swipe bug fix

frontend/src/pages/Chat.jsx

@@ -455,11 +455,15 @@ export default function Chat() {
     setUnreadGroups(prev => { const next = new Map(prev); next.delete(id); return next; });
   };
 
-  // Establish one history sentinel on mount (mobile only) so back gestures are
-  // always interceptable without accumulating extra entries.
+  // Establish two history entries on mount (mobile only):
+  //   floor   — marks the true exit point; always stays below the sentinel
+  //   sentinel — intercepted by handlePopState on every back gesture
+  // Two entries are required so that iOS fires popstate (same-document navigation)
+  // before exiting, giving the handler a chance to push a new sentinel.
   useEffect(() => {
     if (window.innerWidth < 768) {
-      window.history.replaceState({ rc: 'chat' }, '');
+      window.history.replaceState({ rc: 'floor' }, '');
+      window.history.pushState({ rc: 'chat' }, '');
     }
   }, []);
 
@@ -486,8 +490,11 @@ export default function Chat() {
         return;
       }
 
-      // Already at root (Messages list, no chat open) — let the browser handle
-      // it so the next gesture actually exits the PWA. Don't re-push.
+      // Already at root (Messages list, no chat open) — we just popped the sentinel
+      // and are now on the floor entry. Step one more back so the browser exits the
+      // PWA (or navigates to the previous URL). Without this explicit go(-1), iOS
+      // leaves the user stranded on the invisible floor state.
+      window.history.go(-1);
     };
     window.addEventListener('popstate', handlePopState);
     return () => window.removeEventListener('popstate', handlePopState);