rebuild re-registers agent; preserve /run/hyperhive across restarts

hive-c0re/src/coordinator.rs

@@ -26,6 +26,9 @@ impl Coordinator {
     }
 
     pub async fn register_agent(&self, name: &str) -> Result<PathBuf> {
+        // Idempotent: drop any existing listener so re-registration (e.g. on rebuild,
+        // or after a hive-c0re restart cleared /run/hyperhive) gets a fresh socket.
+        self.unregister_agent(name);
         let agent_dir = Self::agent_dir(name);
         std::fs::create_dir_all(&agent_dir)
             .with_context(|| format!("create agent dir {}", agent_dir.display()))?;

hive-c0re/src/server.rs

@@ -77,7 +77,7 @@ async fn dispatch(req: &HostRequest, agent_flake: &str, coord: &Coordinator) ->
             }
             HostRequest::Rebuild { name } => {
                 tracing::info!(%name, "rebuild");
-                let agent_dir = Coordinator::agent_dir(name);
+                let agent_dir = coord.register_agent(name).await?;
                 lifecycle::rebuild(name, agent_flake, &agent_dir).await?;
                 HostResponse::success()
             }

nix/modules/hive-c0re.nix

@@ -37,6 +37,7 @@ in
         RestartSec = 2;
         RuntimeDirectory = "hyperhive";
         RuntimeDirectoryMode = "0750";
+        RuntimeDirectoryPreserve = "yes";
         StateDirectory = "hyperhive";
       };
     };