Any reason not to just add it to the list-o-suppressed-notices? (So the second one in the new-topic widget won't show up.)

The notice is recreate-moveddeleted-warn.

We could also hide the original notice along with the "empty state" interface. I'm not sure if there are any cases where the edit notice might have more recent or more accurate info?

There's a similar scenario with the notice about user not being registered: https://en.wikipedia.org/wiki/User_talk:Asdudfmoaisudfbmdasdfasdf

The disadvantage to hiding the original notice seems to be that it conceals information that people who don't want to add a topic might still want to see, with no indication that it'll be present before you click the button.

The notice within the widget does also contain the minor added "Warning: You are recreating a page that was previously deleted." text, which is probably relevant as a "are you sure?" prompt.

Sorry, I meant hiding it when you open the new topic tool, just like we hide the "empty state" interface when you do that.

Ahh, okay. I misinterpreted it as "hide it on pages where the empty state is showing", sorry. That sounds like a reasonable approach to me -- splitting the difference.

Change 715064 had a related patch set uploaded (by DLynch; author: DLynch):

[mediawiki/extensions/DiscussionTools@master] Hide the top-level warningbox when the new discussion widget is open

https://gerrit.wikimedia.org/r/715064

Change 715064 merged by jenkins-bot:

[mediawiki/extensions/DiscussionTools@master] Hide the top-level warningbox when the new discussion widget is open

https://gerrit.wikimedia.org/r/715064

Patch won't affect the user-not-registered case, as that's not a warningbox. (It's solely targetable as .mw-userpage-userdoesnotexist error, but it could easily be added in to the same behavior.)

Isn’t it possible that there are other .warningboxes that are not duplicated as edit notices, and thus temporarily completely hidden? Also, be aware that this class will be renamed (T270796).

Bartosz did some quick searching and didn’t turn anything up. However, worst case it’ll be the status quo for editing a talk page, I think — with “opening the new topic widget” standing in for “navigating to the source edit page”.

In T289354#7315968, @DLynch wrote:

However, worst case it’ll be the status quo for editing a talk page, I think — with “opening the new topic widget” standing in for “navigating to the source edit page”.

That’s fair. Anyways, we should probably keep an eye out and fix cases where message boxes are not duplicated in edit notices if we find any. But it’s okay to do if/when we find such cases, don’t need to actively search them.