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

[LarytheLord]

Summary

Fixes #13420 — it is currently impossible to persist an empty llm_base_url from the settings UI.

Root cause: store_llm_settings used if not settings.llm_base_url: which catches both None (field not provided at all) and "" (explicitly cleared by the user). When the user:

• saves from Basic view (which intentionally sends llm_base_url: "" to clear advanced settings), or
• deletes the Base URL field in Advanced view and saves,

the backend treated "" the same as "not provided", triggering auto-detection via get_provider_api_base() and overwriting the user's intent. The old base URL kept coming back.

Fix: Split the condition into two explicit branches:

# Before
if not settings.llm_base_url:
    if settings.llm_base_url is None and existing_settings.llm_base_url:
        ...  # preserve existing

# After
if settings.llm_base_url is None:
    ...  # not provided — preserve existing or auto-detect (no behavior change)
elif settings.llm_base_url == "":
    settings.llm_base_url = None  # explicit clear — honor the intent

The None path has identical behavior to before. Only "" changes: instead of triggering auto-detection, it now normalizes to None and returns.

Test plan

• Updated test_store_llm_settings_partial_update to assert None (the correct post-fix behavior) instead of the auto-detected URL
• Added test_store_llm_settings_advanced_view_clear_removes_base_url as a named regression test for this issue
• All 16 tests in test_settings_store_functions.py pass
• Existing MCP save test (test_store_llm_settings_mcp_update_preserves_base_url) continues to pass — the None path (field not sent) is unchanged

🤖 Generated with Claude Code

[enyst]

Hey @LarytheLord thank you for the contribution!

Could you maybe show a video that it works, or logs (though video would be nice I think), and that is still works for the previous issue?

[LarytheLord]

Thanks @enyst — here's the test evidence:

Regression test (test_store_llm_settings_advanced_view_clear_removes_base_url):

settings = Settings(llm_model='gpt-4', llm_base_url='')     # user clears field
existing = Settings(llm_model='gpt-4', llm_base_url='https://my-custom-proxy.example.com')

result = await store_llm_settings(settings, existing)
assert result.llm_base_url is None   # ✅ old URL is gone

Existing behavior preserved (test_store_llm_settings_partial_update and test_store_llm_settings_mcp_update_preserves_base_url):

• When llm_base_url is None (not sent at all, e.g. MCP save), the existing URL is kept — no behavior change.
• When llm_base_url is "" (explicitly cleared by the user), it now normalizes to None instead of re-running auto-detection.

All 3 tests pass:

tests/.../test_settings_store_functions.py::test_store_llm_settings_advanced_view_clear_removes_base_url PASSED
tests/.../test_settings_store_functions.py::test_store_llm_settings_partial_update PASSED
tests/.../test_settings_store_functions.py::test_store_llm_settings_mcp_update_preserves_base_url PASSED

Full suite (16/16): pytest tests/unit/server/routes/test_settings_store_functions.py — all green.

I can record a UI walkthrough too if you'd like, but the logic is fully covered by these tests. The key distinction is the is None vs == "" split in store_llm_settings — the diff is small and focused.

[enyst]

Thank you!