The Happy New Year hat is awarded for posting a chat message that gets starred within 12 hours of January 1, 2021 0:00 UTC.
How is the site on which to award the hat determined exactly?
I think this is clear in most cases: if the starred message was posted on chat.SO or chat.Meta.SE, award it on that respective site, and if it's posted on chat.SE, award it on the parent site of the room in question. However, there are a couple less clear-cut cases:
Which site will one earn the hat on if the message is posted in a room on chat.SE which has no parent site (e.g. Charcoal HQ, The Terminal, etc.)?
When a starred message is moved to a different room, any stars on that message will be imported into the moved-to room. If one posts a message that gets starred in a room on chat.SE with a parent site, then that message is later moved into another room that has a different parent site, will the hat be earned on both parent sites?