fix(auth): a member deletes nobody while the register is out of reach

A person still anonymous on a member was deleted there on the session
alone while the register was out of reach (the reading of the fixes' B1).
But the register may have linked them while their becoming identified on
the member failed, so with both failing, an account of the register's went
without its proof (the short reading's L2). A member now refuses every
deletion while it can't ask the register (decided by the developer on
21 Oct).

In the app, signing out of an anonymous account, which deletes it, signs
the device out all the same when the deletion fails, as a switch already
leaves one behind: the account is left to the instance's pruning of
anonymous accounts unused for 90 days. signInWays gets its doc comment
back.

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_base_server/test/integration/register/member_test.dart

@@ -1085,15 +1085,22 @@ void main() {
           );
         });
 
-        test('of a person anonymous here deletes it here while the register '
-            'is out of reach: becoming identified ends being anonymous, so '
-            "none is the register's", () async {
+        test('of a person anonymous here is refused too while the register '
+            'is out of reach, deleting nothing here: the register may have '
+            'linked her while her becoming identified here failed (the '
+            'short reading, L2)', () async {
           register.failing = RegisterUnavailableException('test');
 
-          await endpoints.account.delete(asAnna());
-
-          expect(await AuthUser.db.findById(session, anna), isNull);
-          expect(hostDeleted, [anna]);
+          await expectLater(
+            endpoints.account.delete(asAnna()),
+            throwsA(isA<RegisterUnavailableException>()),
+          );
+          expect(await AuthUser.db.findById(session, anna), isNotNull);
+          expect(
+            await ServerSideSession.db.findById(session, annasPhone),
+            isNotNull,
+          );
+          expect(hostDeleted, isEmpty);
         });
       });