The first observation of 'What course articles do you have?' was contaminated by an old cache entry. A real cache miss retrieved all four university maps but spent 51.169 seconds across three Writer and Critic passes; after catalog-specific retrieval and review fixes, one uncached production observation passed q21 in 26.821 seconds.
One Ask AI request leaves five different evidence surfaces: public SSE, Langfuse traces, D1 logs, semantic cache, and a hidden shadow run. They expose different data, and no single surface reconstructs the complete retrieval context.
After dissecting Claude Code's 18+ caching mechanisms, I found that you can't touch provider-level prompt cache, but embedding cache, tool result cache, and entity cache are not only within your reach — they deliver even better results. Includes a complete AgentCache interface design and per-tool TTL strategy.
Caching doesn't have to match exact query strings -- semantically similar questions can hit the cache too, skipping the entire RAG pipeline execution.