Turnstile tokens are single-use — the old implementation memoized one
token forever, so every batch after the first would fail verification.
Each sync now runs a fresh invisible challenge, and vote syncing is
debounced 2.5s so rapid ballots coalesce into one batch + one challenge.
OG count 16 -> 17 ran.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>