feat(session): warn before a session ends and say when protection stops

Review findings #1-#3 in internal/APP_REVIEW_2026-10-16.md: every session
end dropped the user onto their real IP with no warning, and the app showed
no errors at all.

- RevoltAlerts (vendored runtime) owns both alerts: a high-importance
  channel, ids 2 and 3, posted from whichever process is alive
- XrayVPNService schedules a 5-minute warning off the deadline it already
  holds, best effort (a warning that cannot be armed never stops a tunnel),
  with its own request code so it cannot clobber the expiry alarm
- the warning intent is handled above the command dispatch: without that it
  would fall through to the final else and stop the tunnel 5 minutes early
- SessionTimer._doDisconnect takes endedMessage: set for ends the user did
  not ask for, which both posts the alert and gives the UI a sentence
- the API being unreachable no longer disconnects a working tunnel; it is a
  display state now, with expiry still enforced natively and server-side
- status_bar.dart renders connect errors, connecting progress and the
  session-end reason

flutter analyze clean; debug APK builds (Kotlin compiles).

Co-Authored-By: Claude Opus 5 <[email protected]>

lib/components/status_bar.dart

@@ -5,6 +5,44 @@ import 'package:revoltvpn/logic/app_colors.dart';
 import 'package:revoltvpn/logic/session_timer.dart';
 import 'package:revoltvpn/logic/vpn_connection.dart';
 
+// Nothing rendered the connection's own messages, so they are collected here
+// in one place: whatever the user most needs to know right now, and whether it
+// is a problem (red) or just progress (dim).
+class _StatusDetail {
+  const _StatusDetail(this.text, {this.isProblem = false});
+
+  final String text;
+  final bool isProblem;
+}
+
+_StatusDetail? _detail(VpnConnection vpn, SessionTimer timer) {
+  final error = vpn.errorMessage;
+  if (error != null && error.isNotEmpty) {
+    return _StatusDetail(error.replaceAll('\n', ' '), isProblem: true);
+  }
+
+  if (vpn.status == VpnStatus.connecting ||
+      vpn.status == VpnStatus.disconnecting) {
+    return _StatusDetail(vpn.statusMessage);
+  }
+
+  // The tunnel still carries traffic; only the control plane is missing, so
+  // this is a warning, not a disconnect (review #2).
+  if (vpn.status == VpnStatus.connected && timer.serverUnreachable) {
+    return const _StatusDetail(
+      'Can\'t reach the server — still connected',
+      isProblem: true,
+    );
+  }
+
+  if (vpn.status != VpnStatus.connected) {
+    final ended = timer.lastEndMessage;
+    if (ended != null) return _StatusDetail(ended, isProblem: true);
+  }
+
+  return null;
+}
+
 class StatusBar extends StatelessWidget {
   const StatusBar({super.key});
 
@@ -24,6 +62,8 @@ class StatusBar extends StatelessWidget {
                 ? 'Connecting…'
                 : (vpn.serverReachable ? 'Ready' : 'Offline'));
 
+        final detail = _detail(vpn, timer);
+
         return Padding(
           padding: const EdgeInsets.symmetric(horizontal: 24),
           child: Column(
@@ -96,6 +136,23 @@ class StatusBar extends StatelessWidget {
                   ],
                 ),
               ),
+              // Until this existed, a failed connect, an expired session and a
+              // cap kill all just turned the button back to idle - the user
+              // could not tell protected from unprotected (review #3).
+              if (detail != null)
+                Padding(
+                  padding: const EdgeInsets.only(top: 6),
+                  child: Text(
+                    detail.text,
+                    textAlign: TextAlign.center,
+                    style: TextStyle(
+                      color: detail.isProblem
+                          ? AppColors.red
+                          : AppColors.textDim,
+                      fontSize: 11,
+                    ),
+                  ),
+                ),
             ],
           ),
         );