feat(llm): auto-configure Google AI Studio URL when LLM_PROVIDER=gemini

When LLM_PROVIDER=gemini, LLMClient automatically uses the Google AI Studio
OpenAI-compatible endpoint instead of requiring manual base_url configuration.
An explicit base_url argument still takes precedence.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/utils/llm_client.py

@@ -28,6 +28,10 @@ class LLMClient:
         if not self.api_key:
             raise ValueError("LLM_API_KEY is not configured")
 
+        # Google AI Studio OpenAI-compatible endpoint
+        if (Config.LLM_PROVIDER or "").lower() == "gemini" and not base_url:
+            raw_url = "https://generativelanguage.googleapis.com/v1beta/openai/"
+
         # Azure Portal provides full endpoint URLs like:
         # https://<resource>.cognitiveservices.azure.com/openai/deployments/<model>/chat/completions?api-version=...
         # The OpenAI SDK expects a base_url and appends /chat/completions itself,

backend/tests/test_llm_client.py

@@ -0,0 +1,72 @@
+import pytest
+from unittest.mock import patch, MagicMock
+
+GEMINI_URL = "https://generativelanguage.googleapis.com/v1beta/openai/"
+
+
+def test_gemini_provider_sets_base_url_automatically():
+    import backend.app.config as cfg
+    orig_provider = cfg.Config.LLM_PROVIDER
+    orig_key = cfg.Config.LLM_API_KEY
+    orig_url = cfg.Config.LLM_BASE_URL
+    try:
+        cfg.Config.LLM_PROVIDER = "gemini"
+        cfg.Config.LLM_API_KEY = "AIzatest"
+        cfg.Config.LLM_BASE_URL = "https://api.openai.com/v1"
+
+        with patch("backend.app.utils.llm_client.OpenAI") as mock_openai:
+            mock_openai.return_value = MagicMock()
+            import importlib
+            import backend.app.utils.llm_client as lm
+            importlib.reload(lm)
+            client = lm.LLMClient()
+            assert GEMINI_URL in client.base_url
+    finally:
+        cfg.Config.LLM_PROVIDER = orig_provider
+        cfg.Config.LLM_API_KEY = orig_key
+        cfg.Config.LLM_BASE_URL = orig_url
+
+
+def test_non_gemini_provider_uses_configured_url():
+    import backend.app.config as cfg
+    orig_provider = cfg.Config.LLM_PROVIDER
+    orig_key = cfg.Config.LLM_API_KEY
+    orig_url = cfg.Config.LLM_BASE_URL
+    try:
+        cfg.Config.LLM_PROVIDER = ""
+        cfg.Config.LLM_API_KEY = "sk-test"
+        cfg.Config.LLM_BASE_URL = "https://api.openai.com/v1"
+
+        with patch("backend.app.utils.llm_client.OpenAI") as mock_openai:
+            mock_openai.return_value = MagicMock()
+            import importlib
+            import backend.app.utils.llm_client as lm
+            importlib.reload(lm)
+            client = lm.LLMClient()
+            assert "openai.com" in client.base_url
+    finally:
+        cfg.Config.LLM_PROVIDER = orig_provider
+        cfg.Config.LLM_API_KEY = orig_key
+        cfg.Config.LLM_BASE_URL = orig_url
+
+
+def test_explicit_base_url_overrides_gemini_auto():
+    """If base_url is passed explicitly, it should NOT be replaced even if LLM_PROVIDER=gemini."""
+    import backend.app.config as cfg
+    orig_provider = cfg.Config.LLM_PROVIDER
+    orig_key = cfg.Config.LLM_API_KEY
+    try:
+        cfg.Config.LLM_PROVIDER = "gemini"
+        cfg.Config.LLM_API_KEY = "AIzatest"
+
+        with patch("backend.app.utils.llm_client.OpenAI") as mock_openai:
+            mock_openai.return_value = MagicMock()
+            import importlib
+            import backend.app.utils.llm_client as lm
+            importlib.reload(lm)
+            client = lm.LLMClient(base_url="https://custom.endpoint/v1")
+            assert "custom.endpoint" in client.base_url
+            assert GEMINI_URL not in client.base_url
+    finally:
+        cfg.Config.LLM_PROVIDER = orig_provider
+        cfg.Config.LLM_API_KEY = orig_key