Streams a sealed deployment's ArtifactBlob to a fetching driver node in
128-KiB chunks (matching the LocalDb cache chunk size). Unknown id, a
non-sealed deployment, and a zero-length blob all collapse to one
indistinguishable NotFound — existence-hiding plus the #485 serve-side guard
(never stream empty bytes as a valid empty config). The impl is named
DeploymentArtifactGrpcService to avoid colliding with the generated
DeploymentArtifactService container type.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Joseph Doherty