The previous SELECT → compare → UPDATE sequence let two concurrent login
requests with the same valid 6-digit code both observe a stale lastTotpAt,
both pass the in-JS replay check, and both succeed. A stolen TOTP (shoulder-
surf, phishing-proxy replay) was usable twice within its 30 s window.
Replace the three callsites (login authorize, self-service enable, self-
service verify) with a shared consumeTotpWindow() helper: a single
updateMany() expresses "window unused" as a SQL WHERE clause, so Postgres'
row lock serialises concurrent writers and whichever commits second sees
count=0 and is treated as a replay.
Backup codes (ticket part 2) are tracked as follow-up work.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
