2 files changed, 48 insertions, 4 deletions
diff --git a/internal/image/registry.go b/internal/image/registry.go
index 7b2a465..2d446e8 100644
--- a/internal/image/registry.go
+++ b/internal/image/registry.go
@@ -12,6 +12,11 @@ type Factory[C any] func(C) (ImageProvider, error)
 // Config exposes the configured image provider name.
 type Config interface {
 	ImageProviderName() string
+}
+
+// GeminiRegistryConfig exposes the settings required by the built-in Gemini image provider.
+type GeminiRegistryConfig interface {
+	Config
 	GoogleAPIKey() string
 	ImageModel() string
 	ImageTextModel() string
@@ -77,6 +82,9 @@ func (r *Registry[C]) New(name string, cfg C) (ImageProvider, error) {
 
 // NewFromConfig resolves the provider name from cfg and constructs it.
 func (r *Registry[C]) NewFromConfig(cfg C) (ImageProvider, error) {
+	if r == nil {
+		return nil, fmt.Errorf("image registry is required")
+	}
 	if isNilValue(cfg) {
 		return nil, fmt.Errorf("image config is required")
 	}
@@ -84,9 +92,9 @@ func (r *Registry[C]) NewFromConfig(cfg C) (ImageProvider, error) {
 }
 
 // DefaultRegistry returns the built-in image provider registry.
-func DefaultRegistry() *Registry[Config] {
-	registry := NewRegistry[Config]()
-	registry.Register(Gemini, func(cfg Config) (ImageProvider, error) {
+func DefaultRegistry() *Registry[GeminiRegistryConfig] {
+	registry := NewRegistry[GeminiRegistryConfig]()
+	registry.Register(Gemini, func(cfg GeminiRegistryConfig) (ImageProvider, error) {
 		geminiProvider := NewGeminiProvider(&GeminiConfig{
 			APIKey:    cfg.GoogleAPIKey(),
 			Model:     cfg.ImageModel(),
@@ -97,7 +105,7 @@ func DefaultRegistry() *Registry[Config] {
 		}
 		return geminiProvider, nil
 	})
-	registry.Register(OpenAI, func(Config) (ImageProvider, error) {
+	registry.Register(OpenAI, func(GeminiRegistryConfig) (ImageProvider, error) {
 		return nil, fmt.Errorf("image provider %q is not implemented", OpenAI)
 	})
 	return registry
diff --git a/internal/image/types_test.go b/internal/image/types_test.go
index 4416870..5916389 100644
--- a/internal/image/types_test.go
+++ b/internal/image/types_test.go
@@ -71,6 +71,36 @@ func TestRegistryNewFromConfig(t *testing.T) {
 	}
 }
 
+func TestRegistryNewFromConfigNilRegistry(t *testing.T) {
+	t.Parallel()
+
+	var registry *Registry[fakeConfig]
+	_, err := registry.NewFromConfig(fakeConfig{name: Gemini})
+	if err == nil {
+		t.Fatal("expected nil registry error")
+	}
+	if !strings.Contains(err.Error(), "image registry is required") {
+		t.Fatalf("error = %v, want nil registry error", err)
+	}
+}
+
+func TestRegistrySupportsCustomConfigWithoutGeminiFields(t *testing.T) {
+	t.Parallel()
+
+	registry := NewRegistry[customConfig]()
+	registry.Register(Gemini, func(cfg customConfig) (ImageProvider, error) {
+		return fakeProvider{name: cfg.name}, nil
+	})
+
+	gotProvider, err := registry.NewFromConfig(customConfig{name: Gemini})
+	if err != nil {
+		t.Fatalf("NewFromConfig() error = %v", err)
+	}
+	if got, want := gotProvider.Name(), Gemini; got != want {
+		t.Fatalf("provider.Name() = %q, want %q", got, want)
+	}
+}
+
 func TestDefaultRegistryNewFromConfig(t *testing.T) {
 	t.Parallel()
 
@@ -133,6 +163,12 @@ func (f fakeConfig) GoogleAPIKey() string      { return f.apiKey }
 func (f fakeConfig) ImageModel() string        { return f.model }
 func (f fakeConfig) ImageTextModel() string    { return f.textModel }
 
+type customConfig struct {
+	name string
+}
+
+func (f customConfig) ImageProviderName() string { return f.name }
+
 type fakeProvider struct {
 	name  string
 	token string