Reviews and guides LLM/AI application engineering: prompt design, prompt caching, multimodal inputs, RAG, agent loops and tool design, resilience (rate limits, retries, fallbacks), memory, model migration, evals, testing, prompt-injection defence, and observability. Synthesises practices from Anthropic, OpenAI, Google, OWASP LLM Top 10, and practitioners (Hamel Husain, Eugene Yan, Chip Huyen). Triggers on "review my prompt", "design a system prompt", "optimise tokens", "set up RAG", "build an agent", "handle rate limits", "migrate to a new model", "write evals", "test my prompt", "audit AI code", "/ai-engineering".