fix: treat llm_base_url="" as explicit clear in store_llm_settings

openhands/server/routes/settings.py

@@ -123,10 +123,9 @@ async def store_llm_settings(
             settings.llm_api_key = existing_settings.llm_api_key
         if settings.llm_model is None:
             settings.llm_model = existing_settings.llm_model
-        # if llm_base_url is missing or empty, try to preserve existing or determine appropriate URL
-        if not settings.llm_base_url:
-            if settings.llm_base_url is None and existing_settings.llm_base_url:
-                # Not provided at all (e.g. MCP config save) - preserve existing
+        if settings.llm_base_url is None:
+            # Not provided at all (e.g. MCP config save) - preserve existing or auto-detect
+            if existing_settings.llm_base_url:
                 settings.llm_base_url = existing_settings.llm_base_url
             elif is_openhands_model(settings.llm_model):
                 # OpenHands models use the LiteLLM proxy
@@ -145,6 +144,9 @@ async def store_llm_settings(
                     logger.error(
                         f'Failed to get api_base from litellm for model {settings.llm_model}: {e}'
                     )
+        elif settings.llm_base_url == '':
+            # Explicitly cleared by the user (basic view save or advanced view clear)
+            settings.llm_base_url = None
         # Keep search API key if missing or empty
         if not settings.search_api_key:
             settings.search_api_key = existing_settings.search_api_key

tests/unit/server/routes/test_settings_store_functions.py

@@ -211,9 +211,32 @@ async def test_store_llm_settings_partial_update():
     assert result.llm_model == 'gpt-4'
     # For SecretStr objects, we need to compare the secret value
     assert result.llm_api_key.get_secret_value() == 'existing-api-key'
-    # llm_base_url was explicitly cleared (""), so auto-detection runs
-    # OpenAI models: litellm.get_api_base() returns https://api.openai.com
-    assert result.llm_base_url == 'https://api.openai.com'
+    # llm_base_url="" is an explicit clear — must not be repopulated via auto-detection
+    assert result.llm_base_url is None
+
+
+@pytest.mark.asyncio
+async def test_store_llm_settings_advanced_view_clear_removes_base_url():
+    """Regression test for #13420: clearing Base URL in Advanced view must persist.
+
+    Before the fix, llm_base_url="" was treated identically to llm_base_url=None,
+    causing the backend to re-run auto-detection and overwrite the user's intent.
+    """
+    settings = Settings(
+        llm_model='gpt-4',
+        llm_base_url='',  # User deleted the field in Advanced view
+    )
+
+    existing_settings = Settings(
+        llm_model='gpt-4',
+        llm_api_key=SecretStr('my-api-key'),
+        llm_base_url='https://my-custom-proxy.example.com',
+    )
+
+    result = await store_llm_settings(settings, existing_settings)
+
+    # The old custom URL must not come back
+    assert result.llm_base_url is None
 
 
 @pytest.mark.asyncio