fn subscribeKeyCondOf

data Ev {
  userId: str
  amount: i64
}

topic Evs: Ev sharded by .userId

policy Evs {
  allow subscribe if caller.isUser("reader")
}

cluster demo {
  role store { journal }
}

fn watch(uid: str) -> () | TopicError io, db {
  for await e in Evs.subscribeKey(uid, from: .Earliest) {
    print("{e.amount}")
  }
}