[2.x] fix(realtime): only force-reconnect on iOS visibilitychange

PR #4654 added a `visibilitychange` listener that forces a fresh
Pusher instance and refreshes the visible discussion list whenever
the tab has been hidden for >5s. That was needed on iOS Safari,
where backgrounding the page silently drops the WebSocket without
firing `close`. On every other platform the WebSocket survives tab
backgrounding fine — but the visibilitychange handler still fired,
causing an unnecessary `GET /api/discussions` request and full list
re-render every time the user switched away and back.

Gate the visibilitychange-triggered `forceReconnect()` on `isIOS()`
so the workaround only runs on the platform that actually needs it.
The `pageshow(persisted=true)` path stays unconditional — bfcache
restoration only fires on browsers that bfcached the page, and the
WebSocket was definitely torn down by then regardless of platform.

`isIOS()` is broader than the existing `isSafariMobile()` core
utility because all iOS browsers use WebKit and share the same
backgrounding pathology — iOS Chrome (`CriOS`) and iOS Firefox
(`FxiOS`) are excluded by `isSafariMobile()` but still need this
workaround.

Regression from #4654.

Author: imorland

extensions/realtime/js/src/forum/extend/Application.ts

@@ -5,6 +5,7 @@ import Application from 'flarum/common/Application';
 import RealtimeState from '../RealtimeState';
 import NotificationToast from '../components/NotificationToast';
 import NotificationToastState from '../states/NotificationToastState';
+import isIOS from '../utils/isIOS';
 
 export default function () {
   extend(Application.prototype, 'mount' as any, function () {
@@ -78,12 +79,17 @@ export default function () {
     app.websocket = new Pusher(wsKey, pusherOptions);
     setupChannels(app.websocket);
 
-    // iOS Safari silently drops WebSocket connections when the tab is
-    // backgrounded or the device sleeps, without firing `close` — pusher-js's
-    // built-in recovery never triggers, so realtime updates go missing until
-    // the page is reloaded. iOS also bfcaches pages on app-switch, which
-    // restores via `pageshow` (persisted=true) and does NOT fire
-    // `visibilitychange` on return. We therefore hook both events.
+    // iOS browsers (all WebKit) silently drop WebSocket connections when
+    // the tab is backgrounded or the device sleeps, without firing `close`
+    // — pusher-js's built-in recovery never triggers, so realtime updates
+    // go missing until the page is reloaded. iOS also bfcaches pages on
+    // app-switch, which restores via `pageshow` (persisted=true) and does
+    // NOT fire `visibilitychange` on return. We therefore hook both events.
+    //
+    // The visibilitychange path is gated on `isIOS()`: desktop browsers
+    // (and Android) maintain the WebSocket fine across tab backgrounding
+    // and don't need a forced reconnect, which would otherwise cause an
+    // unnecessary discussion-list refetch on every tab-switch return.
     //
     // `forceReconnect` constructs a fresh Pusher instance rather than
     // calling `connect()` on the existing one. pusher-js 7.6's default
@@ -134,7 +140,7 @@ export default function () {
       if (hiddenSince === null) return;
       const wasHiddenFor = Date.now() - hiddenSince;
       hiddenSince = null;
-      if (wasHiddenFor > RECONNECT_HIDDEN_THRESHOLD_MS) {
+      if (wasHiddenFor > RECONNECT_HIDDEN_THRESHOLD_MS && isIOS()) {
         forceReconnect();
       }
     });

extensions/realtime/js/src/forum/utils/isIOS.ts

@@ -0,0 +1,22 @@
+/**
+ * Detect whether the current browser is running on iOS / iPadOS.
+ *
+ * All iOS browsers (Safari, Chrome, Firefox, etc.) use WebKit under the hood
+ * and inherit Safari's WebSocket-backgrounding pathology — so this needs to
+ * be broader than `isSafariMobile()` (which excludes Chrome/Firefox on iOS).
+ *
+ * Detects iPadOS 13+ via the MacIntel + maxTouchPoints quirk: iPadOS 13+
+ * reports `navigator.platform === 'MacIntel'` but `maxTouchPoints > 1`,
+ * which desktop macOS never does.
+ */
+export default function isIOS(): boolean {
+  if (/iPad|iPhone|iPod/.test(navigator.userAgent)) {
+    return true;
+  }
+
+  if (navigator.platform === 'MacIntel' && navigator.maxTouchPoints > 1) {
+    return true;
+  }
+
+  return false;
+}