Author the Playwright fixture layer every Chromium extension test depends on - `chromium.launchPersistentContext` with `--disable-extensions-except=$DIR` + `--load-extension=$DIR`, the `channel: 'chromium'` selection that unlocks headless extension support, the `context.serviceWorkers()` + `waitForEvent('serviceworker')` race-handling pattern, and the `extensionId = serviceWorker.url().split('/')[2]` extraction recipe - plus, in references/, the extension load / reload matrix (which edit re-evaluates which surface), the `chrome.storage` test suite (area selection, quota-exceeded, `storage.onChanged`, managed read-only), and the per-surface assertion recipes (popup, content script, background messaging, MV3 auto-suspend survival). Use when authoring or debugging the fixture a Chromium extension test imports, when an edit appears to have no effect and you need the reload matrix, or when authoring popup / content-script / storage tests.