When downloading remote security-sensitive artifacts (e.g., kernels, binaries, containers), require an expected cryptographic digest (e.g., `sha256:`) and verify it before use. Treat missing digests for custom/variable URLs as a policy violation (fail closed) to prevent unverified or tampered downloads. Example config pattern: ```toml [kernel] url = "https://example.com/artifact.tar.zst" digest = "sha256:0123...abcd" # REQUIRED when url is custom/remote ``` Example enforcement pattern (pseudo-code): ```swift let url: URL = config.url let expectedDigest: String? = config.digest guard let expectedDigest else { // Fail closed for non-default/custom URLs throw SecurityError.missingDigestForRemoteDownload } let data = try download(url) let actualDigest = sha256(data) precondition(actualDigest == expectedDigest) ``` Apply this to any code path that fetches from the network using a configurable URL and then executes/consumes the artifact.