Wire a new before/after use case into BOTH the marketplace screenshot carousel and the marketing site diptych — they share backdrops and must stay in sync. Use when the user asks to add a new comparison / demo / before-after example to the extension screenshots, the marketing site's "See it in action" section, or both. Also use when the user mentions adding a new "use case", "scenario", "pair", or "diptych" to the screenshots pipeline. Do NOT use for: tweaking existing screenshots, generating per-locale variants of an existing scene, or marketing copy changes that don't touch the screenshots.
Fix drift between the root README.md and its sources of truth — the marketing hero tagline (apps/marketing/src/i18n.ts), the workspace layout (apps/* + packages/*), and the generated metrics badge block (code health, test coverage, permissions, license, and verified product promises). Use when `pnpm check:readme` fails, when the README parity guard reports a tagline, monorepo-layout, or broken-product-promise mismatch, or after you add / remove / rename a workspace package or change the marketing tagline and the README must follow. Also use when manually auditing README.md for drift from the product or marketing site. Do NOT use for before/after screenshot use cases (that's add-before-after-case) or for editing marketing copy itself — the README mirrors the marketing app, not the other way around.