Update CHANGELOG: Document runtime config bug fix

CHANGELOG.md

@@ -167,6 +167,29 @@
 - ✅ No syntax errors in app.py
 - ✅ UI components properly connected to function parameters
 
+### [BUGFIX: UI Selection Not Applied - Runtime Config Reading]
+
+**Problem:** UI dropdown selections weren't being applied. Selected "HuggingFace" but system still used "Gemini". Root cause: LLM_PROVIDER and ENABLE_LLM_FALLBACK were read at module import time, before UI could set environment variables.
+
+**Modified Files:**
+
+- **src/agent/llm_client.py** (~5 lines modified)
+  - Removed module-level constants `LLM_PROVIDER` and `ENABLE_LLM_FALLBACK` (line 48-50)
+  - Updated `_call_with_fallback()` to read config at runtime (lines 173-175)
+    - Now calls `os.getenv("LLM_PROVIDER", "gemini")` on every function call
+    - Now calls `os.getenv("ENABLE_LLM_FALLBACK", "false")` on every function call
+  - Changed variable references from constants to local variables
+
+**Solution:**
+- Config now read at runtime when function is called, not at module import
+- UI can set environment variables before function execution
+- Changes take effect immediately without module reload
+
+**Verification:**
+- ✅ UI dropdown selection "HuggingFace" correctly uses HuggingFace provider
+- ✅ Logs show "Using primary provider: huggingface" matching UI selection
+- ✅ Each test run can use different provider without restart
+
 ### Created Files
 
 ### Deleted Files