Merge pull request 'Add a mobile banner nudging an install of the PWA' (#21) from feature/pwa-install-prompt into master

# Conflicts:
#	README.md
#	docs/architecture.md

README.md

@@ -389,6 +389,9 @@ Then put it behind your existing reverse proxy like everything else
 - [x] Fixed an album's track rows collapsing to 3 lines on mobile —
       there was always room for one, the breakpoint just assumed
       otherwise — see docs/architecture.md
+- [x] A mobile banner nudging an install of the PWA — the real
+      Chrome/Android install prompt, manual instructions on iOS Safari
+      (no such prompt exists there) — see docs/architecture.md
 - [ ] Try a full party end-to-end with two real accounts (still the main gap)
 - [ ] Try casting to a real Chromecast (only the SDK's own bootstrap is
       confirmed here — no real device/session)

client/src/pwaInstall.css

@@ -0,0 +1,46 @@
+/* ---- Mobile-only "install this as an app" banner - see pwaInstall.ts.
+   A normal-flow element at the very top of <body>, before #app, not a
+   fixed/sticky overlay - pushes the app down by its own height instead
+   of needing to coordinate an offset with shell/Shell.css's own
+   .mobileTopBar/.libraryHeader (already stacked on top of each other at
+   the same breakpoint) or alphaIndex.css's rail. Scrolls away with the
+   page like any other content above the sticky chrome, same as a
+   browser's own native install infobar would. ---- */
+.pwaInstallBanner {
+  display: none;
+  align-items: center;
+  gap: 10px;
+  padding: 10px 14px;
+  background: var(--accent);
+  color: #fff;
+  font-size: 13px;
+  line-height: 1.35;
+}
+
+.pwaInstallText { flex: 1; min-width: 0; }
+
+.pwaInstallBtn {
+  flex-shrink: 0;
+  background: #fff;
+  color: var(--accent);
+  font-size: 12px;
+  font-weight: 700;
+  padding: 6px 12px;
+}
+
+.pwaInstallBtn:hover { background: rgba(255, 255, 255, .85); }
+
+.pwaInstallClose {
+  flex-shrink: 0;
+  background: none;
+  color: #fff;
+  font-size: 20px;
+  line-height: 1;
+  padding: 0 2px;
+}
+
+.pwaInstallClose:hover { background: none; opacity: .8; }
+
+@media (max-width: 720px) {
+  .pwaInstallBanner { display: flex; }
+}

