AI coding agents get stuck — re-reading the same file, retrying the same failing command, burning tokens while cost tools only show the damage after the session ends. DejaLoop is an open-source Claude Code plugin that intervenes live: deterministic checks fingerprint every tool call, a savings counter shows what stopped loops saved, and a semantic judge catches smart loops where every call differs but nothing moves. Fail-open, shadow mode by default. Free, MIT-licensed, no telemetry.