Every production defense against prompt injection—input filters, LLM-as-a-judge, output classifiers—tries to make the AI smarter about detecting attacks.Intent-Based Access Control (IBAC)makes attacks irrelevant. IBAC derives per-request permissions from the user's explicit intent, enforces them deterministically at every tool invocation, and blocks unauthorized actions regardless of how thoroughly injected instructions compromise the LLM's reasoning. The implementation is two steps: parse the user's intent into FGA tuples (email:send#bob@company.com), then check those tuples before every tool call. One extra LLM call. One ~9ms authorization check. No custom interpreter, no dual-LLM architecture, no changes to your agent framework. IBAC is four steps. Start OpenFGA, define the authorization model, write tuples after you parse intent, check tuples before every tool call. You can have this running in minutes.