feat: add DEFAULT_MODEL environment variable

Author: danielcopper

app/api/routes/generate.py

@@ -305,6 +305,10 @@ def _get_default_model(provider: str) -> str:
     """
     Get default model for provider based on available models.
     """
+    # Check if DEFAULT_MODEL is configured
+    if settings.DEFAULT_MODEL:
+        return settings.DEFAULT_MODEL
+
     models = model_registry.get_models()
 
     # Filter models for this provider

tests/test_generate.py

@@ -0,0 +1,57 @@
+from unittest.mock import MagicMock, patch
+
+
+def test_get_default_model_uses_env_config():
+    """
+    Test that DEFAULT_MODEL env var is used.
+    """
+    with patch("app.api.routes.generate.settings") as mock_settings:
+        mock_settings.DEFAULT_MODEL = "gemini/gemini-2.0-flash-exp-image-generation"
+
+        from app.api.routes.generate import _get_default_model
+
+        result = _get_default_model("litellm")
+        assert result == "gemini/gemini-2.0-flash-exp-image-generation"
+
+
+def test_get_default_model_fallback_to_registry():
+    """
+    Test fallback to registry when DEFAULT_MODEL is not set.
+    """
+    with patch("app.api.routes.generate.settings") as mock_settings:
+        mock_settings.DEFAULT_MODEL = None
+
+        with patch("app.api.routes.generate.model_registry") as mock_registry:
+            mock_model = MagicMock()
+            mock_model.id = "dall-e-3"
+            mock_model.provider = "openai"
+            mock_registry.get_models.return_value = [mock_model]
+
+            from app.api.routes.generate import _get_default_model
+
+            result = _get_default_model("litellm")
+            assert result == "dall-e-3"
+
+
+def test_get_default_model_hardcoded_fallback():
+    """
+    Test hardcoded fallback when no models in registry.
+    """
+    with patch("app.api.routes.generate.settings") as mock_settings:
+        mock_settings.DEFAULT_MODEL = None
+
+        with patch("app.api.routes.generate.model_registry") as mock_registry:
+            mock_registry.get_models.return_value = []
+
+            from app.api.routes.generate import _get_default_model
+
+            # LiteLLM/OpenAI provider defaults to dall-e-3
+            result = _get_default_model("litellm")
+            assert result == "dall-e-3"
+
+            result = _get_default_model("openai")
+            assert result == "dall-e-3"
+
+            # Gemini provider defaults to gemini model
+            result = _get_default_model("gemini")
+            assert result == "gemini-2.0-flash-preview-image-generation"