remote-index-cached-as-rows-with-validator

Cache a large published index by parsing it into indexed rows once and re-checking it with the server's own ETag, so a routine freshness check costs a couple of hundred bytes — replaying the stored validator only while rows exist, treating a 200 that parses to nothing as a failure, and never letting a failed check refresh the timestamp. Use when a browsable catalogue is fetched from a static host, or when a cached…