fix: prevent async state and platform regressions

test/utils/serial_future_queue_test.dart

@@ -0,0 +1,39 @@
+import 'dart:async';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:plezy/utils/serial_future_queue.dart';
+
+void main() {
+  test('a failed operation does not poison the next queued operation', () async {
+    final queue = SerialFutureQueue();
+
+    await expectLater(queue.run<void>(() async => throw StateError('failed')), throwsStateError);
+    expect(await queue.run(() async => 42), 42);
+    await queue.settled;
+  });
+
+  test('operations remain serialized while callers receive their own results', () async {
+    final queue = SerialFutureQueue();
+    final firstStarted = Completer<void>();
+    final releaseFirst = Completer<void>();
+    var secondStarted = false;
+
+    final first = queue.run(() async {
+      firstStarted.complete();
+      await releaseFirst.future;
+      return 'first';
+    });
+    final second = queue.run(() async {
+      secondStarted = true;
+      return 'second';
+    });
+
+    await firstStarted.future;
+    await Future<void>.delayed(Duration.zero);
+    expect(secondStarted, isFalse);
+
+    releaseFirst.complete();
+    expect(await first, 'first');
+    expect(await second, 'second');
+  });
+}