A system-level approach to prompt injection: separating instruction and data channels in LLM agents [P](reddit.com)

Prompt injection has emerged as one of the most persistent failure modes in tool-using LLM systems, particularly in agentic workflows where models interact with external data sources. Most mitigation strategies focus on input filtering or model-side alignment, but these approaches struggle because the core issue is structural: Approach I explored a system-level mitigation strategy by introducing a middleware layer (Sentinel Gateway) that enforces a strict separation between: Instruction channel: trusted, runtime-issued commands Data channel: untrusted external inputs (web, files, APIs) Instead of attempting to classify malicious inputs, the system ensures that: All agent actions require a signed, scoped runtime authorization token, effectively decoupling observation from execution. Implementation FastAPI middleware layer for agent tool calls Token-based authorization for execution requests Streamlit interface for inspection and debugging Audit logging of agent decisions and tool usage Supports multi-agent integration patterns (e.g., Claude-based sessions) Local or Postgres-backed persistence layer Repo https://github.com/cmtopbas/Sentinel-Gateway Discussion question I’m interested in feedback on: whether instruction/data separation is a meaningful abstraction for agent safety failure modes in token-based execution gating how this compares conceptually to other agent safety or sandboxing approaches submitted by /u/vagobond45 [link] [Kommentare]