Author continuously-running online evaluations in PostHog AI observability, grounded in a real failure mode you've identified. Use when the user wants an evaluation that automatically scores new generations or whole traces going forward — "create an eval to catch X", "continuously check that responses do Y", "turn this failure into an eval". Covers choosing the target and eval type (hog / llm_judge / sentiment), gating on the team's provider key before an llm_judge eval, scoping which generations trigger it via conditions (property filters + rollout sampling), creating it disabled, verifying scope, and enabling. Finding and ranking the failure modes worth evaluating is its own job — use exploring-ai-failures first. To debug or manage evaluations that already exist, use exploring-llm-evaluations.