fix(#2018): reword tracker tag in agent_exists doc comment to prose (tracker-tag lint)

hive-c0re/src/bin/hivectl.rs

@@ -941,7 +941,8 @@ fn human_bytes(n: u64) -> String {
 /// silently report `false`, which callers turn into a misleading "no
 /// such agent" (or, for the create-user paths, a silent misclassify of
 /// a real agent as a non-agent account). Mapping EACCES to an explicit
-/// "needs root" error fixes that first-run footgun (#2018).
+/// "needs root" error fixes that first-run footgun, where running a
+/// privileged verb without sudo reported as a missing agent.
 fn agent_exists(name: &str) -> Result<bool> {
     let root = Coordinator::agent_state_root(name);
     match root.try_exists() {