0.11.31 — “allowed to choose” is not “exists”

The login `p_anon4720` exists, sits on an account and was assigned by this engine. Typed into the sign-in form, it was told it looked like neither an address nor a login. It looked like both — except that the function checking it was answering a different question.

`checkDisplayName` answers the question “may I give myself this name”. It rejects names reserved for the editors and rejects the shape of an automatically assigned login, so that nobody can pose as a fresh account. Both rules are right and both stay. Signing in, however, poses an entirely different question — “is this even shaped like a login” — because every existing login has to open its account, including one you could never have chosen.

The consequence was the worst available: the door shut precisely for those who had changed nothing yet, which is every new account. An account carried a login from its first second exactly so that it would not begin with an absence — and it was that login refusing entry.

The shape is now checked by `looksLikeLogin`: length, permitted characters, no space at the edges and none doubled. Nothing about reservations, nothing about protected patterns. Separating those two questions is the whole fix; the entry exists because confusing “may be chosen” with “exists” is easy to repeat anywhere one name serves two purposes at once.