529fd13668
(1) RegisterAnonymousViewer now catches the unique-violation
race (SQLSTATE 23505 on Postgres / code 19 on SQLite) and
re-reads by UDID, returning the existing row instead of
surfacing 500 to the second concurrent /tool/signup caller.
New repo test exercises the back-to-back register path.
(2) Add unique index on SocialAccountConnection (AccountType,
AccountId). The auth handler's find-or-link path claimed
this index existed as the dedup backstop; the claim was
accurate as design intent but the schema was missing. Now
matched. Comment in handler updated.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>