CI flake: uploading TUF repo failed because it changed size?

This CI run failed:
https://github.com/oxidecomputer/omicron/pull/5974/checks?check_run_id=26826741783

It's the "helios / build TUF repo" job. Everything seemed to work until it went to upload the TUF repo:

Jun 28 21:55:30.028 INFO assembling repository in `/tmp/tufaceousdm3XlR`, component: OmicronRepoAssembler
Jun 28 21:55:35.966 DEBG assembly successful, cleaning up, component: OmicronRepoAssembler
Jun 28 21:55:36.284 INFO artifacts assembled and archived to `/work/repo.zip`, component: OmicronRepoAssembler
Jun 28 21:55:59.209 INFO [tuf-repo] task succeeded (39.17303593s)
Jun 28 21:55:59.209 INFO all jobs completed in 1775.615926941s
process exited: duration 2255622 ms, exit code 0

found 33 output files
uploading: /work/manifest.toml (8400 bytes)
uploaded: /work/manifest.toml
uploading: /work/repo.zip (1729748621 bytes)
upload error: job 01J1GB9ZVM3BB6928C0W3JN6VM file: expected size 1729748621 != chunk size 1708908173 (after 6ms)

Start with the “helios / build TUF repo” CI job and the linked Buildomat run. Trace the upload of /work/repo.zip and determine why the expected file size differs from the uploaded chunk size; done means the job uploads the assembled repository reliably.