client/src/pwaInstall.ts

@@ -0,0 +1,108 @@
+// Mobile-only "install this as an app" nudge - see docs/architecture.md.
+// Self-mounting like toast.ts (no per-route/per-party state to attach),
+// but the beforeinstallprompt listener below is attached the moment
+// this module is first imported - app.ts does that at the very top,
+// well before boot()'s async login check - rather than lazily on first
+// use like toast.ts: the browser only ever fires this event once per
+// page load, often before any UI exists to react to it, and there's no
+// way to ask for a replay if a listener attaches too late to catch it.
+import './pwaInstall.css';
+
+/** Chrome/Edge/Android-WebView's own install-prompt event - not in
+ *  lib.dom.d.ts (Safari/Firefox never implement it at all). */
+interface BeforeInstallPromptEvent extends Event {
+  prompt(): Promise<void>;
+  userChoice: Promise<{ outcome: 'accepted' | 'dismissed' }>;
+}
+
+const DISMISSED_KEY = 'watchparty:pwaInstallDismissed';
+const MOBILE_QUERY = '(max-width: 720px)';
+
+let deferredPrompt: BeforeInstallPromptEvent | null = null;
+let bannerEl: HTMLElement | null = null;
+
+window.addEventListener('beforeinstallprompt', (e) => {
+  e.preventDefault(); // suppress the browser's own mini-infobar - this banner replaces it
+  deferredPrompt = e as BeforeInstallPromptEvent;
+  renderIfEligible();
+});
+
+window.addEventListener('appinstalled', () => {
+  deferredPrompt = null;
+  removeBanner();
+});
+
+function isStandalone(): boolean {
+  return window.matchMedia('(display-mode: standalone)').matches
+    || (navigator as unknown as { standalone?: boolean }).standalone === true; // iOS Safari's own flag - no display-mode query there
+}
+
+/** No feature-detection exists for "is this iOS Safari" - beforeinstallprompt
+ *  simply never fires there, which is the actual fact this module cares
+ *  about, but by the time that's observable it's too late to show
+ *  install instructions instead. Checked only as a fallback once
+ *  deferredPrompt has had a real chance to arrive - see renderIfEligible. */
+function isIOS(): boolean {
+  return /iphone|ipad|ipod/i.test(navigator.userAgent)
+    || (navigator.platform === 'MacIntel' && navigator.maxTouchPoints > 1); // iPadOS 13+ reports as a Mac
+}
+
+function removeBanner(): void {
+  bannerEl?.remove();
+  bannerEl = null;
+}
+
+function dismiss(): void {
+  localStorage.setItem(DISMISSED_KEY, '1');
+  removeBanner();
+}
+
+async function install(): Promise<void> {
+  if (!deferredPrompt) return;
+  const prompt = deferredPrompt;
+  deferredPrompt = null; // a captured prompt can only ever be used once
+  await prompt.prompt();
+  const { outcome } = await prompt.userChoice;
+  // 'dismissed' here means the user closed the browser's own native
+  // picker without installing - not the same signal as our own close
+  // button (dismiss() above), so this banner stays up rather than
+  // remembering "never ask again" over a single not-right-now.
+  if (outcome === 'accepted') removeBanner();
+}
+
+function renderIfEligible(): void {
+  if (bannerEl) return;
+  if (isStandalone()) return;
+  if (localStorage.getItem(DISMISSED_KEY)) return;
+  if (!window.matchMedia(MOBILE_QUERY).matches) return;
+
+  const ios = isIOS();
+  if (!deferredPrompt && !ios) return; // no install path this module actually knows how to help with
+
+  bannerEl = document.createElement('div');
+  bannerEl.className = 'pwaInstallBanner';
+  bannerEl.innerHTML = ios
+    ? `<span class="pwaInstallText">Installe Watch Party : appuie sur <strong>Partager</strong> puis « Sur l'écran d'accueil ».</span>
+       <button type="button" class="pwaInstallClose" aria-label="Fermer">&times;</button>`
+    : `<span class="pwaInstallText">Installe Watch Party sur ton écran d'accueil pour y accéder plus vite.</span>
+       <button type="button" class="pwaInstallBtn">Installer</button>
+       <button type="button" class="pwaInstallClose" aria-label="Fermer">&times;</button>`;
+
+  bannerEl.querySelector('.pwaInstallClose')!.addEventListener('click', dismiss);
+  bannerEl.querySelector('.pwaInstallBtn')?.addEventListener('click', () => { install().catch(() => {}); });
+
+  document.body.insertBefore(bannerEl, document.body.firstChild);
+}
+
+/**
+ * Called once by Shell.ts after a successful login - covers both the
+ * case where beforeinstallprompt already fired before Shell existed to
+ * react to it (deferredPrompt sitting ready, banner never actually
+ * shown yet) and iOS, which has no event at all to trigger this from.
+ * Also re-checked on resize: crossing the 720px breakpoint live (an
+ * unfolding or rotated device) shouldn't need a reload to notice.
+ */
+export function initPwaInstallPrompt(): void {
+  renderIfEligible();
+  window.addEventListener('resize', renderIfEligible);
+}

client/src/shell/Shell.ts

@@ -5,6 +5,7 @@ import './Shell.css';
 import html from './Shell.html';
 import { auth, getLibraries, logout } from '../api/embyApi';
 import { initMusicBar } from '../musicBar/MusicBar';
+import { initPwaInstallPrompt } from '../pwaInstall';
 import type { LibraryDto } from '../types';
 
 // One icon per Emby CollectionType - only used by the mobile bottom
@@ -56,6 +57,7 @@ export async function renderShell(appEl: HTMLElement): Promise<HTMLElement> {
   // Mounted once, outside #mainContent, so a listen party survives
   // navigating the router - see musicBar/MusicBar.ts's header comment.
   initMusicBar(appEl.querySelector('#musicBar') as HTMLElement);
+  initPwaInstallPrompt();
 
   // Both the sidebar's and the mobile sheet's logout button - same
   // label, same handler, one line each instead of a shared DOM node

docs/architecture.md

@@ -4266,6 +4266,70 @@ ranges genuinely overlapping, not just similar by coincidence), left to
 right in that order, with the long names confirmed actually truncated
 (`scrollWidth > clientWidth`) rather than merely happening to fit.
 
