Not Found? Prove It — Live-Surface Absence Verifier for Catalogs, Inboxes & Marketplaces

"There is no such listing." "That book isn't on the site." "No email about it." "The portal doesn't exist." "It's sold out everywhere." On live surfaces — a marketplace, a bookshelf, an inbox, a dashboard, a directory, a storefront — a confident not found is the most expensive sentence an agent produces, because it usually does not mean the thing is absent. It means the agent searched one spelling, on one tab, under one default filter, on a results page that silently capped at 20, and stopped.

Script-based negative guards exist for codebases and PDFs: they run a command per item and count N of N. They cannot help here, because live surfaces have no command to run. The item hides under a name variant, a former title, a second account, the Sold tab instead of Active, an archived folder, a placeholder page that returns a friendly 200, or a search index that has not caught up. This skill is the absence-verification discipline for those surfaces: expand the variants, exhaust the surfaces, log the coverage, triangulate by a second independent route, and only then issue one of four honest verdicts — never a bare "not found."

Built from a live operation where false negatives caused real damage: a benefits portal confidently declared non-existent that the user then opened himself, documents declared missing that were already in the Downloads folder, and a listing reported absent that was live under a variant author name.

• Before reporting that a listing, product, book, record, message, account feature, page, or person is not found, does not exist, is unavailable, sold out, or has no results.
• When a first search came back empty and the answer matters — money, a deadline, a filing, a purchase, a customer, a deliverable.
• When a previous "not found" was wrong, or the user disputes it.
• When several surfaces could hold the item (multiple accounts, stores, tabs, folders, sites) and nobody has checked them all.
• As a standing gate: any absence or totality claim ("none", "no X", "all Y are…") in a report must pass this workflow before the report ships.