agents: define the work dir name once and test its creation

hive-c0re/src/coordinator.rs

@@ -1135,7 +1135,7 @@ impl Coordinator {
     /// destroy/recreate. A sibling of `state/` rather than inside it, so a
     /// claude started under `work/` never walks up into `state/CLAUDE.md`.
     pub fn agent_work_dir(name: &hive_types::Ident) -> PathBuf {
-        crate::paths::agent_state_dir(name).join("work")
+        crate::paths::agent_state_dir(name).join(crate::paths::WORK_SUBDIR)
     }
 
     /// Per-agent harness-internal state dir. Bind-mounted RW into the