Cloudflare's Clef and Strands' Decider 2B: small decision models returning structured choices in milliseconds. GateKeep wires that pattern into your stack — a FastAPI decision gate routes every agent tool call. Confident decisions take the cheap path; uncertain ones escalate to the frontier model. Over-budget or kill-switched traffic fails closed (hard 402, kill switch, unknown keys blocked). Kit: gating middleware, 3 routing policies, calibration runbook, sourced price tables.