The invitation preview surfaces (/invitations/accept and /register?invitationToken=) are the
only unauthenticated reads of invitation data, and each render costs two database queries.
They are now rate limited before the lookup can touch the database: a generous per-IP bucket
that bounds enumeration across tokens, plus a tight per-IP+token bucket that stops repeated
probing of a single invitation. Tokens are hashed before they reach the rate_limits table.
A throttled lookup says so ("we couldn't check this invitation right now") instead of claiming
the invitation is invalid, and signed-in acceptance is not gated by it.
The callback sanitizer also checked only the origin, which is not enough: an attacker can
smuggle a host into the path of an otherwise same-origin URL — new URL('https://app//evil.com')
keeps our origin but yields a pathname of //evil.com, which navigation sinks resolve as
protocol-relative and follow off-site. Paths are now required to be rooted at a single slash,
and the login redirect re-checks at the sink.
getClientIp is split so server components that only have `await headers()` resolve the client
IP through the same trusted-proxy logic as route handlers.
