fix(agent): gate image model on current-turn media only

pkg/agent/loop.go

@@ -1683,10 +1683,19 @@ func (al *AgentLoop) runTurn(ctx context.Context, ts *turnState) (turnResult, er
 		ts.recordPersistedMessage(rootMsg)
 	}
 
+	currentTurnResolved := resolveMediaRefs([]providers.Message{
+		{Role: "user", Media: append([]string(nil), ts.media...)},
+	}, al.mediaStore, maxMediaSize)
+	var currentTurnMedia []string
+	if len(currentTurnResolved) > 0 {
+		currentTurnMedia = currentTurnResolved[0].Media
+	}
+
 	activeCandidates, activeModel, usedLight, useImageFallback := al.selectCandidates(
 		ts.agent,
 		ts.userMessage,
 		messages,
+		currentTurnMedia,
 	)
 	activeProvider := ts.agent.Provider
 	if usedLight && ts.agent.LightProvider != nil {
@@ -2764,8 +2773,9 @@ func (al *AgentLoop) selectCandidates(
 	agent *AgentInstance,
 	userMsg string,
 	history []providers.Message,
+	currentTurnMedia []string,
 ) (candidates []providers.FallbackCandidate, model string, usedLight bool, useImageFallback bool) {
-	if hasImageMedia(history) && len(agent.ImageCandidates) > 0 {
+	if hasImageMediaRefs(currentTurnMedia) && len(agent.ImageCandidates) > 0 {
 		logger.InfoCF("agent", "Image model selected",
 			map[string]any{
 				"agent_id":    agent.ID,
@@ -2798,14 +2808,12 @@ func (al *AgentLoop) selectCandidates(
 	return agent.LightCandidates, resolvedCandidateModel(agent.LightCandidates, agent.Router.LightModel()), true, false
 }
 
-func hasImageMedia(messages []providers.Message) bool {
+func hasImageMediaRefs(mediaRefs []string) bool {
-	for _, msg := range messages {
+	for _, ref := range mediaRefs {
-		for _, ref := range msg.Media {
 		if strings.HasPrefix(strings.ToLower(ref), "data:image/") {
 			return true
 		}
 	}
-	}
 	return false
 }
 

pkg/agent/loop_test.go

@@ -462,6 +462,7 @@ func TestSelectCandidates_UsesImageModelWhenImageMediaPresent(t *testing.T) {
 		[]providers.Message{
 			{Role: "user", Content: "describe this image", Media: []string{"data:image/png;base64,AAAA"}},
 		},
+		[]string{"data:image/png;base64,AAAA"},
 	)
 
 	if usedLight {
@@ -481,6 +482,48 @@ func TestSelectCandidates_UsesImageModelWhenImageMediaPresent(t *testing.T) {
 	}
 }
 
+func TestSelectCandidates_DoesNotUseImageModelForHistoricalImages(t *testing.T) {
+	tmpDir := t.TempDir()
+	cfg := &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				Workspace:  tmpDir,
+				ModelName:  "text-main",
+				ImageModel: "vision-main",
+			},
+		},
+		ModelList: []*config.ModelConfig{
+			{ModelName: "text-main", Model: "openai/gpt-5.4"},
+			{ModelName: "vision-main", Model: "gemini/gemini-2.5-flash-lite"},
+		},
+	}
+
+	agent := NewAgentInstance(nil, &cfg.Agents.Defaults, cfg, &mockProvider{})
+	candidates, model, useImageFallback := (&AgentLoop{}).selectCandidates(
+		agent,
+		"text-only follow-up",
+		[]providers.Message{
+			{Role: "user", Content: "earlier image", Media: []string{"data:image/png;base64,AAAA"}},
+			{Role: "assistant", Content: "previous response"},
+			{Role: "user", Content: "current text-only turn"},
+		},
+		nil,
+	)
+
+	if useImageFallback {
+		t.Fatal("expected image fallback to be disabled for text-only current turn")
+	}
+	if model != "gpt-5.4" {
+		t.Fatalf("model = %q, want %q", model, "gpt-5.4")
+	}
+	if len(candidates) != 1 {
+		t.Fatalf("len(candidates) = %d, want 1", len(candidates))
+	}
+	if candidates[0].Provider != "openai" || candidates[0].Model != "gpt-5.4" {
+		t.Fatalf("candidate = %+v, want openai/gpt-5.4", candidates[0])
+	}
+}
+
 func TestRunAgentLoop_UsesImageModelForImageMessages(t *testing.T) {
 	tmpDir := t.TempDir()
 	cfg := &config.Config{
@@ -521,6 +564,62 @@ func TestRunAgentLoop_UsesImageModelForImageMessages(t *testing.T) {
 	}
 }
 
+func TestRunAgentLoop_DoesNotUseImageModelWhenOnlyHistoryHasImages(t *testing.T) {
+	tmpDir := t.TempDir()
+	cfg := &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				Workspace:         tmpDir,
+				ModelName:         "text-main",
+				ImageModel:        "vision-main",
+				MaxTokens:         4096,
+				MaxToolIterations: 5,
+			},
+		},
+		ModelList: []*config.ModelConfig{
+			{ModelName: "text-main", Model: "openai/gpt-5.4"},
+			{ModelName: "vision-main", Model: "gemini/gemini-2.5-flash-lite"},
+		},
+	}
+
+	msgBus := bus.NewMessageBus()
+	provider := &mockProvider{}
+	al := NewAgentLoop(cfg, msgBus, provider)
+	agent := al.registry.GetDefaultAgent()
+
+	sessionKey := "image-history-session"
+	_, err := al.runAgentLoop(context.Background(), agent, processOptions{
+		SessionKey:      sessionKey,
+		Channel:         "telegram",
+		ChatID:          "chat-1",
+		UserMessage:     "describe this image",
+		Media:           []string{"data:image/png;base64,AAAA"},
+		DefaultResponse: "fallback",
+		SendResponse:    false,
+	})
+	if err != nil {
+		t.Fatalf("first runAgentLoop returned error: %v", err)
+	}
+	if provider.lastModel != "gemini-2.5-flash-lite" {
+		t.Fatalf("first run provider lastModel = %q, want %q", provider.lastModel, "gemini-2.5-flash-lite")
+	}
+
+	_, err = al.runAgentLoop(context.Background(), agent, processOptions{
+		SessionKey:      sessionKey,
+		Channel:         "telegram",
+		ChatID:          "chat-1",
+		UserMessage:     "now answer text only",
+		DefaultResponse: "fallback",
+		SendResponse:    false,
+	})
+	if err != nil {
+		t.Fatalf("second runAgentLoop returned error: %v", err)
+	}
+	if provider.lastModel != "gpt-5.4" {
+		t.Fatalf("second run provider lastModel = %q, want %q", provider.lastModel, "gpt-5.4")
+	}
+}
+
 func TestNewAgentLoop_StateInitialized(t *testing.T) {
 	// Create temp workspace
 	tmpDir, err := os.MkdirTemp("", "agent-test-*")