Scroll-jacking replaces the browser's scrolling with custom animation. An agent scrolling to reach an element ends up somewhere unpredictable, and cannot tell that it did.
Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.