContextUsagePayload(normalized, contextUsage)
+	outMsg := newMessage(TypeMessageUpdate, normalized)
 	return c.broadcastToSession(chatID, outMsg)
 }

pkg/channels/pico/pico_test.go

@@ -46,12 +46,15 @@ func TestFinalizeTrackedToolFeedbackMessage_StopsTrackingBeforeEdit(t *testing.T
 		context.Background(),
 		"pico:chat-1",
 		"final reply",
-		func(_ context.Context, chatID, messageID, content string, contextUsage *bus.ContextUsage) error {
+		func(_ context.Context, chatID, messageID string, payload map[string]any, contextUsage *bus.ContextUsage) error {
 			if _, ok := ch.currentToolFeedbackMessage(chatID); ok {
 				t.Fatal("expected tracked tool feedback to be stopped before edit")
 			}
-			if chatID != "pico:chat-1" || messageID != "msg-1" || content != "final reply" {
-				t.Fatalf("unexpected edit args: %s %s %s", chatID, messageID, content)
+			if chatID != "pico:chat-1" || messageID != "msg-1" {
+				t.Fatalf("unexpected edit args: %s %s", chatID, messageID)
+			}
+			if got := payload[PayloadKeyContent]; got != "final reply" {
+				t.Fatalf("unexpected content payload: %#v", got)
 			}
 			if contextUsage != nil {
 				t.Fatalf("unexpected context usage: %+v", contextUsage)
@@ -59,6 +62,7 @@ func TestFinalizeTrackedToolFeedbackMessage_StopsTrackingBeforeEdit(t *testing.T
 			return nil
 		},
 		nil,
+		nil,
 	)
 	if !handled {
 		t.Fatal("expected finalizeTrackedToolFeedbackMessage to handle tracked message")
@@ -115,7 +119,8 @@ func TestSend_ThoughtMessageDoesNotFinalizeTrackedToolFeedback(t *testing.T) {
 			Channel: "pico",
 			ChatID:  "pico:sess-1",
 			Raw: map[string]string{
-				"message_kind": MessageKindThought,
+				"message_kind":      MessageKindThought,
+				PayloadKeyModelName: "gpt-5.4-mini",
 			},
 		},
 	}); err != nil {
@@ -134,6 +139,9 @@ func TestSend_ThoughtMessageDoesNotFinalizeTrackedToolFeedback(t *testing.T) {
 		if got := payload[PayloadKeyKind]; got != MessageKindThought {
 			t.Fatalf("thought kind = %#v, want %q", got, MessageKindThought)
 		}
+		if got := payload[PayloadKeyModelName]; got != "gpt-5.4-mini" {
+			t.Fatalf("thought model_name = %#v, want %q", got, "gpt-5.4-mini")
+		}
 		if got := payload["message_id"]; got == "msg-progress" || got == nil || got == "" {
 			t.Fatalf("thought message_id = %#v, want new non-progress id", got)
 		}
@@ -151,6 +159,9 @@ func TestSend_ThoughtMessageDoesNotFinalizeTrackedToolFeedback(t *testing.T) {
 		Context: bus.InboundContext{
 			Channel: "pico",
 			ChatID:  "pico:sess-1",
+			Raw: map[string]string{
+				PayloadKeyModelName: "gpt-5.4",
+			},
 		},
 		ContextUsage: &bus.ContextUsage{
 			UsedTokens:       321,
@@ -174,6 +185,9 @@ func TestSend_ThoughtMessageDoesNotFinalizeTrackedToolFeedback(t *testing.T) {
 		if got := payload[PayloadKeyContent]; got != "final reply" {
 			t.Fatalf("final content = %#v, want %q", got, "final reply")
 		}
+		if got := payload[PayloadKeyModelName]; got != "gpt-5.4" {
+			t.Fatalf("final model_name = %#v, want %q", got, "gpt-5.4")
+		}
 		rawUsage, ok := payload["context_usage"].(map[string]any)
 		if !ok {
 			t.Fatalf("final context_usage = %#v, want map payload", payload["context_usage"])
@@ -193,6 +207,54 @@ func TestSend_ThoughtMessageDoesNotFinalizeTrackedToolFeedback(t *testing.T) {
 	}
 }
 
