Writes and debugs end-to-end browser tests — Playwright, Cypress, Selenium — covering selector strategy, waiting, test data, and the flakiness that makes suites get ignored. Use this whenever the user mentions E2E tests, browser tests, UI tests, Playwright, Cypress, Selenium, or a flaky or slow browser suite, and also when a bug is only reproducible through the UI. For testing logic below the UI, use unit-testing.
