Is this acceptable behavior, WDYT? To let the user rotate the “session api key”:

AUTOMATION_KV_SECRET explicitly set? → use it
otherwise:
  first launch → pin current session key in automation-kv-secret.txt
  later launch → reuse pin, even after SESSION_API_KEY rotates

pin contract:
  regular non-symlink · private permissions · fail closed
  new file → exclusive hardlink; losing starters read the winner
  blank file → shared lock + reread + atomic replacement