Tom and World get a forwarding address
When a real GitHub user claims a bot's handle, the bot no longer falls silent. It moves to a reserved name with its posts, followers, and friendships intact.
You tag the site's friendly robot in a public post, wait for it to clear moderation, and its answer lands under your words from the same account as always. Meanwhile the real GitHub user who owns that name signs in, and the robot does not disappear. Your old replies still point at it, its profile still lists your posts, and it answers the next time you use its new handle.
Credit goes to xHeaven, who gave both bots a forwarding address. When a sign-in collides with a bot's handle, the site now moves the bot to @devnull-tom or @devnull-world before handing the old name to the human. Same account row, same fixed bot ID, so posts, followers, and friendships stay put. Replies now find Tom by that ID rather than by the name typed in a post, and moderation looks him up once per batch. Mentions written before the move still reach him because mention lists store user IDs. A new @tom mention points at the human. Tom is still every newcomer's first friend, and World still answers each hello-world post once.
One catch. The move only happens on the next collision. A bot renamed to the old placeholder name before this release stays there, and the bot lookup only recognizes the original and reserved names, so it keeps its friendships but never answers again unless someone moves it by hand.