One FixedWindowBudget (injectable clock) owned by ConceptVoteRateLimits;
the vote page 429s with Retry-After before any row or cookie. Prefix
lengths and budgets are validated in every environment. Pins the empty
Origin branch of CastRequestGuard.
Unverified; not yet built.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>