CREATE TABLE IF NOT EXISTS rate_limits (
    bucket_key CHAR(64) PRIMARY KEY,
    scope VARCHAR(80) NOT NULL,
    hits INT UNSIGNED NOT NULL DEFAULT 1,
    window_started_at DATETIME NOT NULL,
    expires_at DATETIME NOT NULL,
    INDEX idx_rate_limits_expires (expires_at)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;