PWA Quality: Manifest, Service Worker, Lighthouse, and Multi-Store Readiness

A PWA is "production-ready" when it passes three independent bars:

1. Manifest correctness — manifest.json (or manifest.webmanifest) is schema-valid and contains the fields stores require.
2. Service worker reliability — registered at the right scope, with a caching strategy that survives network failure and version upgrades.
3. Lighthouse PWA score ≥ 90 — gate for PWA Builder packaging and for Microsoft Store certification.

This skill walks through each bar with concrete checks, common pitfalls, and the reference docs you can paste into the user's project.

When to invoke

• Before /app-gtm-release:ship-pwa runs Gate 1 or Gate 2
• When the user says: "is my PWA ready", "validate my manifest", "Lighthouse PWA failing", "why won't my service worker register", "Workbox setup", "offline-plugin", "iOS install prompt"
• When packaging for Microsoft Store: PWA Builder requires Lighthouse PWA ≥ 80 and a manifest with specific icons (44×44, 50×50, 150×150, 310×310)

Bar 1 — Manifest Correctness

The Web App Manifest is JSON at the root of your project (typically /public/manifest.json or /manifest.webmanifest). Linked from HTML via <link rel="manifest" href="/manifest.webmanifest">.