feat: service worker — offline cache, rest-timer notifications, auto-reload on deploy

- public/sw.js: offline-first caching (static cache-first, API network-first,
  navigation network-first); SCHEDULE/CANCEL_NOTIFICATION for rest timer;
  notificationclick focuses/opens app
- main.jsx: SW update detection via updatefound + statechange reloads clients
  automatically when new SW activates (zero-stale deploys)
- nginx: sw.js and index.html both served with no-store/no-cache; hashed assets
  keep public+immutable; sw.js exempt from broad .js immutable rule
- TODO.md: changelog + removed SW and per-exercise chart from pending list

Author: bndct-devops

TODO.md

@@ -55,7 +55,26 @@
 ---
 
 ## Possible next things
-- Service Worker for proper offline support + background push notifications (fixes iOS ding limitation)
+
+### Infrastructure
+- **v1.0.1 release** — merge `dev` → `main`, tag, write release notes (icon fix, Lifty theme, PWA polish, auth, refactor, etc.); update hardcoded `v1.0.0` strings in App.jsx (about modal pill + release link)
+- **CI: explicit frontend build job** — add `npm ci && npm run build` step before `build-and-push` for faster, cheaper feedback on broken JSX/imports (currently only caught inside the Docker build)
+
+### UX / missing features
+- **JSON backup / restore** — full JSON dump of exercises + workouts + sets per profile; CSV export exists but can't be re-imported; needed for migrating between instances
+- **System theme auto-follow** — "System" option in theme picker reads `prefers-color-scheme` and maps to Light/Dark; single media query, no backend change
+- **Exercise picker: body part filter chips** — horizontal scrollable chip row (All / Chest / Back / …) above the list in the add-exercise bottom sheet; reuses existing filter logic from Exercises tab
+- **Exercise picker: inline "New" quick-create** — "+ New Exercise" button inside the picker sheet; opens a small inline form (name + body part) so users don't have to exit the workout to create a custom exercise
+
+### Tech debt
+- **Frontend Vitest tests** — no component tests exist; add Vitest + React Testing Library; smoke tests for `fmtWeight`, `parseWeight`, set-log flow would catch regressions
+
+---
+## Changelog (6 Mar 2026)
+- **Per-exercise 1RM chart** — tap any PR row in the Progress tab → BottomSheet with pure SVG line chart (accent fill + polyline, date labels) + recent-sessions table (date · sets · top weight · est. 1RM); fetches `GET /api/exercises/{id}/history?limit=60`; `TrendingUp` icon hint on PR rows
+- **Service Worker** (`public/sw.js`) — offline-first caching: static assets cache-first, API network-first with stale-cache fallback, navigation network-first; background rest-timer: page posts `SCHEDULE_NOTIFICATION`/`CANCEL_NOTIFICATION`, SW fires `showNotification` via `setTimeout` wrapped in `e.waitUntil`; `notificationclick` focuses existing window or opens `/`; SW works on non-EU iOS 16.4+ for locked-screen rest-timer ding
+- **SW update → auto-reload** (`main.jsx`) — `updatefound` + `statechange` listener reloads all open clients when a new SW version activates, so deploys propagate immediately
+- **nginx cache strategy** — `index.html` + `sw.js` served with `no-store, no-cache, must-revalidate`; hashed JS/CSS/assets served with `public, immutable` (1 year); `sw.js` exempt from the broad `.js` immutable rule via an earlier `location = /sw.js` block
 
 ---
 ## Changelog (2 Mar 2026) — session 3

frontend/nginx.conf

@@ -10,6 +10,12 @@ server {
     try_files $uri /index.html;
   }
 
+  # Service worker must never be cached — browser needs to re-fetch it to detect updates
+  location = /sw.js {
+    add_header Cache-Control "no-store, no-cache, must-revalidate";
+    try_files $uri =404;
+  }
+
   # Hashed assets (JS/CSS) — cache forever, cache-busting is in the filename
   location ~* \.(js|css|woff2?|png|svg|ico|webmanifest)$ {
     expires 1y;

frontend/src/main.jsx

@@ -3,10 +3,22 @@ import { createRoot } from 'react-dom/client'
 import App from './App'
 import './styles.css'
 
-// Register service worker
+// Register service worker + auto-reload when a new version activates
 if ('serviceWorker' in navigator) {
   window.addEventListener('load', () => {
-    navigator.serviceWorker.register('/sw.js').catch(() => {})
+    navigator.serviceWorker.register('/sw.js').then(reg => {
+      // When a new SW is found, wait for it to install then reload all clients
+      reg.addEventListener('updatefound', () => {
+        const next = reg.installing
+        if (!next) return
+        next.addEventListener('statechange', () => {
+          // 'installed' + existing controller = update ready, reload to activate
+          if (next.state === 'installed' && navigator.serviceWorker.controller) {
+            window.location.reload()
+          }
+        })
+      })
+    }).catch(() => {})
   })
 }