Nip44Encrypt test and error return

test/nostr_signer_actor_test.dart

@@ -104,4 +104,30 @@ void main() {
     expect(ts, greaterThanOrEqualTo(before));
     expect(ts, lessThanOrEqualTo(after + 2));
   });
+
+  test('Nip44Encrypt round-trips to self', () async {
+    final plaintext = jsonEncode({'blur_content_warnings': 'false', 'x': '1'});
+    final encrypted = await signer.handle(Nip44Encrypt(plaintext)) as Nip44Text;
+    expect(encrypted.value, isNot(equals(plaintext)));
+
+    // Payload is base64 with the NIP-44 v2 version byte (0x02) first.
+    final bytes = base64.decode(encrypted.value);
+    expect(bytes.first, equals(0x02));
+
+    final decrypted =
+        await signer.handle(Nip44Decrypt(encrypted.value)) as Nip44Text;
+    expect(decrypted.value, equals(plaintext));
+  });
+
+  test('Nip44Decrypt with a foreign key fails', () async {
+    final encrypted =
+        await signer.handle(const Nip44Encrypt('secret')) as Nip44Text;
+    final other = NostrSignerActor(
+      '0000000000000000000000000000000000000000000000000000000000000002',
+    );
+    expect(
+      () => other.handle(Nip44Decrypt(encrypted.value)),
+      throwsA(anything),
+    );
+  });
 }