winston lo

About

Backend engineer who built and iterated a secure, multi-tenant RAG system over a large document corpus, emphasizing strict RBAC/ACL isolation, hybrid retrieval (vector+keyword), reranking, and strong observability to balance relevance, latency, and cost. Also led production refactors/migrations using strangler + feature flags/dual writes and has experience catching subtle real-world failure modes (including in a sensor calibration optimization pipeline).

Key Strengths

• Designed secure RAG backend with early ACL filtering and hybrid retrieval (vector + keyword) plus reranking
• Strong multi-tenant data isolation via retrieval-time filtering and centralized policy evaluation
• Balances relevance, latency, and LLM/infra cost using candidate set limiting, chunking strategy, and caching
• Security-first mindset with access-control audits, detailed retrieval decision logging, and cross-tenant test coverage
• API platform engineering in FastAPI: versioned contracts, backward compatibility, deprecation strategy, and contract tests
• Led low-risk migrations using strangler pattern, feature flags, dual writes, parallel output validation, and canary rollouts
• Deep observability practice (metrics, tracing, structured logs) to diagnose slow dependencies and regressions
• Proactively finds hidden failure modes (e.g., false local minima in calibration optimization) and adds scenario-based validation

Experience

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