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public struct TransientErrorRetryInterceptor: RequestInterceptor {
    public func retry(
        _ endpoint: some NetworkEndpoint,
        dueTo error: any Error,
        attempt: Int
    ) async -> RetryDecision {
        // 1. 비멱등은 재시도 금지 - 게이트는 정책 안의 첫 guard
        guard endpoint.isIdempotent else { return .doNotRetry }
        // 2. 자체 한도
        guard attempt <= maxRetries else { return .doNotRetry }
        // 3. 일시적 에러만
        guard Self.isTransient(error) else { return .doNotRetry }

        // 지수 백오프: 0.5 -> 1.0 -> 2.0
        return .retry(after: baseDelay * pow(2, Double(attempt - 1)))
    }
}

// NetworkEndpoint.swift - '사실'은 엔드포인트가 선언
public var isIdempotent: Bool {
    switch method {
    case .get, .put, .delete: true
    case .post, .patch: false  // 부수효과 중복 위험
    }
}

enum ImageDownsampler {
    static func makeImage(
        from data: Data,
        pointSize: CGSize,
        scale: CGFloat
    ) async -> sending UIImage? {
        let maxPixel = max(pointSize.width, pointSize.height) * scale

        let sourceOptions = [kCGImageSourceShouldCache: false] as CFDictionary
        guard let source = CGImageSourceCreateWithData(
            data as CFData, sourceOptions) else { return nil }

        let thumbnailOptions = [
            kCGImageSourceCreateThumbnailFromImageAlways: true,
            kCGImageSourceCreateThumbnailWithTransform: true,  // EXIF 회전 반영
            kCGImageSourceShouldCacheImmediately: true,  // 디코딩을 지금, off-main에서
            kCGImageSourceThumbnailMaxPixelSize: maxPixel  // 셀 크기만큼만
        ] as CFDictionary

        guard let cgImage = CGImageSourceCreateThumbnailAtIndex(
            source, 0, thumbnailOptions) else { return nil }

        // scale 명시 - 165px / 3 = 55pt (스케일 1 가정 버그 방지)
        return UIImage(cgImage: cgImage, scale: scale, orientation: .up)
    }
}