+## A mobile install nudge for the PWA
+
+Asked for directly: the PWA (see "Progressive Web App" above) existed,
+but nothing ever told a mobile visitor it could be installed at all -
+Chrome's own default mini-infobar is easy to miss/dismiss, and Safari
+has no browser-driven prompt whatsoever.
+
+New `pwaInstall.ts`, self-mounting like `toast.ts` (no per-route/
+per-party state to attach) but with one real difference from that
+module's own lazy-init pattern: `beforeinstallprompt` (Chrome/Edge/
+Android WebView's event for this - not in `lib.dom.d.ts`, Safari/
+Firefox never implement it) can fire before any UI exists to react to
+it, and the browser never replays it for a listener that attached too
+late. The listener itself is a top-level side effect of importing the
+module - `shell/Shell.ts` does that (and calls the module's own
+`initPwaInstallPrompt()`, after `initMusicBar`), and since ES module
+imports all evaluate before an entry file's own top-level code runs,
+that listener is live well before `app.ts`'s `boot()` even starts its
+async login check, regardless of how soon the event actually fires.
+
+Two real install paths exist, and the banner speaks to whichever one
+applies:
+- **Chrome/Edge/Android WebView**: `event.preventDefault()` stashes the
+  captured event (this banner replaces the browser's own default one);
+  clicking "Installer" calls the real `prompt()` and reads back
+  `userChoice` - only an outright 'accepted' removes the banner, since
+  the picker's own 'dismissed' just means "not right now", not "stop
+  asking" (that's what the banner's own close button is for).
+- **iOS Safari**: no such event exists at all, ever - detected instead
+  by user-agent sniffing (there's no clean feature-detection for "is
+  this iOS Safari"), showing manual instructions ("appuie sur Partager
+  puis Sur l'écran d'accueil") with no button, since there's nothing to
+  programmatically trigger.
+
+Mobile-only (`matchMedia('(max-width: 720px)')`, this app's own
+existing breakpoint, re-checked on resize for a live rotate/unfold) and
+suppressed entirely once already running installed
+(`display-mode: standalone`, or `navigator.standalone` for iOS Safari's
+own equivalent flag, which has no `display-mode` query at all). A
+close click remembers "don't ask again" in `localStorage` - not
+re-shown even against a fresh `beforeinstallprompt` on a later visit.
+
+Rendered as a plain normal-flow banner at the very top of `<body>`,
+before `#app` - not a fixed/sticky overlay - specifically to avoid
+needing to coordinate yet another offset with `shell/Shell.css`'s own
+already-stacked `.mobileTopBar`/`.libraryHeader` pair (see the sticky-
+header sections above) or `alphaIndex.css`'s rail. It simply pushes the
+app down by its own height and scrolls away with the page, the same as
+a browser's own native install infobar would.
+
+Verified: full `typecheck`/`build` (client only). No real device
+install flow is triggerable in this sandbox (nothing can fabricate a
+genuine browser installability signal), so checked everything around
+that boundary directly instead: a synthetic `beforeinstallprompt`-
+shaped event (real `Event`, stubbed `prompt`/`userChoice`) dispatched
+into real compiled CSS/JS confirmed the banner appears with the
+install button, that button calls the stub `prompt()` and removes the
+banner only on an 'accepted' outcome, and that the close button both
+removes it and blocks a *second* dispatched event from reopening it.
+Overriding `navigator.userAgent` to an iPhone string confirmed the
+iOS-flavored copy with no install button. A same-event dispatch into a
+real ≥900px-wide `<iframe>` confirmed the banner never renders there
+at all, regardless of the event firing.
+
 ## Known limitations
 
 - Playback always goes through `hls.js` against whatever Emby's