SCU5.0 Fix Logic Technical Documentation: Implementation Details for P0/P1/P2 Remediation Including Path Traversal, SSRF, Async Isolation, and Pair-Thinking Trigger

This technical document records the detailed implementation of all fixes applied during the SCU5.0 remediation cycle. P0-level fixes address startup blocking points and close three directory traversal vulnerabilities (CVSS 7.5 High) by introducing safe_join_path with realpath canonicalization and project-root whitelist verification. P1-level fixes resolve concurrency safety issues by wrapping eight synchronous FastAPI endpoint handlers with asyncio.to_thread, converting class-level variables to instance variables, and implementing atomic JSON persistence using tempfile and os.replace. SSRF protection (CVSS 8.6 High) intercepts private, loopback, link-local, and reserved network ranges, cloud metadata endpoints (169.254.169.254), and internal domain suffixes. A security scoring model deducts 0.1 points per file-write violation and 0.3 points per prohibited operation. The critical Yin-Yang Pair Thinking trigger was repaired by inserting regex-based analytical intent matching before LLM semantic reasoning. Error isolation is achieved through error_id generation with traceback logging only, preventing sensitive stack traces from reaching API responses.