+func TestSend_ToolCallsMessageIncludesModelName(t *testing.T) {
+	ch := newTestPicoChannel(t)
+
+	if err := ch.Start(context.Background()); err != nil {
+		t.Fatalf("Start() error = %v", err)
+	}
+	defer ch.Stop(context.Background())
+
+	clientConn, received, cleanup := newTestPicoWebSocket(t)
+	defer cleanup()
+	ch.addConnForTest(&picoConn{id: "conn-1", conn: clientConn, sessionID: "sess-1"})
+
+	if _, err := ch.Send(context.Background(), bus.OutboundMessage{
+		ChatID:  "pico:sess-1",
+		Content: "",
+		Context: bus.InboundContext{
+			Channel: "pico",
+			ChatID:  "pico:sess-1",
+			Raw: map[string]string{
+				"message_kind":      MessageKindToolCalls,
+				PayloadKeyModelName: "gpt-5.4",
+				PayloadKeyToolCalls: `[{"id":"call_1","type":"function","function":{"name":"read_file","arguments":"{\"path\":\"README.md\"}"}}]`,
+			},
+		},
+	}); err != nil {
+		t.Fatalf("Send(tool_calls) error = %v", err)
+	}
+
+	select {
+	case msg := <-received:
+		if msg.Type != TypeMessageCreate {
+			t.Fatalf("tool_calls message type = %q, want %q", msg.Type, TypeMessageCreate)
+		}
+		payload := msg.Payload
+		if got := payload[PayloadKeyKind]; got != MessageKindToolCalls {
+			t.Fatalf("tool_calls kind = %#v, want %q", got, MessageKindToolCalls)
+		}
+		if got := payload[PayloadKeyModelName]; got != "gpt-5.4" {
+			t.Fatalf("tool_calls model_name = %#v, want %q", got, "gpt-5.4")
+		}
+		if _, ok := payload[PayloadKeyToolCalls].([]any); !ok {
+			t.Fatalf("tool_calls payload = %#v, want parsed array", payload[PayloadKeyToolCalls])
+		}
+	case <-time.After(time.Second):
+		t.Fatal("expected tool_calls message to be delivered")
+	}
+}
+
 func TestSendPlaceholder_EmitsNormalMessageWithoutKind(t *testing.T) {
 	ch := newTestPicoChannel(t)
 	ch.bc.Placeholder.Enabled = true
@@ -257,6 +319,9 @@ func TestBeginStream_CreatesAndUpdatesSameMessage(t *testing.T) {
 	if err != nil {
 		t.Fatalf("BeginStream() error = %v", err)
 	}
+	if setter, ok := streamer.(interface{ SetModelName(modelName string) }); ok {
+		setter.SetModelName("gpt-5.4")
+	}
 	if err := streamer.Update(context.Background(), "hello"); err != nil {
 		t.Fatalf("Update(first) error = %v", err)
 	}
@@ -271,6 +336,9 @@ func TestBeginStream_CreatesAndUpdatesSameMessage(t *testing.T) {
 	if got := first.Payload[PayloadKeyContent]; got != "hello" {
 		t.Fatalf("first content = %#v, want hello", got)
 	}
+	if got := first.Payload[PayloadKeyModelName]; got != "gpt-5.4" {
+		t.Fatalf("first model_name = %#v, want %q", got, "gpt-5.4")
+	}
 
