Multipart vs single-request uploads for large private support attachments

The article argues that choosing an upload method for large private support files should follow tenant isolation rules rather than a fixed file-size cutoff. Ownership must be verified before upload and again before issuing an expiring download link, since a misdelivered file is a serious failure regardless of transfer speed. Ordinary small documents are best sent in a single request because multipart adds coordination overhead, while large files over unstable connections benefit from multipart uploads where only interrupted parts need retrying. The author proposes a 100 MB application-level decision point and a sample Go implementation that selects the transfer mode and verifies stored objects. Multipart uploads require recording part results, honoring Retry-After on rate limits, and explicitly aborting abandoned uploads since no automatic cleanup occurs.