for each agent the hive looks up its record in agent-closures, fetches the closure's narinfo from the cache with the pull token and checks that a signature by the cache's public key covers it. the result is a log line and the gauge hyperhive.agent.closure_pullable, with a reason label when it is 0. nothing is downloaded and deploys still build locally. part 3 of 3: the probe needs the cache facts and the closure read grant from parts 1 and 2.
hive-c0re reads its cache facts from the store every five minutes and writes /run/hyperhive/attic/{netrc,substituter,public-key}, each 0600. it accepts only an https url, so the pull token never travels in clear. hives get a read grant on the agent-closures bucket, and swarm-queue-client a reader for it. part 2 of 3: nothing uses the files or the reader until the probe lands.
