- Fix errcheck: properly handle rows.Close() error via named return + defer closure - Fix gofmt: auto-format billing_cache.go, api_key_service.go, billing_cache_service.go - Add missing rate limit interface methods to 4 test stubs (GetRateLimitData, IncrementRateLimitUsage, ResetRateLimitWindows) - Fix NewBillingCacheService calls missing the new apiKeyRepo parameter