Cache-Status

[mnot]

FWIW, see RFC9211, which might address some of your use case (or be extended to do so).

[KenjiBaheux]

Thanks for sharing.

From a quick read, it seems that Cache-status is only meant to be a response header.

For the Resource-freshness use case (i.e. helping fine tune the values of max-age / stale-while-revalidate), it seems that a request header is needed for the local (device) cache to share what it knows about a particular resource.