Complete verification links and preserve verified login email (#60)

frontend/packages/sxchnge_auth/test/verification_test.dart

@@ -42,6 +42,12 @@ void main() {
       addTearDown(provider.dispose);
       await provider.confirm(scenario.key);
       expect(provider.state.status, scenario.value);
+      expect(
+        provider.state.result?.verifiedEmail,
+        scenario.value == VerificationStatus.verified
+            ? 'alex@example.com'
+            : null,
+      );
       expect(
         provider.state.isSimulated,
         scenario.value == VerificationStatus.verified,
@@ -75,7 +81,23 @@ void main() {
     service.pending.complete(const VerificationResult(isSimulated: true));
     await operation;
     expect(provider.state.status, VerificationStatus.idle);
+    expect(provider.state.result, isNull);
   });
+  test(
+    'a later failed confirmation clears the previous verified identity',
+    () async {
+      final provider = VerificationProvider(
+        const DummyVerificationService(delay: Duration.zero),
+      );
+      addTearDown(provider.dispose);
+      await provider.confirm('demo-valid');
+      expect(provider.state.result?.verifiedEmail, 'alex@example.com');
+      final operation = provider.confirm('bad');
+      expect(provider.state.result, isNull);
+      await operation;
+      expect(provider.state.result, isNull);
+    },
+  );
   test('dispose discards late exception', () async {
     final service = PendingService();
     final provider = VerificationProvider(service);