ZaStoGram_desktop/tasks/2026/08/21/preserve-info-thread-identity-and-lifetime.md

Keep Info pages on their topic or sublist

An Info page is keyed by a peer, a forum topic, or a Saved Messages / monoforum sublist. Four holes dropped that thread:

• Controller::validateMementoPeer compared the sublist but not the topic, so a topic media memento could be answered by the whole-forum page of the same type.
• WrapWidget::returnToFirstStackFrame compared only the peer, so a topic or sublist Profile could unwind onto a whole-chat Profile frame.
• Polls::ListWidget::doCreateMemento always used the peer constructor, so Back restored the whole-chat polls page.
• The wrap subscribed to ForumTopic::destroyed() but not SavedSublist::destroyed(), so a sublist Info page outlived its subject.

SavedSublist::destroyed() already fires for applySublistDeleted and for MegagroupInfo::takeMonoforumData() (MonoforumAdmin clear while the taken object is still alive in setFlags). The new subscription mirrors the topic block and does not retain the sublist.

_historyStack frames are not purged. A wrap constructed for that sublist is removed wholesale, so Back cannot land on its frames. That matches the topic path: the subscription is constructor-time on the initial key.

The General topic (ForumTopic::kGeneralId = 1) is a real ForumTopic*. The new topic() term therefore treats General and the whole chat as different subjects.