Your Semantic Cache Has a Health Problem. Nothing Checks It. Here's the situation: every LLM gateway now ships a semantic cache. GPTCache, LangChain's caches, Redis vector lookup — they all do the same job: store a response, look it up later by embedding similarity, skip a costly LLM call. But they only operate the cache. Store. Lookup. Evict. Nobody diagnoses it. That leaves three silent failure modes running unobserved in production: Cache pollution. A lightly rewritten p...