preview: One chat can now be kept on a tighter storage limit than the rest, from its own page reached from its row on Settings > Storage, with the stricter of the chat's limit and the account's budget winning and "keep this chat whole" beating both; "Free up space now" is no longer dead when a chat's own limit is the only thing in force; and a stopped account session now stops its own coroutines, so removing or switching an account no longer leaves collectors querying a deleted database. MIGRATION 22 (schema 22 -> 23): an account opened by this build or newer cannot be opened by anything older. The older build does not say so -- it sniffs, corrects user_version down and lands at the account picker, which reads as though the account were gone. The way back is any build at or above the one that migrated it.