Subject Line Lab Generates a labeled subject-line + preheader variant set and heuristically pre-scores each variant — spam-trigger flags, desktop + mobile length/truncation, emoji count, and the rendered inbox preview (from-name + subject + preheader) — so weak candidates are cut before they burn a test cell. This is the pre-test bench for the SEND E (Engagement) lever: it sharpens the subject/preheader unit that drafts and hands the ranked survivors, each with a stable variant id, to . Scope guard : this skill drafts and pre-scores subject + preheader variants only. It does not write the bod…