fix(auth): members learn of ended sessions in the background

The full reading's L5: every change or reset of a password told the
members inside the request, up to 500 notices one after another with a
timeout of 10 seconds each, so a member out of reach held the change up
for minutes. Now announceSessionsEnded tells the members of this account's
notices alone, in the background on a session of its own; those not
confirmed wait for the hourly run as before.

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/lib/src/register/sessions_ended.dart

@@ -1,8 +1,11 @@
+import 'dart:async';
+
 import 'package:clock/clock.dart';
 import 'package:halkyon_base_server/src/generated/protocol.dart';
 import 'package:halkyon_base_server/src/halkyon_base.dart';
 import 'package:halkyon_base_server/src/register/accounts_mode.dart';
 import 'package:halkyon_base_server/src/register/deletion_notices.dart';
+import 'package:meta/meta.dart';
 import 'package:serverpod/serverpod.dart';
 import 'package:serverpod_auth_idp_server/core.dart';
 
@@ -80,21 +83,55 @@ Future<DateTime> endSessionsEverywhere(
 
 /// What follows [endSessionsEverywhere] once its transaction holds: the
 /// account's devices here learn that their sessions ended, and the members
-/// are told.
+/// are told, in the background (the full reading's L5: told inside the
+/// request, a member out of reach held a change of password up for its
+/// timeout, and the other notices waiting for minutes), this account's
+/// notices first; those not confirmed are told again hourly
+/// ([deliverSessionNotices], with the pruning).
 Future<void> announceSessionsEnded(Session session, UuidValue account) async {
   await session.messages.authenticationRevoked(
     account.uuid,
     RevokedAuthenticationUser(),
   );
-  await deliverSessionNotices(session);
+  final delivery = _deliverInBackground(session.serverpod, account);
+  _deliveries.add(delivery);
+  unawaited(delivery.whenComplete(() => _deliveries.remove(delivery)));
 }
 
+/// The deliveries [announceSessionsEnded] began, until they end.
+final _deliveries = <Future<void>>{};
+
+/// Tells the members of [account]'s ended sessions, on a session of its
+/// own: the request's may close first.
+Future<void> _deliverInBackground(Serverpod pod, UuidValue account) async {
+  final session = await pod.createSession(enableLogging: false);
+  try {
+    await deliverSessionNotices(session, account: account);
+  } on Object catch (error) {
+    // Its type only: what a member answered tells nobody here more.
+    session.log(
+      'Telling members of ended sessions failed: ${error.runtimeType}',
+      level: LogLevel.warning,
+    );
+  } finally {
+    await session.close();
+  }
+}
+
+/// Waits for the deliveries [announceSessionsEnded] began: tests do.
+@visibleForTesting
+Future<void> sessionNoticesDelivered() => Future.wait([..._deliveries]);
+
 /// Tells the members the sessions ended that they haven't confirmed yet, and
 /// returns how many confirmed; the others stay, counted, for the next time
-/// (the register's hourly pruning, and at once after each change), those
+/// (the register's hourly pruning, and after each change [account]'s alone,
-/// tried least first, 500 at a time. Notices to a member the operator no
+/// in the background), those tried least first, 500 at a time. Notices to a
-/// longer names are dropped.
+/// member the operator no longer names are dropped.
-Future<int> deliverSessionNotices(Session session, {DateTime? now}) async {
+Future<int> deliverSessionNotices(
+  Session session, {
+  DateTime? now,
+  UuidValue? account,
+}) async {
   final members = switch (HalkyonBase.maybeOf(session.serverpod)?.accounts) {
     HoldsRegister(:final members) => {for (final member in members) '$member'},
     _ => const <String>{},
@@ -105,10 +142,11 @@ Future<int> deliverSessionNotices(Session session, {DateTime? now}) async {
     where: (t) => t.member.notInSet(members),
   );
   final notifier = MemberNotifier.of(session.serverpod);
-  // SELECT … FROM "sessions_ended_notice" ORDER BY "attempts", "id"
+  // SELECT … FROM "sessions_ended_notice" [WHERE "account" = $1]
-  //   LIMIT 500
+  //   ORDER BY "attempts", "id" LIMIT 500
   final notices = await SessionsEndedNotice.db.find(
     session,
+    where: account == null ? null : (t) => t.account.equals(account),
     orderByList: (t) => [t.attempts.asc(), t.id.asc()],
     limit: 500,
   );

