test(agent): cover image fallback execution path for image candidates

pkg/agent/loop_test.go

@@ -91,6 +91,33 @@ func (r *recordingProvider) GetDefaultModel() string {
 	return "mock-model"
 }
 
+type imageFallbackProbeProvider struct {
+	calls []string
+}
+
+func (p *imageFallbackProbeProvider) Chat(
+	ctx context.Context,
+	messages []providers.Message,
+	tools []providers.ToolDefinition,
+	model string,
+	opts map[string]any,
+) (*providers.LLMResponse, error) {
+	p.calls = append(p.calls, model)
+	if model == "gemini-2.5-flash-lite" {
+		// This error is non-retriable in text fallback Execute(), but should still
+		// fail over in ExecuteImage() which only treats image size/dimension as terminal.
+		return nil, fmt.Errorf("string should match pattern")
+	}
+	return &providers.LLMResponse{
+		Content:   "image fallback ok",
+		ToolCalls: []providers.ToolCall{},
+	}, nil
+}
+
+func (p *imageFallbackProbeProvider) GetDefaultModel() string {
+	return "image-fallback-probe"
+}
+
 func newTestAgentLoop(
 	t *testing.T,
 ) (al *AgentLoop, cfg *config.Config, msgBus *bus.MessageBus, provider *mockProvider, cleanup func()) {
@@ -620,6 +647,54 @@ func TestRunAgentLoop_DoesNotUseImageModelWhenOnlyHistoryHasImages(t *testing.T)
 	}
 }
 
+func TestRunAgentLoop_UsesImageFallbackExecutionForImageCandidates(t *testing.T) {
+	tmpDir := t.TempDir()
+	cfg := &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				Workspace:           tmpDir,
+				ModelName:           "text-main",
+				ImageModel:          "vision-main",
+				ImageModelFallbacks: []string{"vision-backup"},
+				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"},
+			{ModelName: "vision-backup", Model: "anthropic/claude-3-7-sonnet"},
+		},
+	}
+
+	msgBus := bus.NewMessageBus()
+	provider := &imageFallbackProbeProvider{}
+	al := NewAgentLoop(cfg, msgBus, provider)
+	agent := al.registry.GetDefaultAgent()
+
+	resp, err := al.runAgentLoop(context.Background(), agent, processOptions{
+		SessionKey:      "image-fallback-session",
+		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("runAgentLoop returned error: %v", err)
+	}
+	if resp != "image fallback ok" {
+		t.Fatalf("response = %q, want %q", resp, "image fallback ok")
+	}
+	if len(provider.calls) != 2 {
+		t.Fatalf("provider calls = %d, want 2", len(provider.calls))
+	}
+	if provider.calls[0] != "gemini-2.5-flash-lite" || provider.calls[1] != "claude-3-7-sonnet" {
+		t.Fatalf("provider calls = %v, want [gemini-2.5-flash-lite claude-3-7-sonnet]", provider.calls)
+	}
+}
+
 func TestNewAgentLoop_StateInitialized(t *testing.T) {
 	// Create temp workspace
 	tmpDir, err := os.MkdirTemp("", "agent-test-*")