fixed possible lockups on app start

test/utils/exponential_backoff_test.dart

@@ -0,0 +1,35 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:marianum_mobile/utils/exponential_backoff.dart';
+
+void main() {
+  group('exponentialBackoff', () {
+    test('doubles per attempt starting at base', () {
+      expect(exponentialBackoff(1), const Duration(milliseconds: 500));
+      expect(exponentialBackoff(2), const Duration(seconds: 1));
+      expect(exponentialBackoff(3), const Duration(seconds: 2));
+      expect(exponentialBackoff(4), const Duration(seconds: 4));
+    });
+
+    test('caps at max', () {
+      expect(exponentialBackoff(5), const Duration(seconds: 5));
+      expect(exponentialBackoff(40), const Duration(seconds: 5));
+      expect(exponentialBackoff(1000), const Duration(seconds: 5));
+    });
+
+    test('treats attempt 0 and negatives like the first attempt', () {
+      expect(exponentialBackoff(0), const Duration(milliseconds: 500));
+      expect(exponentialBackoff(-3), const Duration(milliseconds: 500));
+    });
+
+    test('honours custom base and max', () {
+      expect(
+        exponentialBackoff(
+          3,
+          base: const Duration(seconds: 1),
+          max: const Duration(seconds: 3),
+        ),
+        const Duration(seconds: 3),
+      );
+    });
+  });
+}