Split from T402556: InvalidArgumentException: MediaWiki\User\Options\UserOptionsManager::saveOptionsInternal was called on IP or temporary user.

Notifications (Echo) include the page-linked ("Notify me when someone links to a page I created from another page") notification. This notification is sent whenever a mainspace page created by user A is linked from another mainspace page by user B.

This notification includes a mute button that allows the user to mute further notifications regarding that page:

Following the changes made in T402556, this button likely gets stuck for Temporary account holders (this is because it is ultimately backed by user preferences, and Temporary accounts do not have any preferences, making the button fail).

However, @Urbanecm_WMF had some issues reproducing the situation (to get the screenshot above), so it is not clear what the level of breakage in production is ATM. We should check the following:

• Is there a page-linked notification fired for pages that were created by a Temporary account?
  • Expected behaviour: The notification should exist, as notifications should generally work the same for named and temporary accounts.
  • Current behaviour: So far, @Urbanecm_WMF did not manage to get a notification appear (using regular ways), but I might be missing something.
• If the page-linked notification can be triggered, does it have the muting link?
  • Expected behaviour: No mute link is included, as muting is not technically possible for Temporary accounts.
    • If we really want to, we might add a clever "register to do this" prompt, but (a) I have no idea how that could look like (b) the notification would not appear in the new account, meaning there wouldn't be any link to re-click.
  • Current behaviour: When I hack the notification in, the link just gets stuck (with an error visible in the Network tab.