This could also be something that a moderator could send in reply to a thread to lock it, or the OP could also do that, for more forum-like implementations of Fediverse technology.
Sub-threads can also be handled that way without affecting the parent.
@Elizafox I mean, that's certainly simpler, although I can see a couple situations where that's insufficient.
(The biggest situations I can think of are when it's instance moderation that does a :dont_at_me:, and then replies are happening that may need to be dealt with by said moderators.)
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