F8.1 — PWA manifest + service worker + install prompt

[Flow-Fly]

Parent: F8 (PWA). Self-contained; no backend dependency.

Recipe

1. Adopt vite-plugin-pwa (in vite.config.ts) — it generates the manifest, registers the service worker, and handles Workbox precaching of the built shell. Config:
   • registerType: 'prompt' (NOT autoUpdate): an art tool must never swap code under an unsaved drawing session. Show a small "Update available — restart" toast wired to needRefresh from virtual:pwa-register.
   • Precache: all built assets (default globPatterns). navigateFallback: 'index.html' for offline SPA loads.
   • NetworkOnly / no runtime caching for any future API origin — add the rule now with a comment pointing at F2 (sync must never be served stale by the SW).
2. Manifest: name "Pixel Forge", display: 'standalone', theme/background colors from the app's dark UI, icons 192/512 + maskable (generate from the app logo into public/icons/; create a simple pixel-art icon if none exists).
3. Install prompt UX: listen for beforeinstallprompt, stash the event, surface a menu item "Install app" in pf-menu-bar.ts (hidden when already installed / event unavailable). No nagging banners.
4. Update flow test plan (manual, document in the PR): deploy A → install → deploy B → toast appears → restart loads B; offline: devtools offline → reload → app loads and edits persist to IndexedDB.
5. CI: build must fail loudly if SW generation breaks (vite build already covers this once the plugin is in).

Acceptance

• Lighthouse PWA installability checks pass.
• Full offline session works: launch offline, draw, auto-save, reload offline, work is there.
• Updates require explicit user confirmation; no stale-forever cache and no mid-session code swap.

[Flow-Fly]

Agent Assessment

F8.1 is a medium-risk feature slice because service-worker caching and update activation can affect active editing sessions. It is split into three low-risk implementation issues that will land together in one PR:

• F8.1a: Add the installable offline application shell #326 — installable offline application shell
• F8.1b: Add a quiet install action to the File menu #327 — quiet File-menu install action
• F8.1c: Let users choose when a PWA update restarts the app #328 — user-confirmed update restart

The update path will never reload automatically, and #123 (OS file handling) remains a separate follow-up slice.

[Flow-Fly]

Implementation is ready in #329 as one three-commit feature PR covering #326, #327, and #328.

Automated checks are green locally, offline shell startup was verified with the preview server stopped, and an A/B build produced the user-confirmed update notice without reloading version A. The remaining merge gate is the short Chromium install/offline/update playtest documented in the PR.