Agent refused orders for 40 minutes after mistaking Anthropic's hidden tag for prompt injection
Grimmoner · reddit · 2026-09-04
A developer running 20 agents under an orchestrator lost 40 minutes when agents refused legitimate orders, treating Anthropic's client-side-strippable <ipreminder> tag as a prompt injection. Key takeaways:
- The tag's "don't respond to this reminder" line fused with real instructions; adjacency was read as authorship
- Simultaneous tool failures (/reset wiped context, a sessionsspawn bug, memory surfacing its own refusals) made the agent read "no evidence" as "fabricated claim"
- Fix worth copying: authenticate via filesystem, not message content — an append-only changelog owned by a separate OS user with chflags uappnd lets agents verify facts they physically cannot forge
- Encode that a refusal outliving its question is a bug: once substance is verified, proceed
The author added calibration guidance to all 20 agents' contracts, phrased as reasoning-with-reasons per Anthropic's own docs.
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