With ENABLE_ADMIN_CHAT_ACCESS turned off, opening another user's chat was refused, but through direct API requests an admin could still get the whole chat back in the reply to editing or deleting one of its messages, grant themselves read access in the chat's share settings, clone a chat someone shared privately with another user, or delete the chat. They could also send messages into it, attach it as context to their own chat, approve its tool calls, and list or stop its running replies. All of these are now refused for an admin on another user's chat, the same as opening it. With the setting on, admins keep full access as before.
Fixes#31413