handleEmailOTPStart minted and mailed a code on every call, so an
authenticated caller could drive unbounded mail to any address they
typed — an email-bomb primitive against arbitrary mailboxes.
Add a separate otpLimiter (its own sync.Once and map, distinct from the
wake limiter) and throttle each send on two keys before anything is
minted: the caller (user:<id>) and the recipient (email:<lower>). A
refused send mints no code and mails nothing; both cooldowns are
recorded only after delivery succeeds, mirroring the wake path so a
failed mint or delivery never consumes the throttle. The two-key design
stops both one account fanning out across addresses and many accounts
converging on one mailbox.
Forced web onboarding proves a player controls an email before it is
bound to their account. POST /api/v1/account/email/start mints a random
6-digit code, mails it (or logs it server-side when no Mailer is wired —
the demo has no SMTP), and POST /api/v1/account/email/verify redeems it,
flipping users.email_verified in the same transaction that consumes the
code.
Brute force is bounded two ways: a 10-minute TTL and a 5-attempt cap,
both enforced in the repo so the fake and Postgres agree. Only the
sha-256 of the code is stored; the digits live only in the email. Both
routes are app-tier external — verifying your own email is scoped to the
principal, never names another user.
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