The H2O server, on the first request, sends a cookie that includes a signature of all the files a server pushes: https://h2o.examp1e.net/configure/http2_directives.html#http...

If, on subsequent requests, the cookie is sent along with the request, H2O doesn't send those files.

This is still a bit of a hack, and ultimately browsers will have to include some information on what's in the actual cache, with proposals on that pending: https://datatracker.ietf.org/doc/draft-ietf-httpbis-cache-di...