Even mentions copied from the parent will count as characters, and eat up the limited character quota, no?
No, they can be be omitted from the text.
In this comment I will not make an explicit mention, but the message will still be delivered to you.
So once conversation containers for public conversations are implemented, it should be possible for at least a Mitra OP to get notified of every single reply in a thread, even if they are not tagged. Isn’t that correct?
Yes, that is correct.
By the way, I didn’t get the point you had made earlier:
Addressing in ActivityPub is similar to that of E-mail. A message contains a list of recipients and your server delivers a copy of the message to each recipient.
@-mentions, addressing and notifications are different things.
@-mentions are often used to determine recipients, but this is not a requirement. Similarly, applications often generate a notification when you are mentioned, but they may also generate a notification if you're addressed without @-mention.
@jupiter_rowland