Update workdone.md

Author: tanzilahmed0

workdone.md

@@ -136,6 +136,29 @@ This document provides a comprehensive summary of all work completed on the Smar
   - API response format matches shared contract expectations
   - Project system ready for end-to-end testing
 
+### Task B15: LangChain Integration
+
+- **LangChain Agent Setup:**
+  - Created `backend/services/llm_service.py` with LangChain agent configuration
+  - Integrated OpenAI LLM with proper API key validation and error handling
+  - Set up ZERO_SHOT_REACT_DESCRIPTION agent type for query processing
+  - Implemented modular LLMService class with singleton pattern for easy import
+- **Chat Endpoint Integration:**
+  - Updated `/chat/{project_id}/message` endpoint to use LangChain agent
+  - Added graceful fallback to mock responses when OPENAI_API_KEY not configured
+  - Preserved existing functionality while adding LLM capabilities
+  - Ready for future SQL and semantic search tool integration
+- **Dependencies and Environment:**
+  - Uncommented and installed langchain, openai, and duckdb in requirements.txt
+  - All dependencies successfully installed and tested
+  - Service ready for production use when API key is configured
+- **Implementation Details:**
+  - Minimal, modular code following coding protocol
+  - No breaking changes to existing functionality
+  - Clear separation of concerns with dedicated service layer
+  - Proper error handling and fallback mechanisms
+  - Ready for testing with real API key or mock fallback
+
 ---
 
 ## 3. Infrastructure & DevOps
@@ -195,6 +218,7 @@ This document provides a comprehensive summary of all work completed on the Smar
 - ✅ Responsive UI and data visualization (frontend)
 - ✅ Comprehensive testing (unit, integration, E2E setup)
 - ✅ **Project Integration Testing (Task B14)** - Frontend-backend integration verified
+- ✅ **LangChain Integration (Task B15)** - LLM agent configured and integrated
 - ✅ CI/CD and security best practices
 - ✅ Documentation for API, environment, and development
 - ✅ CI/CD pipeline and ESLint compatibility fixes (Node 20.x, ESLint v8, config cleanup)