Authors Playwright `expect(page).toHaveScreenshot()` assertions, configures masks / clips / threshold / maxDiffPixels per test, manages the per-OS / per-browser snapshot directory, and runs the update flow with `--update-snapshots`; references/ carry the responsive-breakpoint viewport matrix (one project per breakpoint, cross-breakpoint matrix report, plus Chromatic / Percy / Storybook test-runner viewport syntax). Use when the project ships self-hosted visual regression coverage in Playwright (no external snapshot service), or needs a unified multi-viewport breakpoint matrix.