Default Compose stores the main server's prepared downloads in the container layer

[Quick104]

Problem

When Prepared file directory (download.artifact_dir) is blank, the main server writes prepared downloads to /tmp/silo-download-artifacts, a sibling of the transcode directory. The default docker-compose.yml mounts /tmp/silo-transcode but not that sibling, so prepared downloads land in the container's writable layer:

• They are lost whenever the container is recreated, which every image update does. Silo then finds ready artifacts with missing output and requeues them, so each update re-prepares every ready download.
• They grow on Docker's root filesystem instead of under SILO_DATA_ROOT, and download.artifact_max_bytes defaults to 0 (no limit).

This affects every default Docker install that prepares downloads on the main server. Dedicated transcode nodes are not affected: with the setting blank they write to download-artifacts inside their transcode directory, which the node examples mount.

Found by reading the code and Compose file while auditing the docs for #1635; not reproduced on a running server.

Options

• Mount ${SILO_DATA_ROOT:-/opt/silo}/download-artifacts:/tmp/silo-download-artifacts on the silo service. This is the smallest change and keeps the sibling rule, which exists so the orphaned-transcode sweep can't delete prepared downloads.
• Or set download.artifact_dir to a mounted path by default in the Compose deployment.
• Either way, consider a non-zero default for download.artifact_max_bytes, or document that the directory is unbounded.

Technical notes

• internal/config/config.go:453 (EffectiveDownloadArtifactDir): blank setting resolves to a silo-download-artifacts sibling of the transcode directory; the comment explains why it must not nest inside it.
• docker-compose.yml: the silo service mounts ${SILO_DATA_ROOT:-/opt/silo}/transcode:/tmp/silo-transcode and nothing for the artifact root.
• internal/transcodenode/server.go:495: nodes default to downloadprepare.ArtifactDirectoryName inside their transcode directory.
• internal/downloads/artifact_repo.go:332 (RecoverMissing): requeues ready artifacts whose output is missing.
• internal/config/admin_settings.go:215: download.artifact_max_bytes defaults to "0".

AI disclosure

• Harness: T3 Code (Claude Code agent harness)
• Tool(s): Claude Code, GitHub CLI
• Model(s): claude-opus-5-5
• Involvement: AI-assisted; filed at the maintainer's request
• Adversarial review: n/a