Streaming bytes into a file

When to use

• Persisting a generated artefact to disk inside the jail.
• Streaming a remote download or generated stream straight into a file without an intermediate buffer.
• Bootstrapping files into a sandbox by retargeting with target: { kind: "sandbox", sandbox_id }.

Notes

• The wire payload does not accept raw content: string or content_b64. The caller opens a channel via the SDK, passes the ContentRef here, then writes bytes into the channel and closes it.
• When cfg.fs.max_write_bytes > 0 and the streamed total exceeds the cap, the write is aborted mid-stream with S218. The default of 0 means no cap.
• Per-chunk idle timeout is 30s. A caller that opens a write but never sends data and never closes the channel is aborted with S216 channel idle for 30s, aborting write so a parked writer cannot leak the temp file.
• The worker writes through a temp file and renames atomically. On crash mid-stream, the temp file is unlinked by TempGuard.
• Approval policy is not hardcoded into this function. Whether a turn requires approval before a write lands is set per-run by the orchestrator's approval_required array.