Retrieval-augmented generation systems often treat retrieved text as helpful evidence, but retrieved text can also contain adversarial instructions, suspicious link patterns, oversized chunks, or secret-exfiltration requests. This paper presents a small-rule guardrail approach implemented through two zero-dependency JavaScript packages: prompt-injection-shield and vector-poison-score. The method is deliberately lightweight. It scans retrieved documents and tool outputs before they are inserted into model context, reports explicit risk reasons, and supports filtering or line stripping as a simple containment step. The contribution is not a replacement for full security review or large-scale benchmark evaluation. Instead, it offers an inspectable baseline that developers can place between retrieval and prompt construction while building, testing, and auditing agentic RAG workflows.