Declare that this end user is also called name.

The store never merges two names of a person by itself: two people can share a name, and a merge it guessed wrong would close one person's facts with another's. This is the declaration that does it. From now on a fact written about name in this end user's memory is a fact about the end user, and the facts already written about name are read so at once (their written words stay as they were). It is the alias the dashboard makes (POST /admin/aliases), for the key's project and this end user.

end_user is the user_id exactly as written, percent-encoded as one path segment. Declaring the same name again answers the same. 409 when name is already declared for somebody else in this memory, 422 when it is not a name.

There is no undo here: DELETE /admin/aliases/{id} removes the alias, and the facts take back the names their words give; two open facts it merged stay one, and a plan it closed stays closed.