TLDR: Setup guides reach your AI agent through surfaces that can hide text from you but not from the model. GuideCheck is an open standard for a constrained, plain-text assistant-guide.txt that a human can read in full before authorizing an agent to act. It ships a five-level conformance ladder, a reference verifier, and a hosted checker. Conformance verifies form, not safety — and the standard says so on every level. The guide you skimmed isn't the guide the model read You point your coding agent at a project's setup guide. "Install this, configure that, run the migration." You skim the page in your browser. It looks reasonable. You approve. The agent runs. Here is the part that should bother you: the guide you skimmed is not necessarily the guide the model read. Setup instructions travel through HTML, rendered Markdown, PDFs, docs sites, copied issue comments, terminal output, even screenshots.…