Docs: Complete Stage 4 wrap-up in dev log

Added comprehensive completion summary:
- JSON export system documentation (post-validation enhancement)
- Final achievements and validation results (10% score)
- Critical issues identified for Stage 5 (LLM quota, vision tool, tool selection)
- Stage 5 readiness assessment with priorities

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

dev/dev_260103_16_huggingface_llm_integration.md

@@ -357,25 +357,84 @@ uv run pytest test/ -q
 ======================== 99 passed, 11 warnings in 51.99s ========================
 ```
 
+### JSON Export System (Post-Validation Enhancement)
+
+**Problem:** Initial markdown table export had truncation issues and special character escaping problems that made Stage 5 debugging difficult.
+
+**Solution:** Converted to JSON export format for clean data structure and full error message preservation.
+
+**Implementation:**
+
+```python
+def export_results_to_json(results_log: list, submission_status: str) -> str:
+    """Export evaluation results to JSON file for easy processing."""
+    export_data = {
+        "metadata": {
+            "generated": datetime.now().strftime("%Y-%m-%d %H:%M:%S"),
+            "timestamp": timestamp,
+            "total_questions": len(results_log)
+        },
+        "submission_status": submission_status,
+        "results": [
+            {
+                "task_id": result.get("Task ID", "N/A"),
+                "question": result.get("Question", "N/A"),
+                "submitted_answer": result.get("Submitted Answer", "N/A")
+            }
+            for result in results_log
+        ]
+    }
+    json.dump(export_data, f, indent=2, ensure_ascii=False)
+```
+
+**Benefits:**
+- No special character escaping issues
+- Full error messages preserved (no truncation)
+- Easy programmatic processing for Stage 5 analysis
+- Environment-aware paths (local ~/Downloads vs HF Spaces ./exports)
+- Download button UI for better UX
+
+**Result:** Production-ready debugging infrastructure for Stage 5 optimization.
+
+---
+
 ### Completion Summary
 
 **Stage 4: MVP - Real Integration** is now **COMPLETE** ✅
 
-**Achievements:**
+**Final Achievements:**
 
 - ✅ HF_TOKEN configured in HuggingFace Space
 - ✅ 3-tier LLM fallback operational (Gemini → HuggingFace → Claude)
 - ✅ Tool name consistency fixed (web_search, calculator, vision)
 - ✅ GAIA validation test passed with 2/20 questions answered (10.0%)
+- ✅ JSON export system for Stage 5 debugging
 - ✅ Agent is functional and deployed to production
 
-**Results:**
+**Validation Results:**
+
+- **Score:** 10.0% (2/20 correct)
+- **Improvement:** 0/20 → 2/20 (MVP validated!)
+- **Success Cases:** Mercedes Sosa albums (3), Wikipedia search (FunkMonk)
+- **Issues Identified:** LLM quota exhaustion (15/20 failed), vision tool failures
+
+**Critical Issues for Stage 5:**
+
+1. **LLM Quota Exhaustion** (P0 - Critical)
+   - Gemini: 429 quota exceeded
+   - HuggingFace: 402 payment required (novita free limit)
+   - Claude: 400 credit balance low
+
+2. **Vision Tool Failures** (P1 - High)
+   - All vision-based questions failing
+   - "Vision analysis failed - Gemini and Claude both failed"
 
-- Improved from 0/20 (total failure) to 2/20 (operational MVP)
-- Web search and answer synthesis working correctly
-- Vision tool needs improvement for Stage 5
+3. **Tool Selection Errors** (P1 - High)
+   - Fallback to keyword matching in some cases
+   - Calculator tool validation errors
 
-**Next Stage:** Stage 5 - Performance Optimization
+**Ready for Stage 5:** Performance Optimization
 
-- Target: Improve from 2/20 to 5/20 questions
-- Focus: Fix vision tool, improve search quality, enhance answer accuracy
+- **Target:** 5/20 questions (25% score) - 2.5x improvement
+- **Priority:** Fix LLM quota management, improve tool selection, fix vision tool
+- **Infrastructure:** JSON export ready for detailed error analysis