improved performance and battery usage on older devices

lib/utils/session_single_flight.dart

@@ -0,0 +1,21 @@
+import '../model/account_data.dart';
+
+/// Joins concurrent calls into the one already running for the same account
+/// session. A run left over from a signed-out session never blocks the next
+/// account's first call.
+class SessionSingleFlight {
+  Future<void>? _running;
+  int? _epoch;
+
+  Future<void> run(Future<void> Function() action) {
+    final epoch = AccountData().sessionEpoch;
+    final running = _running;
+    if (running != null && _epoch == epoch) return running;
+    _epoch = epoch;
+    late final Future<void> current;
+    current = action().whenComplete(() {
+      if (identical(_running, current)) _running = null;
+    });
+    return _running = current;
+  }
+}