This change was reverted earlier (twice!) because the Central Registry did not support the Referrers API call. It now does (verified locally), we we'll try again. Extend Client.Mirror to copy OCI referrers (manifests with subject field) along with the main module manifests and blobs. This ensures that artifacts like signatures and attestations that reference a module are preserved when mirroring between registries. Signed-off-by: Roger Peppe <rogpeppe@gmail.com> Change-Id: I93f2ba9ab172e7bd7e84f8a3743fafe70af4247e Reviewed-on: https://cue.gerrithub.io/c/cue-lang/cue/+/1224156 TryBot-Result: CUEcueckoo <cueckoo@cuelang.org> Reviewed-by: Daniel Martí <mvdan@mvdan.cc> Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>