fix(app): no sheet is left busy by an error nothing expected

An instance's salt of another length made the device's cryptography throw
an ArgumentError, a wrapping's nonce a RangeError, and libsodium or the
keyring may throw their own; none was a refusal, so the step's error
escaped and the sheet stayed busy, which can't be closed. halkyon_keys
now checks the lengths of what comes from elsewhere before libsodium sees
it (KeyRefusal.malformed: a salt, a wrapping, a sealed key's box, a sealed
payload), the device's cryptography turns anything else into the general
failure, and so does every password cubit, the error logged by its type
alone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_keys/test/account_keys_test.dart

@@ -137,10 +137,6 @@ Future<void> main() async {
       for (final tampered in [
         WrappedAccountKeys(nonce: wrapped.nonce, cipherText: cipherText),
         WrappedAccountKeys(nonce: nonce, cipherText: wrapped.cipherText),
-        WrappedAccountKeys(
-          nonce: wrapped.nonce,
-          cipherText: wrapped.cipherText.sublist(1),
-        ),
       ]) {
         expect(
           () => unwrap(tampered, password.keyEncryptionKey),
@@ -177,6 +173,33 @@ Future<void> main() async {
         refusedFor(KeyRefusal.notTheAccountsKeys),
       );
     });
+
+    test('wrappings of other lengths, as an instance might send them, are '
+        'refused rather than thrown on', () {
+      for (final (nonce, cipherText) in [
+        (Uint8List(23), wrapped.cipherText),
+        (Uint8List(25), wrapped.cipherText),
+        (Uint8List(0), Uint8List(0)),
+        (wrapped.nonce, Uint8List(15)),
+        (wrapped.nonce, wrapped.cipherText.sublist(1)),
+        (wrapped.nonce, Uint8List(wrapped.cipherText.length + 1)),
+      ]) {
+        expect(
+          () => unwrap(
+            WrappedAccountKeys(nonce: nonce, cipherText: cipherText),
+            password.keyEncryptionKey,
+          ),
+          throwsA(
+            isA<KeyRefused>().having(
+              (refused) => refused.reason,
+              'reason',
+              KeyRefusal.malformed,
+            ),
+          ),
+          reason: '${nonce.length} / ${cipherText.length}',
+        );
+      }
+    });
   });
 
   test('wrapped again under the recovery key, the phrase opens them', () {