 	rawStreamer := streamer.(*picoStreamer)
 	rawStreamer.mu.Lock()
@@ -290,6 +358,9 @@ func TestBeginStream_CreatesAndUpdatesSameMessage(t *testing.T) {
 	if got := second.Payload[PayloadKeyContent]; got != secondContent {
 		t.Fatalf("second content = %#v, want %q", got, secondContent)
 	}
+	if got := second.Payload[PayloadKeyModelName]; got != "gpt-5.4" {
+		t.Fatalf("second model_name = %#v, want %q", got, "gpt-5.4")
+	}
 }
 
 func TestBeginStream_DefaultStreamingShowsSmallIncrements(t *testing.T) {
@@ -355,6 +426,9 @@ func TestBeginStream_StreamsReasoningAsThoughtUpdates(t *testing.T) {
 	if !ok {
 		t.Fatal("pico stream should support reasoning updates")
 	}
+	if setter, ok := streamer.(interface{ SetModelName(modelName string) }); ok {
+		setter.SetModelName("gpt-5.4-mini")
+	}
 	if err := reasoningStreamer.UpdateReasoning(context.Background(), "thinking"); err != nil {
 		t.Fatalf("UpdateReasoning(first) error = %v", err)
 	}
@@ -372,6 +446,9 @@ func TestBeginStream_StreamsReasoningAsThoughtUpdates(t *testing.T) {
 	if got := first.Payload[PayloadKeyContent]; got != "thinking" {
 		t.Fatalf("first content = %#v, want thinking", got)
 	}
+	if got := first.Payload[PayloadKeyModelName]; got != "gpt-5.4-mini" {
+		t.Fatalf("first model_name = %#v, want %q", got, "gpt-5.4-mini")
+	}
 
 	if err := reasoningStreamer.UpdateReasoning(context.Background(), "thinking more"); err != nil {
 		t.Fatalf("UpdateReasoning(second) error = %v", err)
@@ -389,6 +466,9 @@ func TestBeginStream_StreamsReasoningAsThoughtUpdates(t *testing.T) {
 	if got := second.Payload[PayloadKeyContent]; got != "thinking more" {
 		t.Fatalf("second content = %#v, want thinking more", got)
 	}
+	if got := second.Payload[PayloadKeyModelName]; got != "gpt-5.4-mini" {
+		t.Fatalf("second model_name = %#v, want %q", got, "gpt-5.4-mini")
+	}
 }
 
 func TestBeginStream_ThrottlesIntermediateUpdatesAndFinalFlushes(t *testing.T) {
@@ -473,6 +553,9 @@ func TestBeginStream_FinalizeIncludesContextUsage(t *testing.T) {
 	if err != nil {
 		t.Fatalf("BeginStream() error = %v", err)
 	}
+	if setter, ok := streamer.(interface{ SetModelName(modelName string) }); ok {
+		setter.SetModelName("gpt-5.4")
+	}
 	if err := streamer.Update(context.Background(), "partial"); err != nil {
 		t.Fatalf("Update() error = %v", err)
 	}
@@ -501,6 +584,9 @@ func TestBeginStream_FinalizeIncludesContextUsage(t *testing.T) {
 	if got := final.Payload["message_id"]; got != msgID {
 		t.Fatalf("final message_id = %#v, want %q", got, msgID)
 	}
+	if got := final.Payload[PayloadKeyModelName]; got != "gpt-5.4" {
+		t.Fatalf("final model_name = %#v, want %q", got, "gpt-5.4")
+	}
 	rawUsage, ok := final.Payload["context_usage"].(map[string]any)
 	if !ok {
 		t.Fatalf("final context_usage = %#v, want map", final.Payload["context_usage"])

pkg/channels/pico/protocol.go

@@ -27,6 +27,7 @@ const (
 	PayloadKeyKind        = "kind"
 	PayloadKeyPlaceholder = "placeholder"
 	PayloadKeyToolCalls   = "tool_calls"
+	PayloadKeyModelName   = "model_name"
 
 	MessageKindThought   = "thought"
 	MessageKindToolCalls = "tool_calls"