packages/halkyon_base_server/test/integration/password/password_change_test.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:typed_data';
 
 import 'package:clock/clock.dart';
@@ -7,6 +8,8 @@ import 'package:halkyon_base_server/src/password/password_endpoint.dart'
     show changesBegunPerSession;
 import 'package:halkyon_base_server/src/password/passwords.dart'
     show writeNewPassword;
+import 'package:halkyon_base_server/src/register/sessions_ended.dart'
+    show sessionNoticesDelivered;
 import 'package:serverpod/serverpod.dart';
 import 'package:serverpod_auth_idp_server/core.dart';
 import 'package:test/test.dart';
@@ -24,6 +27,10 @@ final class _Members implements MemberNotifier {
   final sessionsTold = <(Uri, UuidValue, DateTime, UuidValue?)>[];
   bool answering = true;
 
+  /// What a member's answer waits for, as one out of reach keeps it
+  /// waiting; none by default.
+  Future<void>? answerAfter;
+
   @override
   Future<bool> accountGone(Uri member, UuidValue account) async => answering;
 
@@ -34,6 +41,7 @@ final class _Members implements MemberNotifier {
     required DateTime endedBefore,
     UuidValue? keepSession,
   }) async {
+    await answerAfter;
     sessionsTold.add((member, account, endedBefore, keepSession));
     return answering;
   }
@@ -241,6 +249,7 @@ void main() {
           final sessions = await sessionsOf(anna);
           expect(sessions, contains(annasPhone));
           expect(sessions, isNot(contains(annasLaptop)));
+          await sessionNoticesDelivered();
           final (member, account, endedBefore, kept) =
               members.sessionsTold.first;
           expect(member, _todo);
@@ -307,6 +316,7 @@ void main() {
             kept,
           );
           expect(await sessionsOf(anna), {annasPhone, annasLaptop});
+          await sessionNoticesDelivered();
           expect(members.sessionsTold, isEmpty);
         });
 
@@ -566,10 +576,23 @@ void main() {
           );
         });
 
+        test('is done without waiting for the members: one out of reach '
+            "holds no change up (the full reading's L5)", () async {
+          final reached = Completer<void>();
+          members.answerAfter = reached.future;
+          await change();
+          expect(members.sessionsTold, isEmpty);
+          reached.complete();
+          await sessionNoticesDelivered();
+          expect(members.sessionsTold, hasLength(1));
+          expect(await SessionsEndedNotice.db.count(session), 0);
+        });
+
         test('tells a member that missed it again, hourly, until it '
             'confirms', () async {
           members.answering = false;
           await change();
+          await sessionNoticesDelivered();
           expect(await SessionsEndedNotice.db.count(session), 1);
 
           members.answering = true;
@@ -1042,6 +1065,7 @@ void main() {
           expect(sessions, hasLength(1));
           expect(sessions, isNot(contains(annasPhone)));
           expect(sessions, isNot(contains(annasLaptop)));
+          await sessionNoticesDelivered();
           expect(members.sessionsTold.single.$2, anna);
           expect(members.sessionsTold.single.$4, isNull);
         });

packages/halkyon_base_server/test/integration/register/register_test.dart

@@ -7,6 +7,8 @@ import 'package:halkyon_base_server/src/register/deletion_notices.dart';
 import 'package:halkyon_base_server/src/register/instance_api.dart';
 import 'package:halkyon_base_server/src/register/register_protocol.dart';
 import 'package:halkyon_base_server/src/register/remote_register.dart';
+import 'package:halkyon_base_server/src/register/sessions_ended.dart'
+    show sessionNoticesDelivered;
 import 'package:http/http.dart' as http;
 import 'package:http/testing.dart';
 import 'package:serverpod/serverpod.dart';
@@ -677,6 +679,7 @@ void main() {
               (account: annaOnTodo, endedBefore: now),
             );
             // Every member is told to end the account's sessions too.
+            await sessionNoticesDelivered();
             expect(members.sessionsTold.single, (_todo, annaOnTodo, now, null));
 
             final forReset = await remote.beginPasswordSignIn(
@@ -809,6 +812,7 @@ void main() {
                 password: device.newPassword(),
                 keepSession: annasPhone,
               );
+              await sessionNoticesDelivered();
               expect(members.sessionsTold.single, (
                 _todo,
                 annaOnTodo,