Promote Postbox's internal MutableMessageHistoryThreadIndexView.Item to a
public top-level type MessageHistoryThreadIndexItem; drop Postbox's empty
EngineMessageHistoryThread namespace class and its nested Item.
MessageHistoryThreadIndexView.items is now [MessageHistoryThreadIndexItem]
directly (no wrap/unwrap step in the init). The two consumer iteration
sites (ChatListNodeLocation.swift, ShareControllerNode.swift) don't need
changes -- they iterate without type annotation and only read fields that
exist on both the old nested Item and the new top-level type.
Collapse TelegramCore's public extension EngineMessageHistoryThread into
a proper class definition:
public final class EngineMessageHistoryThread { class Info { ... } }.
After this, EngineMessageHistoryThread is a pure TelegramCore type --
consumers that only use EngineMessageHistoryThread.Info no longer need
import Postbox for the outer name to resolve.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
isaac